Scope of research and development work onsubstitute alloys at the NationalMetallurgical Laboratory

B. R. NIJHAWAN

THE axiom that "Necessity is the mother of inven-tion" illustrates the basis for the development ofsubstitute families of alloys on which feverish acti-

vity spurts forth in the wake of war emergencies ; thishowever, has not been the only main axis for sustainedwork on the metallurgy and growth of substitute fer-rous and non-ferrous alloys at the National MetallurgicalLaboratory. In early identification of research themesand development projects at the National MetallurgicalLaboratory, it was strongly felt that the indigenousgrowth of metallurgical and engineering industriesafter the initial impact of the imported technology hadworn out. would inevitably center around indigenousminerals and metals. Whilst the chronic shortage offoreign exchange in the midst of equally chronic importof foreign aid, did succeed in keeping the broad basedthemes of substitution and substitute materials andalloys in theoretical limelight, it was the two successivewar emergencies that brought home the importance,short-term and long-range value and scope of thesubstitution and substitute products and highlightedthe value and importance of research and developmentthemes on which the National Metallurgical Laboratoryhad been engaged in an almost lone effort since adecade earlier when peace reigned supreme in our sub-continent.

Almost right from its inception, the National Metal-lurgical Laboratory carefully surveyed the indigenousmineral arena around and embarked upon some majorresearch and development projects on substitute alloysand substitute processes and processing techniques inthe background of effectively utilizing the indigenousmetals to the maximum optimum extent whilst elimina-ting or reducing the contents of others in which ourresources were either scanty or almost totally non-existent . In the wake of depleting mineral resourcesfurthermore, researches and applied technological effortare continuously directed towards mineral conservationon the one hand and making the maximum effective

use of available resources on the other. The subject ofsubstitute alloys has always tended to be somewhatcontroversial adjudged on the basis of indigenous availa-bility of primary metals not only in relation to metal-lurgical acceptability of the substitute alloys and alter-native processes but also vis-a-vis their productioneconomics, market acceptance and serviceability. Andthe National Metallurgical Laboratory has indeed bornethe brunt of this controversy through the years inpersevering with the "substitute" development themesin its long-range research programming whose valuehas today been truly well recognized and appreciatedin relation to the potential substitute end products-the gaps in indigenous resources being successfullybridged in the background of inescapability of metalsubstitution during the current plans.

This then is the general context covering the scope ofresearch and development work on substitution andsubstitute alloys at the National Metallurgical Labora-tory. Whilst pursuing the research themes of potentialvalue, one has indeed been confronted with very vasttechnical literature on the subject though rich in itstechnical contents, but presenting nevertheless a diffusedarray of dispersed and scattered references on thesubjects, set loose in the formidable number of worldpatents and published papers. Some themes of substitu-tion are still in the formulation stages within the over-all scope of projected programme of work at theNational Metallurgical Laboratory. In the overall surveyand study of technical and research data available onthe subject, potential gaps are consequentially uncoveredoffering useful scope for fundamental and appliedresearch studies as also for examining known andaccepted modes of substitution with a view to theirapplications ultimately for the development of newfamilies of alloys based on indigenous raw materials.

Metals in which our country, whilst possessing someresources, is highly deficient are copper, lead and zinc,etc. The metals in which we are potentially rich areiron, aluminium, :itanium, magnesium, beryllium,

Dr B. R. Nijhawan, Director, National Metallurgical Laboratory,Jamshedpur.

manganese, zirconium, etc. Metals such as nickel, tin,molybdenum, tungsten either do not exist or are per-

14

Nifltatratr: Scope of research and development work all .c,h.stituie allots

haps found in isolated uneconomic pockets, even thoughwith more intensified and comprehensive explorationand prospecting some economic deposits may yet befound. The one non-ferrous metal whose resourcesare abundant in India is aluminium : on account ofits versatile properties, it has already found multipleend uses and is substituting zinc in many applications.In the case of alloy, tool, special and stainless steel, itwas considered necessary by the National MetallurgicalLaboratory to formulate and develop families of indi-genous substitute alloy compositions, eliminating orminimising as far as possible alloying elements such as,nickel, molybdenum, tungsten, cobalt, etc. The scopeof substitution presents a vast technical spectrum, com-plex and challenging in its theoretical and fundamentalaspects and to an equal measure if not more, in itsapplied technology. Research and development themeson the subject of substitution and substitute alloys haveso far covered the following, at times somewhat empiri-cal in their identification and objectives but scienti-fically pursued and sustaining nonetheless :

Development of substitute alloy, tool and stain-less steels including high temperature creep-resistant alloys based on chromium, manganeseand nitrogen compositions.

2.

3.

4.

5.

6.

7.

8.

9.

Transformation and ageing characteristics of subs-titute alloys and stainless steels and their theore-tical implications and studies.Development of iron-aluminium alloys and pro-jected iron-manganese-aluminium compositionsfor high temperature oxidation resistance appli-cations.Substitute magnetic materials including soft andhard magnetic alloys.Nickel and copper-freealuminium-magnesiumsit ions.

coinage alloys based onand manganese compo-

Development of substitute nickel andelectrical resistance beating elements.

steel.

cobalt free

Development of manganese bearing substitutebrasses and the applications of manganese in subs-titute alloys.Hot-dip aluminising of steel to replace galvanizingof steel.Substitute surface treatments including P.V.C.coated steel and chromated steel sheets, the latterto replace hot-dip and electrolytic tinning of

electrical grade conduc-10. Substitute aluminium

12.

13.

14.

15,

Aluminium based substitute alloysfriction aluminium bearing alloys,

tors.including anti-

Improved mild steels for structural purposes andthe development of indigenous low alloy highstrength steels.Thermo-mechanical and processing treatments forultra high strength steels.Physical metallurgy of substitution of alloys inclu-ding theoretical consideration in the substitutionof metals in alloys.Substitution in refractory products including the

development of indigenous dense carbon aggregateto replace imported anthracite.

16. Survey of the scope and economics of substitutionwith indigenous materials and metals for engine-ering, ordnance and defence applications.

17. Industrial scale application and economics ofsubstitution of metals. Economic recovery andutilization of strategic indigenous non-ferrousmetals.

Planning and execution of research studies in the abovefields require analytical assignment of priorities, scientificpruning during execution and sustained applicationsthereafter. Researches in these fields of theory andpractice are endless and the last word can hardly be saidon the subject. Nevertheless, studies on the subject haveestablished clear trends and research channels alongwhich the ultimate solution would lie. One needs a lotof perseverance anywhere and more so in India. forindustrial scale implementation and applications ofresearch results particularly when the Indian industryitself is in development stages and may tend in somecases to look askance at any deviations from the conven-tional alloy compositions or standard processing techni-ques. In this connection, it is necessary to emphasizethat it is the industry alone that can handle and solvethe inevitable dilliculties, shortcomings, snags and bottle-necks in proving and disproving and accepting theresults of painstaking researches. Research by itself isnot the main means to an end. With this backgrounda broad outline of the work at the National Metallur-gical Laboratory is now furnished in the above fieldshighlighting current approaches and future lines of workin each case as far as possible.

Development of substitute alloy, tool and stainless steelsincluding high temperature creep-resistant alloysbased on chromium , manganese andnitrogen composition

Following the basic themes of development of substitutealloys based on indigenous alloying elements to theexclusion of those whose resources are deficient or totallynon-existent in India, such as nickel. cobalt, molybde-num. tungsten. tin, etc., research and development workconducted at the National Metallurgical Laboratoryhave resulted in the formulation of processes for theproduction of nickel-free austenitic stainless steel alloysfrom entirely indigenous raw materials.

The research and development work on nickel-freeaustenitic stainless steels based on chromium, manganese,nitrogen and copper is very significant in the contextthat India possesses little or no reserves of nickel andimports to the tune of 10 000--I5 000 tons of nickel-bearingaustenitic stainless steel, chiefly in the form of sheets forfabrication into utensils etc. These substitute stainlesssteels developed at the National Metallurgical Laboratoryhave been made fully austenitic and non-Ferro-magneticdespite their being wholly nickel-free, by virtue of theirhigh optimum nitrogen contents--an element readilyavailable in nature. Comprehensive investigations werecarried out on the determination of physical, mechanical

15

Nijharoan : Scope of research and development work on substitute alton.c

and high temperature creep properties of the new steelsdeveloped. Concurrently, work was also done on theindustrial scale production of these stainless steelsincluding assessment of production costs, yielding valueand range of industrial products obtainable under Indianmarket conditions and requirements. Tests were conduc-ted to determine the low temperature and sub-zero tensileand impact properties, high-temperature tensile strength,weldability, oxidation resistance and ageing characteris-tics of different compositions of the nickel-free austeniticstainless steels.

On account of almost total non-availability ofresources of nickel in India a long range research projectwas taken up in the National Metallurgical Laboratoryto develop nickel free austenitic stainless steels prosses-sing significant corrosion resistance under specific mediaand adequate ductility and deep drawing characteristicsfor undergoing cold forming operations. A broad basedresearch programme led to the development of a family ofchromium-manganese-nitrogen austenitic stainless steels.

Some typical compositions of the four broad rangesof the austenitic stainless steels are given below. l'headdition of copper up to it maximum of 1 % assists insomewhat improved corrosion resistance but affects thedeep forming characteristics of the stainless steels andin the following ranges of chemical composition of thestainless steels. addition of' copper has been excluded.

A. Chromium ... 17.54%0

Manganese ... 12'57%

Nickel ... NilCarbon ... 0.054%Nitrogen ... 0-21%,

B. Chromium ... 16.68

Manganese ... 14.13%

Nickel ... NilCarbon ... 0.055%Nitrogen ... 0.49%

C. Chromium ... 17-710//0

Manganese ... 17.55%

Nitrogen ... 0.525%

Carbon ... 0'08%

D. Chromium ... 20.9;0

Manganese ... 13.8%Nitrogen ... 0.68%

Carbon ... 0'12%

E. Chromi ur ... 21-56%

Manganese ... 18-47%Nitrogen .. 0.8%

Carbon ... 0.06°',,

In each of the above composition ranges, sulphur,

phosphorus and silicon contents are below 0.06%j0.0601, and P% respectively.

Meltitw technique uncl production of ingots

The technique of making the austenitic low carbonnickel-free Cr-Mn-N austcnitic stainless steels is verysimilar to the standa-d procedure of making 18-8 austeni-tic stainless steels. The important point to rememberin melting these stainless steels is that loss of nitrogenoccurs in the melt with longer holding time and in orderto minimise the loss of nitrogen, the period after theadditions of nitrogen hearing ferro-alloys to the meltshould be as short as possible. In direct electric arc fur-nace melting, it is desirable to reduce the period afteroxidation of the melt for reasons of carbon pick up inthe manufacture of the 18 -8 austenitic stainless steels,but in the case of Cr-Mn-N stainless steels this aspectis of still greater importance. Since the additions ofcold nitrogen-bearing ferro-alloys will prolong the melttime, it is preferable to preheat the nitrogen bearingferro-alloys up to 600' C separately. For the same reason,it is preferable to attain a high melt temperature beforethe additions of these Ferro-alloys.

Raw materials used in the preparation of these meltsat the National Metallurgical Laboratory consisted of mildsteel scrap. ferritic stainless steel scrap, low carbonferro-chrome. nitrided elecrrolytic manganese. nitridedlow carbon Ferro-manganese. ferro-silicon and Fe-Cr-Mn-N master alloys : all of these ferro-alloys wereprepared in the National Metallurgical Laboratory fromIndian chrome and manganese ores and subsequentnitriding of the ferro-alloys, and Fe-Cr-Mn alloyobtained.

The heats of Cr-Mn-N stainless steels were made inhigh frequency induction furnace as also in direct arcelectric furnace. Furnaces that have been actually usedare :

Basic lined high frequency induction furnaces of 75lb, 20 lb and 5 lb capacities.

2. 2-ton basic high frequency induction furnace.

3. 0'8-ton basic direct arc electric furnace.

4. 3-ton basic direct are furnace.

Since no refining or carbon pick - up takes place inthe high frequency furnace , it is indeed relatively easierto make the stainless steel in the induction furnacesduring melt trials of which normal losses of variousalloying elements were determined.

The basic high frequency induction furnace heats aremade by first charging the furnace with low carbonsteel scrap or ferritic stainless steel scrap . The furnaceis then started and on softening of the charge. lowcarbon ferro -chrome is gradually added. A part of thelow carbon ferro-chrome is often replaced by nitrogencontaining ferro -chrome to raise the nitrogen input ofthe charge . Balance of the charge consisting of eithernitrided electrolytic mangnese or Fe -Cr-Mn- N master

16

I I I PrTrT'Ir""" I

1Vijlranan : Scope of research curd c /erelopruevc t work on srrhslilutc alloys

alloy is slowly added to the molten bath which is keptat a low temperature. During such addition period,care should be taken to see that the bath is not sudden-ly cooled down by abrupt addition of large quantitiesof material at a time : this precaution is taken to avoidthe formation of bridge on the top of the melt whichmay at times be difficult to break. After completion ofmelting, ferro-silicon is added to the bath and sometime is allowed for the melt to attain the pouring tem-perature. The pouring temperature is controlled between1500C 1550"C. The melt is poured into preheatedladles and thence into the ingot moulds which haveearlier been properly dressed with lime to facilitatestripping and dried beforehand. The ingots are im-mediately capped soon after the completion of pouringand jets of water are directed on the top of the"capped" ingots. Capping gives rise to a sound anddefect-free ingot top as per the observations and ex-perience gained at the National Metallurgical Labora-tory. At times, when available, Armco ingot iron wasalso somewhat used along with the mild steel scrapbut generally its use was avoided owing to its high cost.

The procedure of melting these stainless steels indirect are electric furnace is similar to the procedureof melting normal low carbon stainless steel. For thisreason, the melting procedure of normal stainless steelswill be briefly described and any difference necessaryin the melting procedure of the Cr-Mn-N stainless steelswould be pointed out. The melting of normal stainlesssteels takes place in three stages.

(a) The oxidizing stage--The aims in this stage are(i) to obtain a sufficiently low carbon value to

make up for any carbon pick up during thelater stage and

(ii) to obtain a sufficiently high temperature tominimise or completely avoid arcing in laterstages. The oxidation of the melt can bebrought about either by oxygen lancing oriron ore additions . former is preferred onaccount of relatively shorter time requiredand ready high temperature obtained.

(b) The reducing stage---the oxygen-saturated meltmust be deoxidised in order to take a substantialportion of chromium from the slag back to thesteel melt, in case the starting material is straightchromium steel scrap : this deoxidation is alsoneeded to reduce subsequent losses of alloyingelements which would occur in case effectivedeoxidation has not been earlier accomplished.Ferro-silicon is used for deoxidation in the caseof these nickel-free stainless steels. Since alu-minium combines with nitrogen, the use of thiselement for deoxidation purposes is not possiblein the manufacture of Cr-Mn-N stainless steel.

ferro-alloys, such as nitrided electrolytic man-ganese, nitrided ferro-manganese or nitrogen-bearing ferro-chrome are added last after requi-site preheating. These alloy additions are thenthoroughly rabbled into the bath. In certaincases, these nitrogen-hearing alloys may he addedeven during the reducing stage. Having madethe additions of the alloying elements and mea-surements of the pouring temperature whichshould be below 1600-C, the melt is ready fortapping. It is advisable to take a sample fromthe bath, quench it for immediate magnetic test-ing which should clearly show it to be totallynon-magnetic. The melt is now poured in a ladleand a slag cover is maintained over it. The steelis poured from the bottom of the ladle througha magnesite nozzle into properly dressed ingotmoulds as stated earlier.

Mechanical capping and water quenching of the ingottops should be done in a similar way as referred toearlier.

!lot working operations

The ingots after being stripped from the ingot mouldsare heated to 980 "C in a gas fired furnace and soakedat this temperature for sufficient time to allow fullhomogenization . The temperature is then raised to theforging temperature of 1150 'C and the ingots are forgedby pneumatic hammers into flat bars suitable for roll-ing into sheets . During forging, reheatings have to becarried out due to loss of temperature of the bar.

The slabs on cooling are ground to remove surfacedefects and cut to proper size for rolling into sheets.The slabs are slowly reheated to a temperature of1150°C and rolled into sheets. Reheating and rollinghas to be repeated before obtaining the final thicknessof the hot rolled sheets.

Annealing

For solution annealing the sheets are reheated in anelectric furnace to 1050°C and quenched in oil.

Pickling

Pickling of the sheets is carried out by first degreasingthe sheets in a suitable solvent and carrying out thepickling operation in two stages. The sheets are firstpickled in a solution containing 6 H ,,SO, and 2%HC'I at 50-60°C whereby the scale on the surface ofthe sheets gets loose and dislodged. The second pickl-ing solution is composed of 10°0 H NO;, and 1% HEPickling is carried out at a temperature of 50-60°Cwhereby the scale still remaining on the sheet surfaceafter the first pickling operation is completely removed.

c) Finishing stage-after removing the first slag, afresh finishing slag of lime and flurospar isprepared : requisite alloy additions are thenmade . In the manufacture of C'r-.Mn-N stainlesssteels as pointed out earlier , the nitrogen -bearing

Plr.1•sical Properties

Physical properties determined on specimens made fromthe forged and solution treated bars are given below.

17

allo r^

The solution treatment was carried out by soaking at1050°C followed by quenching in water. Chemical composition Average permeabilih

Chemical composition Young"; modulo;

Heat No. L-65/2

Cr ... 21.5

Mn ... 13.2%

N ... 0.75°.,

C ... 0'00"/,',

Si ... 1,27"..

28,15X1t)6 th;sq . (determined

by resonance vibrating method)

Heat AVo. E-13 1105

- given above

Co-ellicient of thermal e\pan-

Chemical cowilosition Rc;istivii%

Heat No. E-13

Cr ... 21.4°;,

Mn ... 13'4%

N ... 11 71"„

C 0.11°„

S i (1'4(1",J

74'50 micro ohm cm.

Chemical compo; ilion Saturation induction

Heat No. E--/?

given ahoseLees than 250( ) gausses formagnetizing field of 2 340oersted;

Chemical composition Sion

Heat No. A-87

.C

Cr ... 22-67% 30-100 15.7 X I0-° C

Mn ... 14'88% 30-2(X) 16.47 do

N ... 0.67 % 30-200 17'57 do

C .. 0 -05 °0 30 -5() 18-08 do

Si ... 0-58'a 30-1(1X) 23'7 do

l00-500 I8'5 do

51X)-1000 29-00 do

Results of tensile tests in solution treated condition and after cold rolling ('t'hickness of sheet -0.050" 0.040")

Chemical Percentage Direction of Max- stress Llongation 00 on Hardnesscomposition reduction test tons sq. in. I each G.L. V.P.N.

Heat No. B.

Cr ... 20'9 0°, 58 65Mn ... 13 (So!ution neared)N ... O.6S°„ 10% Longitudinal 70.78C ... 0.12-, Transverse 67-47Si ... 0-70% 20% Longitudinal 76'17

Transverse 74.4230% Longitudinal X5.98

45.3 270

34'4 33237.5 32826.6 37525-0 38718'8 429

18

1Vijhanwan : Scope of research and derelopment work on aubstitute alloys

Sub-zero tensile tests

A special fixture was made for sub-zero tensile testing.Specimens of I inch G. L. were tested immersed inpetroleum ether cooled to the desired temperature byliquid air. Results of the tests are given below :

Results of sub-zero tensile tests

HeatNo.

B,

B ,

B°

Temperature

MaximumstressKglmm2

Elongation O,,; on25 mm G.L.

Room temperature 97-01 45'3---10°C 114'8 46.8-20°C 99'90 43.7-30°C 1l4'2 43.7

Room temperature 104' 1 48'4-10°C 122.3 53'0-20°C 116.1 50.0-30°C 122'6 46.8

Room temperature 94'82 50.0--10°C 102'8 Broken outside G.L.-20-C 104-7 50.0-30C 109.7 Broken outside G.L.

Weldability, oxidation resistance and low temperaturetensile properties of different compositions of chromium-manganese nitrogen stainless steels were determined.Chemical composition of the steels used in the investiga-tions are given in Table I.

TABLE I Chemical composition of Cr-Mn-N stainless steels

HeatNo. Cr % Mn% N % C% Si %

B2 20.9 13.8 0.68 0'l2 0-70

B, 22-07 16.63 1101 0-04 0'04

B5 179 16'93 0-69 0'05 0128

B4 17.59 16.93 0-66 0'04 0'31

TABLE 11 Tensile properties of the welded specimens

Tensile ElongationHeat strength % on 25 mm Location ofNo. Filler metal kgimm2 G.L. fracture

B2 Parent metal 95,4 5010 Base metal

181/8 type 84.4 31'0 At the weld

Parent metal 100.3 21.8 At the weld

18'8 type 10816 25.0 At the weld

Weldabilitl' tests

Welded specimens were prepared by argon arc welding.Strips cut from the annealed sheets of 0.035-0040 in.thickness were welded using 18/8 type stainless steelwelding rods and thin strips cut from the original sheetsas filler metal. Single layer butt joints were produced.The welded strips were ground smooth at the weld andtensile specimens made from the strips were tested atroom temperature. Results of the tests are given inTable It. Tensile properties of unwelded base metal arealso given in Table Ill for the purpose of comparison.Results of low temperatre impact tests (V-notch Charpyspecimens) are given in Table IV.

TABLE III Tensile properties of unwelded base metal

Heat Tensile strength Elongation %No. kglntnt2 on 25 mm. G.L.

B2 94.2 45.3

B, 102 500

TABLE. IV Results of low temperature Charily impact tests

Chemical composition Temperatures Energy of fractureHeat No. E-28 C. in ft. lb.

Cr ... 21.3% 25 204

Mn ... 14'1%

N 0'64% 0 188

C 0.05%

S1 0.30% -20 1 70

-40 152

50 104

57 76

-60 72

-70 58, 60

Results of high temperature short time tensile tests(Hounsfield Tensometer. Specimen No. 13, 0'632 in.G. L.) are given in Table V.

19

Niihawan : Scope of rr.vcarch and development work on substitute alloys

TABLE V Results of high temperature short time tensile tests

Chemical cotposi_ °r° ElongationLion Heat No . temperature Ma'. stress 0.632 in.E-68 2 C. ions 'sq. in. G. L.

Results of (nrrosin; r tests

Corrosion tests were carried out on specimens of thesestainless steels in several media such as 65 1„ nitric acid,vinegar . Lime-juice !- 1 °,, NaCI, citric, acid : Na('I. Saltspray tests were also conducted. The results of the testare given in Table VII.

Cr ... 2I'5% 200 43'7 50

Mn 13.2%;,

N ... 11.7ti°;, 301) 41'3 32

C ... ()0 6°„

Si ... 0.27°;, 450 39'3 37

Deep dratejnt. tests

Deep drawing tests were carried out using a SwiftCupping Press of 6" capacity. Flat bottom mandrillwas used and a pressure of 80 Ib,sq. in. was maintainedon the pressure plate. Grease-graphite was used as alubricant. Results of the test are given in Table VI.

TABLE VI Results of deep drawing tests carried out in SwiftCupping Press

Pressure on pressure plate-80 lb sq. in.I uhricanl-C; cease-ar:iphite

NominalcompositionCr : Mn : N

Blankdiameterin inches

Thicknessof sheetin inches

Mas. draw-ing pressureIb,sq. in. Remarks

21140.7 3'1, 0.035 750 Good cup

22 171 3.8 0'038 800

18 170.7 3'8 0035 680

21 : 140.7 4 0.035 890 Good cup

22171 4 0'037 970

18 : 17 : 0-7 4 0.035 800

21 : 14 : 0.7 4-1 0036 990 Good cup

22 17 : I 4-1 0.040 1020

18 : 17 : 0.7 4* 1 0035 830

21 : 140.7 4'2 0036 1050 Good cup

22 : 17 : 1 4.2 0.038 1050

18 170.7 4.2 0.038 1000 Cracked onside

20

'I'Aiti.i VII Results of corrosion tests

Chemical corn-Timeof test

Loss inweight ingm dm=

posiIion Medium Temp. hours day

Heat No. A-44

Cr ... 17'54% 65%,, Nitric boiling 38 0'293id

Mn ... 13'49 °„

ac

N ... 0.59C ... 0.05 Vinegar 414.I"C 95 010010Si ... 0.250 0 0'(x)10

Lime-juice 41_- 1 C 72 0.1801 1 % NaCl 0-197

5%Citric 41±1°C 64 0'0045acid-i- 1% 0.14NuCISalt spra Room 48 0.0055y(50%NaCI) Temperature 000305% SI-.Iphu- 41= I C 11 55.59ric acid 61'50

heat No. B,

Cr ... 20.9°,

(aerated)

65% Nitric boiling 48 0. 1173acid 0.1153

Mn ... 13.8%N ... 0 68%C ... 0'12°,,, Vinegar 41±I C 72 NegligibleSi ... 0'700/,

Linie-juice 41 +-1 'C 72H!-I`O'NaCI5% Citric 41±-1C 72acid -f - I%NaClSalt spray5% NaCl

5%Sulphu-

Room tern- 48perature

41±I`C 1j

NegligibleA few rustspots visible87.76

ric acid 94.31(aerated)1% Hydro- 41±1 C I 18.04)chloric acid(aerated)

Oxidation resistance tests

Oxidation resistance tests at 900°C were carried out init thermal balance on specimens of heat nos. B2, Baand B, in an atmosphere of dry oxygen. Test was alsoconducted on a specimen of 18, .8 stainless steel for thepurpose of comparison. Results of the tests showed thatthe steels B2 and B., had slightly higher oxidation rateat 900°C than 18,8 stainless steel . Steel no. B; containing

NiJhawan : Scope of research and derelopnuant work on suhstltute alloys

17.9% chromium showed much higher oxidation rate.Specimens of heat 132 and B, showed non-uniformscaling.

Metallographic studt>

Detailed metallographic studies have been carried outon this steel. In the solution treated condition it showeda completely austenitic structure in the compositionalrange covered by the typical compositions B, C, I)and E given. A solution treating temperature of 1050'Chas been used for these steels. Structural changes during,ageing have also been extensively studied for ageingtemperatures between 300 and I000'C and for periodsup to 500 hours, The steels are normally of austeniticstructure and practically no changes in structure havebeen detected up to an ageing temperature of 300°C.Structural changes have, however, been observed onageing at 400''C for 72 hours and at 500 C for 24 hours.Photomicrographs of the solution treated steels as wellas of' the steels in the aged conditions are shown inFigs. I to 4.

Transformation and ageing characteristics ofsubstitute alloys and stainless steels andtheir theoretical implications and studies

With a view to determining the suitability of nickel-freechromium-manganese-nitrogen austenitic stainless steelsdeveloped at the National Metallurgical Laboratory forhigh temperature applications, the study of the ageingcharacteristics at elevated temperatures was undertaken.Test specimens were taken from some heats which hadbeen hot-rolled into sheets and then solution treated.The metallographic examination of those steels showedsingle phase austenitic structure after solution treatment.The steels investigated contained 17-2211,, chromium,8-18°o manganese, 0.4-0.9°o nitrogen and carbon beingless than 0-10/'0'. The test specimens were subjected todifferent holding temperatures ranging from 300 to1000°C for periods varying from I hr to 100 hr in theelectric furnaces. After ageing, the specimens werequenched in water at room temperature. Metallographicexamination, hardness measurements and corrosion testsin the media of 65% boiling nitric acid, citric acid,vinegar, limejuice and salt-spray were carried out afterageing treatment. Hardness measurements of the speci-mens, in general, did not show any significant changein their hardness values.

Metallographic examination was carried out with thehelp of optical as well as with an electron microscopePlastic Fornvar and carbon replicas were preparedfrom the different heat-treated specimens for transmis-sion electron microscopic examination. The surfaces ofthe test specimens were carefully prepared mostly bythe electrolytic method for micro-examination. The

I Hear No . B,. Structure in the solution treated Condition.larked oxalic elertrolrtie x 250

Composition

Cr ... 22'07%M11 ... 10'03 0'Si ... 0'400,N ... 1.010",C ... 0.04°,,

2 Heal No. B5. Structure in the solrNion treated condition.Etched oxalic electrolytic ;; 250

i t 300ll i l d th thi i ng aa agemeta ograp c exam nat on revea eor 400"C even for a prolonged period did not bring Composition

about any marked precipitation. The precipitated phase Cr ... 17.09%increased with time and temperature and this precipita- Mn

Si... I6'93°,,

80'tion appears to have taken place by nucleation and N

......

%20.69

growth process. The precipitated phase was found C ... 0'050,/x,

21

Nijhawan: Scope of research and development work on suhstitute alloys

3 Heat No. B. Aged at 600-C for 6 hours. Etched oxalicelectrolytic X450

CompositionCr ... 20.09%Mn ... 13.08%Si ... 0.70%C 0.12%

5 :\'i-free % iainles , ^ eel shuiving lamellar type of pretipitatiunderelopeal lit, tuucleariw, and growth process after ageing at700 C fur l 000 hours

N ... 0.68% Fornivar replica x 6 000

mostly along the grain-boundaries in the form of dark- stainless steel showing lamellar type of precipitationetching nodules having lamellar structure. The interla- developed by nucleation and growth process aftermellar spacing in the nodules was marked to be less ageing at 700`C for 1000 hr and Fig. 6 shows nickel-freeat lower temperatures whilst it increased with rise inthe ageing temperatures. It was further noted that ahigher percentage of nitrogen content promoted moreprecipitation in the steels. Fig. 5 shows nickel-free

4 Neat No. B,. Aged at 600'C for 72 hours . Etched oxalicelectrolytic x 450

Composition-as above.

6 Ni-free stainless steel specimen showing twinning but absenceof precipitation after ageing at 400°C for 1 UUU hours.Formvar replica x 6 000

22

Nrfhawau : Scope of research and development work on substitute alloys

stainless steel specimen showing twinning but absenceof precipitation after ageing at 400 `C for 1000 hr.

Further work has related to the study of the ageingcharacteristics of nickel - free stainless steels of differentcompositions by identification of the different phasesformed after ageing treatment under various conditionsby electron diffraction and electron microscopy.

X-ray' diffraction studies on the high- temperatureageing characteristics of Ni freestainless steel

The nature and structure of the precipitated phases inchromium-manganese-nitrogen steels containing I8-22";,chromium, 12--14"%, manganese, 0.4 0.811„ nitrogen and0.05-0.3 carbon during sub-critical ageing and coldworking treatments have been studied using mainly X-raydiffraction and spectroscopic analyses. The austeniticphase in the chromium-manganese-nitrogen steels re-mained stable up to 30-4011, (' of cold reduction. Withfurther cold working a h.c.c. phase. having a latticeparameter of 2'868 A was observed: this phase change isidentical to the transformation occurring in 180„ chro-mium, 8g%0 nickel austenitic stainless steels on cold-

N N

V

working but unlike Hadfield austenitic manganese steel.The lattice parameter of austenite showed continuousdecrease during the sub-critical ageing indicating adecrease in solute atom concentration of the matrix.Cr2N and Cr2,,C6 types of precipitates were observedduring ageing treatments depending on the carbon ornitrogen content of the steel . With carbon/nitrogen ratioin steels below 0.01, only Cr2N was observed after sub-critical ageing , whilst with a ratio above 0'3 of carbon/nitrogen , Cr2N and CrS3Ce appeared above 500°C andonly Cr23C, was noted at temperature lower than500-C. For a ratio of O' I to 0.3 of carbon/nitrogen, theprecipitated products showed only Cr,,N at temperatureabove 500"C: while Cr2N and Cr_3C8 were observedbelow 500°C.

The activation energy of' the formation of CreN type ofprecipitate during ageing was determined to vary from3385 to 3871 KCal gm. mol.

The matrix remained austenitic after prolonged sub-critical ageing and no ferrite was detected since nitrogenretained in solid solution even after such ageing treat-ments, was sufficient to stabilize the austenitic phase.

X-ray diffraction powder patterns and photomicrogaphsof Cr-Mn-N stainless steels are shown in Figs. 7 13.

I

7 X-ray dfllraet,on powder photograph of solution treated Ni-1reeN-0'IC) (COKE Can, dia. 11.46 CM)

stainless steel showing orrl, • austenite lines (21 Cr-14 AM-0-7

8 X-ray diffraction powder photograph of solution treated Ni -ftee .stainless steel .showing both austenite and mariensite ferrite linesafter 75%%u cold-working (Fe K^,, radiation)

23

Nijhawan : Scope of research and development work on substitute alloys

C r2N

N

I

9 a'-rat diffraction powder pltotuuraplr of the extracted residues front a 21 Cr-14 Aln-0'7 N-O'IC Ni-free stainless steel aged at700 Cl 000 fir turning only Cr2 .V type precipitates (Cr KK Rad., care. dia . 5.73 cm)

5. '3 Cam d'ea , C r K .( (2c>:d )

C r 2 1-4

1 1 1 1 11 U t II

1. __.--------._ _-------- -_C. ^,. 2 3 6

10-IX-tar difii acvion powder photograph of the extracted residues from a 22 Cr - 14 Mn - 0.4 N-0.320 aged at 700'01 000 hr showingboth Cr2 A curd CrP3 C. Carbide. ( 11.46 cm cant . dia. Cr K-_ tad.)

I I Phototnicro groph of 21 Cr-14 Wn-0.7 N-0.1 C steel aged at 12 Photomicrograph of the same steel as in Fig . 11-aged at 700600 C for 10 hr. (Picral etched) x 450 C for 100 hr . (Picral etched) x 450

24

Nijhawan : Scope of research and development work on substitute alloys

13 Photomicrograph oj' the sauce steel as in Fig. 11- aged at800`C for 100 hr. ( Picral etched) x450

Lott- nickel and trickel-substantive free stainless steel

In the development of fully austenitic Cr-Mn-N stainlesssteels no data have been published to show effect of themanganese content on the properties of the steel, whichhas been investigated in detail and the optimum manga-nese content necessary to yield a stable austenitic struc-ture with 17% chromium was established. The beneficialeffect of small additions of nickel and copper on thework hardening of these steels on cold working, hasbeen shown. As the manganese content was lowered,the tendency of steel to undergo martensitic transfor-mation was noticed and conditions were then investi-gated which could produce low nickel steels comparablein mechanical properties to the 17-7 precipitationhardening stainless steels.

17°-, chromium steels with manganese ranging from4-8",, were made. In these steels nitrogen content wasranging from -2 to 10,,', the steels having lower manganesecontent having lower nitrogen content. A special cappingprocedure of the ingot tops was used in order to retainnitrogen. The steels were then hot forged at 1230°Cand hot rolled at 1200°C to give 18-23 gauge sheets.The sheets were pickled and then given a standardisingsolution treatment at 105°C followed by quenching in oil.The equation, 0.12 (%Cr-13.8) =(%C+ %N), derivedfrom phase data has been shown to relate the quantitiesof ferrite forming element chromium with the austeniteforming elements carbon and nitrogen to give the phaserelationship at 1050°C. It has been further shown thatthe excess of the ferrite forming element over austeniteforming elements can be quantitatively related to theamount of ferrite present in the steel at 1050°C bythe equation : % delta ferrite =110 [0.12 (Cr-13.8)-{(%Cr . °';,N)-; 0.05 (°%%Ni-- %Cu))]. The mechanical pro-perties of steels containing varying amounts of manga-nese was determined. The co-efficient of thermal expan-sion for a steel containing 12% manganese was de-

termined and found to be of the same order as18-8 Cr-Ni steel. The deep drawing properties ofseveral steels were determined in a Mohr and Feder-haff and in a Swift cupping testing machine. Thebeneficial influence of nickel on deep drawing propertieshas been reported. The corrosion resistance of severalsteels, with varying manganese contents, was determinedin 650-„ boiling nitric acid ; it has been shown that boththe manganese content and the presence of delta ferritein small quantities have no significant effect on corrosionrate. The effect on hardness after cold working delta-ferrite free steels containing varying amounts of manga-nese shows that as manganese decreased from 12% to 6%,hardness increased for the same amount of cold working.The effect of the quantity of delta ferrite in reducinghardness obtained after cold working is shown for 8%manganese steels. It is further shown that, though ferritedecreases the hardness after cold working 6% manganesesteels, no clear relationship exists between the amountof delta ferrite and the hardness obtained in cold work-ing as in the case of 8% manganese steels. The effect ofnickel and copper on decreasing the hardness on coldworking, and on conferring resistance to tempering aftercold working was noticed. The superiority of 8°/a man-ganese steel over 6°1, manganese steel, considering all themechanical properties, in cold rolled condition has beenshown. It was noticed that no significant increase instrength occurred on liquid air quenching solution trea-ted steels, though some increase occurred in 30% coldreduced steels after this treatmant. This shows thatsub-zero treatment to increase the strength of this type ofsteels in annealed condition will not be effective. Ontempering the 30% cold reduced and liquid-air quenchedspecimens of &% manganese steels the elongation wasfound to drop to 0% at 500°C. On ageing solutiontreated steels containing 6% manganese at 750°C for14 hours, the steels were found to have excellent pro-perties. For this treatment to be effective, about 7°„ferrite and 1% nickel were found to be essential. Theisothermal transformation curve for a 12% manganesesteel was determined and the pearlite like structureobtained was noted. Welding trials and sensitisation testsshowed that steels having more than 0 03",o carbon aresubject to weld decay but those having carbon contentof this order or less were not subject to this defect.Metallographic study of the various structures obtainedduring the course of this investigation was made. AnX-ray diffraction study of two l8% manganese steelsafter solution treatment and 30°x" cold working wascarried out. 18-8 Cr-Ni steels were also tested in similarconditions for purposes of comparison. It has been shownthat while 18-8 Cr-Ni steel partially transformed tomartensite on cold working, no such transformation wasobserved in the Cr-Mn-N stainless steel.

An attempt' has been made to study the compatibilityof some stainless steels , commercial 304 and nickel-freeaustenitic stainless steels developed at the NationalMetallurgical Laboratory with liquid lead in the tempera-ture range 600 -950°C. The kinetics of penetration ofliquid lead in these steels have been studied and activationenergies involved calculated.

It was observed that lead forms a diffusion band with

25

Nijhawan : Scope of research and development work on substitute alloys

304 steel and also diffused into its grain boundaries.At higher temperatures. some of the constituents of 304steel diffused out and reacted with lead giving a brittlephase. This steel undergoes fissure type of corrosionwhile nickel-free austenitic stainless steel developed at theNational Metallurgical Laboratory only gave a diffusionband with absence of fissure corrosion.

In the commercial 304 stainless steel, two types of diffu-sion were observed , diffusion along grain boundary anddiffusion in bulk. Possibly because of chromium diffusionout of 304 steel into lead, a brittle phase is present in thediffusion band . The liquid lead has violently attacked thesteel along the grain boundaries, forming fissures.

Analysis data

Material C Mn Ni Cr other elementsoo

o/^o

o;o

o^a

Commercial 304 0-05 0'6 11,41 17'56 ...

Ni-free austenitic 0'05 13.3 ... 2073 Si 0.24

steel NML product N 068

Tool steel

TABLE Vill Chemical composition of steels( Per cent)

Steel CMn Si W Cr V Ti N Al

t •81 -54 -23 6. 4 4 - 50 1,35 0v15 •3

2 •83 -43 '20 6'6 4.42 1.41 . .. 0.12 '6

3 ' 80 54 24 6'3 4 18 l'S 0 l3 8

4 85 59 28 6'7 4 40 l 56 1

S '84 -53 12 6-6 4'5 1-52 .3

6 '82 •53 -32 6.8 4.45 1.49 -48

Experimental heals result.s

Table IX shows the hardness of all steels in the ingotcondition after annealing and forging :

'FABLE IX Hardness of steels in ingot condition

Steel No.

I

As-castcondition

Hardness V.P.N.

As-annealed As-forgedcondition condition

640 330 360

680 347 375

630 320 355

644 318 358

685 334 385

632 315 360

Standard high speed tool steel containing proportionatelya great amount of non-indigenously available tungsten, 2exhibits controlled properties of red hardness, wearresistance and resistance to softening at higher tem- 3pering temperature coupled with high hardness whichare essentially prerequisite requirement for cutting, 4shaping or forming of materials. Since this important 5alloying element e.g. tungsten, is specially availableto a few countries, alternative efforts have been madeduring and following World War 11 in different countriesto substitute tungsten with molybdenum to producemolybdenum type of high speed steels. Owing to thesevere non-availability in India of tungsten and molybde-num. a project was taken up at the National MetallurgicalLaboratory with a view to replacing or minimising non-indigenous elements and to develop indigenous toolsteels with comparable cutting properties and hothardness to 18-4 I high speed tool steel.

With the above objective in view, a large number ofheats were made. Three grades of tool steels were selected-one containing high carbon without tungsten, the

second with tungsten with I "^, carbon and the last withmedium tungsten with -S '„ ' were made in numbers withvariation in alloying elements. Chromium, vanadium,titanium, aluminium and nitrogen in combination withone another were added with a view to developing asuitable range of tool steel which can be favourablycompared with the standard IS 4-1 high speed steel.Table VIII shows the compositions of steel investi-gated.

Table X shows the hardness after tempering treatment.

TABLE X Hardness after tempering

at 550 C at 600-C at 650'CSteel

Single Double Single Double Single Double

1 804 810 755 790 625 700

2 851 856 805 825 670 750

3 790 804 770 765 700 695

4 842 850 775 775 655 655

5 870 880 806 790 675 670

6 841 845 760 770 635 645

26

Nt)hawan : Scope of research and tierelopntent work on substitute al/ovs

As-cast hardness of the tungsten -free tool steel has beeninvestigated and shown along with the chemical composi-tion of the steels (Table Xi).

TABLE XII Chemical composition of die steels in the first series

1-teatN

Co^

Sio/

Mno%

Cr Tip

Vo 0 ,o ^0 /0

TABLE XI As-east hardness of tungsten -free tool steel

1 0.8 -2 '6 1'00'9 •3 •8

Steel C Cr V Al Ti V.P.N.0// O,° 2 0.8 '2 '6 2.0

0.9 '3 •8

7 1'75 11'5 1.12 ... '25 652 3 0-8 0.2509

8 1.85 11.5 2'5 .. 28 6904 0.5

9 1'95 8'5 3-5 ... ... 6715 0.5

10 1'78 8'4 3'5 ... 26 7056 I'0

II 119 12'5 1•12 •9 '26 741

12 119 84 2'5 •9 23 750

acked bo at 900'C Th hp x . e ardness of theannealed condition is given in Table XIII.

steels in

From the present investigation, it was observed that6-7 tungsten, 4-5" , chromium, 1- 1- 5 1vanadium steelcontaining aluminium, nitrogen and titanium as alloyingelements developed 840 to 860 V. P. N. hardness afteroil quenching from 1200"C and double tempering treat-ment at 550'C. Further work on tool behaviour andservice characteristics is in progress. However, fromthe observed hardness data of these steels, it was clearthat these steels can be recommended for makingvarious tools like taps, hacksaw, metal handsaw blades,machine thread dies, drills and other lathe machinetools.

TABLE XIII Hardness of steel in annealed condition

Steel No.

I

2

Die Steel

With development of alloy steels embracing high alloysteels, die steels of diversified grades are used. The choiceof die steels are primarily based on wear resistance, shockresistance and other high temperature properties. Workwas taken up to develop suitable die steel employingindigenous alloying elements on the basis of the composi-tions given in Table XII. Of the two ranges of carbon,one containing 0.7 to 0.8% carbon and the other con-taining 0.8 to 0.9°x, were selected. Chromium, vanadiumand titanium were added with a view to developingsuitable range of composition, of part of the first seriesof 0'8 to 0.9%%, carbon has been studied in respect ofeffect of austenitizing temperature and tempering tem-perature (Table XII).

Experimental results

After casting the die steel ingots were slowly cooled andannealed prior to forging. The ingots were forged to2" x 2" sq. The die steel bars were then annealed in a lime

As-anncacd

255

261

'.'.70

Effec t of atlsten iti2in temperature

Several austenitizing temperatures were used to studythe effect of grain coarsening on the as-quenched hard-ness of the steel . The results are given in Table XI V.

TABLE XIV Effect of austenitizing temperature

SteelHardness (Y.P.N.)

Austenitizing temperature

800-C 850`C 900C 950'C

5 832 880 817 771

2 840 880 830 792

1 837 883 820 783

27

Nijhawan : Scope of research and detrelopment work on substitute alloys

TABLE XV Ilardness, obtained under different austenitizing conditions

Tempering temperature 'C'

600 550Austenitizing Steel Steel Steel Steel Steeltemperature I 2 5 1 2°c vim vpn vpn vpn vpn

500 450Steel Steel Steel Steel Steel Steel Steel5 1 2 5 1 2 5vpn vpn vpn vpn vpn vpn vpn

800 382 270 .. 397 389

850 389 334 380 410 415

900 400 393 ... 432 436

950 407 400 ... 448 459

1000 411 403 375 499 461

1100 ... ... ... 508 450

1150

... 490 422 518 505

392 493 460 418 520 530 451

499 476 ... 524 540 ...

... 507 512 ... 533 560

302 512 ... 410 538 564 499

... ... ... 505 514 422

... ... ... 450 500 ---

High carbon, chromium and vanadium steels have been investigated in relation to optimum treatment cycles and resultant physicalproperties for die steel applications. Service behaviour of these steels will be determined by having trials with dies made of thesesteels. However, from the hardness characteristics, it is observed that these steels are suitable for dies' for minting and coining, coldblanking, forming suunping, small press tools, shear blades, etc.

Effects of hardening temperature on the temperingcharacteristics of a number of austenitizing temperatureswere followed to study the effect of the tempering behavi-our of the above steels in the range of 450-600°C.Table XV shows the hardness obtained after temperingunder different austenitizing conditions.

High temperature creep research

Studies on the high temperature creep behaviour ofCr-Mn-N type austenitic steel were undertaken. Twotypes of alloys in this group were taken up one with lowcarbon (below 01%) and the other with high carbon(say about 0 - 41';,J solution treatment at different tem-peratures in the range 1050 1200 ' C has given to thecreep test specimens . made from material hot-forgedfrom 4 " square ingot size down to about I I" square sizebars . Creep tests were conducted at 650 'C under15 kg. per sq. cnt . stress . The data so far obtainedestablished that the solution temperature had a strongbearing on the creep resistance of these alloys . The highertemperature treatment led to severe loss of ruptureductility, which was studied on the basis of structuralchanges in the material . Creep test specimens wereprepared from I I" sq. size bars, hot - forged front 4"square ingots . Hot forging was done at 1180°C - propercare was given to control the finishing temperature forforging otherwise cracking of bars was encountered. Thehot forged bars were given solution treatment at differenttemperatures in the range 1050- I200 'C by soaking atthese temperatures followed by water quenching. Testspecimens were machined from these heat treatedbars.

Hardness of the material in the as-solution treated con-dition is given below . These results show that there isprogressive drop in hardness stiith higher temperaturetreatments.

Solution treatment Vickers Hardnesstemperature Number°C (HV 30)

As hot forged 411

1050 320

1100 315

1150 303

1200 284

High sensitivity creep tests were carried out at 650'Cand 15 kg. per sq. cm. stress according to the corres-ponding British Standard Specifications. In fact, thecontrol of temperature was within much narrower limitsviz., ±1-5'C. The results show that there is all roundimprovement on creep properties on solution treatment--creep rate is reduced and rupture life and ductilityare increased. Further tests in this series are inprogress.

The materials treated at higher temperature showedabnormal grain growth and there was considerable loss ofductility in the subsequent creep tests. This question ofloss of ductility is being more fully examined from thepoint of view of structural changes. Work on specimensgiven different ageing and mechanical treatment beforecreep tests is under progress, which is expected to definethe optimum conditions of heat treatment required toobtain good creep resistance and fair rupture ductility.Taking the Cr-Mn-N austenitic steel as the base composi-tion the work was directed to evolve suitable composi-tion which would provide in the alloy a strong matrixhardened by stable precipitates of alloy carbides ornitrides and suitable intermediate phases.

As some of the creep tests last serveral tens of thou-

28

N'ijhatiran : Scope of research and derelopmen: x•ork on substitute alloys

sands of hours , every care was taken in setting upthe creep laboratory to ensure smooth running of thehigh temperature creep tests according to well-establis-hed practices abroad . Loading units had earlier beencalibrated, axiality reduced to minimum and the tem-perature was measured and controlled thrice a dayin the three zones of the specimens and regulatedthrougout the test period closer than ± 1.5°C of thetest temperature . The longest test so far conductedwas over 6 000 hours.

Development of iron-aluminium alloys and projectediron -manganese-aluminium compositions for hightemperature oxidation resistance applications

The project of developing Fe-Al alloys at the NationalMetallurgical Laboratory is aimed at developing substi-tute alloys with indigenous materials for applications atelevated temperatures from furnace hardware to turbomachines to replace nickel-bearing austenitic stainlesssteels.2 Besides heat-resistance the cheapness and availa-bility of aluminium are further incentives for employmentof these alloys. Furnace hardware provides an especiallyfruitful area of exploitation of iron-aluminium alloys.

The iron-aluminium system also shows some interestingmagnetic and electrical properties and may find fruitfulapplications in these fields-work is underway at theNational Metallurgical Laboratory on this subject.

Additions of silicon and carbon to iron containing7-91;, aluminium alloys were tried with a view toincreasing the fluidity of melt as the binary alloysof iron and aluminium are viscous. Heats were deoxidizedwith calcium. Cast ingots were annealed at 800°C.Forging and rolling were carried out from 1150 C.down to 800°C. Results obtained are given in Table XVI.

TABLE XVI Mechanical properties of some Fe-Al alloys

[lot-rolled 0' 1"thick sheet

Ingot1Heat %composition as cast Max. 010

No. Hardness stress Elonga-Al Si C VPN t.s.i. tion

is 7.36 1.65 02 364 54-64 15

2S 8.85 0-78 0.8 327 59.55 nil

3S 7-20 1.1 1'0 425 Notworkable

Air-melted calcium-deoxidized iron-aluminium alloyswere hot workable up to 12°,o aluminium content andbeyond this aluminium percentage only cast alloys willhave to be used for heat resistant applications. Coldworking and finishing of alloys was restricted to 6%aluminium content. The tensile strength of 5% alloys was42 TSI which fell to 31 TSI for an 8% alloy. Elongation

value also fell from 6-25 to 2. Rapid decrease in ductilitywith increase in the aluminium content as observed inmechanical working appeared to be inherent with thesystem and was not due to hydrogen which did notincrease in the same way. The corrosion resistance andheat resistance increased with aluminium content of thealloys. The 5% aluminium group of alloys can safely beemployed up to 800°C whilst a 12% Al alloy appeared topossess adequate oxidation resistance at this temperaturebut follows the same pattern at 1000'C. Air meltedcalcium deoxidized ferritic iron-aluminium alloys can beemployed in hot worked condition up to 12% aluminiumcontent and as-cast condition beyond 35%.

Minute additions of Ti, Zr, V, B and Ce resulted ingrain refinement, increase in hardness and tensile strength.Additions of Si and C to Fe-8% Al alloys increased thefluidity of melt. The rolled sheets had high tensile strengthof the order of 55-60 TSI, the ductility, however, waspoor, elongation being around 15% only. Addition ofvanadium to fix the carbon as vanadium carbide gaveexcellent results improving the ductility, elongationrising to 12'5%.

Fe-Al-Mn alloys also provide cheap stainless alloyswith good scope to replace stainless steels. A compo-sition Fe-6 to 8%, Al-20 to 25"% Mn has been deve-loped at the National Metallurgical Laboratory whichhas a tensile strength of 45 TSI and elongation 11-71%0with good corrosion resistance.

Substitute magnetic materials including softand hard magnetic alloys

A study has been made of soft and permanent magnetmaterials in terms of domain boundaries and rotation ofatomic magnetic moments, particularly in relation toimpurities, inclusions of anisotropy and magnetostriction.

These factors have been critically examined in relationto substitute alloys for soft and hard magnetic mate-rials.

A case has been made for iron-aluminium alloys assoft magnetic materials which can develop high per-meabilities in the range of 15-16% aluminium whenthe alloys is in the disordered state and has least valuesof crystal anisotropy and magnetostriction. These alloyscan replace nickel alloys for many applications.

Tetragonal and hexagonal metallic and non-metalliccrystals like Mn-Al and barium-ferrite are associatedwith high degree of magnetic anisotropy and capable ofgiving coercive force 3 000 oersteds , work at theNational Metallurgical Laboratory shows that thesecan replace Alnico alloys in several applications. Refe-tence has been made to the development of permanentmagnets from ultrafine elongated particles of iron and itsalloys capable of giving an energy product of 40 mega-gauss oersted.

Demand for magnetic materials is multiplying inIndia following the rapid growth of telephone, electronicsand other industries. At present, most of the demandin India is met by import. This project was takenup with a view to developing detailed technical know-how for their production and to develop, if possible.permanent magnets and other magnetic materials from

29

Nijharran : Scope of research and rlerelopntent work on sahstitute alloys

14 After cooling the specimens at 2 C;•.sec. Ji•om 1200-600 Cx13000

15 After- tempering Jro3 hrs. at 610 C X1 3Ur1U

Electron micro ^rnplrc of the alloy containing Co-12ou Al-11°o Ca-6% Ni-1rI% and Fe-52°,a after cooling at 2 C/see. from 1200to 6U0 C and tempering at 600 C'

indigenous sources. The work on development ofmagnetic materials was pursued actively under the follow-ing heads

(i) Tempering characteristics of some Alnico typepermanent magnets.

(ii) Study of magnetic and electrical properties ofceramic permanent magnets.

(iii) Study of binary and ternary alloys of manganese-aluminium iron.

This phase corresponded to'BaO, 6Fe2O3. After sinteringabove 1200 deg.C. a tetragonal phase PbO, 2Fe2O3(c-15.8917 k, a -78142 A) was also formed. In heavilyleaded ferrites the dominant phase was PbO, 6Fe2O3isomorphous with BaO, 6Fe2O,. Metallographic exa-mination of sintered compacts showed that the BaO,6Fe2O., phase progressively formed as the sinteringtime was increased. The PbO, 2Fe2O3 phase could notbe microscopically identified.

Soli ftrriles

Electron microscopic study of precipitation duringtempering of Alnico specimens containing Co-12%Al- I I ('u (u% : Ni 19% and Fe 52% was carriedout. The critically cooled specimen 2°C'sec. showed afinely distributed phase (Fig. 14), which appeared to firstgo into solution during tempering at 600''C(Fig. 15) andthen grew in size on prolonged tempering (Fig. 16).

Changes in the coercive forces observed during tem-pering of Alnico magnets could well be explained interms of changes in the dimensions of this phase. Similarwork on Alcomax type of magnets undertaken to studythe effects of different alloying elements on the coolingrates to de,elop optimum magnetic properties madegood progress.

X-ray structural studies on phase formed duringsintering at various temperatures were carried out. Itwas found that calcined powders of barium-ferrite con-taining PhO showed the presence of only one hexagonalphase of lattice parameter c-23054 A, a-5.863 A.

Work on soft ferrites was taken up to study the suita-bility of' indigenous raw materials for their manufacture.Preliminary work on nickel-zinc ferrites using purest rawmaterials was taken up. The oxides (NiO-ZnO-Fe2O.,)were taken in mol-proportion of 35 : 15 : 50. mixedtogether thoroughly, calcined at 1100°C, pul%erisedto ---300 mesh, and then pressed in the form of anchorrings for testing. Final sintering was carried out at1250°C and magnetic properties determined. Suitabilityof some indigenous raw materials is also being lookedinto.

Ceramic magnets show improvement in the magneticproperties if the fine powder is pressed in a high mag-netic field and sintered mass cooled when the field is onfrom above its Curie point. These types of treatmentswhilst significantly improving the magnetic properties,contribute to their production cost. The different stepsof manufacturing are shown in following flow-sheet.

30

Nijha ►ran : Scope of research a#ul derelopare n t irork on substitute allots

16 After tempering ai 600-C for 200 ln-. x 10 OUO

17 Netr 1, 2 and _ 1 passe coin .X ntdt, of Al-Alg a/lot

properties suitable for coinage purposes. Studies carriedout with copper-base manganese bearing alloys indicatedthat they can he successfully used for coinage purposes.However, to get a good surface finish, suitable forstamping. great care was needed during hot rolling.Further, the alloys were found to be tough and requiredgreater power for rolling compared to other commonlyused copper-base alloys.

The possibilities of using aluminium alloys for lowerdenomination coins were also examined in view of thefact that aluminium is indigenously available. Coldrolling, polishing and stamping properties of aluminiumalloys containing 1 • l °' ' manganese, 1.5°%' ) magnesium,4.2%,c magnesium were studied in detail in collaborationwith the Government of India Mint, Bombay. On the basisof detailed experimentation, it was found possible tosuccessfully produce polished coins from both annealedand cold-rolled aluminium alloys.

On the basis of erosion-corrosion tests carried outunder simulated laboratory conditions, the alloy contai-ning 3-5-5 - 00%, Mg was most suitable to get necessarycorrosion and wear resistant properties. On the basisof these studies, the use of aluminium containing about4°,/o magnesium was accepted by the Government ofIndia for minting low denomination coins. 1, 2 and3 Paise coins based on the N.M.L. compositions areshown in Fig. 17.

Flow sheet of the process

Weighing

Edge runner mill

Briquetting press (to make I"dia. I" high briquettes)

Calcination

Roll crusher

Ball mill

Sieving

Mixer (binders andlubricants)

Granulating machines

Classification of granules

Pressing into compacts

Sinter furnace with programmecontroller

Grinding, polishing

Magnetizing

Nickel and copper free coinage alloys based onaluminium - magnesium and manganese compositions

Although nickel is eminently suitable for coinage alloys,its non-availability in India poses a real problem. Thisproject3 was taken up to develop coinage alloys contain-ing no nickel and having metallurgical and physical

Development of substitute nickel and cobalt freeelectrical resistance heating elements

Non-availability of nickel and cobalt in the countryforms the basis of the comprehensive work' at theNational Metallurgical Laboratory on substitute elec-trical resistance alloys. Alloys based on Fe-Cr-Al systemwith 10--200%o Cr and 3-8% Al with small but significantadditions of Zr and misch metal have been developedat the National Metallurgical Laboratory. The produc-tion technology of these substitute alloys from melting

31

Nijhawnn : Scope of re'.search and deielopinent work on substitute alloys

to the finished wire has been standardized for implemen-tation on an industrial scale, Physical properties suchas electrical resistivity. grain growth and high tempera-ture scaling resistance of the substitute alloys have beenstudied. Studies on accelerated life tests based onA.S.T.M. standards of the substitute alloys comparefavourably with conventional alloys. References havebeen made to industrial applications of the substitutealloys developed at the National Metallurgical Labora-tory in another paper of the symposium.

From the start of Second Five-Year Plan, attentionhas been turned towards production and utilization ofelectric power as the prime mover in various industrialand domestic appliances. Thus, gradually electricalheating is replacing solid fuel, gas and oil heating.Increasing applications of electrical heat with all itsattendant conveniences will fail to register their fullimpact unless compact electrical heating elements havinglong service lives are indigenously available at a reason-able price.

Conventional t\pes of' heating elements used for dom-estic and industrial heating applications contain highand low content,, of' nickel and cobalt respectively.Resources of nickel and cobalt hardly exist in India.Thus the entire demands of heating elements used inIndia ate imported thereby involving heavy drain offoreign exchange.

Desirable characteristics, that are needed for thefinished product of electrical heating elements, are thefollowing :

1. High electrical resistivity and low temperatureco-efficient of resistivity.

2. Good resistance to scaling and oxidation abovethe red heat temperatures.

3. Low co-efficient of thermal expansion.4. Comparatively high melting point and low melting

range.5. High temperature strength and stability of struc-

ture at elevated temperature.6. Low specific gravity.7. Good cold drawability of' the material to enable

final cold drawing operation to produce finegauges of the wire.

With a ' iev^- to developing electrical heating elementsfree from nickel and cobalt , comprehensive research anddevelopment work have been underway at the NationalMetallurgical Laboratory for several years resulting inthe development of' electrical heating elements basedmainly on indigenous raw materials.

It has been established that chromium and aluminiumwhen used as alloying additions to iron , increase boththe scaling resistance and electrical resistivity of theheat - resistant elements . Aluminium has been found toexert a more pronounced effect than chromium. Theseconsiderations have led to the adoption of Fe-Cr-Albased heating elements in various countries . One of thechief difficulties With this type of alloys is their strongtendency towards grain growth during use at elevatedtemperatures , rendering the material thereby weak andbrittle . So, at each stage of hot working, extreme care

has to be exercised in controlling the temperature andamount of' working closely following pre-determinedmechanical working and heat-treatment cycles. Further-more, extremely deleterious effects of carbon, otherimpurities and inclusions on scaling resistance andworkability of these special alloys necessitate theirexclusion and proper control by using selected basemelting charge and taking recourse to precision meltingand casting techniques. Pouring temperature exercisesconsiderable influence on the hot workability of thealloy ingots.

Successful development of Fe-Cr-Al alloys of optimumcomposition based essentially on Indian alloying ele-ments aims at eliminating or otherwise reducing someof the defects like poor workability, poor creep charac-teristics, low strength at high temperatures and brittle-ness due to grain growth, by suitable additions of minoralloying elements besides improving and standardizingthe melting, casting and fabrication techniques. Theeffect of various indigenous alloying elements in opti-mum combination to obtain maximum ease in fabri-cation and final requisite high temperature propertiesand service life was worked out. Detailed study hasalso been made to formulate optimum melting andcasting techniques. Melting and finishing and pouringtemperature and hot and cold workability were someof the factors exhaustively examined during these com-prehensive investigations. The range of' analysis was asfollows

Cr ... ... 820%Al .. 3 8"Traces of other elements- Zr and misch metal.

Plant operation

The process has been described in a simplified way ona flow-sheet shown below :

Flow-sheet of the process for production of NML heating element of24 swg size

Melting of fresh charge andscrap and casting of ingot,

at suitable temperatures

Surface preparation of ingotfor forging

iHot rolling to wire rods of Hot forging to bars at con-nmachined forged bars at suit- F trolled starting & finishing

able temperature range temperature

Processing for wire drawingWire drawing with inter-stage annealing at suitable

temperature

d

Inspection, Spooling &Packaging

32

Ni/hawan : Scope of research and development work on substitute alloys

The fresh melting charge for the melt includes iron,low carbon ferro-chrome, commercially pure alminium,niisch-metal and Ferro-zirconium.

The result of accelerated life test of NML heatingelement wire has been reported in the following Table(XVII) together with the similar test results for nichromeand kanthal DS.

TABLE XVII Accelerated life test results

Accelerated life test results (hours) toburn out at different temperatures

Material at 1150"C at t200`C

N.M.L. E31 166 90

Kanthal DS 310* 165*

Nichrome 145 67

*From Kanthal Hand Book (1954)

Weldability studies

Experiments were carried out to develop properconditions of welding of the electrical resistance wires tomake up for the occasional breakage during wire drawing.Wires of different gauges (from 0064 to 0"128 in. dia.)were electrical resistance welded. The welding currentand mechanical pressure were varied. It was found thatexcept in a few cases, the welds showed brittle behaviourdue to coarse grain structure. Use of argon gas andsuitable flux has been contemplated to avoid oxygenpick up during welding and further work is being done toensure fine grain size by proper adjustment of the weld-ing parameters and post welded mechanical treatment.Major development work on the project has beencompleted. The process has been released to theindustry.

Development of manganese bearing substitute brassesand the applications of manganese insubstitute alloys

Copper alloys containing manganese offer a wide range ofsingle phase alloys having good ductility, strength andother special properties. With the use of electrolyticmanganese, superior properties of these alloys have beenobtained in work carried out at the Bureau of Mines.The possibilities of using these alloys are very promisingin India, which has large resources of manganese andhas to depend mostly on imports for zinc, nickel, etc.However, scanty data exist on various properties of thesealloys for their commercial exploitation. In view of this,a detailed programme for studies on production techniqueand various properties of binary and ternary alloyscontaining manganese was taken up at the NationalMetallurgical Laboratory.

Studies carried on binary alloys showed that additionsof manganese up to 40% progressively increased the

hardness and tensile strength at first rapidly and thenslowly. The percentage of elongation, on the other hand,showed no marked change and varied between 52-47%,for alloys containing 5-40% manganese. Addition ofzinc to alloys containing 80-60°% copper and 3U 10%manganese showed that these ternary alloys have lowerstrength and hardness compared to binary copper-man-ganese alloys. Alloys containing nickel were however,stronger and varying nickel content from 4-8% slightlyincreased the hardness and tensile strength. Comparedto conventional copper alloys, e.g. brass, german silver,etc. alloys containing manganese were stronger. Thealloys were further found to possess adequate deepdrawing properties when the composition was withinthe alpha solid solution field.

The corrosion resistance properties of copper-man-ganese alloys were found to be quite inferior and itdecreased with increase in manganese content. Replace-ment of manganese partly by zinc or nickel increasesthe resistance to corrosion, the effect being more mar-ked for nickel than zinc. Copper-manganese alloys werealso found to be susceptible to stress corrosion crac-king but were in general more resistant than copper-zinc alloys.

On the basis of investigation carried out at theNational Metallurgical Laboratory, it has been possibleto determine various factors in the melting, casting andfabrication of these alloys. With proper control ofvacuum dehydrogenating manganese at 400-500°Cpouring temperature (1100-980`C) the temperaturedecreasing with increase in manganese content, rollingtemperature (850-750°C for alloys containing more than10% Mn), etc. it is possible to successfully produce andhot work these alloys in any conventional type offurnaces. Copper-manganese alloys have different engi-neering applications such as bolts and tie-rods, shaf-ting, rivets, valves, automobile lamp bodies, lamp bases,domestic and industrial plumbing, etc. The possibilitiesof using alloys 65 Cu-25 Zn-10 Mn can be examined.for the cartridge 'cases. These can be used to substi-tute maganese-bronze where the corrrosive conditionsare not very severe. There are many other possibleuses of manganese brass, e.g. pipes for oil refineriesand utilities, shaft for marine uses, water meters,centrifuges in sugar industry, etc., where these can besubstituted by copper alloys containing Mn but toascertain this, a more detailed study on the corrosionresistance properties under different conditions is required,which is under progress at the National MetallurgicalLaboratory.

India has vast deposits of manganese ore. High gradeores are mostly exported and approximately an equalquantity of low grade ores is being dumped in themining area.

Electrolytic manganese produced from domestic lowgrade ore can be substituted for other forms of manga-nese, especially ferro-manganese, now being employedin practice.

In the commercial production of stainless steel, lowcarbon ferro-manganese having the composition 80-851/1',,manganese, 0'1-0.75 % carbon, 0-17-0-22% phosphorusis generally used. Electrolytic manganese can advantage-

33

Nijharvan : Scope of research and development work on substitute alloys

OVERSIZE

ORE

JAW CRUSHERC_ -ROLL CRUSHER

BALL MILL

CLASSIFIER

11

I

I

C-35 MESH

_ STORAGE B

T--NS

REDUCING KILNS COKE OVEN GAS

COOLER I

CALCINE STORAGE

FILTER

pbN ARSENIC PRECIPIT

LEACH TANKS

TION TANK

4

AIR

AMMONIA

FILTER 1+I SLUDGE

ANODE SLUDGECONTAININGMANGANESE

DIOXIDE

SULPHIDE RECIPITATIONTANK

T

14 SULPHURIC ACI^

AMMONIUM SULPHATE

AMMONIUM SULPHATE

KAOLIN

FILTER

C

SUL141UR oepXIDE

SULPHURIC ACIDCELL FEED TANK

ELECTROLYTIC CELLS

SPENT LIQUOR

MANGANESE

18 Flow sheet for production of electyolI'ric manganese

ously be used in place of low carbon Ferro-manganesefor the production of stainless steels.

Electrolytic manganese metal finds applications in theproduction of stainless steels, tool-steels, low-alloy steelsmade in the basic electric furnace, in carbon steels, low-alloy steel, silicon electrical steels made in the basicopen hearth furnace, nickel-free coinage alloys, high andlow expansion alloys, etc.

Extensive laboratory scale investigations at the Na-tional Metallurgical Laboratory led to the developmentof a patented process for the successful production ofmanganese metal of 99% purity from low-grade ores. Apilot plant for producing 100 lb/clay of electrolyticmanganese has has been installed and is in full scaleoperation to meet the needs of different research anddevelopment projects underway at the National Me-tallurgical Laboratory. The process has been leasedto an Indian firm for commercial scale production to

I

meet the home and export requirements of high purityelectrolytic manganese . The How-sheet of the NMLprocess for the production of electrolytic manganeseis shown in Fig. 18.

Hot-dip aluminising of steel to replacegalvanizing of steel

In view of the exceedingly scanty resources of zinc inIndia, its substitution in one of its major applications i.e.galvanizing of steel, attracted early attention at theNational Metallurgical Laboratory wherein significantresearch and development work have been done5-8 in hot-dip aluminising of mild and high tensile steel wire, hard-ware items, etc. based on optimum prefluxing and hot-dip techniques. Laboratory scale research was extendedon to pilot plant scale trials. A review of the results so farobtained including physical properties, corrosion resis-tance and metallurgical characteristics of the alumini-sed steel in the background of their potential appli-cations in Indian industry for diverse applications hasbeen given in another paper of the symposium.

We have at the National Metallurgical Laboratorydeveloped techniques to hot-dip aluminise ferrousmaterials with a view to substituting zinc used in gal-vanizing for imparting corrosion resistance to iron andsteel products. In the context of present nationalemergency our efforts acquire urgency to tideover foreign exchange shortage. It is, therefore, im-perative to switch over to aluminising as aluminiumis indigenous and we can hope to be self-sufficient indue course because of our bauxite reserves whereaszinc will always have to be imported as we do nothave sufficient zinc ores.

Figures for annual corrosion losses in India havebeen estimated at the staggering level of Rs 180 crores.The need for development of methods and techniquesof preventing corrosion to suit Indian conditions, utiliz-ing as far as possible indigenous materials is keenlyfelt.

India has been importing progressively increasing quan-tities of zinc, 50 to 700/0 of which are used in gal-vanizing. All the galvanizing plants in India for coatingsheet, wire, tubes and other hardware are potentialconcerns likely to be interested in switching over toaluminising under the stress of current foreign exchangeshortage.

Work at the National Metallurgical Laboratory relatesto the use of different types of fluxes for hot-dip alu-minising and has been covered by three Indian Patents.These have since been released to a number of Indianfirms for commercial exploitation.

Besides atmospheric corrosion applications, aluminisedmaterials find uses for heat resistance owing to resis-tance to oxidation and scaling up to 800'C. Pilotplant trials have been in progress since 1960 and offerfacilities to interested firms for supply of samples fortrial, testing and examination and to licencees forpractical demonstrations and process 'know-how' forscale up to industrial units.

Aluminised steel wire has been put to extensive fieldtrials at Beach Road, Vishakhapatnam, since 1961 on

34

Ni%haxan : Scope oJ' research and development work on substitute alloys

telephone lines and have indicated superior corrosionresistance to saline atmosphere.

One 0.70 mile loop (225 lb) aluminised iron wire150 lb mile (10 swg) was erected at Viskhapatnam on30 12 -1961. Alongside, a pair of galvanized iron wire300 lb/mile of equal length was also erected. Six twistand Britannia joints were introduced.

Resistance of galvanised iron and aluminised iron wires in ohmsrnile :

Successful trials were undertaken at the NationalMetallurgical Laboratory to aluminise wiles to meetthe above specifications. Effect of variation of diffusionparameters i.e. temperature, time of dipping and com-position of bath were studied and optimum conditionswere defined to aluminise the ACSR steel core wire tothe above specifications.

The National Metallurgical Laboratory has designeda Strip Aluminising Plant based on know-how acquiredon batch scale sheet aluminising and continuous wirealuminising plant (Fig. 19).

30.12.61. 3.7.62. 31.12.62. 10.2.63. 24.8.63. 1.1.64.

G.I. Wire3(0.) 1 b,inile 22 27 79 55 *6551i20 450/140*

Aluminisedwire 150lb mile 44 58 60 60 70 105'84*

*with old and new loops

Additional trials with aluminised wire are likely tobe taken up at four different places. The results ofthe exposure field test at Visakhapatnam as given above,show a resistance of 650 ohms'mile on 24.8.1963 forgalvanised wire against 70 ohms/mile for aluminisedwire indicating, thereby the complete failure of thegalvanized wire. The figure for aluminised wire indicatesits highly satisfactory serviceable condition even after21 years of trial run.

Hot-dip aluminising o1' ACSR core wire

ASTM B341-63T lays down the following chemicalcomposition for ACSR core wire :

Carbon ... 0-50-0-950,'o

Mn ... 0.50-1.30%

P max ... 0.040 %

S max ... 0.050 %Si ... 0-10-0-30%

It also specifies the following mechanical propertiesfor the aluminised wire for this application.

Nominal dia. Stress at 1% U.T.S. mini- Elongationextension mum % on 10 in.minimum G.L. minimum

0.05-0.19 " 170000-1350000 185000-165 000 3.5-5.0psi psi

The minimum weight of coating is in the range of0.23-0.38 oz/sq. ft. for these wires. The wires shouldalso pass the wrap test.

Substitute surface treatment including P.V.C. coatedsteel and chromated steel sheets, the latter toreplace hot-dip and electrolytic tinning of steel

The project on P.V.C. coating of steel sheets was takenup at the National Metallurgical Laboratory to replacegalvanizing of steel sheet and other end products.Various techniques of coating steel sheets with Y.V.C.plastisols self-adhesive powders and films were studiedincluding metal-P.V.C. laminates. In making the metal-P.V.C. laminates, an elastomeric adhesive has been usedfor bonding 0.3 mm and 0 1 mm films.

Chemical resistance of the black sheet-P.V.C. lami-nates was found to be good towards various reagentssuch as N1100 HCI, H2SO4, HNO3, 300,o citric acid,oxalic acid, 30% NaOH, NH4OH and Na:CO3. Thechemical resistance of metal-P.V.C. laminates are givenin Table XVI-II.

Corrosion resistance of the laminates towards marineand industrial atmospheres was tested by salt spray,A.R.D. and C.R.L, tests. It was found that the lami-nates are quite resistant to the aforesaid environmentsand compare very well with alkyd-melamine coatedgalvanized sheets. Their resistance is much superior tothat of galvanized sheets. Atmospheric exposure testsfor evaluating atmospheric corrosion are under way.

The bond strength of the laminates with the elasto-meric adhesive ustd in these experiments is about 8 to10 lb per inch width. Work with other adhesives is inprogress. It is contemplated to use a thermo-plasticadhesive which will permit continuous bonding onstrip line.

Further work is under way in making `Plastisols'with the P.V.C. resins made in the country and studytheir properties as coating material for corrosion pro-tection. Work is also contemplated to use P.V.C. resinsfor dip coating in a fluidized tank and experiments areplanned in this direction.

Chromated steel sheets

In the almost total non-existence of tin resources inIndia and the total import of tin to meet the needs ofhot dip tinning and electrolytic tinning industry in India.the subject of substitute coatings to replace tinningassumes topical importance. In this connection, workon electrolytic chromium plating on steel has beentaken up at the National Metallurgical Laboratorycorresponding to the development of `Cansuper' steelsheet by Fuji Iron and Steel Company in Japan. The

35

.Vijhawan : Scope of research and development work on substitute alloys

19 Strip aliuninisiae plum

steel sheet after alkaline phosphate treatment Na3PO4)passes through sulphuric acid pickling bath and theninto an electrolytic chromium bath containing Cr2O3-12- 131,', in I IOU of II SO_,- the pinholes in the coatingare thereafter filled by chromate dipping treatment ina 10",, ('r,O., solution, yielding a coating thicknessof 0.05.

Comprehensive work on similar line was taken upat the National Metallurgical Laboratory. The bathconditions required to give a uniform thin coating ofchromium on cold rolled sheets were determined. Thechromic to sulphuric acid ratio was maintained at 100:I and the time treatment extended over to 10 minutes.Corrosion tests carried out in boiling sodium chloridesolution and 1°o citric acid indicated that the use of thin

lacquer over the coating improved the corrosion resis-tance considerably. The results obtained are interesting andfurther large-scale trials to assess the suitability of thisprocess for commercial exploitation are in progress.

Pack chrmnising

Resistance to high temperature oxidation can be con-ferred on steel both by chromium and aluminiumcoatings. Aluminised steel is resistant up to about 800'C.Chromised steels are also useful up to about900°C but oxidation is extensive at 1000 - C andabove. The possibility of developing coatings whichcan withstand higher temperatures is, therefore, aninteresting field of research.

36

Nijhawan : Scope of research and development work on substitute alloys

TABLE XVIII Chemical resistance of metal-PVC laminates (Black sheet bonded with PVC films 0.3 and 01 mm)

S1. PVC film Change of weight per cent

No. Reagent thickness mm after one week's immersion Remarks

1. l0%HCI 0.3 0'21 (loss) After dipping the samples for 3 hr. in 10% HCl,0.1 0.25 (loss) H2SO, and HNO3, hydrogen evolved vigorously even

2. 10%HSSO4 0.3 0.42 (loss) though the edges were protected and hence the dipping011 0'30 (loss) di^,cuni in Lied.

3. l0%HNO3 0'3 0'22 (loss)0.1 0'35 (loss)

4. N/100 HCI 0.3 0.14 (increase)O' l 0.20 (loss)

5. N/100 H2SO. 0.3 0.01 (increase)0.1 0.08 (loss)

6. N/100 HNO3 0.3 0.23 (increase) Weight change in the reagents indicated is not coi:si-0.13 (increase) derable and hence the laminates are quite resistant.

7. 30% Acetic Acid 0'3 0.11 (increase)0.1 0.21 (increase)

8. 30% Citric Acid 0.3 0.50 (loss)0.1 0.60 (loss)

*9. 20% Oxalic Acid 0.3 0.09 (increase) *Reacted with the bond as the solution got coloured.0'1 1,2 (increase)

10. 30% Na2CO3 0'3 0'07 (loss)0.1 0.13 (loss)

H. 30% NaOH 0.3 0.084 (increase)0.1 0.2 (increase)

12. 28% NH,OH 0.3 0.25 (loss)0.04 (increase)

Co-diffusion of chromium and aluminium , therefore,suggested itself as one line of enquiry . The complexoxide film that would result in service from Cr2O3 andA1203 and the lower oxides can be assessed for their pro-tective value to arrive at a suitable coating for useabove 1000°C. A master alloy of chromium and alu-minium was prepared by alumino-thermic reduction ofchromite. It can be easily kept packed in this alloypowder at 800 °C added to the pack to facilitatechromium diffusion through Cr2Br 3. Grey-matt oxidationresistant coatings were obtained.

Substitute aluminium electrical grade conductors

As indigenous resources of copper are not sufficient tomeet the mounting engineering demand for the transmis-sion of electricity, it is being increasingly replaced byaluminium as a national policy. It is estimated thatalmost 50'1', of the estimated production of 70 000 tonsof aluminium in 1965-66 will be used to transmitelectricity. However, there is acute shortage of electricgrade aluminium, i.e. aluminium with greater than99.7%, purity. As the demand of electric grade alu-minium is at present greater than Indian production,the difference is met largely by import from Canada,United States, Germany and East European countries. Thesituation can be substantially improved if aluminium ofcommercial purity, i.e. 99.4-99 5% aluminium, can beupgraded by alloy conditions and/or heat treatment.

This forms the basis of a current research projectat the National Metallurgical Laboratory.9 To developan aluminium alloy of high conductivity from com-mercial aluminium it was necessary to undertake a

basic programme of research to study the effect ofaddition of silicon, iron, manganese, magnesium onthe electrical conductivity and the tensile propertiesof electric grade aluminium. Silicon, iron and titanium arenormally present in commercial aluminium as dissol-ved impurities and exercise an adverse effect on itselectrical conductivity. Its conductivity may be impro-ved by removing these soluble impurities from thelattice of aluminium by (i) heat treatment and(ii) suitable alloy addition or (iii) by both. Theirremoval constitutes the subject matter of a researchpaper which is being presented at this symposiumfrom the National Metallurgical Laboratory. However,the following conclusions can be drawn from the workso far conducted :

(i) Commercial aluminium after optimum Solutiontreatments and quenching resists the removal ofsolutes from its lattice during ageing.

(ii) The rate of removal of solute atoms is fasterin aluminium-silicon alloys and decreases inbinary aluminium alloys with magnesium, man-ganese and iron in that order.

(iii) The addition of magnesium to aluminium-siliconalloys substantially increases the rate of removal ofdissolved silicon from the lattice of aluminium.

(iv) The effect of cold working prior to ageingtreatment to acceleration of the precipitationprocesses is much less in aluminium-silicon alloysthan in duralumin type of alloys.

37

Nijhawan : Scope of research and development work on substitute alloy's

In order to project the results of laboratory investiga-tions to commercial scale production, an aluminiumalloy was made using aluminium of commercial purity.This alloy was successfully rolled and drawn into wireat the works of Messrs. Indian Cable Company. Thewire was also tested at their Laboratory and was foundnot only to satisfy the requirements of Indian standardbut also to excel it.

Its tensile strength in the hard drawn condition wasapproximately 171%, more than that of the wire drawnfrom electric grade aluminium ; in the same conditionits conductivity was 61.4%-0 ]ACS which is an improve-ment of 1.4"'/%, IACS over the minimum acceptable valueof the Indian Standard Specifications and representsimprovement of 0-b°%, IACS over the standard value.Its elongation on 10" gauge length is 3'5% against 1.9%specified in the standard. It is noteworthy that improve-ment in the conductivity has been achieved along witha substantially increased strength of the conductor.Large scale trials are at present in progress at theworks of Messrs. Indian Cable Company.

Aluminium-based substitute alloys includingantifriction aluminium bearing alloys

Common plain hearing materials are bronzes, copperlead mi^tures and lead base and tin base white metals.Practically, all these conventional plain hearing materialscontain non-ferrous metals like tin, copper. lead andantimony. As these metals are very scarce in India,research work on the possibility of development ofaluminium based plain bearing materials was taken up.In this connection. extensi%e work has been carried outwith the aim of developing both soft aluminium basebearing materials which could he bonded to steel back-ing for substituting copper- lead and white metal typesof bearings, and solid plain bearings for bushing typeof applications for replacement of phosphor-bronze,leaded bronze and similar type of solid bearings. As aresult of such work, it has been found that soft alu-minium base bearing with small quantity of lead andantimony might suitably replace conventional overlaytype of hearing alloys whereas aluminium bearings in-corporating suitable quantity of zinc, silicon and ma-gnesium might replace leaded bronze and phosphor-bronze for solid hearing applications.

As the experimental aluminium base substitute bear-ing alloys of both the groups contain very small qu-antity of scarce non-ferrous alloys, introduction of suchbearings will effect considerable economy in use ofnon-indigenous metals.

For the overlay type of bearing the total amount ofantimony and lead is less than I0%, the balance isaluminium. For the solid hushing type of bearing, zincup to 201(, has been used and the total percentage ofother alloying elements like copper, lead and antimonyis less than 10%.

Development of controlled friction materials

The aim of the project was to develop suitable combina-tion of controlled friction materials which will give co-

efficient of friction not exceeding 0 16 in. long serviceunder repeated sliding condition . At present importedfabric friction liners are used in combination withphosphor-bronze . These are fitted to the bogie andhind truck sliders -of some type of locomotives. Thefriction between the two is utilized to damp out in acontrolled way the sinusoidal oscillation set -up whenthe engine or bogie turns round a curved track. Theimported material which is being used currently deve-loped high friction in service . Higher co-efficient offriction reduced the effectiveness of spring control oncurves.

Work was taken upLaboratory to develop a

at the National Metallurgicalsuitable substitute which will

give more effective service. Preliminary experimentsrevealed that no conventional pair of material is likelyto give in dry running condition as low friction valuesas desired.

The work finally led to the development of a newantifriction material based on thermo-setting plasticmixed with about 20;o P.T.F.E. and 5% asbestos. Thesolid lubricant P.T.F.E. could be impregnated only tothe surface layer of' the composite material to econo-mise its consumption. The P.T.F.E. impregnated com-posite material in combination with grey cast iron gavesatisfactory result after long time of test. This materialis under long term test under actual service conditions.

Indigenous production of electrical contact spring

Phosphor-bronze is widely used as electrical contactspring in various electrical equipment. This material isan imported item and there was no indigenous pro-duction of this material. The Indian Railways were in-terested in the production of such spring indigenouslyat the first instance and finally in the development ofa substitute contact spring based on indigenous rawmaterial.

The work was entrusted to the National Metallurgi-cal Laboratory. At the first phase of the work thetechnical know-how for the production of standardphosphor-bronze spring material has been developedstarting from melting and casting procedure, hot andcold working and finally stabilizing treatment so as toimpart the desired physical and mechanical propertiesto the spring.

The possibility of development of bimetallic or tri-metallic spring using mostly indigenous materials isunder study at the National Metallurgical Laboratory.

Improved mild steels for structural purposes andthe development of indigenous low alloyhigh strength steels

Basic principles underlying the development of lowalloy weldable structural steel, otherwise known asimproved mild steel, were studied in relation to reportedtechnical literature and work on the subject has beenindicated in another paper.

The investigation at the National Metallurgical Labo-ratory covered low alloy 0'5 Mo-B bainitic steels, wherelow temperature impact toughness indicated a gradual

38

N,jhaivau : Scope of research and development work oar substitute alloys

TABLE XIX Test results of one of the tonnage scale heats of low-alloy high tensile structural steels

'Tensile test Charpy impact value at

Yield stress EL.% Room

Max. stress kgjsq . cm. kg sq . mm. R. A. 2" GL temp. 0°C -20C -40"C -60°C

*N76.23 47'5 25 38. 28 22 21 23**A55.12 42'87 65'5 35 41 - - - -

*Normalised**Annealed

lowering of transition temperature range with increasingNb contents and particularly so when the Nb additionsrange from -010/,-0'03°,x,. Studies of low carbon Nb-V-Nand Nb-Ti steels show high yield strength and loweredtransition temperature ranges, which have been attri-buted to the combined effects of grain-refinement andprecipitation, besides solid solution strengthening effects.

Development of lute' allot' high tensile structural steel

Use of low alloy high tensile steels as structural steel willresult in considerable steel economy as this group ofsteels has much better strength to weight ratio comparedto conventional structural steels in addition a weldablesteel would cause further saving. A recent study of theNational Council of Applied Economic Research hasshown that the use of welding may lead to a savingup to 24% in the consumption of structural steels.

From these considerations a broad-based investigationwas taken up with the objective of developing structuralsteels possessing adequate mechanical properties, hot andcold working characteristics, optimum corrosion resis-tance and favourable welding characteristics based essen-tially on indigenous alloying elements.

There are various processes by which the strengtheningof the steel can be achieved. These are :

(i) strengthening of the matrix by solid solution effect.

(ii) strengthening through grain refinement and in-creasing pearl ite/ferrite ratio.

(iii) strengthening through dispersion of extremely fineprecipitates in the matrix.

The work in this Laboratory was aimed to utilize allthe three effects, without increasing pearliteiferrite ratioknown to adversely affect weldability. Use of judiciousquantity of manganese, silicon and vanadium has beenmade to achieve the first two effects. Finally, efforthas been made to get a finely dispersed vanadium nitridein the matrix of the steel to achieve further strengthening.The results of the tests have been encouraging. Ithas been found that by addition of suitable quantity ofmanganese, silicon and with small quantity of vanadium,weldable quality steels with maximum tensile strengthof about 42 tons per sq. inch and yield stress of about30 tons per sq. inch could be produced in the experi-mental heats whereas by utilizing the process of disper-sion hardening, strength as high as 50 tons per sq. inch

could be obtained in low carbon steels. Weldability testof the latter group of steels is under progress. It isexpected that in view of low carbon content andlow pearlite; ferrite ratio the steels will be weldableas well.

After analysing results of initial trials, it low carbonsteel with carbon content in the range of 0'08-0'2011,0with optimum percentages of manganese (0'8-2'0%) sili-con (0'15-035',), copper (0.2-0.5°%,) and vanadium(0'05-0.2%) was selected for making heavy tonnage scaleheats. Copper content of this heat was slightlyhigher than that specified. Tensile test results andCharpy impact values of the heat are given in theTable XIX.

Thermo-mechanical and processing treatments forultra high strength steels

In recent years, the demand for steels with vastlyimproved mechanical properties has multiplied. The pro-cess of producing low cost ultra high strength steels bythermo-mechanical treatment (TMT) has drawn wideattention. Work has already been taken up in NationalMetallurgical Laboratory on the development of highstrength steels based on thermo-mechanical treatments.The process of producing ultra high strength steels byTMT methods is not yet well established. Moreover,extreme high strength is not the only engineering propertyrequired of steel. It is true that thermo-mechanicallytreated steel does not often possess good oxidation andcorrosion resistant properties.

Attempts are, therefore, made to develop at theNational Metallurgical Laboratory high strength lowalloy steels by utilizing some of the thermo-mechanicalmethods such as "ausforming" and "controlled rolling."The work has been taken up on the improvement inthe strength and ductility and impact properties ofausformed low alloy steels having controlled additionsof some alloying elements like Mn, Si, N, etc. on whichno data are available.

At present ausform deformation are being carriedout mainly by forging and rolling using proper tem-perature and deformation conditions. It is also proposedto study the effect of TMT on the austenitic stainlesstype and maraging type of steels, developed from indi-genous sources, in future.

The mechanism involved in all these processes is oftencomplex and will be studied based on electron micro-scopy of thin film and X-ray diffraction examinationof residual stresses.

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Nijliawan : Scope of research and development work on substitute alloys

Physical metallurgy of substitution of alloys includingtheoretical consideration in the substitution ofmetals in alloys

Survey of the scope and economics of substitutionwith indigenous materials and metals for engineer-ing, ordnance and defence application

Substitution of one metal by another either as a baseor as an alloying element is neither simple nor straightforward. Substitution has been studied from the pointsof view of effects of substitute alloying elements on (i)phase transformations including reaction kinetics. (ii)structural features such as, their distribution and influenceon vacancies and stacking faults, (iii) volume change,(iv) nature of carbides and carbide transformations inalloy steels (v) precipitation hardening including co-herency of precipitates and (vi) on plastic deformation.The substitution of nickel, molybdenum, cobalt, copper,etc. with indigenous metals such as manganese, titanium,aluminium and magnesium, introduces complex factorsand requires for successful end applications modifica-tions in heat treatment and thermo-mechanical proces-sing of the substitute alloys. In this connection anotherpaper has been prepared for this symposium.

Substitution in refractory products including thedevelopment of indigenous dense carbonaggregate to replace imported anthracite

Low ash carbon is the main constituent of electrodes,carbon linings of metallurgical furnaces and carbon pas-tes used in Soederberg electrodes. For these applications,it should be free of volatiles, strong, dense, non-shrin-king and capable of yielding hard dense carbon particlesof varying sizes. In the United Kingdom and othercountries, low ash anthracites find considerable appli-cation in the production of paste and structural carbon.In India, there are no known low ash anthracitedeposits.. Available calcined petroleum coke is cavitatious render-ing it difficult to yield dense grains of greater than 3mesh B.S.S. site. Thus, the crux of the problem, sofar as production in India of carbon refractories andelectrode pastes is concerned, is to find a suitablesubstitute for anthracite coke. Investigations were there-fore undertaken1' at the National Metallurgical Labo-ratory to find out whether readily as ailable corbonaceousmaterials in India namely uncalcined petroleum cokefrom oil refineries of Dighboi and Gauhati and coalsfrom Assam coal fields could be processed to yielddense carbon.

Investigation' conducted indicated that it was possibleto make sound carbon aggregates out of Assam coalsthough their bulk density and apparent specific gravityvalues were km suggesting considerable intra-particulateporosity. The more important factors affecting the pro-perties of the final compacts were as in the case ofuncalcined petroleum coke, granulometric compositionof coal powders, nature and quantity of binder andheat treating schedules. Introduction of char in thesebodies in certain proportions was beneficial in as muchas it increased the compression strength considerably.Utilisation of liner coal and char powders and binderwith higher coking value may bring about furtherimprovements.

The scope for substitution in ordnance and defenceapplications requires judicious analytical approach andcritical scrutiny for obvious reasons. The work at theNational Metallurgical Laboratory in these strategicfields is relatively of recent origin . The progress of thework requires close co-ordination with ordnance anddefence establishments which is not always so easy toachieve in actual practice. The substitution work hadtherefore, to be exceedingly selective . An important fieldcovers the substitution of cartridge brass by B.S.-14-72-H-12 aluminium, 2.5% copper alloy. The rigid physicaland metallurgical requirements for cartridge brass casesare specific and severe in view of sudden and heavyexpansion and contraction before and after the ignitionof' explosive charge within--any malfunctioning of thecartridge cases will seriously damage the gun barrel. Ithas been reported that deep drawing rimming steelcartridge cases have been in use and attention will bedirected towards the development of substitute cartridgecase alloys.

Another field which has attracted our attentionfollowing the Sino -Indian conflict, is the light-weightarmy hardware and fighting vehicles including the lightarmour tank and related military equipment. In thesefields U.S. Army's growing family of light army hard-ware and equipment is indeed a tremendous logisticalimprovement over heavier weapons and war equipment.The U.S. M 113, an impressive light weight mobiletactical equipment weighs less than half of its predec-essor 59, the 20 tons, all steel armoured personnelcarrier-the M 113 is fitted with aluminium alloyarmour which took Kaiser Aluminium and ChemicalCorporation 10 years to develop and which is nowdesignated 5083. Welded aluminium alloy used asarmour has had its own specification (MIL-A-46027)since I95X. -physical properties of the material inthis specification are most closely approximated bycommercial alloys 5083 and 5456 possessing 0.21,„ yieldstrength of 37 000 50 000 psi, and tensile strength of45 000 to 55 000 psi and elongation min. of' 9'.. Thehull of M 113 is all-aluminium, from the heaviestarmour plate to the smallest support brackets andfixtures. Alloy 7039 corresponding to Army SpecificationMIL-A-46063 (•2",, Mn, 2-7"„ Mg, 0.20°. Cr, 4'0%Zn, aluminium base alloy) possesses maximum tensilestrength of 60 000 psi and annealed strength of 32 000psi and has resulted from a search for superior armourplate material, offering a combination of high tensileproperties, good toughness and weldability, good resi-stance to stress-corrosion cracking and favourable pro-perties at cryogenic temperatures. A modification of7039, designated X 7139 ( containing zirconium) is alsonow available. The U.S. Army's General Sheridan lightweight reconnaissance vehicle also uses heat treatablealloy 7039. The alloy 5083 answering to MIL-A-46027Army Specification, has been used in Army M-109 allaluminium armoured, self-propelled 105 mm howitzerand is a 0.7 Mn, 4.5% Mg, 0.15% Cr-- aluminium base

40

Nijhawan : Scope of research and development work on substitute alloys

alloy and possesses maximum tensile strength of 52 000psi and annealed strength of 42 000 psi. Concertedattention will be paid to the development of light weightarmy hardware alloys along the above lines in closecollaboration with the Indian Ordnance and DefenceEstablishments.

industrial scale application and economics of subs-titution of metals- economic recovery and utilisa-tion of strategic indigenous non-ferrous metals

The substitution of metals and alloys cannot in itsultimate analysis be divorced from incidental themessuch as the recovery of secondary metals and refiningof secondary metallic values during the production ofprimary metals and processing of primary alloys. Inother words, maximum use has to be made of theexisting resources. howsoever scanty these might be,such as in the case of zinc necessitating the recoveryof other non-ferrous metals and alloys such as copperand brass as sources of secondary metallic values. Workon these fields is also currently in active progress at theNational Metallurgical Laboratory including the re-covery of zinc from dross and treatment of ashes,skimmings and swarfs.

On themes relating to working of metals, uses haveto be made of technological developments such as cladd-ing of metals and composite metals to reduce higheralloy content and related working process calculated tolower alloy contents of the finished end products andcomponents. In these fields, the National MetallurgicalLaboratory has deen active though industrial scale im-plementation of these techniques and processes has yetto be fully adopted.

The subject of industrial scale applications and eva-luation of economics of substitution of metals are per-haps the most difficult, though not inseparable featuresof substitution and have always tended to be some-what controversial adjudged on the basis of metallurgi-cal acceptability of the substitute alloys, overall econo-mics and service performance. It is in these fields thatindustry has to play its leading role in industrial scaletrials of the substitute alloys and in providing answersto applied research conducted in laboratories to upgradethe substitute end products as also their productioneconomics. Basic and applied research can hardly func-tion in isolation and a plea is therefore made to theIndian industry to come forward and play a leading rolein assisting research in attaining self-sufficiency througheffective substitution of metals and alloys. The ponder-

ous task of substitution of metals and alloys is not easyand certainly not without its due share of pitfalls andheartbreaks and yet the satisfaction of pursuing well-worthobjectives is highly rewarding. The scope of work onsubstitution of metals and alloys which forms themain theme of short-term and long-range programmesat the National Metallurgical Laboratory, presents abroad-based spectrum to the Indian scientists andmetallurgists, challenging in its planning, execution andapplications, placing indeed a high premium on re-search ingenuity and applied technology and in whichthe National Metallurgical Laboratory is fully engagedand totally dedicated today.

Acknowledgements

The author wishes to thank the research staff activelyengaged on the work of substitute metals and alloysat the National Metallurgical Laboratory-some referencesto whose scientific papers, reports and work havebeen made

References

I . Compatibility studies of some stainless steels-M. C. Naikand R. P. Agarwala. J.I.S.L, Oct. 1965.

2. Development of iron-aluminium alloys-S. M. Arora, S. S.Bhatnagar, P. K. Gupte and B. R. Nijhawan ; Annual Tech-nical Meeting; Indian Inst. of Metals, 1964.

3. Studies on properties of binary copper-manganese alloys byA. K. Lahiri, K. P. Mukherjee and T. Banerjee ; Trans. ofIndian Institute of Metals, Vol. 17, June 1964, p. 81.

4. Electrical resistance alloys ; Research and Industry, January I,61, 1-3.

5. Aluminising of steels by the aqueous flux process by S. M.Arora, P. K. Gupte and B. R. Nijhawan ; Trans. Indian Inst.of Metals, Vol. 11, June 1958, pp. 57-72.

6. Linseed oil as an organic flux in hot-dip aluminising of steelsby S. M. Arora, P. K. Gupte and B. R. Nijhawan ; NMLTechnical Journal,. Vol. I, No. 3, pp. 9-16 (1959).

7. Hot-dip aluminising of M. S. Wire on pilot plant scale byS. M. Arora, A. N. Kapoor, P. K. Gupte and B. R. Nijha-wan ; NML Technical Journal, Vol. III, No. 4, pp. 4-9(1961).

3. Atmospheric corrosion resistance of aluminised M. S. Wireexposed to saline atmosphere at Visakhapatnam by S. M.Arora, A. N. Kapoor, P. K. Gupte and B. R. Nijhawan ;NML Technical Journal, Vol. V. No. 3, pp. 5-9 (1963).

9. Electrical conductivity of aluminium-silicon and aluminium-silicon-magnesium alloys by Manjit Singh and RajendraKumar ; Trans. Indian Inst. of Metals, March 1965, Vol. 18,p. 34.

10. Production of dense carbon aggregates from carbonaceousmaterials of varied volatile contents for use in carbon pro-ducts in general and Soederberg paste in particular by P.Prabhakaram and H. P. S. Murthy ; NML Technical Journal,Nov. 1961, Vol. III, No. 4. pp. 13-15.

Nijhawan : Scope of research and development work on substitute alloys

Discussions

Mr W. E. Duckworth , (BESRA. London) : Referring tothe Ni-free stainless steels Dr Nijhawan pointed outthat they did not transform at subzero temperaturesto martensitic condition in the same way as the 18 : 8stainless steels : in fact there is a transformation inthe 18 : 8 stainless steel which is extremely useful forthe production of a high strength controlled transfor-mation steels coming into use for aircraft applications.Does the author see any way of modifying theNi-free stainless steels so as to produce the same sort ofcontrolled transformation characteristics which are soextremely useful in the 18: 8 series of stainlesssteels

Dr B. R. Nijhawan, (Author) : The paper I have justpresented did not include controlled transformationstudies. This subject will be discussed exclusively in asubsequent paper indicating in detail the T.T.T. trans-formation characteristics and how controlled transfor-mation could be applied. This is a field which is stillvery much open for study and investigation and wehope to do some substantial work on this aspect butwhat we are basically concerned with is the com-parison of the Ni-free stainless steels with the 18 : 8series of stainless steels for various applications andfrom the point of view of substitution of Ni essen-tially by manganese and nitrogen. These steels cannotobviously replace each and every end product appli-cation of 18:8 stainless steels especially as their in-ter-crystalline or weld decay properties are relativelydeficient. We are now thinking of alloying the Ni-freestainless steels with niobium up to a certain percentage,which might be less than to improve their welddecay properties. These are aspects in the study ofwhich we are now actively engaged.

Mr M. B . Shankar , (Hindustan Aeronautics Ltd., Ban-galore : I fully agree with Dr Nijhawan that ourproblem of substitution cannot be tackled on a uni-versal basis. We need have in view only one or afew particular applications. The substitute alloy deve-loped may not have exactly all the properties of theoriginal material conforming to all the end productapplications. I understand that Ni-free stainless steelsdeveloped at the NML are very adequate for stainlesspurposes and not meant for high temperature char-acteristics or weldable stabilised conditions.

Dr G. P. Chatterjee, (Hindustan Steel Ltd., Durgapur) : We are just stepping into the field of manu-facture of stainless steel at Durgapur and we areplanning to produce also the Ni-free austenitic steeldeveloped by the NML. Barring these two disadvantagesregarding the heat resistance properties and weldability,I believe there are many applications where these steelscould be utilized: as a compromise we are also thinking ofproducing new stainless steel with Ni partly substi-tuted to the extent of 50% by Mn. It has beenestablished that the properties of these substitutestainless steels are very similar to those of thenickel-hearing is : 8 stainless steels, but of course, theseare not exactly the same and strictly speaking thereis no question of absolute replacement. I believe thatin a country like ours without any resources of Ni,extensive study of these two types of stainless steelsi.e. Ni-free and semi Ni-free will bring extremelyuseful results. Such steels should be introduced in ourindustry including the services and if the consumersco-operate with us in bringing us their problems Iam sure suitable adjustments can be made to eliminateall practical difficulties.

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