HOT ROLLING OF PLATES FOR SPACE SHIPS

AT PLATE MILL, BSP

MARAGING STEEL

• Maraging steels are a family of low carbon, age hardenable,martensitic steels having a combination of ultra high strength,coupled with very high toughness, good weldability, ease ofheat treatment and machinability.

• Alloys are characterized by very low carbon content and• Alloys are characterized by very low carbon content andsubstitutional elements (Ni, Co, Mo, Ti, Al etc.,)

• Strengthened by precipitation of inter-metallic in a tough low-Strengthened by precipitation of inter metallic in a tough lowcarbon Fe-Ni martensite matrix.

• Maraging is derived from martensite + aging implying agehardening of martensitic structures.

• Major applications include:• Rocket motor casings• Light aircraft landing gear

P h f• Power shafts• Low temperature tooling

SPECIALITY OF MIDHANISPECIALITY OF MIDHANI MARAGING STEEL

FOR AEROSPACE APPLICATIONS

• MIDHANI is the only producer of maraging steels in India

• The organization guarantees fracture toughness of > 90 MPa √meven at high yield strength of 1800 MPa

• Use of carefully controlled thermo-mechanical treatment coupledwith unique two / three stage solution treatment developed byMIDHANI helped in meeting customer needs.

SURPASSING INTERNATIONAL STANDARDGuaranteed Minimum Properties

SPECIFICATIONGuaranteed Minimum Properties.

0.2% PS(MPa)

UTS(MPa)

KIC(MPa√ m)

AICMA-FE-PA95 1620 1720 -W.Nr. 1.6359.4 1620 1720 -AMS 6520C 1690 1758 -AMS 6520C 1690 1758MiL-S-46850D 1650 - 83MDN250 1725 1765 90

1350 1750 2050Yield Strength in MPa

PRODUCTION ROUTE OF MDN 250PRODUCTION ROUTE OF MDN 250AT MIDHANI

VACUUM INDUCTING MELTING

VACUUM ARC REMELTING

VACUUM ARC REMELTING

INGOTSLABS

FORGE PRESS

SLABS155 (T) x 1300 (W) x

FORGE PRESS / HAMMER2350 (L) in mm

PRODUCTION ROUTE OF MDN 250PRODUCTION ROUTE OF MDN 250AT MIDHANI

SLABSSLABS

• Chemical analysis in XRF• Macro-examination of Top & Bottom

d f l bends of slab• Metallographic Examination• Visual Inspection of Slabs• Visual Inspection of Slabs• NDT & Testing• Pre dispatch Inspection by BSP• Pre dispatch Inspection by BSP

Inspected slabs are rolled into plates atInspected slabs are rolled into plates at BHILAI STEEL PLANT

MDN 250 SLABS PLATES

SLABS155 (T) x 1300 (W) x 2350 (L) in mm

Hot rolling at BSP

PLATES9.3 (T) x 2400 (W) x 10000 (L) in mm9.3 ( ) 00 (W) 0000 ( )

2/3 Stage solution treatment

HEAT TREATMENTat MIDHANI

Grinding, UT, Testing

PLATES7.8 (T) x 2250 (W) x 9500 (L) in mm

PLATES MOTOR CASE

PLATES7 8 (T) x 2250 (W) x 9500 (L) in mm7.8 (T) x 2250 (W) x 9500 (L) in mm

At approved vendors of VSSC

Fabrication of Motor CaseVSSC

Ageing at 450 o C for 3hrsAgeing at 450 C for 3hrs

Testing

Final properties (min) Proof Stress: 1725 MPa, UTS: 1765 MPa,%Elongation: 13, Fracture toughness: 90 MPa√ m

CHALLENGES TO BSP

SIZE OF MDN SLABS• Slab size for reheating furnace is 200-250 (T) x 1100-1800 (W) mmSlab size for reheating furnace is 200 250 (T) x 1100 1800 (W) mm• Climbing of thinner slabs in pusher type reheating furnace

Pilot slabs of 200 mm are charged before the MDN 250 slabs toPilot slabs of 200 mm are charged before the MDN 250 slabs toavoid overlapping

MILL CAPACITY• Roll separating force 4500 ton• Roll separating force 4500 ton• Maraging steel is a high strength material (more than 1000 MPa in as-

rolled condition)rolled condition)

Soaking zone temperature regime and time is stabilized in viewwith material chemistry and mill capacitywith material chemistry and mill capacity

CHALLENGES TO BSP

SLAB DISCHARGING & PLATE FINAL FINISHINGTEMPERATURE

• Faster cooling rate of the stock during rollingHigh draft schedule is done in roughing stand from 155 to 18High draft schedule is done in roughing stand from 155 to 18

mm thicknessFinish rolling temperature is aimed below 8000CFinish rolling temperature is aimed below 800 C.

MONITORING OF SULPHUR & OXYGEN IN FLUE GASESMONITORING OF SULPHUR & OXYGEN IN FLUE GASES• Specified Sulphur content : 400 ppm (max) and Oxygen : < 2%

S l h t t d O i th f t h iSulphur content and Oxygen in the furnace atmosphere iscontrolled and achieved sulphur content is 40ppm and oxygen is0 5% in the flue gas of the reheating furnace0.5% in the flue gas of the reheating furnace

ROLLING PLAN OF MDN 250 PLATES ATROLLING PLAN OF MDN 250 PLATES AT BHILAI STEEL PLANT

Preparation of protocol for rolling by BSP, MIDHANI, VSSC officialsCh i Pl i fi li d• Charging Plan is finalized

• Calibration status of reheating furnace, temperature measuring instruments areensuredensured

• Arrangement for measuring flue gas analysis for S & O2

• Arrangement for job temperature measurement in soaking zone at both yardArrangement for job temperature measurement in soaking zone at both yardside and mill side of the furnace

• Planning of 200 mm thick pilot slabs and 10-12 mm high tensile plates rollingbefore and after the campaign

• Ensuring the facilities for material handling like magnetic crane etc.

ROLLING PLAN OF MDN 250 PLATES ATROLLING PLAN OF MDN 250 PLATES AT BHILAI STEEL PLANT

IDENTIFICATION OF MDN 250 SLABS AT BHILAI STEEL PLANT

ROLLING PARAMETERS INROLLING PARAMETERS IN MDN 250

• Reheating furnace temperature regime-• Preheating zone: ~ 11800C ± 100C (around 2hrs)g ( )• Heating zone: ~ 12800C ± 200C (around 1hr min.)• Soaking zone: ~ 12500C for 3hrs and ~ 12800C for 1hr min. ± 100C• Total residence time in furnace: 7-8 hrsPeriodic measurement of slab temperature carried out with contact “K” rangejob thermocouples for controlled thermal regime.

• Flue gas measurement:• Sulphur content of the fuel : 400 ppm max.• Oxygen in the furnace atmosphere : within 2% max.

170 b d li d lt i b f hi t d• 170 bar descaling pressure and salt spraying before roughing stand• Temperature of rolling: 1000 to 11000C at roughing stand

780 t 7300C t fi i hi t d780 to 7300C at finishing stand• Controlled pass schedule at roughing and finishing stand

MDN 250 INPUT & OUTPUT SIZESMDN 250 INPUT & OUTPUT SIZES

SL. No

Heat No Nominal Slab SizeT x W x L (mm)

Nominal Plate size to be rolled

Weight (Kgs)( )

T x W x L(mm)( g )

1 K6400 155 x 1300 x 2350 9.3x2400x10000 & above 4382

2 K6398 155 x 1300 x 2350 9.3x2400x10000 & above 4268

3 K6407 155 x 1300 x 2350 9.3x2400x10000 & above 41944 K6399 155 x 1300 x 2350 9.3x2400x10000 & above 4176

5 K6405 155 x 1300 x 2350 9.3x2400x10000 & above 4150

6 K6404 155 x 1300 x 2350 9.3x2400x10000 & above 4081

7 K6408 155 x 1300 x 2350 9.3x2400x10000 & above 3975

8 K6415 155 x 1300 x 2350 9.3x2400x10000 & above 3968

9 K6409 155 x 1300 x 2350 9.3x2400x10000 & above 3956

10 K6411 155 x 1300 x 2350 9.3x2400x10000 & above 3950

PREPARATORY ACTIVITIES

CHARGING SEQUENCECHARGING SEQUENCE

ROLLING OF SLABS

Roughing stand

• Slab entry temperature: 1050 to 11000C• Slabs are rotated clockwise 900 and rolled in

same directionsame direction.• Draft schedule :

140-125-110-95-80-65-50-35-25-18

Finishing Stand

• Entry temperature: above 1000 0C• Draft schedule:

17.5-14.4-13.2-12.4-11.4-10.3-9.8-9.6• Exit Temperature: 780 to 7300C

ROLLING OF SLABS

• Cross cut shear:• Mother plate is cut into 9-10m length

plates and are identified using hotchalk

Vi l I ti• Visual Inspection:• Plates are inspected. Final thickness,

width length are measuredwidth length are measured• Top and bottom inspection

JOINT INSPECTION REPORT

Sl.No. Plate No. Actual measurements (mm) Surface quality Plate Nominal size (mm)

Thickness Width Length Top  Bottom T W L1 K6411A 9.30, 9.35, 9.40, 9.40, 9.35, 9.55 2360, 2380,2375 10000 OK OK 9.3 2400 100002 K6411B 9.40, 9.40, 9.40, 9.45, 9.45, 9.55 2450, 2350, 2350 9800 OK OK 9.3 2400 100003 K6415A 9.65, 9.50, 9.50, 9.80, 9.70, 9.70 2470, 2450, 2450 9530 OK OK 9.3 2400 100004 K6415B 9 55 9 60 9 75 9 70 9 75 9 90 2450 2450 2480 9870 OK OK 9 3 2400 100004 K6415B 9.55, 9.60, 9.75, 9.70, 9.75, 9.90 2450, 2450, 2480 9870 OK OK 9.3 2400 100005 K6399A 9.50, 9.50, 9.60, 10.0, 9.75, 9.60 2460, 2450, 2450 10120 OK OK 9.3 2400 100006 K6399B 9.60, 9.55, 9.75, 9.65, 9.65, 9.95 2460, 2445, 2360 10000 OK OK 9.3 2400 100007 K6404A 9.55, 9.90, 9.90, 10.0, 10.0, 9.80 2400, 2440, 2440 9540 OK OK 9.3 2400 100008 K6404B 9.75, 9.70, 9.80, 9.75, 9.80, 9.95 2440, 2440, 2370 9890 OK OK 9.3 2400 100009 K6398A 9.45, 9.65, 9.50, 10.05, 9.75, 9.65 2450, 2450, 2460 10260 OK OK 9.3 2400 10000

10 K6398B 9.60, 9.55, 9.70, 9.70, 9.70, 9.95 2460, 2450, 2480 10300 OK OK 9.3 2400 10000

11 K6407A 9 70 9 70 9 78 9 97 9 77 9 80 2380 2420 2420 9860 OK OK 9 3 2400 1000011 K6407A 9.70, 9.70, 9.78, 9.97, 9.77, 9.80 2380, 2420, 2420 9860 OK OK 9.3 2400 1000012 K6407B 9.65, 9.65, 9.90, 9.82, 9.87, 9.90 2420, 2430, 2360 9800 OK OK 9.3 2400 1000013 K6405A 9.73, 9.45, 9.55, 9.99, 9.63, 9.65 2460, 2420, 2400 10030 OK OK 9.3 2400 1000014 K6405B 9.45, 9.52, 9.65, 9.55, 9.72, 9.96 2420, 2420, 2380 10080 OK OK 9.3 2400 1000015 K6400A 9.65, 9.55, 9.70, 10.10, 9.90, 9.75 2495, 2460, 2460 10690 OK OK 9.3 2400 1000016 K6400B 9.70, 9.65, 10.07, 9.80, 9.80, 10.10 2460, 2460, 2470 9570 OK OK 9.3 2400 1000017 K6408A 9.65, 9.55, 9.53, 9.98, 9.70, 9.71 2465, 2440, 2440 9680 OK OK 9.3 2400 1100018 K6408B 9 53 9 50 9 75 9 65 9 65 9 88 2435 2440 2470 9700 OK OK 9 3 2400 1000018 K6408B 9.53, 9.50, 9.75, 9.65, 9.65, 9.88 2435, 2440, 2470 9700 OK OK 9.3 2400 1000019 K6409A 9.55, 9.49, 9.46, 9.94, 9.70, 9.65 2450, 2420, 2425 9600 OK OK 9.3 2400 10000

20 K6409B 9.50, 9.58, 9.56, 9.63, 9.68, 9.80 2430, 2370, 2430 9650 OK OK 9.3 2400 10000

METALLOGRAPHY RESULT OF MDN 250METALLOGRAPHY RESULT OF MDN 250 AFTER SOLUTION TREATMENT

a) Optical Micrograph b) Fractrograph

JOURNEY WITH MDN 250 ROLLING

Rolling Campaign Qty (Tons)Oct 2009 20Feb 2012 39Jan 2018 42Nov 2018 – in 2 campaigns 84p gOrders received - 2019 410 Order expected till 2021-22 620Order expected till 2021 22 620

Bhilai Steel Plant has added one more feather in itsBhilai Steel Plant has added one more feather in itscap by association in the space mission of onesatellite per month

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