SKI Report 98:32 SE9900008

Revised edition

Hydride Re-orientation in Zircaloy andits Effect on the Tensile Properties

Kwadwo Kese

August 1998

ISSN 1104-1374ISRNSKI-R-98/32-SE

30- 07

STATENS KARNKRAFTINSPEKTIONSwedish Nuclear Power Inspectorate

SKI Report 98:32

Revised edition

Hydride Re-orientation in Zircaloy andits Effect on the Tensile Properties

Kwadwo Kese

Department of Materials Science and Engineering,Royal Institute of Technology, SE-100 44 Stockholm, Sweden

August 1998

SKI Project Number 97228

This report concerns a study which has been conducted for the Swedish Nuclear PowerInspectorate (SKI). The conclusions and viewpoints presented in the report are those of

the author and do not necessarily coincide with those of the SKI.

Norstedt Tryckeri AB,Stockholm 1998

Summary

Based on literature studies and experimental work, investigations were carried out to determine

the stress and thermal conditions required for the reorientation of hydrides from an initial

circumferential orientation to a radial one. The section of microscopic reference was transverse,

in hydrided ring samples of Zircaloy. It was found that, both the degree of reorientation and the

relative amount of radial hydrides achieved, were dependent on the hydrogen content of the

material, given the same stress and thermal conditions. The need to take most of the hydrides into

solution at the uppermost temperature of the thermal cycle, in order for complete reorientation to

occur, became also clear. In general, an upper temperature of 500°C, in combination with an

orientation stress in the interval 150-200MPa was found to be adequate for the reorientation to

radial hydrides.

On the basis of these inital results, attempts were then made to produce ring test samples in which

the hydrides had assumed the radial orientation. These were subsequently subjected to the tensile

test in order to investigate the effect of hydride reorientation on the tensile properties of the

material. The tests, which were conducted at room temperature and higher temperatures (100°C,

150°C, 200°C, 250°C, 300°C), showed that the hydrides were brittle at room temperature but

became less so at higher temperatures. With the exception of the samples which were tested at

room temperature, all the other samples did show a ductile failure. At the strain rate employed in

the present work (0.02cm/min) therefore, the radial hydrides could not be said to have a reducing

effect on the ductile characteristics of Zircaloy at higher temperatures.

Sammanfattning

Genom litteraturstudie och experimentella försök har man undersökt de termiska- och

spänningsvillkor som krävs för att åstadkomma hydridomorientering i Zircaloy. Man har utgått

från ringprover av hydrerade rör av materialet. Hydridorienteringen defineras m.a.p de radiella

och tangentiella riktingarna i ett tvärsnitt. Till en början hade hydriderna en tangentiell

orientering och man har kommit fram till att såväl omorienteringsgraden som mängden

omorienterade hydrider är beroende av materialets vätehalt om man utgår från samma spännings-

och termiska villkor. Ett annat viktigt resultat var att en förutsättning för hydridomorientering är

återupplösningen av hydrider vid den högsta temperaturen under värmebehandlingen. Allmänt

gäller att en upplösningstemperatur av 500°C i samband med en orienteringsspänning i intervallet

150-200MPa är tillräcklig för att åstadkomma radiella hydrider.

Utgående från de föregående resultaten har man försökt att tillverka ringprover som innehöll

radiella hydrider. Man har sedan dragprovat dessa för att undersöka vilka samband som skulle

råda mellan det radiella tillståndet och dragegenskaperna. Försöken utfördes vid rumstemperatur

och högre temperaturer (100°C, 150°C, 200°C, 250°C, 300°C). Det visade sig att hydriderna var

spröda bara vid rumstemperatur och blev alltmer duktila vid högre temperaturer. Med undantag

av de prov som testades vid rumstemperatur visade alla andra prover duktilt brott. Vid den

töjningshastighet som rått under de här testerna (0.02cm/min) kan man således inte konstatera

någon draghållfasthetsnedsättningseffekt i Zircaloy orsakad av radiella hydrider vid förhöjda

temperaturer.

n

Dedicated

To

Kerttu and Jan-Erik Bergsten

" Av Herren har den blivit detta, underbartdr det i vdra ogon."

Ps. 118:23

in

Acknowledgement

I have had the privilege of working under the able supervision of Prof. Kjell Pettersson. I have

always drawn inspiration from the keen interest he has shown throughout the course of this

project. Here is therefore to thank you, Prof., for the enormous support and encouragement.

I wish to thank Per-Olof Soderholm, Nils Lange, and Hans Bergquist for the technical assistance

relating to the project.

Magnus Oscarsson was generous in placing at my disposal his collection of literature material

relating to the subject of investigation; Lars Ekman was the one who made me to understand the

operation of the various test equipment; Torbjorn Narstr6m was forthcoming when I needed help

with the software: to these post-graduate students at the Division of Mechanical Metallurgy I

would like to express my sincere gratitude. I would also like to thank Pal Efsing for reading

through the manucsript and offering useful suggestions.

The discussions that I had with Ann Svensson who also, almost concurrently, did conduct studies

in different aspects of the subject are also noted here as having been helpful.

I should also like to thank Kristina Wendt for the administrative work in connection with this

project.

Finally the interest shown by Irene Jansson, Marika Wallin, Kofi Akosah and S. Appiah-Kubi in

regard of the progress of this work is also acknowledged with much appreciation.

Finally, the financial support by the Swedish Nuclear Power Inpectorate (SKI) is gratefully

acknowledged.

IV

ContentsSummarySammaniattningAcknowledgement

1 BACKGROUND .. 1

2 THEORETICAL CONSIDERATIONS 3

2.1 Hydrides in Zirconium 32.1.1 The Zr-H System 32.1.2 Hydride Precipitation— nucleation and growth 42.1.3 Stress Re-orientation of Hydrides in Zircaloy 4

3 LITERATURE REVIEW — RELATED WORK BY OTHERS 6

4 EXPERIMENTAL 8

4.1 Work Schedule and Tools for Analysis 84.1.1 Definitions and Methods of Evaluations of Relevant Parameters 8

4.2 Auxiliaries 104.2.1 Determination of Hydrogen Content 104.2.2 Metallographic Analysis 10

4.3 Experimental Procedure 114.3.1 Determination of the stress-thermal conditions for hydride re-orientation 114.3.2 Production of Test Samples with Radial Hydrides 114.3.3 Tensile Testing of 'Radial' Specimens 12

5 RESULTS AND DISCUSSION 13

5.1 Determination of the Stress -Thermal Conditions 135.1.1 Results 135.1.2 Discussion 185.1.3 Conclusion , 21

5.2 Tensile Testing of Specimens Containing 215.2.1 Discussion 215.2.2 The "fully oriented" samples 265.2.3 Conclusion 33

5.3 Fractography 33

6 SUGGESTIONS FOR FURTHER WORK 36

7 REFERENCES 37

8 APPENDIX 38

1 Background

When the hydrogen content exceeds the solubility limit in Zircaloy, hydride precipitation may

occur. The hydrides are generally thought to be brittle and can, in sufficiently large quantities,

impart brittle characteristics to the alloy. This material embrittlement has, as a result of

extensive research work, been shown to be non-existent at temperatures in excess of 150°C, in

a manner reminiscent of the ductile-brittle transition behaviour observed in ferritic steels. It is

however not quite clear if this behaviour can be attributed to the brittle characteristics of the

hydrides, or to the composite behaviour of the metal-hydride mixture. When a crack is

present, then according to the general theories of delayed hydride cracking (DHC), the

process of crack propagation is driven by the combined mechanisms of diffusion and

precipitation whereby hydrogen atoms diffuse to the stressed crack tip and later precipitate as

the hydride; when it has grown large enough, the hydride cracks and the process continues in

a like manner. A necessary condition for this to occur is for the hydride to remain brittle at the

temperatures concerned. At temperatures higher than 150°C one would expect a breakdown in

this mechanism if the hydrides became ductile. The work of Efsing [1] has shown however,

that crack propagation does occur in hydrided Zircaloy at 300°C. Therefore, if one asserts that

a ductile-brittle transition in the hydride could be the sole factor underlying the exhibition of a

similar behaviour in the alloy, then one has to find an explanation for Efsing's observation in

yet another hydrogen-related crack propagation mechanism. Photomicrograph studies (see

Fig.l) of regions around cracks reveal a hydride network structure in the immediate vicinity

of a growing crack, instead of the single isolated hydride that the DHC theory might give an

impression of. The direction of crack propagation is found to be parallel to the orientation of

the hydrides which, in turn, is perpendicular to the direction of the applied stress. It is

believed that this network, whose formation is diffusion-related, constitutes a metal-hydride

composite the mechanical properties of which are quite different from those of the parent

microstructure. In particular, the network is thought to have a local fracture toughness value

that is lower than in other parts of the material. The amount of hydride contained in this

network is important to the extent that, a certain minimum of hydride presence is necessary

for the conditions of crack propagation to be met. This last point implies that one considers

the formation of the hydride structure with reduced toughness properties as a time-dependent

process and that a necessary pre-requisite is the existence of a crack in a stressed material.

The crack first propagates through a composite network and is stopped on reaching a tougher

material; after some time, diffusion and growth have proceeded to such an extent that the

necessary network structure for crack propagation is formed, crack propagation is resumed

and the process is repeated.

Figure 1. The hydride structure at the tip of a crack in a

DHC sample in which the test was discontinued

before fracture occurred. ca lOOOx

One way to test the present hypothesis is to study the temperature dependence of material

properties in a microstructure where the hydrides are oriented in a direction perpendicular to

the applied stress. This is to achieve a mutual orientation between hydride and applied stress

similar to that observed at the crack tip in the type of microstructure alluded to above.

Moreover, in tubular Zircaloy cladding material, stress reorientation of hydrides has been

observed to occur, resulting in the deterioration of the mechanical properties. In a transverse

section the hydrides have assumed a radial orientation when the reorienting stress was

tangential. In this project therefore, the aim is to determine

a) the stress level required to achieve hydride reorientation in Zircaloy cladding material

b) the relationship that exists between temperature and ductility in such a material containing

radially oriented hydrides.

Theoretical Considerations

2.1 Hydrides in Zirconium

Figure 2. The Zr-H phase diagram.

2.1.1 The Zr-H System

Atomic Percent Hydrogen30 40 SO

0 0.2

Zr0.6 0.B 1 12 1.4

Weight PerceijL Hydrogtin

Fig. 2 [2] shows that the Zr-H equilibrium phase diagram is of the eutectoid type. The system

consists of two solid solution phases of hydrogen in zirconium known as the a- and P- phases,

and three hydride phases known respectively as the y-hydride, the 5-hydride and the e-

hydride. Table 1 summarises some of the crystallographic properties of the various phases

that can exist at temperatures below 550°C. The metal sublattice transforms its structure

between these phases changing [3] for instance from a hep structure for cx-Zr, through fee for

8, to fct for y and e whilst the hydrogen invariably occupies the tetrahedral sites in preference

to the octahedral interstitial sites in a rather random manner. In the bec structure of the (3-Zr

however, the hydrogen location is not known with certainty [3].

Table 1. Crystallographic data for the different phases of the Zr-H system [3].

Phase Crystal Structure Lattice Parameter

(nm)

Density (g/cm3)

a-Zr

y(ZrH)

5(ZrH,6)

8(ZrH2)

hep

fct

fee

fct

a0.323

0.460

0.478

0.498

c0.515

0.497

-

0.445

6.51

5.82

5.64

5.61

2.1.2 Hydride Precipitation nucleation and growth

The hydrides are normally precipitated from supersaturated solutions in the form of discs [4]

with a preponderant preferred orientation that traces to the material processing history. In

tubular cladding material for example, the manufacturing process is controlled to leave the

finished product with a deliberate texture the ultimate aim of which is to assure peripheral

orientation of the hydrides. Such a microstructure has been found to be desirable from the

point of view of the fracture properties of the material [4].

The type of hydride that forms has been found [3] to depend on factors such as grain size, heat

treatment, method of hydriding and specimen purity. High cooling rates are reported as

generally favouring the formation of y-hydrides whilst at slow cooling rates, the level of

specimen purity as determined by the oxygen content may result in the formation of 8-

hydrides at high oxygen contents (above lOOOppm) and of y-hydrides at low oxygen contents

(below 200 ppm).

A unified theory of nucleation and growth of hydrides in zirconium is not to be found in the

literature; nevertheless, much research effort has been done, as indicated by Pettersson [2] in

his study of the subject. In general, it is believed that the nucleation of hydrides is

heterogeneous and occurs in the hep-lattice as a result of a shear transformation caused by the

gliding of Shockley partial dislocations on alternate basal (0001) planes of the matrix, and a

subsequent diffusion of hydrogen atoms to the resultant high energy sites. The said

transformation leads to the formation of fee areas within the hep lattice. In the recrystallized

and annealed state, heterogeneous nucleation, evenly distributed in the grain boundaries, is

proposed in the literature whereas twin boundaries and transgranular nucleation sites are

proposed for the cold-worked state. It appears therefore that the site for hydride nucleation is

influenced by the internal stress state of the material as well as prevailing temperature

conditions.

2.1.3 Stress Re-orientation of Hydrides in ZircaloyC.E. Ells [4] has shown that the theory of stress orientation of Fe16N2 precipitates in iron

which was derived by J.C.M. Li can also be used largely to describe the same phenomenon of

hydrides in zirconium. The angular deviation of the traces of the individual hydride platelets

in relation to a reference direction in the same plane of sectioning is usually assigned the

value <|). In the present discussion, this reference is chosen to be the direction perpendicular to

the applied stress. For a pre-selected limit of angular deviation denoted by x (in degrees), one

would like to determine the proportion of hydrides whose <j>-values fall within the range 0-x°.

Expressed as a percentage, this quantity is also called the fN parameter in the literature [2],

where N has the same definition as x above. For tubular specimens for instance, the ASTM

standards B 353-91 and B 811-90 specify a radial hydride as one oriented within 0-40° of the

radial direction in the transverse section [1]. Ells defined a quantity, Ra, as the ratio between

the number of hydrides with (Rvalues in the (0-x°) range, to the number in the complementary

range and arrived at the following expression

Rc = Roexp(Vc5aco/kT) (1)

where

Ro = the value of Rc in the absence of an applied stress.

GOO = the effective stress during nucleation at a nucleation site.

CO = cos2(3, where |3 is the angle between the stress direction and the normal to the hydride

such that 0 <co< 1.

5 = the linear strain of the lattice in the direction of the applied stress due to formation of a

new phase.

Vc = the volume of the nucleus.

Since Ra is an orientation parameter, Eq.(l) describes that the orientation of hydrides in

zirconium has an exponential dependence on the applied stress. Two different premises for

stress orientation must be distinguished: (i) orientational growth of stable precipitates and (ii)

orientation of nucleation. In the first case, the achievement of perceptible orientation under

the constraint of the normal times of experiment is dependent on the hydrogen concentration

gradient existing between parallel and perpendicular hydrides, the sense of orientation being

relative to the direction of the applied stress. Ells has estimated, using reasonable

assumptions, that the effect of the said concentration gradient would be small in comparison

with the effect of the applied stress on nucleation. One comes therefore to the conclusion that

hydride orientation occurs as a result of nucleation orientation rather than through the

orientational growth of stable precipitates. Later work by others including Ells [5] has

however shown that when hydride is present, stress-induced movement of hydrogen in

zirconium can occur, and this is generally accompanied by hydride orientation even though

much longer times are required for its observation. One further observation is that, when all

the hydrogen is in solution at the upper temperature of a thermal recycling process, stress

orientation appears to be due to a martensitic memory effect. When hydrides are present at the

upper temperature, stress-induced growth may be used to explain much of the observed

reorientation.

3 Literature Review Related Work by Others

Marshall and Louthan [6] investigated the effects of hydrogen content and hydride orientation

on the mechanical properties of Zircaloy at room temperature conditions. In order to achieve

radial hydrides, specimens were solution annealed at 415 °C for 16 to 18 hrs and then loaded

and cooled to room temperature in 6hrs. The applied stress range was 0-174 MPa; their aim

must therefore have been to achieve different degrees of reorientation in the different

specimens. The specimens were then tested to fracture at room temperature and the relevant

mechanical properties evaluated. From their observations they concluded that the influence of

hydrogen on the mechanical properties was determined by the orientation of the hydride

platelets. They were able to show that reductions in strength and ductility were caused by the

amount of hydride that was oriented perpendicular to the deforming stress and that parallel

hydrides had relatively little effect.

- In a similar experiment Bell and Duncan [7] solution heated test specimens (of hydrided

cold-worked and heat-treated Zr-2.5%Nb pressure tubing) at 500°C for lhr; furnace cooling

was then started until 450 °C where tensile loading was applied, and cooling was continued

down to room temperature.The applied stress varied among the specimens as 200, 150, 100,

75, and 17 MPa. Upon evaluation of the results they concluded that stress-induced hydride

orientation is more pronounced when the temperature of initial precipitation is increased and

that there is a minimum applied stress for hydride reorientation when the initial precipitation

temperature was below 430°C. In this experiment the effect of hydride orientation on the

mechanical properties was not considered.

- Hardie and Shanahan [8] also carried out an investigation on stress reorientation and came

to the conclusion that only hydride taken into solution can become re-oriented. They stressed

however the importance of having a manufacturing texture that gives a high concentration of

basal poles parallel to the direction of the applied stress. Still on the effect of fabrication

texture, Parry and Evans [9] observed from their experimental results that the hydrides did

precipitate in the direction parallel to the direction of grain deformation. The degree of

directionality increased with increasing strain, the minimum strain for directionality to occur

being about 7%.

- In another experiment, Price [10] determined the effect of radially oriented hydrides on the

tensile properties of a Zr-2.5wt%Nb pressure tubing. In this case, hydride reorientation was

achieved through the corrosion hydriding of internally pressurised samples. He observed that

under the biaxial stress state resulting from the kind of loading employed, hoop stresses in

excess of 138 MPa was adequate for the achievement of complete radial reorientation. By

conducting transverse tensile tests on the hydrided specimens using a reduced ring test

technique it was revealed that the material with radial hydrides had a ductile-brittle transition

temperature below 100°C; above this temperature serious reduction in ductility occurred only

in the case of massive surface hydride precipitation. He also noted that specimen geometry

had an effect on the tensile strength and the per cent elongation.

- Garde et al [11], when they investigated the ductile properties of irradiated Zircaloy-4,

concluded that the decrease in ductility observed in the material was due the combined effects

of localised hydride distribution and the orientation of the hydride precipitates relative to the

loading direction. They also noted that the extent of reduction in ductility depended on the

method of testing, asserting the comparatively high severity of the burst test in relation to

either the tube tensile test or the ring tensile test as a method for ductility evaluation.

- The last to be considered in this series is another work by Parry and Evans [12] which, in

several respects, has direct similarities with the current project. The main difference is the

geometry of the test specimens which, in their case, was of the conventional tensile type with

cylindrical gauge length. They however showed in the same paper that this should not affect

test results. Their work covered, among other things, aspects of stress reorientation of the

hydrides and its effect on the tensile properties of Zircaloy under both room-temperature and

other elevated-temperature conditions. Their conclusion was that hydride orientation, texture,

test temperature and metallurgical condition (referring to the irradiated /unirradiated states)

were important contributory factors to the tensile behaviour of the material. One further

important observation they made was that the strain rate can also have a major influence on

the results obtained from such tests.

4 Experimental

4.1 Work Schedule and Tools for Analysis

Based on relevant literature studies, it was expected through experimental work to establish

the thermal and stress conditions necessary for hydride reorientation to occur. Having

achieved this, several samples with reoriented hydrides were produced. The samples were

then subjected to the tensile test. Finally, the results of the tensile tests were analysed and the

relevant parameters evaluated.

4.1.1 Definitions and Methods of Evaluation of Relevant Parameters

Ductility : The ability of a material to deform plastically without fracture. Strain to

fracture and percentage reduction in area are used as measures of ductility

[13].

Strain to fracture: The permanent extension in length (measured by fitting the broken pieces

together) expressed as a percentage of the original gauge length.

In this project the total plastic strain is determined.

It is determined as the ratio between the measured displacement of the

cross-head to the gauge length. The gauge length is taken to be 20% of the

ring circumference. This is based on the method used by Garde et al.[l 1].

Reduction in area :The maximum decrease in cross-sectional area at fracture expressed as a

percentage of the original cross-sectional area.

(A o -A b r e a k ) /A oxl00

Tensile Strength : Maximum value of F/Ao during a test to failure.

Specimen Description

The specimen was received as hydrided Zircaloy tubes of 100 mm-length. The average wall

thickness and outer tube diameter were 0.65 and 9.65 millimetres respectively. They were cut

into approx. 3mm long rings which served as the test samples. For a more detailed description

of the test material and how samples are mounted on the testing machines, see Refs.l&14 or

the appendix.

Test Equipment

1. Creep Machine Type Bofors 3,6 Mp with a vertical bore type furnace

-used for the production of oriented samples.

2. Instron Tensile Testing Machine equipped with a 10-ton load cell, a load amplifier

(D2000), a strain gauge transducer with direct coupling to a Lab View Macintosh program

which gives a voltage-vs. displacement reading. Mounted on the Instron is a vertical bore

furnace.

Speed of travel of crosshead during tensile testing: 0.02cm/min = 0.0002/60 m/s

Load-Voltage conversion factor : 1 volt. = 6455.3 kg

Illustrative Calculation of basic parameters.

Sample Identification : P 44

Sample dimensions : initial wall thickness, to= 0.675mm

wall thickness at fracture section, tf = 0.64 mm

initial axial length, l0 = 3,265mm

axial length at fracture section, lf = 2.79 mm

initial outer diameter, d0 = 9.65 mm

Initial cross-sectional area, Ao = 210 Jo = 2(0.675)(3.265) = 4.40775 = 4.408 mm2

Cross-sectional area at fracture, Af = 2(2.79)(0.64) = 3.571 mm2

Area reduction for P44 = (Ao- Af) / Ao x 100% = (4.408 - 3.571) / 4.408x 100% = 18.98 %

Initial outer circumference, Co =rc d0 = 30.316 mm

Gauge length (=20% of Co) = 6.06 mm

At time t (= 15s, say), during the tensile test the quantities are evaluated as follows

Displacement = (time x 0.0002)/60 = 0.00005 m

Loadl = 6455.3 x voltage = 6455.3 x 0.00046 = 2.969438 kg

Load = Loadl x 9.81 = 29.130187 N

Strain = Displacement x 1000 / Co = (0.00005 x 1000)/ 6.06 = 0.00825083

Stress = Load / Ao = 29.130187 / 4.408 = 6.60848157

4.2 Auxiliaries

Under this heading various supporting activities, as opposed to the main experimental work,

are described. Their function is mainly auxiliary and often recurrent and are better treated

separately.

4.2.1 Determination of Hydrogen Content

In order to determine the hydrogen content, a small bit of the material was cut off each

specimen after the tensile test. The hydrogen content of the cut-off bit was then determined

using the vacuum extraction method. The results obtained from such analyses are the values

of ppm hydrogen used throughout this report for the test samples.

4.2.2 Metallographic Analysis

Sample preparation

Samples for metallographic analysis were first cast in Bakelite. They were then ground down

in succession on emery paper grades 240, 320, 600, 1200 after which they were washed in

water and ethanol. Upon drying they were polished in two stages on polishing cloths smeared

with diamond paste.The samples were then etched.

Etching

The etching solution was made up of: 40 parts% hydrogen peroxide, 40 parts% acetic acid, 15

parts % nitric acid and 5 parts% hydrofluoric acid by volume. Etching time was 16 seconds

followed by successive washing under the tap and in ethanol. The final step was the use of the

ultra-sonic bath and subsequent washing-off with ethanol and drying.

10

Microscopic examination and photography

Polished and etched specimens were examined under the light-optical microscope with the

main objective of determining the orientation of the hydrides. Photomicrographs were taken

as has been found necessary.

4.3 Experimental Procedure

The experimental procedure is arranged into three main different phases to reflect the defined

objectives of the project. This section will therefore discuss each one of them in turn.

4.3.1 Determination of the stress-thermal conditions forHydride re-orientation

Hydrided tubular specimens were cut into test rings of 3mm nominal axial length. The rings

were placed in the creep machines and then subjected to different conditions of temperature

and stress. The results, in terms of degree of hydride re-orientation were determined through

metallographic analysis. The tests differed from each other in the type of thermal re-cycling

(namely, highest temperature reached, time at temperature, method of cooling to room

temperature) and the applied-stress characteristics (namely, stress magnitude and its point of

application in the thermal cycle). A summary of the different attempts is presented in Table A

in the Appendix and photomicrographs of the more interesting cases are shown on pages 14-

17 and 19-20. The reported results have been based on the method of visual inspection of the

metallographic sections in the microscope rather than the much more quantitative method of

determining the hydride orientation through the f N - value. The visual method is adequate for

the purpose of this part of the work namely, the achievement of full radial re-orientation of

the hydrides.

4.3.2 Production of Test Samples with Radial Hydrides

Based on the results of 4.3.1, production parameters for the achievement of radial hydrides in

test samples were determined. The chosen parameters were those corresponding to Test KP16

in Table A. The idea was to replicate the results corresponding to fully re-oriented hydrides

by subjecting the samples to the same experimental conditions as in KP16. Since several of

such 'radial' samples were to be produced, this part of the project was called the production

11

part. Hydrided ring test samples of similar dimensions as in 4.3.1 were prepared. These were

then placed in the creep machines and heated to 500 °C. After holding at that temperature for

lhr. the furnace was shut down and the specimens were allowed to cool in the closed furnace

down to room temperature. At 425 °C during the cooling process, loads corresponding to a

tensile stress of about 150MPa were applied; this loading condition was maintained

throughout the cooling process The samples thus produced were then subjected to the tensile

test.

4.3.3 Tensile Testing of 'Radial' Specimens

Six different test temperatures (25°C, 100°C, 150°C, 200°C, 250°C, 300°C ) were chosen at

which tensile tests were to be conducted. About 8 samples were assigned to each test

temperature. At each test temperature the samples differed from one another by the ppm H

value. Each test sample was placed in the Instron and heated to the pre-determined test

temperature and held for lhr after which tensile loading was applied at that constant

temperature until rupture occurred. The load-extension process was both monitored and

recorded on the computer.

The dimensional changes on each of the ruptured samples were then noted and recorded.

Small bits of the tested samples were cut off for hydrogen content analysis and the remaining

part was prepared for metallographic examination to determine the extent of reproducibility

achieved, with respect to hydride re-orientation. Photomicrographs of only those samples that

contained full radial hydrides are shown in this report (see Section 5.2.2).

12

5 Results and Discussion

5.1 Determination of the Stress -Thermal Conditionsfor Hydride Re-orientation

5.1.1 Results

The results are presented in Table A of the Appendix and the photomicrographs of the more

interesting cases are shown in Figs.3-14 below. The photomicrographs are grouped as

follows: 1. hydrided only sample; 2. sample with circumferential hydrides only; 3. sample

with circumferential + hydride particles; 4-7..samples with mixed radial and circumferential

hydrides; 8-9. samples with varying hydride orientation toward radial; 10-12. samples with

predominantly radial hydrides.

Sample 1

The sample had only been hydrided without any subsequent attempt at stress reorientation.

The hydrides have precipitated as particles. (Fig.3)

Sample 2

Complete circumferential orientation of the hydrides. The sample was heated to 300°C and

loaded and held for 24 hrs. The applied stress was 140 MPa. The results show that hydride

reorientation did not occur since hydrides here have the characteristic manufacturing texture

orientation. (Fig.4)

Sample 3

The micro-structure shows circumferential hydrides on a background of smaller hydride

platelets. These platelets, which are uniformly distributed throughout the matrix, do seem to

have a certain degree of orientation relative to the peripheral direction. Apart from cooling in

air the other difference between this sample and Sample 2 is that the applied stress was

158MPa. (Fig.5)

Samples 4-7

Characteristic to this group is the presence of both radial and circumferential hydrides. The

kind of heat treatment as well as the applied stress differed widely between the samples.

(Figs.6-9)

13

» ; * . '.':•.••'

Figure 3. Sample 1 Test H Sample as-hydrided only without any attemptat hydride reorientation

Figure 4. Sample 2 Test KP 3 Circumferential hydrides. Sample was heatedto 300°C, loaded (140MPa) and held for 24hr. (140x)

14

" ; < . • > > > - . * • : _ :

Figure 5. Sample 3 Test KP 4 Circumferential hydrides and differentlyoriented smaller hydride platelets. Same heat treatment as Sample 2except for air cooling and an applied stress of 158MPa.

(140x)

15

Figure 6 Sample 4 Test KP17 Circumferential and radial hydrides. Solution-heat treatedlhr at 500°C, furnace cooled and loaded (184MPa) at 450°C.Cooling was continued down to 350°C where it was held for 48hr. (140x)

Figure 7 Sample 5 Test KP 23 Circumferential and radial hydrides.Same heat treatment as Sample 4 except that cooling was continueddirectly to room temperature and a much lower stress, 103MPa, wasapplied. (140x)

16

\i- '. .• ,-].-,: '.,•.>,.•

Figure 8. Sample 6 Test KPX Circumferential and radial hydrides.Heated to 300°C, loaded (103MPa) and held 6 1/2 days (157hr).

(140x)

Figure 9. Sample 7 Test KP 11 Circumferential and radial hydrides.Solution-heated lhr at 500°C; furnace cooling to 318°C, loading(220MPa) and holding 23hr. (140x)

17

Samples 8-9

These samples contain hydrides that show varying degrees of orientation toward the radial

direction. The temperature of load application was relatively higher in these samples than in

the others whilst the applied stress was among the lowest. (Figs. 10, 11)

Samples 10-12

The micro-structure shows a predominant amount of completely reoriented radial hydrides.

The samples had the same solution temperature and in two of them, KP15 and KP16, the

temperature for stress application was almost the same, 420°C and 425°C respectively .The

stress levels ranged from moderate to high (150-200 MPa) in comparison with what obtained

in the other samples.(Figs. 12, 13,14)

5.1.2 Discussion

The minimum heat treatment temperature used in these experiments was 300 °C. At that

temperature none of the tests resulted in significant degrees of hydride reorientation; the

applied stress varied between 140 MPa and 160 MPa. Length of time of load application did

not seem to have much effect on reorientation at this temperature since KPX, taken through

the test for almost 7 days, did not show a result different from those taken through much

shorter test times. When the heat treatment temperature was increased to 500°C, more

reoriented hydrides could be observed. At this temperature, the magnitude of the applied

stress seemed to have a clear influence on hydride reorientation. This fact is exemplified by

tests KP 15 and KP16 where the only significant difference between them was the magnitude

of the applied stress. For KP 15,200 MPa was applied and the result was a micro-structure

showing predominantly fully oriented hydrides throughout the cross-section, whereas a

similar structure had regions of mixed radial and circumferential hydrides in the case of

KP16, where the applied stress was 150 MPa. Too much stress may however not be applied at

this temperature since the risk for dimensional changes could be high. This was especially

observed to be the case in KP12 where a 200 MPa stress was applied at 495 °C. The sample

subsequently showed dimensional changes even though completely oriented hydrides was

obtained. At still higher heat treatment and loading temperatures, 560 °C and 550°C

respectively for KP22, a much lower stress was required to effect hydride reorientation. In the

cited test, complete reorientation could not be achieved; instead, the hydrides were observed

to have assumed varying degrees of orientation toward the radial direction. This may perhaps

be an indication of the fact that, all things being equal, there is a minimum stress that may be

applied at the temperature concerned in order for hydride reorientation to occur.

18

Figure 10. Sample 8 Test KP 22 Hydrides showing varying degrees oforientation toward the radial direction. Solution-heated lhr at 560 °C, cooled to 550°C and loaded (107MPa).

(140x)

Figure 11. Sample 9 Test KP 24 Hydrides showing varying degrees oforientation toward the radial direction plus circumferentialhydrides. Solution-heated lhr at 500 °C, cooled to 450°C andloaded (103MPa). (140x)

19

> > / ' ' < ' • ' ••••t'-\\:;:,V:'r.'*.•>'•' • ; • I ; ' ; , - ' : ' ' • • " • . * • •

Figure 12. Sample 10 Test KP 12 Predominant amount of radialhydrides. Solution-heated lhr at 500°C, cooled to 495°Cand loaded (200MPa). (70x)

Figure 13. Sample 11 Test KP 15 Radial hydrides. Solution-heatedlhr at 500°C, cooled to 420°C and loaded (WOMPa). (70x)

itm

Figure 14. Sample 12 TestKP 16 Radial hydrides. Solution-heatedlhr at 500°C, cooled to 425°C and loaded (ISOMPa). (70x)

20

Even though the present work did not specifically look at the of. effect of the hydrogen content

on the extent of achievable reorientation, the observations made above could lead one to infer

that the higher the hydrogen content the moreNdifficult it is for complete reorientation to

occur. This follows from the fact that the essence of employing higher heat treatment

temperatures stems from the need to take most of the hydrides into solution in order for stress

orientation of nucleatipn to occur. Since there is a hydrogen solubility limit at each

equilibrium temperature, it follows that more hydrides will be left undissolved the higher the

hydrogen content. Then, since hydride dissolution increases with temperature, more hydrides

can be dissolved as higher heat treatment temperatures are selected.

5.1.3 Conclusion

It can therefore be concluded that a combination of factors are necessary in order to achieve

complete reorientation of hydrides in Zircaloy. These include the value of the highest

temperature reached in a thermal treatment, and the stress applied. The fraction of oriented

hydrides to be obtained at a selected highest temperature depends on the hydrogen content.

The lower the hydrogen content, the higher the fraction of radially oriented hydrides. It is

therefore not possible to obtain proportionately equal amounts of radial hydrides in different

samples having different hydrogen contents, given the same thermal and loading conditions.

Using a hydride dissolution temperature of 500 °C, a minimum applied stress of 150MPa

would be adequate for the achievement of radial hydrides in samples containing up to about

350ppm hydrogen; for higher ppm hydrogen values, then higher stress values, up to about

200MPa, would be necessary.

5.2 Tensile Testing of Specimens ContainingRe-oriented Hydrides

5.2.1 Discussion

Ductility is evaluated primarily in terms of the variation of the tensile properties with

temperature. These properties include the tensile strength, the total strain at fracture and the

area reduction. In addition, the variation of these properties with the hydrogen content at

constant test temperature is also evaluated. The results are presented graphically in Figs. 15-

20.

21

Tensile Strength

As Fig. 15 indicates, tensile strength decreased with temperature for the tested specimens. The

highest recorded value was 522 MPa corresponding to P41 which was tested at room

temperature whilst the lowest was 247 MPa corresponding to P61 which was tested at 300°C.

At constant temperature (Fig. 16) the tensile strength did not seem to vary significantly with

the hydrogen content even though slight increases at higher hydrogen contents could be

observed at the lower temperatures (25 °C, 100°C, 150°C). Also at these temperatures, an

initial drop in tensile strength was observed for hydrogen contents up to about 300ppm.

Total Strain at Fracture

The total strain at fracture increased with temperature (Fig. 17), reaching a maximum at

around 250°C and falling off again with increasing temperature. The highest elongation

recorded, 47%, was at 300°C and corresponded to P42. Even at room temperature relatively

high strains were recorded, the highest being 25% for P41, the same sample that had the

highest tensile strength. The total strain varied with the hydrogen content in an irregular

manner, fig. 18, between the different temperatures. Whilst it decreased with the hydrogen

content at 100°C, it did increase at room temperature. At the higher temperatures, 250 °C and

300°C, it almost remained constant over the hydrogen content range.

Area Reduction

The area reduction also increased with increasing temperature, Fig. 19. At 300°C as much as

76% area reduction was recorded for P46. Only two samples (P57 and P56 respectively)

showed zero or almost none area reduction, and these occurred at room temperature. Even at

room temperature as much as 30% area reduction was recorded (P2). At constant temperature,

Fig.20, the area reduction showed, in general, only slight decreases with increasing hydrogen

content. At 100°C the trend was relatively more pronounced than at the other temperatures for

hydrogen contents up about 800ppm. The behaviour at 25 °C exhibits the same kind of

anomaly as with the total strain, where property increase was observed instead of a decrease

at higher hydrogen contents.

22

9

ot,

4

CO

600

500 -

400

300

it

r* 200

100

0

1•

1 1—

• Ii

—1 1 1 1

1r

1

1 1 1

_• 1

1 , 1 ,

50 100 150 200 250Test Temperature, C

300 350

Figure 15. Variation of Tensile Strength with Temperature.

MP

a

O i l

L.

CO

Ten

<

600 "

500

400

300

200

100

uC

AA A

- A

)

A A

• • "

500

* m, A

1000

ppm H

• • •

1

1500

*

• T= 300 CAT=250 C• T=200 C• T=150 C• T=100 CAT=25 C

2000

Figure 16. Variation of Tensile Strength with Hydrogen Content at Constant Temperature.

23

*3

•**

U.

<

:rain

w

o

50

45

40

35

30

25

20

15

10

5

50 100 150 200

Test Temperature, C

250 300 350

Figure 17. Variation of Total Strain with Temperature.

60

en

20

# xX

XX

B T= 300 CT= 250 C

•# T= 200 CXT= 150 C@T= 100 CXT= 25 C

0 500 15001000

ppm H

Figure 18. Variation of Total Strain with Hydrogen Content at Constant Temperature.

2000

24

Figure 21 Sample P57, tested at 25 °C. A photo sequence showing progressivehydride deformation from the least stressed section (top) to the fracturesection (down). The picture in the middle depicts the situationjust before fracture.Hydride deformation is not observed throughthe sequence. (70x)

27

Figure 22 Sample P 47, tested at 100°C. A photo sequenceshowing progressive hydride deformation from theleast stressed section (top) to the fracture section (down).The picture in the middle depicts the situation just beforefracture. Limited hydride deformation can be observedthrough the sequence. (70x)

28

Figure 23 Sample P 50, tested at 150 °C. A photo sequence showingprogressive hydride deformation from the least stressedsection (top) to the fracture section (down). The middlepicture depicts the situation just before fracture. Limitedhydride deformation is observed through the sequence.

(70x)

29

w'y?' I

Figure 24 Sample P 59, tested at 200°C. A photo sequence showingprogressive hydride deformation from the least stressedsection (top) to the fracture section (down). The middlepicture depicts the situation just before fracture. Extensivehydride deformation can be observed (70x)

30

'-•>' '-if" . ' v-

Figure 25 Sample P 60, tested at 250°C. A photo sequenceof progressive hydride deformation. Top: leaststressed section. Middle: section depicting situationjust before fracture. Down: fracture section. Lowhydride density is observed just before and afterfracture. . (70x)

31

Figure 26 Sample 61, tested at 300°C. A photo sequence of progressivehydride deformation. Top & Middle: least stressed section(140x, 70x respectively). Down: fracture section (70x). Muchlower hydride density is observed at the fracture section.

32

5.2.3 Conclusion

Under the conditions of the present experiment the radial hydrides do not seem to change the

tensile properties of Zircaloy-2 at the temperatures involved. Even though other tests have shown

that material embrittlement may result from radial hydrides, there are certain factors that may be

important in regard to the outcome of such experiments. The first is the type of stress state that

prevails in the material. The results of the present experiment go to confirm the observations of

Garde [11] and Slattery [15] that the biaxial stress state as usually obtains in thetube-burst test is

more sensitive to hydride embrittlement than the ring tensile test. The second factor is the applied

strain rate. As indicated earlier in this report, Parry and Evans [12] came to the conclusion that

the strain rate employed can have a very important effect on the outcome of such tests. In the

present work the applied strain rate was 0.02cm/min and constant for all test cases. At 150°C they

observed that the hydrides were ductile at 0.0127cm/min whereas 50.8cm/min led to brittle

behaviour of the hydrides. In particular, at 200°C, they observed that the hydrides became brittle

only at strain rates exceeding 25.4cm/min; at strain rates below this value the hydrides were

observed to have no effect on the ductility of the material. Thus, by comparison, the strain rate

used in the present test was rather low; this could explain the retention of ductile properties

observed here. Specimen geometry could also have an influence on the results. It is likely that a

ring sample with a reduced section could be more sensitive to hydride embrittlement than the

plain ring that was used in this experiment. It is therefore concluded that the brittle characteristics

of hydrides in Zircaloy could be closely dependent on both the prevailing stress state and strain

rate as well as the temperature.From the discussion on hydride disintegration and dissolution, one

may furthermore conclude that the observed retention of ductile behaviour could be the result of

the fact that the structure of the ductile matrix is re-instated at the fracture zones as a direct

consequence of the hydride depletion phenomenon.

5.3 Fractography

Fractography was carried out on one of the samples that showed brittle fracture. The sample was

P57 and was tested at room temperature and had full radial hydrides. The fracture surface was

examined under the SEM; Figure 27 and 28 show the results at 500x and 2000x magnifications

respectively. The aim was to investigate if the fracture surface had any similarities with that

which obtains in delayed hydrided cracking (DHC), the mechanism of which was briefly

described in the introductory part of this report. A characteristic feature of a DHC fracture

surface is the presence of a so-called fish-bone pattern [1] that runs parallel to the direction of

crack propagation, Figs.29 and 30. At the lower magnification, Figure 27, the fracture surface of

33

the test sample shows features that resemble those of a DHC surface but, at still higher

magnification, Figure 28 , one clearly observes features quite different from those that would

have been caused by a DHC. What is observed here is a different type of brittle fracture surface.

It is thus indicated that the crack growth mechanism under DHC conditions is slightly different

from that of a purely mechanical failure caused by radial hydrides.

Figure 27. Fracture surface of P57. At this magnification the features resemblethose of a DHC fracture surface.

"-;....» . -.» ' V f c * ; . •

r -Figure 28. Fracture surface of P57 at a higher magnification.

Characteristic features of a DHC fracture are not seen

34

s

Figure 29. Fracture surface of an irradiated specimen. Note the fish-bonepattern parallel to the direction of propagation.

Adapted from [1].

3& ,>£****

Figure 30. Magnifications of the large markings seen on the overview picture.

Adapted from [1],

35

6 Suggestions for Further Work

In order for definite conclusions to be drawn on the effect of radial hydrides on the tensile

properties of Zircaloy, it is hereby suggested that further work be carried out to specifically study

the effect of different strain rates on the ductile-brittle characteristics of radial hydrides in

Zircaloy. It would also be of interest to investigate how different test methods and sample shapes

do affect the behaviour of radial hydrides in Zircloy.

To shed light on the subject of hydride deformation it is further suggested that a quantitative

analysis be carried out to ascertain the mechanisms of both the observed hydride disintegration

and the apparent attendant hydride dissolution, and how they are influenced by temperature and

stress.

Finally it would be interesting to study the electromagnetic properties of the hydrides, with the

aim of developing a non-destructive method of determining the orientation of the hydrides and

especially, of the transition between the two orthogonal orientations dealt with in this project.

36

7 References8 Efsing, P., Delayed hydride Cracking in Irradiated Zircaloy, Ph.D. Thesis, Royal Institute

of Technology, Stockholm 1998.

9 Pettersson, P., and McPherson, M., Fracture Toughness ofHydrided Zircaloy Tube-methodological studies, Internal Report-SKI Project 93118, Inst. Matl. Sci. & Eng., Dept.Mech. Met., Royal Institute of Technology, Stockholm 1997.

10 Zuzek, E., and Abriata, J.P., The H-Zr (Hydrogen-Zirconium) System, Bull. Alloy PhaseDiagrams, Vol. 11 No.4 1990, pp. 385-388.

11 Ells, C.E., The Stress Orientation of Hydride in Zirconium Alloys, J. Nucl. Mater., 35,1970,pp.306-315.

12 Ells, C.E., and Simpson C.J., Stress Induced Movement of Hydrogen in Zirconium Alloys,Proceedings of International Conference on Hydrogen, Eds. I.M. Bernstein and A.W.Thompson, ASM Metals Park, 1974, pp. 345-360.

13 Marshall, R.P., and Louthan, M.R., JR., Tensile Properties of Zircaloy with OrientedHydrides, Trans. ASM, Vol.56,1963, pp. 693-700.

14 Bell, L.G., and Duncan, R.G., Hydride Orientation in Zr-2.5% Nb; How it is Affected byStress, Temperature and Heat Treatment, Atomic Energy of Canada Limited, AECL-5110,1975.

15 Hardie, D., and Shanahan, M.W., Stress Orientation of Hydrides in Zirconium -2.5%Niobium, J. Nucl. Mater., 55 (1975) 1-13.

16 Parry, G.W., and Evans, W., The Effect of Strain on the Directional Precipitation ofZirconium Hydride in Zircaloy-2, AECL-1707, Dec. 1962.

17 Price, E.G., Hydride Orientation and Tensile Properties ofZr-2.5 wt% Nb Pressure TubingHydridedwhile Internally Pressurized, Can. Met. Quart., Vol.11, No.l, 1972, pp.129-138.

18 Garde, A.M., Smith, G.P., and Pirek, R.C., Effects of Hydride Precipitate Localization andNeutron Fluence on the Ductility of Irradiated Zircaloy-4, Zirconium in the NuclearIndustry: 11th International Symposium, ASTM STP 1295, E.R. Bradley and G.P. Sabol,Eds., 1996, pp. 407-430.

19 Evans,W., and Parry, G.W., The Deformation Behaviour of Zircaloy-2 ContainingDirectionally Oriented Zirconium Hydride Precipitates, Electrochem. Technol., Vol.4No. 5-6,1966, pp. 225-231.

20 Ashby, M. F., and Jones, D.R.H., Engineering Materials - An Introduction to theirProperties and Applications, 1st edition, Pergamon Press, 1980.

21 Svensson, A., En Studie av Omslagsbeteendet hos Hydrerad Zircaloy, Project Report,Dept. Mech. Met., Royal Institute of Technology, Stockholm 1998.

22 Slattery, G.F., The Mechanical Properties of Zircaloy-2 Tubing ContainingCircumferentially Aligned Hydride, Applications-related Phenomenon for Zirconium andits Alloys, ASTM STP 458,1969, pp.95-110.

37

8 Appendix

List of Appendices

1 .Table A. Results of Temperature-Stress Orientation Attempts

2/TableB. Sample Data Sheet.

3. Figure Al. Fixture for Holding Test Rings onto Testing Machines

38

Table A. Results of Thermal-Stress Orientation Attempts.

[f.c.t - furnace cooling to.. a.c.t - air cooling to.. circ- circumferential

RT- room temperature C = °C]

Test

T3

KP4

X

KP11

KP12

KP14

KP15

KP16

KP3

KP17

Description

Heat to 300C; hold and load 24

hr

- same as KP3-

Heat to 300C; hold and load 157hr

Solution heat 500C lhr; cool to

318C, load hold 23hr

Solution heat 500C lhr; load495C and cool to RT

Sample in pre-heated furnace

314C; hold lhr and load 43 hr

Solution heat 500C lhr; f.c.t420C and load.

Solution heat 500C lhr; cool to425C and load.

Heat to 300C; hold and load 24

hr

Solution heat 500C lhr; cool to

450C and load; f.c.t 350C and

hold 48hr.

Stress(MPa)

140

-do-

103

220

200

200

200

150

158

184

MethodofCooling

f.c.t RT

a.c.t RT

f.c.t RT

f.c.t RT

f.c.t RT

f.c.t RT

f.c.t 80Cand a.c.tRT

f.c.t 77C

and a.c.t

RT

f.c.t RT

a.c.t RT

DimensionalChanges

none

none

none

none

yes

none

none

none

none

none

Results

circ. hydrides

circ.hydrides

and hydride

particles

mixed radialand c i rc .hydrides.

mixed radial

and circ^

hydrides

predominantlyradialhydrides

mixed radial

and c i rc .

hydrides

predominantlyradialhydrides

predominantly

radial

hydrides

few radial

hydrides in

places

predominantly

radial

hydrides

Test

HI

KP19

KP21

H2

KP22

KP23

KP24

H

Description

untested; copper- plated before

hydriding.

Solution heat 500C lhr; cool to

430C and load.

Solution heat 500C lhr; cool to

450C and load.

untested

Solution heat 560C lhr; cool to

550C and load.

Solution heat 500C lhr; cool to

450C and load.

Solution heat 500C lhr; cool to

450C and load.

untested

Stress

(MPa)

115

127

107

93

103

MethodofCooling

f.c.t RT

f.c.t RT

f.c.t RT

f.c.t RT

f.c.t RT

DimensionalChanges

none

none

none

none

none

Results

circ. hydrides

predominantly

circ. hydrides

more circ.

than radial

hydrides

circ. hydrides

more radial

hydrides

more radial

varying

degree radial

and circ.

hydride

particles

n

Table B. Sample Dataspppppp

£pp

ppppppp

pp

pp

ppppppPpPPPp

p

pppp

SamplePS7PS5P56P41P30P33P44P2P24P47P3P25P26P38P20P31P4P58P49P51P50P17P12P18P7P5P53P59P48P16P27

T C

252525252525252525

100100100100100100100100150150150150150150150150150200200200200200

P19 i 200P8P22P6OP28P2BPis'"'P54P35P39P34P61P46P42P40P23P36P1OP37

200200250250250

2502502 5 0250250

ppm233320320540S82

1047112014401450

332460630760810832898

1004212278342344647

7268148268951402015 8 06 5 0670763862

1044168452SOOS025308 0 9810

1000300 270300 390300; 605300i 800300300300300

1230128015501561

M«SpIn(MPi466.11501,26463,3

522.45506,35514,97493.06512.64515,71401,46404,8

414,51405,12

400,3431,44408,05416,68389,32363,45380.48366,77362,4

375,92366,61368,92379,93296,14303,18288,13309,93324,9

319,83322.42319.93276,84285,11274,36291,15272.43281,4

274.83281,67247,61256,51266,17274,3

271,29274,81252,38272.2

Ao(mm2)

4.434,1364,4354,354,424.25

4,4084.15

4,3384,52

4.3564,356

4.49SS4,1854,164.474.034.16

. . 4,394,374,354,49

•4,234,384,39

3,84,4814.42

4,4824.0924t2564,374,43

4,25254,374,34

4.4814,324,29

4.34,5563,887

4.34,409

4,314,4494,1094.026

4,834.2

Aflna|(miTi2)4.43

3.7884,3928

3,2894,3693,389

3,80162.9023,6482,223

2.172.21762,40562.00082,3562,3792.1841,6371,6131.7021,7791,5961,6821,9961,7051.605

1,56941,55

1,54581,55441,58921,6351.662

1.61661.2771.51

1,49861,5611,4521.20B

1,43841,64721,345

1,03881.322

1,0692.IJO780,9721.2641,378

MaxLoacKkg)210.49211.34209.45231.67227,99223,1

221.55216.86228.05184,97179,75184,06185,16170,76182,95186.22171.17165,09162.65169.49162,63165J7162,09163.68165,09147,17135,27136,6

131,64129,27140.96142,47

145.6138,68123,32126.14125,32128.22119,13123,35127,64111,6

108.53115,29116.94124,4

113,65112.78124,26116.94

MaxTravel:mm0.6

10.7

1,520,951,191,151,43

1,32,33

22,251,712,172.282,182,012,282,572,262,322,32

2.32.2

2,292.152,462,52

2.52,32.5

2.522.37

2,42,482.512.462.492.5

2.592,6

2,282.37

2,42,85

2,42.22,22,3

2.28

corr.clrc(mm)6,0826,06

6,0416,05

6,0326,056,06

6,0446,06

6,0566.0856,0536,0546,0856,012

6.066.0446.0786,07

6,0446,044

. . 6,0446,0566,0826,0826.0446,0416,0326,0416.09

5,9286,044

6,026,06

6,0446,0326,0856,0446,0416,0446,06

6.0546,0826,0476.026

8,05.6,066,06

6,0386,1

Strain % Area red.,%9,865175929. 0

16.5 12,2211.59' 0.96

25.12396894 24.3915,74933687: 1,1519.66942149 20,25

18.9823,65982793

21.4538,47424042

32.8637,2723.25

35,637,9241517

35,9735973633,2561217737,5123395942.3393739737,3924553338.3851753838,3851753837.9788639436,1723117437,6520881335,57246856

40,7841,77718833

42,137.7542,16

41,6942422239,36877076

39,641.0324288641,61140584

40,4241,1978822

41,2742,85241562

42,937,72

38,96744492

13,7530.07

L_ 15,9150,8150,1849.0946,4952,1943,3645,5645,8160.6563,2661,05

59,164,4560,2454,2361,1657.7664.9864,9365,5162,0162,6662,5862,4861,9870,7765,2166,5463,8666,1571,9168,4357.6268,72

39,74i 76,4347.29505476: 69,33

39,61: 75,9736,336.3

38,0920834737,37704918

73,7775.8673,8367,19

Figure Al. Fixture for Holding Test Rings onto the Testing Machines(a) front and side views of the two halves of the fixture(b) the fixture assembly with the rings mounted.

IV

STATENS KARNKRAFTINSPEKTIONSwedish Nuclear Power Inspectorate

Postadress/Postal address Telefon/Telephone Telefax

SKIS-106 58 STOCKHOLM

Nat 08-698 84 00Int +46 8 698 84 00

Nat 08-661 90 86Int +46 8 661 90 86

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