MECHANICAL PROPERTIES OF Zr 2.5Nb PRESSU

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BARC/2012/E/002

MECHANICAL PROPERTIES OF Zr-2.5Nb PRESSURE TUBE

MATERIAL MANUFACTURED EMPLOYING FORGING ROUTES

FOR PHWR700 - PART I: TENSILE BEHAVIOR

by

A.K. Bind, R.N. Singh, Saurav Sunil, J.K. Chakravartty

Mechanical Metallurgy Division

and

A. Ghosh, P. Dhandharia, N.S. More, S. Vijayakumar, A.G. Chhatre

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BARC/2012/E/002

GOVERNMENT OF INDIA

ATOMIC ENERGY COMMISSION

BHABHA ATOMIC RESEARCH CENTRE

MUMBAI, INDIA

2012

MECHANICAL PROPERTIES OF Zr-2.5Nb PRESSURE TUBE

MATERIAL MANUFACTURED EMPLOYING FORGING ROUTES

FOR PHWR700 - PART I: TENSILE BEHAVIOR

by

A.K. Bind, R.N. Singh, Saurav Sunil, J.K. Chakravartty

Mechanical Metallurgy Division

and

A. Ghosh, P. Dhandharia, N.S. More, S. Vijayakumar, A.G. Chhatre

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BIBLIOGRAPHIC DESCRIPTION SHEET FOR TECHNICAL REPORT (as per IS : 9400 - 1980)

01 Security classification : Unclassified

02 Distribution : External

03 Report status : New

04 Series : BARC External

05 Report type : Technical Report

06 Report No. : BARC/2012/E/002

07 Part No. or Volume No. :

08 Contract No. :

10 Title and subtitle : Mechanical properties of Zr-2.5Nb pressure tube material

manufactured employing forging routes for PHWR700 - Part 1: tensile behavior

11 Collation : 45 p., 23 figs., 3 tabs.

13 Project No. :

20 Personal author(s) : 1) A.K. Bind; R.N. Singh; Saurav Sunil; J.K. Chakravartty 2) Agnish Ghosh; Priyesh Dhandharia; Nitin S. More; S. Vijayakumar; A.G. Chhatre

21 Affiliation of author(s) : 1) Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai

2) Engineering Directorate, Nuclear Power Corporation of India Limited, Mumbai

22 Corporate author(s) : Bhabha Atomic Research Centre, Mumbai - 400 085

23 Originating unit : Mechanical Metallurgy Division, BARC, Mumbai

24 Sponsor(s) Name : Department of Atomic Energy

Type : Government

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BARC/2012/E/002

30 Date of submission : December 2011

31 Publication/Issue date : January 2012

40 Publisher/Distributor : Head, Scientific Information Resource Division, Bhabha Atomic Research Centre, Mumbai

42 Form of distribution : Hard copy

50 Language of text : English

51 Language of summary : English

52 No. of references : 15 refs.

53 Gives data on :

60

70 Keywords/Descriptors : PHWR TYPE REACTORS; PRESSURE TUBES; ZIRCONIUM ALLOYS; NIOBIUM ALLOYS; YIELD STRENGTH; COLD WORKING; ELONGATION; STRAIN RATE; TENSILE PROPERTIES

71 INIS Subject Category : S21

99 Supplementary elements :

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Content Page No.

Abstract

1

Nomenclature

2

1. Introduction 3

2. Experimental 5

3. Results and Discussion 5

4. Conclusions 10

Acknowledgements 10

Reference 11

List of tables 13

List of figures 13

Tables 17

Figures 19

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Tensile behavior of Zr-2.5Nb pressure tube material

manufactured employing forging routes

A. K. Bind1, R.N. Singh1, Saurabh Sunil1, J.K. Chakravartty1,

Agnish Ghosh2, Priyesh Dhandharia2, Nitin S. More2, S. Vijayakumar2, A. G. Chhatre2

1

Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Trombay,

Mumbai-400085.

2

Engineering Directorate, Nuclear power Corporation of India Ltd., NUB, Anushaktinagar,

Mumbai-400094

Abstract

In order to obtain improved in-reactor performance NFC, Hyderabad had produced few tubes of

Zr-2.5Nb alloy by employing forging to break the cast structure. To break the cast structure and to obtain

more homogeneous microstructure both double forging and single forging were employed.

Subsequently the forged material was used to manufacture pressure tube by employing hot extrusion,

cold pilgering and autoclaving. The material was received in the form of spools of length of about 100

mm each. The tubes were slit at 120 degree and then cold flattened. The plates were stress relieved at

400 °C for 24 hour. The both longitudinal (L) and transverse (T) tensile samples were machined from

these plates. Tensile properties were evaluated by carrying out uniaxial tension tests at temperatures

between 25 and 325 °C and under strain-rate of 1.075 x 10-4 /s. Analysis of tensile results showed that

both yield and ultimate tensile strengths of this alloy decreased monotonically with increasing test

temperatures. Both strength and elongation values were comparable for the samples (L & T) obtained

from front and back end of the tube manufactured by single and double forging routes. Transverse

samples showed higher strength and lower uniform elongation values as compared to longitudinal

samples. Double forged material showed higher strength but comparable elongation values as

compared single forged material for L & T samples obtained from front end and back end of the tube.

The yield strength of double forged material at 25 °C is higher than the PHWR700 specification of a

maximum value of ~586 MPa. The observed deviation from specification can be corrected by

changing thermo-mechanical processing parameters appropriately.

Keywords: Zr-2.5Nb alloy, Tensile properties, Yield strength, Ultimate Tensile Strength,

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Nomenclature

ACR Advanced CANDU Reactor

AERB Atomic Energy Regulatory Board

ASME American Society of Mechanical Engineers

BARC Bhabha Atomic Research Centre

CANDU reactor Canada Deuterium Uranium reactor

CWSR Cold Worked and Stress Relieved

DBLA Double forged back end longitudinal orientation

DBTA Double forged back end transverse orientation

DFLA Double forged front end longitudinal orientation

DFTA Double forged front end transverse orientation

e Plastic strain

eu Uniform plastic strain

et Total plastic strain

EDM Electro Discharge Machining

IPHWR Indian Pressurized Heavy Water Reactor

L Longitudinal orientation

LE Leading end

mm millimeter

MPa Megapascal

MWe Megawatt electrical

Nb Niobium

NFC Nuclear Fuel Complex

NPCIL Nuclear Power Corporation of India Ltd.

O Oxygen

PHWR Pressurized Heavy Water Reactor

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1. Introduction

Cold-worked and stress relieved (CWSR) Zr-2.5Nb tubes is being used as pressure

tubes for Indian Pressurized Heavy Water Reactors (IPHWR) [1-5]. The pressure tubes serve

as miniature pressure vessels operating at about 300 °C with a coolant pressure of ~ 10 MPa.

The design of the pressure tube is based on section III of the ASME pressure vessel code,

which specifies the criteria of maximum design stress on the basis of ultimate tensile strength,

yield strength, creep and stress-rupture strengths at the operating temperature. For pressure

tube alloys (both Zircaloy-2 and Zr-2.5Nb alloy) one third of the ultimate tensile strength has

been found to be the limiting property [6].

Recent in-reactor dimensional changes measurement by NPCIL in IPHWR220 MWe

has revealed that the diametral creep rate exhibited by some of the tubes is significantly

PT Pressure Tube

s second

S Engineering stress

SBLA Single forged back end longitudinal orientation

SBTA Single forged back end transverse orientation

SFLA Single forged front end longitudinal orientation

SFTA Single forged front end transverse orientation

T Transverse orientation

TE Trailing end

UTS Ultimate Tensile Strength

wppm Weight in parts per million

YS Yield Strength

Zr Zirconium

α-Zr Alpha zirconium having HCP crystal structure

β-Zr Beta zirconium having BCC crystal structure

°C Degree Celsius

εpl True plastic strain

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greater than design value. Also, large variability in the axial elongation and diametral creep

rates of the pressure tubes across the reactor core were observed. In order to achieve the

design life of 30 years for Zr-2.5Nb pressure tubes, several discussion and meetings were held

between the BARC scientists, NPCIL engineers, NFC engineers and AERB safety regulators.

A series of investigations were initiated by reactor operators and safety engineers to evaluate

the effect of relaxing the diametral creep limit form present 3 % to 4.5% on thermal

hydraulics of the coolant channels and structural integrity of coolant channel assembly.

Another initiative was to reexamine the alloy chemistry and microstructure based on the

experience gained both nationally and internationally with the objective of improving

in-reactor performance of the pressure tubes. Causey et al. [7] has reviewed the relationship

between alloy chemistry and in-reactor performance of CANDU pressure tubes. The

evolution of alloy chemistry for Zr-2.5Nb pressure tube material is shown in table 1 [7]. It

may be noted that initially Nb content range was between 2.4-2.8 wt percent which has been

narrowed down since 1987 to 2.5-2.8 wt percent. Carbon content has been reduced from 270

wppm in 1976 to a range between 40-60 wppm to reduce deuterium intake. Over the years

oxygen concentration has been increased from 900-1300 to 1200-1500 wppm because of its

beneficial effect in reducing diametral creep. Initially iron content was specified to be less

than 1500 wppm, which was reduced to less than 650 wppm as it was expected to promote

deuterium pick up. However, recent irradiation studies have suggested role of iron in

reducing diametral creep and axial elongation and hence iron content specified for ACR700 is

900-1300 wppm. Another notable improvement is the specification for chlorine (<0.5wppm)

as reduced chlorine content was reported to improve fracture toughness [8]. Puls et. al. [9]

have summarized the typical microstructural features of CANDU Zr-2.5Nb pressure tubes.

The thickness of α-Zr grains is suggested to be in the range about 0.3 to 0.5 µm, with

transverse and axial grain dimensions respectively 5 and 50 times of radial dimension. The α

-Zr grains have a texture that has resolved basal-pole fractions oriented approximately one

third in the radial, most of the remainder in the transverse, and only a small fraction in the

longitudinal direction of the pressure tube. Recent microstructural investigation carried out at

Materials Group, BARC [10] has indicated that the grain size of α-Zr grains in some of the

cold worked and stress-relieved (CWSR) Zr-2.5Nb alloy pressure tubes used in Indian

PHWRs are finer as compared to AECL pressure tubes [9] and a large variation in β-Zr phase

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Another difference between the manufacturing practice followed by NFC, Hyderabad

and AECL vendors is the mode and degree of hot working to break the cast structure. At

NFC, Hyderabad 350 mm diameter ingots are hot extruded to 230 mm diameter billets to

break the cast structure whereas 585 mm dia ingots are hot press forged followed by rotary

forging to billet diameter of 210 mm by AECL vendors [8, 9,11]. It was felt that the

increased diametral creep in some pressure tubes and variability in axial elongation and

diametral creep among the pressure tubes of reactor core could be attributed to mode and

degree of hot working. Hence, NFC attempted nine routes to manufacture Zr-2.5Nb alloy

pressure tube having desirable microstructure, texture and mechanical properties. Based on

the investigation of microstructure and texture, out of the nine routes, tubes manufactured by

two routes were identified for detailed mechanical properties characterization. In this report,

tensile behavior of the Zr-2.5Nb pressure tubes manufactured employing forging route is

described.

2. Experimental

The flow sheets used for manufacture of the Zr-2.5Nb alloy pressure tubes are shown in

figure 1. The forged material was received in the form of spools of length of about 100 mm

each. The tubes were slit at 120° and then cold flattened. The plates were stress relieved at

400 °C for 24 hour. The both longitudinal (L) and transverse (T) tensile samples were

machined from these plates. Tensile specimens (gage dimensions 31 x 6.0x 3.5 mm) with

their axes parallel to the longitudinal/transverse direction of the pressure tubes were machined

from flattened pieces using EDM wire cutting. The tensile tests were carried out in the

temperature range of 25 – 325 °C under a nominal strain-rate of 1.075 x 10-4 /s. The test

matrix is described in table 2.

All tension tests were conducted using an Instron machine fitted with a resistance

heated furnace with temperature control of ±1°C. For elevated temperature tests the

specimens were soaked for one hour prior to the load application.

3. Results and Discussion

Fabrication flow sheets for manufacture of Zr-2.5Nb pressure tube material using

conventional, single forged and double forged routes is shown in Fig. 1. In Indian practice hot

working is carried out by extrusion [12] whereas in forging routes hot working is carried out

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and chemical composition both double forging and single forging were employed instead of

hot extrusion in two stages practiced till now [12]. Another notable difference is the use of

larger diameter ingot for double forged material thereby imparting higher degree of hot work,

which is expected to be advantageous in breaking the cast structure. In steel industry it is

common practice to use an area reduction of 200% to break the cast structure [13-14]. The

critical thickness reduction required to break the cast structure is expected to vary with alloy

chemistry, strain-rate and hot working temperature [14]. Thus an ingot diameter reduction

from 550 mm to 230 mm during hot forging for double forged material is expected to be

beneficial in obtaining uniform microstructure and mechanical properties. Subsequently the

forged material was used to manufacture pressure tube by employing hot extrusion, stress

relieving, cold pilgering and autoclaving. Both hot extrusion and hot forging impart varying

degree of efficiency in breaking the cast structure. The subsequent manufacturing steps are

identical for all the three routes. The tensile behaviour of Zr-2.5Nb pressure tube

manufactured from the three routes are described in terms of engineering stress-plastic strain

curves, true stress-true strain curves, yield strength (YS), ultimate tensile strength (UTS),

uniform elongation and total elongation. An inter-comparison between strength and

elongation values is also provided.

Engineering stress (S) vs. plastic strain (e) curves for Zr-2.5Nb pressure tube material

manufactured by double forging route (fig. 1) obtained using samples machined from the

front end of the tube is shown in fig. 2. The tensile tests were carried out in the temperature

range of 25 – 325 °C using tensile samples machined with its axes parallel to (a) longitudinal

(L) and (b) transverse (T) direction of the tubes. The flow stress was observed to decrease

with increase in test temperature from ambient to 300°C. Reduction in uniform elongation

was also observed with increase in temperature. Engineering stress vs. plastic strain curves for

Zr-2.5Nb pressure tube material manufactured by double forging route (fig. 1) using samples

machined from back end of the tube is shown in fig. 3. The tensile tests were carried out in the

temperature range of 25 – 325 °C using tensile samples machined with its axes parallel to (a)

longitudinal and (b) transverse direction of the tubes. Similar to the flow behavior of the

samples obtained from the front end of the tube, with increase in temperature flow stress for

the samples obtained from the back end was also observed to decrease with increase in test

temperature from ambient to 300°C. Reduction in uniform elongation was also observed with

increase in temperature.

Engineering stress vs. plastic strain curves for Zr-2.5Nb pressure tube material manufactured

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shown in fig. 4. The tensile tests were carried out in the temperature range of 25 – 325 °C

using tensile samples machined with its axes parallel to (a) longitudinal and (b) transverse

direction of the tubes. Here too the flow stress and uniform elongation was observed to

decrease with increase in test temperature. Engineering stress vs. plastic strain curves for

Zr-2.5Nb pressure tube material manufactured by single forging route (fig. 1) obtained using

samples machined from the back end of the tube is shown in fig. 5. The tensile tests were

carried out in the temperature range of 25 – 325 °C using tensile samples with its axes parallel

to (a) longitudinal and (b) transverse direction of the tubes. Here too the flow stress and

uniform elongation was observed to decrease with increase in test temperature.

Engineering stress vs. plastic strain curves for Zr-2.5Nb pressure tube material manufactured

by conventional route (fig. 1) obtained using samples machined from a location about 2 m

from the front end of the tube is shown in fig. 5 [15]. The tensile tests were carried out in the

temperature range of 25 – 300 °C using tensile samples machined with its axes parallel to

longitudinal direction of the tubes. Here too the flow stress and uniform elongation was

observed to decrease with increase in test temperature.

The data in figures 2-6 were analyzed to obtain true stress vs. true plastic strain curves for

Zr-2.5Nb pressure tube material and corresponding plots are shown in figures 7 to 11. These

figures bring the influence of temperature and sample orientation on tensile behaviour. The

inter-comparison between tensile properties of double forged, single forged, conventional

material is provided as a function of test temperature, sample location and sample orientation.

Fig. 12 shows the influence of test temperature and sample location (Front & Back) on

longitudinal tensile properties (a) strength (YS & UTS) and (b) % uniform (eu) and total

tensile elongation (et) of Zr-2.5Nb pressure tube material manufactured by double forging

route in the temperature range of 25-325°C. Both strength and elongation values are

comparable for the longitudinal samples obtained from front and back end of the tube

manufactured by Double forging route. Fig. 13 shows the influence of test temperature and

sample location (Front & back) on transverse tensile properties of Zr-2.5Nb pressure tube

material manufactured by double forging route in the temperature range of 25-325°C (a)

strength (YS & UTS) and (b) % uniform (eu) and total tensile elongation (et). Both strength

and elongation values are comparable for the Transverse samples obtained from front and

back end of the tube manufactured by Double forging route. The comparable values of both

longitudinal and transverse tensile properties obtained using samples machined from the font

and back end of the tubes suggest uniformity in tensile properties of the tubes manufactured

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Fig. 14 shows the influence of test temperature and sample orientation (L & T) on tensile

properties (a) strength (YS & UTS) and (b) % uniform (eu) and total tensile elongation (et) of

Zr-2.5Nb pressure tube material manufactured by double forging route in the temperature

range of 25-325°C obtained using samples machined from the front end. Fig. 15 shows the

influence of test temperature and sample orientation (L & T) on tensile properties (a) strength

(YS & UTS) and (b) % uniform (eu) and total tensile elongation (et)of Zr-2.5Nb pressure tube

material manufactured by double forging route in the temperature range of 25-325°C obtained

using samples machined from the back end. Transverse samples showed higher strength and

lower uniform elongation values as compared to longitudinal samples obtained from both

front and back end of the tube manufactured by Double forging route.

Fig. 16 shows the influence of test temperature and sample location (front & back) on tensile

Zr-2.5Nb pressure tube material manufactured by single forging route in the temperature

range of 25-325°C obtained using longitudinal samples. Strength was higher and elongation

values were lower for samples obtained from front end as compared to that obtained from

back end for the longitudinal samples of the tube manufactured by single forging route. Fig.

17 shows the influence of test temperature and sample location (Front & Back) on tensile

range of 25-325°C obtained using transverse samples. Both strength and elongation values

are comparable for the Transverse samples obtained from front and back end of the tube

manufactured by Single forging route.

Influence of test temperature and sample orientation (L & T) on tensile properties of

Zr-2.5Nb pressure tube material manufactured by single forging route in the temperature range of

25-325°C obtained using samples machined from front end of the tube is shown in fig. 18 (a)

strength (YS & UTS) and fig. 16(b) % uniform (eu) and total tensile elongation (et). The

influence of test temperature and sample orientation (L & T) on tensile properties of

Zr-2.5Nb pressure tube material manufactured by single forging route in the temperature range of

25-325°C obtained using samples machined from back end of the tube is shown in fig. 19(a)

strength (YS & UTS) and fig. 19(b) % uniform (eu) and total tensile elongation (et).

Transverse samples showed higher strength and lower elongation values as compared to

longitudinal samples obtained from both front and back end of the tube manufactured by

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Influence of test temperature and forging (Single - S & Double - D) on tensile properties of

Zr-2.5Nb pressure tube material in the temperature range of 25-325°C obtained using samples

machined from front end with its axes parallel to longitudinal direction of the tube is shown in

fig. 20(a) strength (YS & UTS) and fig. 20(b) % uniform (eu) and total tensile elongation (et).

Double forged material showed higher strength and higher total elongation values as

compared single forged material for longitudinal samples obtained from front end of the

tubes. The Influence of test temperature and forging (S & D) on tensile properties of Zr-2.5Nb

pressure tube material in the temperature range of 25-325°C obtained using transverse tensile

samples machined from front end is shown in fig. 21(a) strength (YS & UTS) and fig. 21(b)

% uniform (eu) and total tensile elongation (et). Double forged material showed higher

strength but comparable elongation values as compared single forged material for transverse

samples obtained from front end of the tubes.

Influence of test temperature and forging (S & D) on tensile properties of Zr-2.5Nb pressure

tube material in the temperature range of 25-325°C obtained using longitudinal samples

machined from back end is shown in fig. 22(a) strength (YS & UTS) and fig. 22(b) %

uniform (eu) and total tensile elongation (et). Double forged material showed higher strength

but comparable elongation values as compared single forged material for longitudinal samples

obtained from back end of the tubes. The influence of test temperature and forging (S & D)

on tensile properties of Zr-2.5Nb pressure tube material in the temperature range of 25-325°C

obtained using transverse samples machined from back end is shown in fig. 23(a) strength

(YS & UTS) and fig. 23(b) % uniform (eu) and total tensile elongation (et). Double forged

material showed higher strength but comparable elongation values as compared single forged

material for transverse samples obtained from back end of the tubes.

The tensile properties of the double forged and single forged material obtained using

longitudinal specimens are compared with the PHWR700 specification in table 3. Though the

single forged material met PHWR700 specifications both at 25 and 300 °C, the double forged

material exhibited slightly higher strength as compared the specified maximum. Since the

pressure tubes of PHWR700 will be joined to the primary heat transport circuit by roll joint to

the end fitting, high room temperature yield strength is expected to result in higher residual

stress in the roll joint, which could be detrimental to the integrity of the pressure tubes. It is

suggested that the thermo-mechanical processing parameters may be adjusted to correct the

deviation in the strength of the double forged material as compared to PHWR700

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4. Conclusions

• Both strength and elongation values are comparable for the longitudinal and

Transverse samples obtained from front and back end of the tube manufactured by

Double forging route

• Transverse samples showed higher strength and lower uniform elongation values as

compared to longitudinal samples obtained from front end or back end of the tube

manufactured by Double forging route

• Both strength and elongation values are comparable for the longitudinal and transverse

samples obtained from front and back end of the tube manufactured by Single forging

route

• Transverse samples showed higher strength and lower uniform elongation values as

compared to longitudinal samples obtained from front end and back end of the tube

manufactured by Single forging route

• Double forged material showed higher strength but comparable elongation values as

compared single forged material for L & T samples obtained from front end and back

end of the tube.

• The yield strength of double forged material at 25 °C is higher than the PHWR700

specification of a maximum value of ~586 MPa.

• The observed deviation from specification can be corrected by altering the

thermo-mechanical processing parameters.

Acknowledgement

Constant encouragement and invaluable support provided by Dr. S. Banerjee, Chairman,

Department of Atomic Energy & Secretary, Atomic Energy Commission, Government of

India, Dr. R. K. Sinha, Director, BARC, Dr. A. K. Suri, Director, Materials Group, BARC,

Mumbai, Mr. S. A. Bhadwaj, Director (T), NPCIL and Mr. N. Saibaba, DCE, NFC,

Hyderabad is acknowledged. Authors are thankful to Shri S. K. Jha, Shri S. Tonpe, Shri K.

Vaibhav and Shri V. Deshmukh of NFC, Hyderabad for providing the material for this study.

Technical assistance provided by Shri P. S. Shembe in tensile testing is thankfully

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References

1. Chaedle, S. A., Coleman, C. E., and Light, H., Nuclear Technology, 57, (1982) 425.

2. Ross-Ross, P. A., Atomic Energy of Canada Limited Publication 3126 (1968).

3. Bell, L. G., J. Nuclear Materials, 57, (1975) 258.

4. Ibrahim, E. F., and Cheadle, B. A., Canadian Metallurgical Quarterly, 24 (1985) 281.

5. Srivastava, D., Dey, G. K., and Banerjee, S., “Evolution of microstructure during

fabrication of Zr-2.5 wt. Pct. Nb alloy pressure tubes”, Metall. Trans. A, 26A 2707 (1995).

6. Singh, R. N., Kishore, R., Sinha, T. K., and Banerjee, S., “Tensile Properties of Zr-2.5Nb

Pressure Tube Alloy between 25 and 800 °C” BARC Report No. 2000/E/029.

7. Causey, A. R., Christodoulou, N. W., Davies, G., Griffiths, M., McDougall, G. M.,

Moan, G. D., Ploc, R. A. and Puls, M. P., “Relationship Between Pressure Tube

Processing, Impurity/Alloying Element Concentrations and Performance in CANDU

Reactors”, Chinese Journal of Rare Metal Materials and Engineering, Vol. 30, Supp. 1

(2001) pp. 24-34.

8. Theaker, J. R., Choubey, R., Moan, G. D., Aldridge, S. A., Davis, L., Graham, R. A. and

Coleman, C. E., “Fabrication of Zr-2.5Nb Pressure Tubes to Minimize the Harmful

Effects of Trace Elements” Zirconium in the Nuclear Industry: Tenth International

Symposium, ASTM STP 1245, 1994, pp. 221-242.

9. Puls, M. P., Tapping, R. L. and Walker, Z. H. “ACR-700 Advances in Materials”, Physics

in Canada, Vol. 60 (2004) pp. 369-381.

10.Srivastava, D., Neogi, S., Dey, G. K., Banerjee, S., Ramadasan, E. and Anantharaman, S.

“Microstructural examination of Zr-2.5Nb pressure tube S-07 from Kakrapar Atomic

Power Station Unit -2” BARC report No. BARC/E/2011/007.

11.IAEA TECDOC1037 “Assessment and management of ageing of major nuclear power

plant components important to safety: CANDU pressure tubes” August 1998, p-19

12. Srivastava, D., Dey, G. K., and Banerjee, S., “Evolution of microstructure during

fabrication of Zr-2.5 wt. Pct. Nb alloy pressure tubes”, Metall. Trans. A 26A (1995) 2707.

13.Nisbett, Edward G., “Steel forgings: design, production, selection, testing, and

application” ASTM International, 01-Jan-2005 page 27.

14.Semiatin, S.L. , “Metalworking: Bulk Forming,”ASM handbook Volume 14A ,2005,

p-249.

15.Bind, A. K., Dhandharia, P., Ghosh, A., More, N. S., Singh, R.N., Chakravartty J.K.,

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of Zr-2.5Nb pressure tube material in the temperature range of ambient to 300°C,” 2011:

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List of tables

Table 1: Changes in Alloying/Impurity Element Specifications (in ppm by weight except Nb)

for Zr-2.5Nb PTs [9]

Table 2: Details of fabrication route, tube number, test temperatures and sample orientation

used in this work.

Table 3: Comparison of tensile properties of the Zr-2.5Nb alloy investigated in this work with

PHWR700 specification, viz., UTS at 300°C >469MPa, YS at 300°C > 324 MPa and YS at

25 °C < 586 MPa. The deviations from PHWR700 have been indicated in bold font.

List of figures

Fig. 1 Fabrication flow sheets for manufacture of Zr-2.5Nb pressure tube material using

conventional, single forged and double forged routes.

Fig. 2: Engineering stress (S) vs. plastic strain (e) curves for Zr-2.5Nb pressure tube material

manufactured by double forging route (fig. 1). The tensile tests were carried out in the

temperature range of 25 – 325 °C. Tensile samples were machined from the front end of the

tube with its axes parallel to (a) longitudinal and (b) transverse direction of the tubes.

temperature range of 25 – 325 °C. Tensile samples were machined from the back end of the

manufactured by single forging route (fig. 1). The tensile tests were carried out in the

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manufactured by conventional route (fig. 1). The tensile tests were carried out in the

temperature range of 25 – 300 °C.

Fig. 7: True stress (σ) vs. true plastic strain (εpl) curves for Zr-2.5Nb pressure tube material

Fig. 12: Influence of test temperature and sample location (Front & back) on tensile properties

of Zr-2.5Nb pressure tube material manufactured by double forging route in the temperature

range of 25-325°C (a) strength (YS & UTS) and (b) % uniform (eu) and total tensile

elongation (et). Both strength and elongation values are comparable for the longitudinal

samples obtained from front and back end of the tube manufactured by Double forging route.

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elongation (et). Both strength and elongation values are comparable for the Transverse

Fig. 14: Influence of test temperature and sample orientation (L & T) on tensile properties of

elongation (et). Transverse samples showed higher strength and lower uniform elongation

values as compared to longitudinal samples obtained from front end of the tube manufactured

by Double forging route.

values as compared to longitudinal samples obtained from back end of the tube manufactured

Fig. 16: Influence of test temperature and sample location (front & back) on tensile properties

of Zr-2.5Nb pressure tube material manufactured by single forging route in the temperature

elongation (et). Strength was higher and elongation values were lower for samples obtained

from front end as compared to that obtained from back end for the longitudinal samples of the

tube manufactured by single forging route.

samples obtained from front and back end of the tube manufactured by Single forging route.

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by Single forging route.

elongation (et). Transverse samples showed higher strength and lower elongation values as

compared to longitudinal samples obtained from back end of the tube manufactured by Single

forging route.

Fig. 20: Influence of test temperature and forging (SFLA & DFLA) on tensile properties of

Zr-2.5Nb pressure tube material in the temperature range of 25-325°C (a) strength (YS &

UTS) and (b) % uniform (eu) and total tensile elongation (et). Double forged material showed

higher strength and higher total elongation values as compared single forged material for

longitudinal samples obtained from front end of the tubes.

Fig. 21: Influence of test temperature and forging (SFTA & DFTA) on tensile properties of

higher strength but comparable elongation values as compared single forged material for

transverse samples obtained from front end of the tubes.

longitudinal samples obtained from back end of the tubes.

(22)

Table 1: Changes in Alloying/Impurity Element Specifications (in ppm by weight except Nb)

Zirconium Balance Balance Balance Balance Balance Balance

* It is expected that the ingot processing will maintain the chlorine concentration < 0.2 wppm.

(23)

Table 2: Details of fabrication route, tube number, test temperatures and sample orientation

Conventional 19-2557-2 25, 70, 150, 250, 300 and 325 Longitudinal

Table 3: Comparison of tensile properties of the Zr-2.5Nb alloy investigated in this work with

PHWR700 specification, viz., UTS at 300°C >469MPa, YS at 300°C > 324 MPa and YS at

25 °C < 586 MPa. The deviations from PHWR700 have been indicated in bold font.

Fabrication

Single Forged Front End Longitudinal 574 398 509 13.1

Single Forged Back End Longitudinal 546 380 487 16.3

Double

Forged Front End Longitudinal 610 412 550 17. 3

Double

(24)

Fig. 1 Fabrication flow sheets for manufacture of Zr-2.5Nb pressure tube material using

(25)

Fig. 2: Engineering stress vs. plastic strain curves for Zr-2.5Nb pressure tube material

(a)

(26)

(a)

(27)

(a)

(28)

(a)

(29)

pl

(30)

Fig. 7: True stress vs. true plastic strain curves for Zr-2.5Nb pressure tube material

(a)

(31)

(a)

(32)

(a)

(33)

(a)

(34)

(35)

Temperature, °C

elongation (et). Both strength and elongation values are comparable for the longitudinal

(a)

(36)

Temperature, °C

(a)

(37)

Temperature, °C

(a)

(38)

Temperature, °C

values as compared to longitudinal samples obtained from back end of the tube manufactured

(a)

(39)

Temperature, °C

elongation (et). Strength was higher and elongation values were lower for samples obtained

from front end as compared to that obtained from back end for the longitudinal samples of the

tube manufactured by single forging route.

(a)

(40)

Temperature, °C

samples obtained from front and back end of the tube manufactured by Single forging route.

(a)

(41)

Temperature, °C

by Single forging route.

(a)

(42)

Temperature, °C

elongation (et). Transverse samples showed higher strength and lower elongation values as

compared to longitudinal samples obtained from back end of the tube manufactured by Single

forging route.

(a)

(43)

Temperature, °C

higher strength and higher total elongation values as compared single forged material for

longitudinal samples obtained from front end of the tubes.

(a)

(44)

Temperature, °C

transverse samples obtained from front end of the tubes.

(a)

(45)

Temperature, °C

longitudinal samples obtained from back end of the tubes.

(a)

(46)

Temperature, °C

transverse samples obtained from back end of the tubes.