Astm stp 529 1973

Contents Introduction 1 Reactor Vessel Steels—Fracture Behavior Irradiation Strengthening and Fracture Embrittlement of A533-B Pressure Vessel Steel Plate and Submerged-Arc Weld— J.. W.,

ASTM SPECIAL TECHNICAL PUBLICATION 529 John Moteff, symposium chairman

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®by A M E R I C A N S O C I E T Y F O R T E S T I N G A N D M A T E R I A L S 1973

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September 1973

Foreword

The Symposium on Effects of Radiation on Substructure and Mechanical

Properties of Metals and Alloys was presented at Los Angeles, Calif., 26-28 June

1972 in conjunction with the Seventy-fifth Annual Meeting of the American

Society for Testing and Materials The symposium was sponsored by ASTM

Committee E-10 on Radioisotopes and Radiation Effects John Moteff, Materials

Science and Metallurgical Engineering Department, University of Cincinnati,

served as chairman of the symposium committee, which consisted of C J

Baroch, A L Bement, E Landerman, F R Shober, and K M Zwilsky The six

sessions were presided over by: (1) L R Steele, (2) H Bohm, (3) J R Weir, (4)

T.T Claudson, (5) I P Bell and K.M Zwilsky, and (6) S.D Harkness and

C Y Li

Related ASTM Publications

Irradiation Effects on Structural Alloys for Nuclear Reactor Applications, STP

484 (1971), $49.25 (04-484000-35) Analysis of Reactor Vessel Radiation Effects Surveillance Programs, STP 481 (1970), $26.00 (04-481000-35) Irradiation Effects in Structural Alloys for Thermal and Fast Reactors, STP 457 (1970), $36.00 (04-457000-35)

Contents

Introduction 1

Reactor Vessel Steels—Fracture Behavior Irradiation Strengthening and Fracture Embrittlement of A533-B

Pressure Vessel Steel Plate and Submerged-Arc Weld—

J A WILLIAMS AND C W HUNTER 5

Radiation-Induced Changes in the Fracture Extension Resistance

(R-Curve) of Structural Steels—J R HAWTHORNE AND

H E W A T S O N 17

Reactor Vessel Steels—Structure and Impurity Effects

Effect of Composition on the Sensitivity of Structural Steel to

Irradiation Embrittlement—A E POWERS 31

Discussion 39

On the Radiation Hardening Mechanism in Fe-C-Mn Type

Alloys—MILAN BRUMOVSKY 46

The Role of Some Alloying Elements on Radiation Hardening

in Pressure Vessel Steels—N IGATA, K. WATANABE,

AND S SATO 63

Discussion 75

Property Changes Resulting from Impurity-Defect Interactions

in Iron and Pressure Vessel Alloys—F A. SMIDT, JR.,

AND J A SPRAGUE 78

Damage-Function Analysis of Neutron-Induced Embrittlement

in A302-B Steel at 550 F (288 C)—C Z. SERPAN, JR. 92

Microstructural Changes—Neutron-Induced Voids and Phases

Effects of Microstructure on Swelling and Tensile Properties of

Neutron-Irradiated Types 316 and 405 Stainless Steels—

K R GARR, C G RHODES, AND D KRAMER 109

Discussion 119

Effects of Second-Phase Particles on Irradiation Swelling of

Austenitic Alloys—W K. APPLEBY AND U E W O L F F 122

Void Formation in Type 1.4988 Stabilized Stainless Steel—K

EHRLICH AND N H PACKAN 137

Swelling and Tensile Property Evaluations of High-Fluence

EBR-II Thimbles—R L. F I S H , J L. STRAALSUND, C W

HUNTER, AND J J HOLMES 149

Neutron Irradiation Damage in a Precipitation-Hardened

Aluminum Alloy—R T. K I N G , A. JOSTSONS, AND

K FARRELL 165

Discussion 181

A Comparison of the High-Temperature Damage Structures in

Accelerator and Reactor Irradiated Molybdenum—

B L EYRE AND J H EVANS 184

On the Swelling Mechanism in the Irradiated Boron-Containing

Stainless Steel—I V. ALTOVSKII, L A. ELESIN,

P A PLATONOV, AND E G SAVEL'EV 199

Charged-Particle-Induced Voids and Computer Experiments

Nickel Ion Bombardment of Types 304 and 316 Stainless

Steels: Comparison with Fast-Reactor Swelling Data—

W G JOHNSTON, J H ROSOLOWSKI, A M TURKALO,

AND T LAURITZEN 213

Void Swelling Behavior of Types 304 and 316 Stainless Steel

Irradiated with 4-MeV Ni"^ Ions—S.G. M C D O N A L D AND

ANTHONY TAYLOR 228

Discussion 241

Studies of Void Formation in Proton-Irradiated Type 316 and

Titanium-Modified 316 Stainless Steels—D W KEEPER,

A G PARD, AND D KRAMER 244

Ordered Defect Structures in Irradiated Metals—G L

KULCINSKI AND J L BRIMHALL 258

Discussion 272

A Diffusion Model for the Effect of Applied Stress on Void

and Loop Growth—J L. STRAALSUND, G L G U T H R I E ,

AND W G WOLFER 274

Attrition and Stabilization of Void Nuclei: Critical Nucleus

Size-J R BEELER,JR., A N D M F BEELER 289

Production of Voids in Stainless Steel by High-Voltage

Discussion 324 Void Formation in Some Nickel-Aluminum Alloys During 20-

MeV C+^and46.5-MeV Ni*^ Irradiation—J A HUDSON,

S FRANCIS, D J MAZEY, AND R S NELSON 326

Mechanical Behavior-Ductility Materials Performance Prediction from Irradiation Test Data

—H H YOSHIKAWA 337

High-Temperature Embrittlement of Ferritic and Austenitic

Stainless Steels Irradiated up tb 1.6 x 10^^ n/cm^(>0.1

MeV> — P H VAN ASBROECK, M SNYKERS, AND W

VANDERMEULEN 349

Effect of Irradiation on the Microstructure and Creep-Rupture

Properties of Type 316 Stainless Steel—E E. BLOOM AND

J O STIEGLER 360

Discussion 381 Ductility of Irradiated Type 316 Stainless Steel—J J HOLMES,

A J LOVELL, AND R L F I S H 383

Effects of Fast-Neutron Irradiation on Tensile Properties and

Swelling Behavior of Vanadium Alloys—R. CARLANDER,

S D HARKNESS, AND A T SANTHANAM 399

Burst Testing of Zircaloy Cladding from Irradiated

Mechanical Behavior—Creep, Fatigue, and Tensile

Influence of Neutron Spectrum and Microstructure on the

Post-irradiation Creep Rupture Behavior of an Austenitic

Fatigue Behavior of Irradiated Thin-Section Type 348 Stainless

Steel at 550 F (288 C)—H H SMITH AND

P SHAHINIAN 451

In-pile Stress Rupture Strength of Three Stabilized Austenitic

Influence of Irradiation on the Creep/Fatigue Behavior of Several

Austenitic Stainless Steels and Incoloy 800 at 700 C—

C R BRINKMAN, G E KORTH, AND J M BEESTON 473

Discussion 491 Effect of Neutron Irradiation on Fatigue Crack Propagation in

Types 304 and 316 Stainless Steels at High

Tempera-tures—P. SHAHINIAN, H E WATSON, AND H H SMITH 493

Effects of Irradiation on the Tensile and Structural Properties

of FV548 Stainless Steel—J S. W A T K I N , J P.

SHEP-HERD, AND J STANDRING 509

Effect of Neutron Irradiation on Vanadium—J F MclLWAIN,

C W C H E N , R BAJAJ, AND M S WECHSLER 529

STP529-EB/Sep 1973

Introduction

The 1972 Symposium on Effects of Radiation on Substructure and

Mechani-cal Properties of Metals and Alloys was the sixth in a series of related

international conferences that have been held biennially The symposium,

sponsored by ASTM Committee E-10 on Radioisotopes and Radiation Effects,

had the primary objective of providing a forum for a comprehensive review of

current technology in the development and evaluation of metallic materials for

advanced nuclear reactor designs This was accomplished by bringing together

the world's experts in nuclear radiation effects on structural materials

In the rapidly expanding field of reactor technology, there is a vital need to

bring together those individuals performing laboratory research and conducting

theoretical studies of a fundamental nature with reactor designers representing

the nuclear industries, nuclear utilities, and government This communication

becomes even more critical in view of the requirement for standard procedures

of evaluating materials performance and for the establishment of more stringent

specifications for reactor structural materials

The coupling of the number of atoms that have been displaced from their

normal lattice positions in a metal, as well as the rate of atom displacements, due

to exposure in a nuclear reactor environment, with changes in mechanical

properties and in physical dimensions is rapidly replacing older measures of the

radiation-induced transformations, such as the fluence of those neutrons above

some specified energy or the nvt parameter In essence, we are now beginning to

report our irradiation data on the basis of the primary e/jfec/s—generally denoted

as radiation damage, but preferably should be designated as a radiation-induced

transformation On the other hand, secondary effects—more appropriately

designated radiation-effects, refer to the changes in the physical or mechanical

properties that can be measured in the macroscopic sense

One of the major problems in radiation effects research is to identify the

particular types of atomic scale radiation-induced transformation events that

take place in an irradiated specimen from the particular combination or relative

magnitudes or both of the radiation effects they produce Conversely, another

major problem in radiation effects research is to establish the types and relative

magnitudes of the radiation effects that can result from a particular type of

radiation-induced transformation This circumstance becomes especially

pro-nounced with the increased use of charged particle irradiations as a means of

2 EFFECTS OF RADIATION ON METALS AND ALLOYS

accelerated studies in the effects of radiation to materials The fact that a few

hours of accelerator irradiations can produce radiation-induced transformations

equivalent—as measured by the density and size of voids that are produced, for

instance, to those produced by several years in reactors such as EBR-II—makes it

even more important to standardize experimental techniques and test

para-meters

In order to cover the important aspects of the general topic of radiation

effects, 35 papers contributed by recognized experts from at least seven

countries were carefully selected by the symposium committee and were

arranged into six sessions This volume is accordingly divided by session topic to

facilitate the readers' review in terms of his preferred interest A subject index is

also included as a further aid in the review of the technology presented in this

volume The topics include (1) reactor vessel steels—fracture behavior, (2)

reactor vessel steels—structure and impurity effects, (3) microstructural

changes—neutron-induced voids and second phases, (4) microstructural

changes—charged particle induced voids and computer experiments, (5)

mechanical behavior—ductility, and (6) mechanical behavior—creep, fatigue, and

tensile

The use of the electron microscopy, as a means of correlating

radiation-induced transformations with radiation effects, was quite apparent from this

symposium There should be no question that the observed microstructure of

irradiated metals and alloys, as a common denominator, plays a key role in the

interpretation of experimental data and in the development of theories and

models on which engineers may predict changes in the performance of reactor

components as a function of time-temperature and stress while in a nuclear

environment This circumstance was clearly revealed in the detailed discussions

that followed many of the papers The authors and attendees are commended

for their excellent presentations and participation in this exciting field of

radiation effects to metals and alloys

The members of the Symposium committee were John Moteff, chairman; C J

Baroch, co-chairman; A L Bement, Edward Landerman, F R Shober, and

Klaus Zwilsky.The symposium committee gratefully acknowledges the assistance

of D N Sunderman, chairman, ASTM committee E-10, for his leadership and

encouragement

/ Moteff

Professor of Materials Science, Materials Science and Metallurgical, Engineering Department,

University of Cincinnati, Cincinnati, Ohio 4S221;

symposium chairman

Reactor Vessel Fracture Behavior

Steels-/ A Williams^ and C W Hunter^

Irradiation Strengtinening

and Fracture Embrittlement of

A533-B Pressure Vessel Steel

Plate and Submerged-Arc Weld

REFERENCE: WilUams, J A and Hunter, C W., "Inadiation Strengthening and

Fracture Embrittlement of A533-B Pressure Vessel Steel Plate and Submerged-Arc

Weld," Effects of Radiation on Substructure and Mechanical Properties of Metals and

Alloys, ASTM STP 529, American Society for Testing and Materials, 1973, pp

5 - 1 6

ABSTRACT: Plate and weld material of ASTM A533 Grade B, Class 1 steel furnished

by the Heavy Section Steel Technology Program was characterized for irradiation

strengthening and fracture embrittlement Plane strain fracture toughness, K^^, in the

longitudinal orientation was determined ftom specimens irradiated at 540 F (282 C)

to neutron fluence levels of 2 and 8 x 1 0 n/cm (E > 1 MeV); longitudinal tension

specimens were irradiated at 510 F (265 C) at 2, 4, 6, and 8 x 1 0 ' ^ n/cm^ ( £ ' > 1

MeV) Yield strength was more sensitive to irradiation strengthening than the

ultimate strength, and the yield strength increase (Aa ksi) as a function of fluence

(•!>) and temperature {T, deg F) may be described by:

A0y5 = 22 [ 1 -exp(-<I>/5 X 1 0 ' * ) ] + $ / 1 0 ' ^ ( 4 3 - 0.0038D Irradiation levels of 2 and 8 x 10^^ produced shifts of 185 F (103 C) and 275 F (153

C) in the 50-ksi\Ain K^^ fracture toughness transition of A533 plate; the measured

shifts agree closely with those predicted, 153 F (85 C) and 282 F (157 C), from a

proposed correlation of shift in transition and change in yield strength Fracture

toughness ^ j ^ , and tensile properties of plate material were independent of the

orientation The fracture toughness of ASTM A533-B submerged-arc weldment metal

irradiated at 540 F (282 C) to a fluence of 3 x l O ' ' n/cm^ {E > 1 MeV) exhibited a

marked sensitivity for irradiation embrittlement; the indicated shift of the

50-ksi/in ^ j j fracture toughness transition level was approximately 390 F The

yield and ultimate tensile strengths of ASTM A533-B sub-arc weld were determined

for 510 F (265 C) irradiations to fluences of 0.5 x 10^^ n/cm^ and 4.0 to 4.6 x l O ' ^

n/cm^ (£• > 1 MeV) Irradiation strengthening of weld yield properties is slightly

greater than the longitudinal base properties,

KEY WORDS: radiation effects, fracture toughness, mechanical properties,

irradia-tion, reactor pressure vessel steels, thick plate material, submerged arc welding, steels

The prevention of fracture in light water-cooled nuclear pressure vessels is

essential to nuclear safety Vessel materials are selected to preclude fracture; the

evaluation of the effect of irradiation on material behavior is important to assure

that fracture cannot occur The determination of fracture properties in heavy

sections and the performance of large prototypic structural tests become

impractical and nearly impossible in the irradiated condition Therefore,

1 Senior research engineer and senior research scientist, respectively, Hanford Engineering

Development Lab., Westinghouse Hanford Co., Richland, Wash 99352

6 EFFECTS OF RADIATION ON METALS AND ALLOYS

property prediction and structural modeling relationships offer potential in

assessing actual structural behavior However, the evaluation and understanding

of intrinsic material behavior in the irradiated condition are vital to allow an

intelligent application of these relationships The principal objective of this work

is to investigate the strengthening and fracture embrittling effect of neutron

irradiation on ASTM A533 Grade B, Class 1, 12-in.-thick pressure vessel steel

plate and submerged-arc weld

Embrittlement by irradiation was evaluated using the plane strain fracture

toughness, K^^., derived from the development of linear elastic fracture

mechanics by Irwin and others [i,2,5] ^ K^^ is a quantitative test for evaluating

brittle behavior of pressure vessel materials; it permits calculation of critical

fracture load-flaw size relationships The transition temperature, 7T, is the

temperature above which K^^ toughness increases rapidly with increasing

temperature It was measured for A533-B in this work at the 50-ksi/in A^j,,

fracture toughness level Irradiation caused the transition to occur at a higher

temperature; the shift in transition temperature (AIT) is a measure of

irradiation embrittlement

The tensile properties of A533-B were studied in detail to determine the

material sensitivity to the range of test temperatures and irradiation fluences of

interest in reactor pressure vessel steel The strength properties are significant to

the fracture behavior of a material and interpretation of fracture toughness tests

Normally, irradiation will increase the yield strength of a material and the

relationship of irradiation strengthening to fracture embrittlement is valuable in

estimating material behavior

Experimental Procedure

Materials

Plate and submerged-arc weldments of ASTM A533 Grade B Class 1 steel used

in this investigation were obtained from the Heavy Section Steel Technology

(HSST) Program The plate specimens were from the 12-in.-thick HSST plate 02;

the nominal composition of the plate was 0.22C, 1.48Mn, 0.68Ni, 0.52Mo,

0.25Si, 0.018S, and 0.012P, balance iron The plate was normalized at 1675 F

(913 C); plate sections were flame cut and then stress-relieved at 1150 F (621

C)['/] The submerged-arc weld specimens were from Section 51A of HSST

weldment 51 The weld metal composition of the weldment, as determined from

Section 51B by Canonico[5], was 0.12 to 0.16C, 1.23 to 1.38Mn, 0.39 to

0.53MO, 0.72 to 0.76Ni, 0.013 to 0.017P, 0.008 to 0.015S, 0.05 to O.lSSi, 0.15

to 0.33Cu Welds were stress-relieved at 1150 F (621 C) A comprehensive

fabrication history, including manufacture, heat treatment, inspection, and

sectioning has been documented for plate [4] and weldments [6] by Childress

Specimen Irradiation

The Engineering Test Reactor (ETR), a light-water moderated thermal reactor,

at the National Reactor Testing Station (NRTS), was used for specimen

2 The italic numbers in brackets refer to the list of references appended to this paper

WILLIAMS AND HUNTER ON PRESSURE VESSEL STEEL PLATE 7

irradiations A reusable specimen assembly was designed for use in the M-3

pressurized hot-water loop of the ETR[7] Irradiation temperatures were

maintained by controlling the water temperature with heat exghangers and

electric heaters; with water temperature in the loop at 508 F (264 C), gamma

heating produced an irradiation temperature of 510 F (265 C) in the tension

specimens and 540 F (282 C) in the fracture toughness specimens The

specimens were irradiated in contact with the loop water; loop pressure was

1500 psi and water chemistry was controlled at a pH of 10.1 and an Oj content

of < 1.0 ppm

The typical maximum flux was 8 x 10^ ^ n/cm^-s {E > 1 MeV) Flux monitors

of Al-O.lCo and iron wires in the irradiation assembly were analyzed after each

reactor operating cycle to enable calculation of the fluence of the specimens

The last flux {E > 1 MeV) was determined from the iron monitor utilizing the

fission spectrum-averaged cross section for the ^^Fe (n,p) ^^Mn reaction The

^**Co activity was measured from the aluminum-cobalt wire to determine the

thermal flux The counting and analyses were performed by the Radiation

Measurements Section at NRTS

Testing

Tensile properties were evaluated with miniature buttonhead specimens; the

gage length was 1.25 in long by 0.174 in diameter with an intermediate reduced

section of 0.220 in diameter between the gage length and the 0.375-in.-diameter

buttonheads Fracture toughness specimens were one-inch-thick compact tension

(ITCT) type specimens Tensile testing was conducted and analyzed as per

ASTM Tension Testing of Metallic Materials (E 8-70) and procedures of ASTM

Test for Plane Strain Fracture Toughness of Metallic Materials (E 299-70T) were

employed in the testing and data analysis for determining fracture toughness All

fracture specimen tests were subjected to the ASTM criteria of valid plane strain

fracture toughness K^^ measurements; the criteria provide for sufficient

specimen thickness, planar dimensions, and crack sharpness to promote

minimum intrinsic plane strain fracture toughness through elastic constraint The

50kSi/in A"!^ toughness level was utilized in this work in defining the transition

temperature For this A533-B material the 50-ksi/in Kj^ level occurs at a

temperature above which the toughness rapidly increases with temperature

[7,8] Also, based on the K^Ja^^ ratio criteria of the ASTM E 299-70T,

50-ksi\/'in is a practical maximum measurable toughness level with a ITCT

specimen for this A533-B material The irradiated ITCT specimens were fatigue

cracked after irradiation to obtain a sharp crack and simulate a crack generated

in an irradiated material condition rather than a flaw existing prior to

irradiation Tension specimens were tested at a strain rate of 0.008 min"', and

fracture specimens were tested at a stress-intensity rate of 40 000 psi in ''^

min"'

Further details of materials, test specimens, specimen irradiations, flux

measurements, testing, crack preparation, and fracture test analysis are available

elsewhere [7,9,10]

8 EFFECTS OF RADIATION ON METALS AND ALLOYS

Results

Longitudinal Tensile Behavior ofA533 Plate

The longitudinal yield and ultimate tensile properties of the A533 plate in the

unirradiated condition and for 510 F (265 C) irradiations to fluences of

approximately 2, 4, 6, and 8 x 1 0 " n/cm^ were evaluated over the test

temperature range of - 319 F (-195 C) to 550 F (288 C) The results presented in

Fig 1 show that all levels of irradiation elevate the yield strength The

TEMPERATURE, T

FIG l-The yield strength of irradiated and unirradiated ASTM A533 Grade B, Class 1

steel from HSST plate 02 as a function of test temperature Longitudinal (Rj orientation

irradiation sensitivity, or property response produced by irradiation, was greater

for the yield strength than for the ultimate strength Also, the yield strength

irradiation sensitivity exhibited a greater dependence on test temperature Such

irradiation sensitivity and dependence on test temperature are demonstrated in

Table 1

TABLE l-Comparison of percent change in yield and ultimate strength ofA533 plate at

different irradiation fluences and test temperatures

49

40

1019

Percent n/cm^-s Ultimate

30

27

Change

8 x Yield

WILLIAMS AND HUNTER ON PRESSURE VESSEL STEEL PLATE

No saturation of the effects of irradiation on the yield properties of A533

plate was evident at the highest fluence; however, a very great increase in the

level of exposure above those of interest in reactor pressure vessels would be

required for significant additional effects

Transverse Tensile Behavior ofA533 Plate

Transverse tensile properties for irradiated and unirradiated ASTM A533-B

were cursorily examined to determine if there were any significant orientation

effects Figure 2 compares yield strength properties between transverse and

IRRADIATED

1 7 - 2 4 x l 0 l 9 n / c m 2 | E > l M e V ) 51(fF

HSST PLATE 02 LONGITUDINAL ORIENTATION

HS ST PLATE 02 TRANSVERSE OR IENTATI ON

©UNIRRADIATED

A IRRADIATED 2.7-3.1xlOl' n/cm^ (E> 1 MeV), 510°F DIRRADIATED 4.5-4.6x101' n/cm^ (E> 1 MeV), 510°F

100 200 TEMPERATURE, °F

FIG 2—Comparison of transverse and longitudinal yield strength! for irradiated and

unirradiated ASTM A533-B pressure vessel steel HSST plate 02 as a function of test

temperature

longitudinal orientations Unirradiated transverse tension tests were conducted

over a temperature range of -250 F (~ 156 C) to 500 F (260 C) There were no

observable effects on yield or ultimate strength attributable to a difference

between longitudinal and transverse orientations Similarly, transverse tension

specimens irradiated to approximately 2.9 and 4.5 x 1 0 " n/cm^ and tested

from room temperature to 500 F (260 C) exhibited a response to irradiation

comparable to longitudinal specimens

Weld Metal Tensile Behavior ofA533 Submerged-Arc Weldment

The effect of irradiation on the yield and ultimate tensile strength of ASTM

A533-B sub-arc weld is shown in Fig 3; base plate properties are also shown for

comparison The results are from tests conducted at room temperature to 500 F

(260 C) for 510 F (265 C) irradiations to fluences 0.5 x 1 0 ' ' n/cm^ and 4.0 to

4.6 X 1 0 ' ' n/cm^ (E>\ MeV) The specimen axes were parallel to the weld

direction and plate surface The yield strength sensitivity to irradiation was

slightly greater for the weld than for the base plate over the test temperature

range investigated The weld ultimate strength was also more sensitive to

irradiation than was the base plate; however, the irradiated ultimate strength of

the weld did not exceed that of the base plate at the highest fluence investigated

10 EFFECTS OF RADIATION ON METALS AND ALLOYS

FIG 3-Yield strength of irradiated ASTM A533-B submerged-arc weld Plate properties

are shown for comparison

since ultimate strength of the weld metal was considerably lower than that of

the base plate in the unirradiated condition

The ultimate strength of weld metal was less sensitive to irradiation than the

yield strength, which was similar to the relative irradiation sensitivities of the

yield and ultimate strengths for plate material The weld ultimate strength

increased only 45 percent while yield strength increased 75 percent after

irradiation to 4.3 x 1 0 ' ' n/cm^ (£•> 1 MeV) and testing at room temperature

Fracture Toughness, K^^, Behavior ofA533 Plate

The effect of irradiation embrittlement on the fracture toughness is shown in

Fig 4 for Ki^ specimens irradiated at 540 F (282 C) to neutron fluence levels of

2 and 8 X 10' ® n/cm^ (E > 1 MeV) in the ETR; all specimens were of

longitudinal (RW) orientation from the quarter-thickness position of a 12-in

ASTM A533 Grade B, Class 1 steel plate

Irradiation embrittlement at 2 and 8 x 10'^ caused a shift of 185 F (103 C)

and 275 F (153 C) respectively in the 50-ksi/in K^^ fracture toughness

transition level of unirradiated A533-B The trend above the 50-ksi/in

toughness level at both irradiation conditions was for increasing toughness with

increasing temperatures The rate at which toughness will increase or the level

that may be obtained at higher temperatures cannot be accessed by currently

avaitable data of this study

A greater shift in the 50-ksi\/'in K^^ fracture toughness transition level of

230 F (128 C) for a fluence of 2 x 10» ^ n/cm^ (£• > 1 MeV) had been previously

reported [7] The previous 230 F (128 C) shift had been determined by using

WILLIAMS AND HUNTER ON PRESSURE VESSEL STEEL PLATE 11

90

3

O UNIRRADIATED RW ORIENTATION

« UNIRRADIATEDWR ORIENTATION

D IRRADIATED, MO"F, 1.7-a4xlDl'n/cm^ IE>1 MeVl

/^ IRRADIATED, 540°F, 7.7-&4xl0l'n/cm^ (E>1 MeV)

- ASTM A533 B

TEMPERATURE, "f

FIG 4—Irradiated and unirradiated K/^ fracture toughness as a function of temperature

for ASTM A533 Grade B, Class 1 steel from HSST plate 02 Fracture toughness of longitudinal (R W) and transverse (WR) orientations of unirradiated material is compared The closed points of 1.7 to 2.4 x 10^^ n/cm^ are ASTM invalid

the fracture toughness of unirradiated specimens in which the fatigue precrack

had been prepared with too high a stress intensity level; this blunt precrack

resulted in higher K^^ values and consequently a lower estimate of the

50-ksi/in K^^ fracture toughness transition temperature in the unirradiated

condition

Unirradiated K^^^ fracture toughness results of transverse (WR) specimens are

compared in Fig 4 with unirradiated longitudinal specimens The plane strain

fracture toughness, K^^, properties of longitudinal (RW) and transverse (WR)

orientation are observed to be identical within the valid measurement limits of

ITCT specimens

Fracture Toughness, K^^, Behavior of A533 Submerged-Arc Weld Metal

The fracture toughness of ASTM A533-B submerged-arc weldment metal

irradiated at 540 F (282 C) to a fluence of 2.7 to 3.1 x lỐ n/cm=^ {E>1 MeV)

is compared with unirradiated weld metal in Fig 5 The specimens were taken

from the longitudinal orientation of the weld; the plane of the crack was normal

to the plate surface and the propagation direction was parallel to the weld

direction The observed shift of the 50-ksi/in ATj^ fracture toughness transition

level is approximately 390 F (216 C) Even after this shift, the 3 x 10'^

irradiated weld metal has a toughness equivalent to the 2 x 10* ^ irradiated base

plate, since the unirradiated SO-ksi/in K^^ fracture toughness transition of weld

metal was at such a low temperaturẹ As discussed in the preceding section, more

conservative fatigue crack preparation at lower stress intensity levels might have

yielded lower values of Âj^ in the lower-temperature tests of unirradiated

material This would have placed the 50-ksi/in K^^ fracture toughness

transition level at a somewhat higher temperature, yielding a smaller estimate of

12 EFFECTS OF RADIATION ON METALS AND ALLOYS

the irradiation embrittlement sensitivity of A533-B submerged-arc weld metal

Using the data of Shabbits et al [8], in which the unirradiated 50-ksi/in K^^

fracture toughness transition level occurs at -175 F (-115 C), the irradiation

shift is only 315 F (157 C)

Functional Expression for Irradiation Strengthening

A significant effect of irradiation on strength was observed for all fluence

levels and test conditions of A533 plate and submerged-arc weld; low fluences of

2 X 10'^ n/cm^ produced a pronounced change in yield strength, ACT^^,

followed by a linearly fluence-dependent AOy^ above 2 x i C n/cm^ (E> 1

MeV) At a fluence of 2 x 10'® n/cm^, irradiation primarily affected the

athermal component of yield stress, whereas at higher fluences the

fluence-dependent of AOy^ was greater at lower test temperatures The increase

in the athermal component of the yield strength of A533 plate at fluences below

the lowest experimental result at 2 x lO'* n/cm^ is probably best described by:

A a y , = ^ ( l - e x p - * / ^ ) (1) where ^ = 22 ksi,

B=5x 10»»n/cm2,

$ = fluence, n/cm^

and

Equation 1 is similar to that used by Makin et al [II] The slope of the linear

dependence of Aa upon fluence decreases as the test temperature is increased;

this slope is given by:

in which T is temperature in deg F Thus, the yield stress increase (ksi) of this

HSST A533-B plate as a function of fluence and temperature may be described

by:

AOy^ = 22 [1 - exp (-<I>/5 x 10'«)] + * / 1 0 ' ' (4.3 - 0.00387) (3)

WILLIAMS AND HUNTER ON PRESSURE VESSEL STEEL PLATE 13

A fit of this equation is compared in Fig 6 with the actual data of Fig 1

Equation 3 was derived from tensile test data at strain rates of approximately

10'^ s'' Increasing the strain rate normally affects the thermal component and

therefore increases the low-temperature yield strength but does not effect the

high-temperature strength It is expected that irradiation would effect the yield

strength strain-rate sensitivity at low temperatures but not at high temperatures

The Correlation of Irradiation Strengthening with

the Shift in Fracture Toughness Transition

The fluence-dependence of yield strength described in the foregoing and

shown in Fig 6 is similiar to that observed for the Charpy V-notch

IRRADIATION FLUENCE, n/cm^X 10^'(E>lMeV)

FIG 6~The effect of irradiation fluence on the yield strength of A533-B is shown for

different test temperatures The curves are the fit of the Aa by Eq 3

irradiation-induced embrittlement of the 6 in ASTM A302-B reference plate

[12,13] Thus, consistent with the concept that irradiation hardening elevation

of yield strength forces cleavage fracture under elastic loading to a higher

temperature [14,15\, a correlation between increases in yield stress (Aay^) and a

shift in the K^^ transition temperature (ATT) should exist Two uncertainties in

correlating development must be recognized:

1 A definition of the measure for K^^ transitional behavior is needed, since

data fully describing irradiated K^^ to higher toughness in the transition are not

available

2 A direct correlation of shift in ^ j ^ from a change in yield strength requires

14 EFFECTS OF RADIATION ON METALS AND ALLOYS

a knowledge of the strain rate sensitivity and the stress-strain behavior in the

plastic zone of the fracture specimen

The fracture toughness transition for A533-B investigated in this study has

been defined to occur at the 50-ksi/in plane strain fracture toughness level

because K^^ fracture toughness of A533 increases rapidly above the 50-ksi/in

level [7], and the SO-ksi/in level is the maximum valid Kj^, measurement that

can be measured in the unirradiated A533-B with a ITCT fracture specimen The

confidence in assessing the fracture mechanics transition behavior with a small

(ITCT) specimen is not unfounded, although many initially believed that K^^

data would not exhibit the strong toughness transition of the C^ impact energy

data, since the C^ toughness increase was attributed to insufficient specimen size

and constraint rather than to a consequence of the intrinsic material property

changes However, as a result of specimen testing up to 12 in in thickness by

Wessel [8], Loss [16], and Shabbits [17], it is now accepted that/T,^ data are

very responsive to the toughness transition and that even large sections

dynamically loaded will still exhibit the toughness transition Further, it is now

common to assume that the irradiation-produced shift in the K^^ data should be

very similar to the shift in the C^ data [18,19] It is important, however, to note

that the similarity in ^'j,, and C^, transitions in pressure vessel steels is limited to

the onset of transition or start of rapid increase in toughness The higher energies

of Cy transition finally develop as a result of loss of constraint and the upper

shelf is coincident with the attainment of 100 percent plastic dimpling [14]

The valid ^ j ^ transition in this material is obtained maintaining specimen

constraint, and the mode of failure throughout is by cleavage fracture As such,

the ITCT fracture specimen measures just the start of K^^ transition at the

50-ksi/in toughness level

The second uncertainty is too complex for rigorous resolution by present

analytical and experimental methods However, Cottrell [20] has considered the

germane factors and, based on the concept that brittle fracture occurs when the

yield stress is greater than the cleavage microcrack growth stress, has predicted

the following dependency of a shift in the ductile-brittle transition temperature

(ATT) upon AOy^:

ATT 5degF (4)

Aa ksi

The irradiation effect on the 50-ksi/in K^^ fracture toughness transition level

of A533 plate was a shift of 185 F (103 C) at a fluence of 2 x 10'» n/cm^ {E >

1 MeV); increasing the fluence fourfold shifted the transition only an additional

90 F (50 C) or a total of 275 F At a test temperature of 0 F, fluence levels of 2

and 8 X 10^^ n/cm^ (E>1 MeW),Aay^ is 30.6 and 56.4 ksi, respectively Upon

substitution into Eq 4, ATT values of 153 and 282 F are calculated, which

correspond well with the experimentally measured shifts in the K^^ Thus, the

correlation is consistent with the concept that irradiation embrittlement in these

materials is a consequence of irradiation hardening by the mechanism of elevated

WILLIAMS AND HUNTER ON PRESSURE VESSEL STEEL PLATE 15 yield strength forcing cleavage fracture under elastic loading to higher

temperatures The correlation facilitates the use of tension specimens currently

included in reactor pressure vessel surveillance capsules to help estimate

irradiation embrittlement and establish test temperature ranges of fracture and

Cy specimens

Conclusions

Irradiation produced a pronounced increase in yield strength to fluences of

approximately 2 x 1 0 " n/cm^ (£• > 1 MeV), above which the yield strength

Unearily increased with fluence at a more gradual rate Irradiation fracture

embrittlement resulted in a shift of the K^^ toughness transition curve to higher

temperatures The fluence dependence of the irradiation embrittlement shift

correlated with the fluence dependence of the yield strength; this correlation is

consistent with the principles that

1 Brittle behavior only occurs in these materials when the temperature is so

low that the yield strength at the crack root in a flawed specimen is high enough

that the cleavage fracture stress is exceeded

2 The irradiation shift or extension of brittle behavior to higher temperatures

is a consequence of a compensation for the irradiation-increased yield strength

by a decrease in the thermal component of yield strength

In both unirradiated and irradiated conditions, as the temperature is increased

the decreasing yield strength necessitates that increasing amounts of precleavage

plastic strain are required to attain the cleavage stress at the crack root in a A'j^,

test; thus the K^^ toughness increases very rapidly with temperatures above the

transition temperature

References

[I ] Irwin, G.R in Structural Mechanics, Pergamon, New York, 1960, pp 557-594

[2] Irwin, G.R., Krafft, J.M., Paris, P.C, and Wells, A.A., "Basic Aspects of Crack

Growth and Fracture," NRL Report 6598, Naval Research Laboratory, 21 Nov

1967

[3] Brown, W.F., Jr., and Srawley, J.E in Plane-Strain Crack Toughness Testing of High

Strength Metallic Materials, ASTM STP 410, American Society for Testing and

Materials, 1966

[4] Childress, C.E., "Fabrication History of the First Two 12-Inch Thick ASTM A533

Grade B, Class 1 Steel Plates of the Heavy Section Steel Technology Program,

Documentary Report 1," ORNL-4313, Oak Ridge National Laboratory, Feb 1969

[5] Canonico, D.A., "Characterization of Heavy-Section Steel Weldments," Heavy

Section Steel Technology Program Semi-Annual Progress Report, 28 Feb 1969, pp.,

29-35, O R N L 4 4 6 3 , Oak Ridge National Laboratory, Jan 1970

[6\ Childress, C.E., "Fabrication Procedures and Acceptance Data for ASTM A533

Welds and a 10-inch-Thick ASTM A543 Plate of the Heavy Section Steel

Technology Program, Documentary Report 3 , " ORNL-4313-3, Oak Ridge National

Laboratory, Jan 1971

[7] Hunter, C.W and Williams, J.A., Nuclear Engineering and Design, Vol 17, No 1,

Aug 1971, pp 131-148

[8] Shabbits, W.O., Pryle, W.H., and Wessel, E.T., "Heavy Section Fracture Toughness

of A533 Grade B Class 1 Steel Plate and Submerged Arc Weldment," WCAP-7414,

Westinghouse Nuclear Energy Systems, Dec 1969

16 EFFECTS OF RADIATION ON METALS AND ALLOYS

[9] Williams, J.A., Hellerich, C.L., and Hunter, C.W., "Irradiation Damage to

Heavy-Section Vessel Steels," Heavy Section Steel Technology Program

Semi-Annual Progress Report, 28 Feb 1969, pp 104-116, ORNL-4463, Oak Ridge

National Laboratory, Jan 1970

[10] Hunter, C.W., Hellerich, C.L., and Williams, J.A., "Irradiation Effects on the

Fracture of Heavy-Section Pressure Vessel Steels," Heavy Section Steel Technology

Program Semi-Annual Progress Report, 31 Aug 1969, pp 77-90, ORNL-4512, Oak

Ridge National Laboratory, March 1970

[11] Makin, M.J., Whapham, A.D., and Minter, F.J., Philosophical Magazine, Vol 7,

1962, p 285

[12] Sterne, R.H., Jr and Steele, L.E., Nuclear Engineering and Design, Vol 10, 1969,

pp 259-307

[13] Hawthorne, J.R., "Trends in Charpy-V Shelf Energy Degradation and Yield

Strength Increase of Neutron-Embrittled Pressure Vessel Steels," NRL Report

7011, Naval Research Laboratory, 22 Dec 1969

[14] Hunter, C.W and Williams, J.A., "Fracture Toughness and Fractography of

Irradiated Pressure Vessel Steels," U.S.-Japan Seminar on Irradiation Effects in

Metals and Structural Materials, Kyoto, Japan, 28-30 Sept, 1971

[15] Hunter, C.W and Williams, J.A., Transactions, American Nuclear Society, Vol 14,

No 2, Oct 1971, pp 585-586

[16] Loss, F.J., "Dynamic Tear Test Investigations of the Fracture Toughness of Thick

Section Steel," NRL Report 7056, Naval Research Laboratory, 14 May 1970

[17] Shabbits, W.O., "Dynamic Fracture Toughness Properties of Heavy-Section A533

Grade B Class 1 Steel Plate," Westinghouse Nuclear Energy Systems, WCAP-7623,

Dec 1970

[18] Corten, H.T and Sailors, R.H in Fracture Toughness, ASTM STP 514, American

Society for Testing and Materials, 1971, pp 164-191

[19] Mager, T.R., "Postirradiation Testing of 2T Compact Tension Specimens,"

Westinghouse Nuclear Energy Systems, WCAP-7561, Aug 1970

[20] Cottrell, A.H., Transactions, Metallurgical Society, American Institute of Mining,

Metallurgical, and Petroleum Engineers, Vol 212, April 1968, pp 192-203

/ R Hawthorne^ andH E Watson^

Radiation-Induced Changes in the

Fracture Extension Resistance

(R-Curve)of Structural Steels

REFERENCE: Hawthorne, J R and Watson, H £., "Radiation-Induced Changes in

the Fracture Extension Resistance (R-Curve) of Structural Steels," Effects of

Radiation on Substructure and Mechanical Properties of Metals and Alloys, ASTM

STP529, American Society for Testing and Materials, 1973, pp 17-28

ABSTRACT: The effects of irradiation on the fracture extension resistance of

low-and medium-strength steel plates were explored using R-curve assessment procedures

newly developed at the Naval Research Laboratory The study employed four thick

plates of A212-B, A302-B, A533-B, and A543-1 steel The plates were specifically

selected to depict a broad range of pre-irradiation dynamic tear (DT) upper-shelf

toughness Irradiations were conducted at low temperatures, < 450 F (232 C), and

at an elevated temperature, ~ 550 F (288 C)

A subsize R-specimen (0.4 in thick), patterned after the 5/8-in dynamic tear

specimen, was employed for pre- and postirradiation R-curve determinations

R-curves were constructed by plotting specimen energy absorption per unit fracture

surface area against relative crack extension distance

Radiation exposure was revealed to have a highly detrimental effect on R-curve

performance The effect was observed for all test plates regardless of their

pre-irradiation shelf toughness level The effect encompassed R-curve performance at

temperatures corresponding to the dynamic tear upper shelf and at temperatures

within the dynamic tear transition regime The primary detrimental change for the

upper-shelf condition was a reduction in R-curve level A tendency for irradiation to

reduce R-curve slope was also evident The analysis suggests that, with sufficiently

high fluence, neutron irradiation can cause a transition from rising R-curve to flat

R-curve behavior at upper-shelf temperatures

KEY WORDS: radiation effeiJts, embrittlement, pressure vessel steels, fracture

strength, neutron irradiation, nuclear reactors

Two general effects of neutron radiation on structural steels are a yield

strength elevation and a notch toughness degradation [1,2] ?• Jointly, these

effects signify reduced resistance to fracture (crack) extension This study

explores changes in fracture extension resistance produced by neutron radiation

for four steel compositions: A212-B, A302-B, A533-B, and A543-1 The

compositions (plate) depict a nominal yield strength range of 40 to 95 ksi; each

composition has been employed or is proposed for nuclear reactor pressure

vessels

The study applies experimental procedures evolved at NRL for characterizing

the fracture extension resistance of structural metals [J-7] The specimen for

fracture resistance determinations is patterned after the dynamic tear specimen

Research metallurgist and mechanical engineer, respectively Reactor Materials Branch,

Naval Research Laboratory, Washington, D.C

[8] but features a range of crack-run distances Specimen energy absorption for

fracture is determined using conventional impact test equipment Subsequently,

resistance (R) curves of the form E/A (fracture energy absorption per unit

fracture area) versus Aa/B (relative crack extension distance for thickness 5 ) are

constructed Individual R-curve performance is judged on the basis of both

R-curve slope and level R-curve slope represents the rate at which fracture

resistance increases against an advancing crack while R-curve level represents the

resistance of the metal at a given point (increment) of crack extension

Typically, at dynamic tear (DT) upper-shelf temperatures ductile metals exhibit

rising R-curve features while brittle metals exhibit flat R-curve features The

latter is illustrative of plane strain fracture behavior It should be noted that

R-curve assessment procedures apply equally well to the DT upper-shelf regime

and to the DT energy-transition regime In this study, the effect of radiation on

R-curve performance in both regimes was investigated

Materials and Irradiation

Chemical compositions and heat treatments of the four plates acquired for the

study are given in Table 1 The plates were specially selected to depict a broad

range of DT upper-shelf toughness The A212-B and A302-B plates were from

old production melts The A533-B and A543-1 plates were from recent

production melts and, accordingly, represent new advances in melting and

processing technology Pre-irradiation strength and notch ductility are indicated

in Table 2 Except for the A302-B plate, irradiation assessments involved the

transverse (WR) orientation only

Low temperature, < 450 F (232 C) and elevated temperature, 550 F (288 C)

irradiations were conducted All exposures were performed in the Union Carbide

research reactor (UCRR), F-5 fuel core facility Fluences were determined from

iron dosimeter wires in the assemblies For the low temperature irradiations

(capsules), peak exposure temperatures only were determined using

low-melting-point alloys in the specimen array

Subsize R-specimen Design

The standard specimen for R-determinations (thickness B • 1.0 in.) [8] is far

/ -L = 7.0"

7 "

B = 0.4

NOTCH TIP SHARPENED WITH PRESSED

Aa

0.4 0.8 1.2 (1.8)

w

0.80 1.20 1.60 (1.63)

FIG i-The subsize fracture resistance fR) specimen developed for irradiation studies

HAWTHORNE AND WATSON ON STRUCTURAL STEELS W

3 o , ^ u ' = ' ; = " '3 ft^ g 0 1- M "^ §

t- ;c +1 o 2 "3 ;2 -g 73

^ 1! "^ -o >

.H 1 -o :S 2

•i 1 s £ i

J2 3 Zj* V5 *3 i« « S 9> «

20 EFFECTS OF RADIATION ON METALS AND ALLOYS

HAWTHORNE AND WATSON ON STRUCTURAL STEELS 21

too large overall for most reactor irradiation facilities; therefore, the subsize

R-specimen shown in Fig 1 was developed Individual specimen configurations

feature a crack run-to-thickness ratio Afl/5 of 1,2, or 3 The specimen notch is

one thickness, B, deep and is pressed-notch sharpened in the manner of the

5/8-in DT specimen [9] Test equipment normally employed for DT specimen

assessments was adapted in this case for pre- and postirradiation R specimen

/ / / /

/ / / /

/ / /

/ ,70F NDT+70

' ( 2 t C)

y ^ t _ l-IN, DT SPECIMEN y^ P (REFERENCE)

CRACK RUN RATIO (4?) CRACK RUN RATIO (-^)

FIG 1-General correlation observed between the l.O-in.-thick reference R-specimen (solid

curve) and the 0.4-in.-thick subsize R-specimen (dashed curve) at dynamic tear (DT) upper

shelf (100 percent DTE) temperatures The temperature dependence of R-curve behavior

observed with the reference R-specimen is also illustrated (Test temperatures for individual

curves are listed.)

The correspondence of R-curves developed with the 1.0-in standard R

specimen and with the 0.4-in subsize R specimen for the DT upper-shelf

condition is shown in Fig 2 The R-curve slope denoted by the subsize specimen

is about 40 percent of the R-curve slope described by the reference specimen

The energy absorption values for the respective Type 3 configurations

(AalB = 3) appear in the ratio of approximately 1:1.85 Data from standard

specimens for temperatures within the DT transition region are also shown in

Fig 2 and illustrate the decrease in R-curve slope and level with decreasing

temperature in this region Flat R-curve performance generally develops at about

the DT mid-energy transition (50 percent DTE) temperature in agreement with

the fracture transition elastic (FTE) temperature for the steels in moderate

thickness

Correlations were also observed between the subsize specimen and the 5/8-in

DT specimen As noted in Fig 3, the Type 3 configuration describes an energy

FIG 3-An example of the typical correspondence observed between the 0.4-in.-thick

subsize R-specimen (Type 3, Aa/B = 3), and the 5/8-in.-thick DT specimen

transition in the same temperature interval as the DT specimen The ratio of

shelf energy absorption values [£'(DT)/£'(R-Type 3)] typically exceeded the

ratio of the respective fracture surface areas Similar points of correspondence

were observed between the Type 1 R-specimen configuration (Aa/B = 1) and the

Charpy-V specimen

Experimental Results

Seven irradiation assessments were conducted Table 2 lists the plate, the plate

orientation and the irradiation conditions involved in each assessment Overall,

very consistent trends in pre- versus postirradiation R-curve performance were

noted

An illustration of typical pre-postirradiation observations is given in Fig 4

The data pertain to the A212-B plate (WR orientation) The left-hand graph

HAWTHORNE AND WATSON ON STRUCTURAL STEELS 23

o

60

•a

.=2 0

cu 55

24 EFFECTS OF RADIATION ON METALS AND ALLOYS

refers to the pre-irradiation condition; the right-hand graph shows findings for

the postirradiation condition, < 4 5 0 F (232 C); ~ 2.5 x 10'® neutrons

(n)/cm^ > 1 MeV A very pronounced detrimental effect of irradiation on

R-curve performance is immediately obvious from the two graphs The primary

change is a reduction in R-curve level A tendency for irradiation to reduce

R-curve slope is also observed but is smaller by comparison Significantly,

reduced R-curve performance after irradiation was observed not only for DT

upper shelf temperatures but for all temperatures within the DT transition

regime

Figure 5 presents a summary of R-curves developed for the various pre- and

postirradiation DT upper shelf conditions The detrimental effects of

irradiation on R-curve performance described with Fig 4 are most evident in this

summary The figure illustrates well the primary effect of irradiation on R-curve

level as opposed to R-curve slope for these steels (thin-section case) The R-curve

slope reduction is most apparent with the A302-B plate (WR orientation)

irradiated at < 450 F (232 C) For all upper-shelf assessments, R-curve level was

generally proportional to the related DT upper-shelf energy level

Discussion

The preferential effect of irradiation on R-curve level over R-curve slope for

the steels and conditions examined is in general accord with upper-shelf

condition behavior predicted by the ratio analysis diagram (RAD) In Fig 6, the

relative RAD positions of the individual plates before and after irradiation are

shown based on 5/8-in DT and yield strength determinations The data points

in all cases fall above the Ki^^/a^^ ratio line,^ 0.4 Since this ratio line represents

the critical edge for plane strain fracture for a specimen thickness of 0.4 in., flat

R-curve performance should not be expected for the subsize R specimen for any

of the upper-shelf conditions described

The fracture mechanics relationship ^i Jay5 ^ ( 5 / 2 5 ) * ' ^ [10] denotes that

the K^JOy^ ratio describing the critical edge for plane strain fracture increases

with increasing section thickness (B) because of increased plane strain constraint

For components of 5 in thickness, the K^Ja^^ ratio for the onset of plane

strain fracture is approximately 1.4, according to the formula In Fig 6, it is

noted that one point representing the postirradiation condition falls between the

1.4 and 0.4 ratio lines In this case, flat R-curve performance could be expected

for a 5 in thick component but not for a 0.4-in.-thick component The point is

thus made that thickness has a significant influence on the transition from rising

R-curve to flat R-curve characteristics at upper-shelf temperatures This

important fact must not be overlooked in predicting material postirradiation

R-curve behavior Aside from component thickness interactions, the

predomi-nant effect of irradiation on fracture extension resistance nonetheless is clearly a

reduction in R-curve level for the materials investigated

Plane strain fracture toughness to yield strength ratio line

HAWTHORNE AND WATSON ON STRUCTURAL STEELS 25

26 EFFECTS OF RADIATION ON METALS AND ALLOYS

m

g i l l

( q i - t j ) A9aaN3 J " I 3 H S l a N I - S / S

HAWTHORNE AND WATSON ON STRUCTURAL STEELS 27 Conclusions

The nature of radiation-induced changes in the fracture extension resistance

(R-curve behavior) of reactor pressure vessel steels has been successfully explored

A subsize R-specimen {B = 0.4 in.), patterned after the 5/8-in DT specimen, was

specially designed for the study R-curve performance was established by

plotting fracture energy absorption per unit fracture area (E/A) against relative

crack extension distance {AajB) Consistent trends in pre- and postirradiation

R-curve performance were observed

Primary conclusions drawn from the study were as follows:

1 Radiation exposure has an appreciable detrimental effect on the R-curve performance of A212-B, A302-B, A533-B, and A543-1 steel plates, regardless of

the level of pre-irradiation upper-shelf toughness A detrimental effect is observed with determinations at DT upper shelf temperatures and with determinations at temperatures within the DT transition regime

2 The primary irradiation effect on R-curve behavior is a reduction in R-curve level The effect translates to reduced metal resistance to a given increment of crack extension A tendency for irradiation to reduce R-curve slope

was also observed

3 Both R-curve level and slope are quite sensitive to temperature, dropping rapidly at temperatures progressively below the DT upper shelf temperature

4 The R-curve level varies proportionally with the DT upper-shelf level for

both the pre- and postirradiation conditions

5 The analysis suggests that irradiation can produce a transition from rising R-curve to flat R-curve behavior (upper-shelf condition) with sufficiently high exposure The transition should not develop abruptly with increasing fluence The ratio analysis diagram for the DT upper-shelf condition denotes a dependency on thickness of the transition from rising R to flat R-curve behavior

that should be taken into account in analyzing postirradiation R-curve performance

Acknowledgments

This study was sponsored jointly by the Office of Naval Research and the U.S

Atomic Energy Commission, Division of Reactor Development and

Technol-ogy (Fuels and Materials Branch) The continuing support of these sponsors is greatly appreciated We thank The Babcock & Wilcox Company and the Lukens Steel Company for their respective donations of the A302-B and A533-B plates

used in this study

We express our appreciation to the individual members of the Reactor Materials Branch who contributed to the reactor experiment operations and postirradiation test operations Particular thanks are expressed to W E Hagel, B

H Menke, and F F Newman for their major contributions to these operations

References

{l] Hawthorne, J.R., "Trends in Charpy-V Shelf Energy Degradation and Yield

Strength Increase of Neutron Embrittled Pressure Vessel Steels," NRL Report

7011, Naval Research Laboratory, 22 Dec 1969; also Nuclear Engineering and

Design, Vol 11, No 3, AprU 1970, pp 427-446

28 EFFECTS OF RADIATION ON METALS AND ALLOYS

[2] Hawthorne, J.R., "Postirradiation Dynamic Tear and Charpy-V Performance of

12-in Thick A533-B Steel Plates and Weld Metals," Nuclear Engineering and

Design, Vol 17, No 1,1971, pp 116-130

[3] Pellini, W.S and Judy, R.W., Jr., "Significance of Fracture Extension Resistance

(R-Curve)- Factors in Fracture-Safe Design for Nonfrangible Metals," Welding

Research Council Bulletin 157, Dec 1970

[4] Goode, R.J and Judy, R.W., Jr., "Fracture Extension Resistance (R-Curve)

Features of Nonfrangible Aluminum Alloys," NRL Report 7262, Naval Research

Laboratory, June 1971; aho ASM Metals Engineering Quarterly, American Society

for Metals, VoL 11, No 4, Nov 1971, pp 39-49

[5] Judy, R.W., Jr and Goode, R.J., "Fracture Extension Resistance (R-Curve)

Concepts for Fracture-Safe Design with Nonfrangible Titanium Alloys," NRL

Report 7313, Naval Research Laboratory, Aug 1971

[6] Pellini, W.S., "Integration of Analytical Procedures for Fracture-Safe Design of

Metal Structures," NRL Report 7251, Naval Research Laboratory, March 1971

[7] Judy, R.W., Jr and Goode, R.J., "Fracture Extension Resistance (R-Curve)

Characteristics for Three High-Strength Steels," NRL Report 7361, Naval Research

Laboratory, Dec 30, 1971

[8] Puzak, P.P and Lange, E.A., "Standard Method for the 1-Inch Dynamic Tear Test,"

NRL Report 6851, Naval Research Laboratory, 13 Feb 1969

[9] Lange, E.A., Puzak, P.P., and Cooley, L.A., "Standard Method for the 5/8-Inch

Dynamic Tear Test," NRL Report 7159, Naval Research Laboratory, 27 Aug

1970

[10] "Tentative Method of Test for Plane-Strain Fracture Toughness of Metallic

Materials," ASTM E 399-70T, 1970 Book of ASTM Standards, Part 31, American

Society for Testing and Materials

Reactor Vessel Steels—

Structure and Impurity Effects

A E Powers^

Effect of Composition on the

Sensitivity of Structural Steel

to Irradiation Embrittlement

REFERENCE: Powers A.E., "Effect of Composition on the Sensitivity of Structural

Steel to Irradiation Embrittlement," Effects of Radiation on Substructure and

Mechanical Properties of Metals and Alloys, ASTM STP 529, American Society for

Testing and Materials, 1973, pp 3145

ABSTRACT: About 75 low alloy steels that have been irradiation tested at 450 to

550 F (232 to 288 C) have been chemically analyzed for copper, aluminum, total

nitrogen, and combined nitrogen Uncombined nitrogen content has been found to

have a strong modifying action on the effectiveness of copper in controUing

sensitivity to irradiation embrittlement at 450 to 550 F (232 to 288 C)

KEY WORDS: neutron irradiation, radiation effects, irradiation, embrittlement,

structural steels, pressure vessels, copper, aluminum, nitrogen

Data by Carpenter et al [7]^ established that neutron irradiation

embrittle-ment of commercial, low-alloy, pressure-vessel steel can vary considerably from

steel to steel and from heat to heat Irradiation embrittlement is commonly

measured by the increase in the fracture transition temperature produced by a

given neutroii fluence The fracture transition temperature is defined here as the

temperature for 30 ft-lb energy absorbtion by Charpy V-notch impact

specimens Some steels, when irradiated to a fluence of 1 x 1 0 " neutrons

(n)/cm^ ( > 1 MeV) at an irradiation temperature of ~500 F (260 C), will

exhibit increases in fracture transition temperature (ATT) of 200 to 250 F (111

to 139 C) These steels are termed radiation sensitive for the purposes of this

discussion On the other hand, at the same fluence some steels having insensitive

behavior will exhibit a ATT of as little as 50 to 100 F (28 to 56 C) Irradiation

sensitivities are seen, of course, between the two extremes

It should be emphasized that the irradiation response under consideration is

that which occurs at irradiation temperatures from 450 to 550 F (232 to 288 C)

Steels that are irradiated at temperatures under 300 F (149 C) invariably show a

sensitive response [2-6] One exception is seen, however, in high-purity carbon

and nitrogen-free iron and iron alloys that show insensitive behavior at low

irradiation temperatures [5,7,8] Both the Bettis Atomic Power Laboratory [9]

and the Naval Research Laboratory [4,14] have shown that steels that are

insensitive when irradiated at temperatures between 450 and 575 F (232 and

302 C) will show a sensitive behavior when irradiated at 200 F (93 C) In other

1 Metallurgist, Knolls Atomic Power Lab., General Electric Co., Schenectady, N.Y 12301

words, irradiation-sensitive steels will show the same ATT at an irradiation

temperature of 500 F (260 C) as at 200 F (93 C) whereas insensitive steels show

a temperature dependence of response between these two temperatures as shown

in Fig 1 It would appear that the variation among commercial steels in

sensitivity at elevated temperatures may be caused by differences in annealing

tendencies during irradiation [10] Wide variations in irradiation response have

been found among various heats of the same type of steel [1 ] This variability

cannot be explained solely by differences in microstructure or in the content of

the commonly-analyzed alloying elements

One factor in commercial steel that can vary from heat to heat and steel to

steel is the degree of deoxidation by aluminum and other strong deoxidants A

feasible way to measure the degree and character of deoxidation is to measure

the proportion of combined and uncombined nitrogen It is the uncombined

nitrogen that is free to interact with irradiation-produced vacancy clusters and

subsequently alter the thermal stability of these clusters A preliminary

investigation into the effect of deoxidation practice on irradiation sensitivity was

published by the author in 1968 [11] It was found that complete deoxidation

to remove all nitrogen from solution promoted irradiation-sensitive behavior It

would appear that nitrogen, which is readily diffusable in iron at 500 F (260 C),

facilitates the thermal instability of vacancy clusters

Subsequently, the Naval Research Laboratory (NRL) presented evidence that

copper is an important element in controlling irradiation sensitivity in structural

steel [4,12-17] In one report NRL analyzed the steels for the distribution of

nitrogen [15] In this case, all of the steels were insufficiently deoxidized with

aluminum such that they contained greater than 10 ppm uncombined nitrogen

All of these steels exhibited increases in fracture transition temperature of less

POWERS ON SENSITIVITY OF STRUCTURAL STEEL 33 than 100 F (56 C) when irradiated to fluences of 2.3 and 3.0 x 10'^ n/cm^ (>1

MeV) in spite of 0.20 percent copper in some of them

Procedure

The Knolls Atomic Power Laboratory (KAPL) has been analyzing samples of a

number of steels obtained from KAPL, Bettis, and NRL for which irradiation

data are available Analyses have been made for copper, aluminum, total

nitrogen, and combined nitrogen The combined nitrogen was separated by the

ester-halogen technique developed by Beeghly [18] The steel is dissolved in

bromine-containing methyl acetate and the insoluble residue, consisting largely

of aluminum nitride, is analyzed for nitrogen content If the aluminum content

is low, a sihcon nitride will likely precipitate [79] The difference between the

total nitrogen and the ester-halogen nitrogen is considered to be the uncombined

nitrogen

Results

The results of the chemical analyses for copper, aluminum, total nitrogen, and

combined nitrogen are given in Table 1 along with an indication of the

irradiation sensitivities of the steels at elevated irradiation temperatures (450 to

550 F) (232 to 288 C) The ATT values are normalized to a fluence of 1 x 10'^

n/cm^( > 1 MeV) using the assumption that ATT is proportional to ($t) '^^ that

IS, the ATT data are plotted against the square root of the fluence, and

straight-line extrapolation or interpolations are used to normalize ATT to 1 x

1 0 ' ' n/cm^ Uncertainties arise in the comparative ATT values because various

irradiation temperatures from 450 to 550 F (232 to 288 C) have been used This

means that a ATT value from a 550 F (288 C) irradiation would probably have

been higher if an irradiation temperature of 450 F (232 C) had been used These

uncertainties are augmented by the uncertainties of fluence and transition

temperature determinations The result is that while a sensitive steel having a

ATT of 220 F (122 C) can be distinguished from an insensitive steel having a

ATT of 60 F (33 C), one should be cautious of rating the relative sensitivities of

steels whose ATT values differ by only 30 F (17 C)

Table 1 is in three parts Part A lists KAPL, Bettis, and NRL steels that have

been irradiated by the respective laboratories and chemically analyzed by the

General Electric Company under KAPL sponsorship Part B lists ASTM A-508

Class 2 steels that were irradiated by Bettis and also chemically analyzed by the

General Electric Company under KAPL sponsorship Part C lists

laboratory-melted steels that were irradiated and chemically analyzed by NRL

By a detailed examination of Table 1 it becomes apparent that copper has an

important effect in promoting irradiation sensitivity in structural steels The

steels in Parts A and B are listed in the order of decreasing copper content It can

be seen, however, that the irradiation sensitivities are not necessarily in the order

of decreasing copper content Part of this lack of order in decreasing ATT may

be due to the varying irradiation temperatures between 450 and 550 F (232 and

288 C) Nevertheless, there are numerous examples of relatively insensitive