4340 fracture toughness.pdf

$: 4340 fracture toughness.pdf$
AMMRC MS 79-1

FRACTURE TOUGHNESS AND STRESS

CORROSION CHARACTERISTICS OF

ULTRAHIGH-STRENGTH 4340 STEEL -

SUMMARY REVIEW

February 1979

Approved for public release; distribution unlimited.

ARMY MATERIALS AND MECHANICS RESEARCH CENTER Watertown, Massachusetts 02172

OFFICIAL FILE COpy

AMMRC MS 79-1

FRACTURE TOUGHNESS AND STRESS

CORROSION CHARACTERISTICS OF

ULTRAHIGH-STRENGTH 434D-STEEL -

SUMMARY. REVIEW

February 1979

Approved for public release; distribution unlimited .

,

, ~. ,

ARMY MATERIALS AND MECHANICS RESEARCH CENTER Watertown. Massachusetts 02172

OfHCIAL fiLE COpy

The findings in this report are not to be construed as an official

Department of the Army position, unless so designated by other

authorized documents

Mention of any trade names or manufacturers in this repert

shall not be construed as advertising nor as an official

indorsement or approval of such products or companies by

the United States Government.

DISPOSITION INSTRUCTIONS

Destroy thts report when :t IS no longer needed

Do r;ot return IT to the ortgrnator.

The findings in this report are not to be construed as an official Department of the Army position, unless 50 designated by other authorized documents

Mention of any trade names or manufacturers in this report shall not be construed as advertising nor as an official indorsement or approval of such products or cornpanies by the United States Government.

DISPOSITION INSTRUCTIONS

Destroy this report when :t is no longer needed,

Do r',ot return ,t to the originator

UNCLASSIFIED $LCURllV CLASSltlCATlON OC THIS PAGE (W’hon Data Entorrd)

REPORTDOCUMENTATIONPAGE READ INSTRUCTIONS BEFORE COMPLETING FORM

. REPORT NUMBER 2. GOVT ACCESSION NO. 5. RECIPIENT’S CATALOG NUMBER

AMMRC I% 79-l I I . TITLE (md Subtitle)

FRACTURE TOUGHNESS AND STRESS CORROSION CWAPACTERISTICS OF I:LTRA~ITCH--STRENCTE 4,140 STEEL - SUMMARY REVIEW

5. TYPE OF REPORT & PERIOD COVERED

Final Report 6. PERFORMING ORG. REPORT NUMBER

‘. AU THOR(u)

Anthony K. Wong, Milton Levy, and Walter F. Czyrklis

6. CONTRACT OR GRANT NUMBER(s)

I. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK AREA & WORK UNIT NUMBERS

Army Materials and Mechanics Research Center D/A Project: lX464621D073 Watertown, Massachusetts 02172 DRXMR- Eb'

mCMS Code: 6446210730012

I. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

U. S. Army Materiel Development and Readiness February 1979

Command, Alexandria, Virginia 22333 '3. NUMBER OF PAGES

18 i4. MONITORING AGENCY NAME CL ADDRESSfit dilferenf from Confrolllng Of/ice) 15. SECURITY CLASS. (of this report)

Unclassified 15a. DECLASSlFlCATlON’DOWNGRADING

SCHEDULE

16. DISTRIBUTION STATEMENT (of thlu Report)


17. DlSTRlBUTlON STATEMENT (of the abstract entered in Block 20, if dlllerenl from Report)

IS. SUPPLEMENTARY NOTES

19. KEY WORDS (Continue on reverse side i/ necessary end identily by block number)

Fracture toughness Stress corrosion High strength steels

434C steel Frojectiles tlumidity

10. ABSTRACT (Continue on reverse side If necessary end Idcntrfy by block number)

(SEE REVERSE SIDE)

DD FoRM 1473 1 JAN 73 EDITION OF 1 NOV 65 IS OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Dara Entered)

UNCLASSIFIED ,

REPORT DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM

I. REPORT NUMBER 2. GOVT ACCESSION NO. ,. RECIPIENT'S CATALOG NUMBER

AMMRC MS 79-1 ,. TI TL E (Wid Subtitle) , TyPE OF REPORT & PERIOD COVERED

FRACTURE TOUGHNESS AND STRESS CORROSION CHARACTERISTICS OF l1LTRAIlIGH-STRENGTH Final Report

4340 STEEL - SUl-lMARY REVIEW • PERFORMING ORG. REPORT NUMBER

7. AUTHORr.) .. CONTRACT OR GRANT NUMBER(s)

Anthony K. Wong, Mil ton Levy, and. Walter F. Czyrklis

". PERFORMING ORGANIZATION N .... ME AND ADDRESS '0. PROGRAM ELEMENT, PROJECT, TASK AREA 6; WORK UNIT NUMBERS

Army Materials and Mechanics Research Center PiA Project: lX464621D073 Watertown, Massachusetts 02172 ~CMS Code: 6446210730012 DRXMR- E~i

II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

U. S. Army Materiel Dev e 1 opmen t and Readiness February 1979 Command, Alexandria, Virginia 22333 ". NUMBER OF PAGES

18 ,. MONITORING AGENCy NAME" ADDRESS(il dllf.tent from Conlro/llnj Office) ". SECURITY CLASS. (ot thle report)

Unclassified 15., OECL ASSI FIC A TION.' DOWNGRADING

SCHEDULE

••• DISTRIBuTION STATEMENT (of th", Report)


17. DISTRIBUTION STATEMENT (of the abstract entered In Blocl< 20. II dlttoren! Irom Report)

'0. SUPPLEMENTARY NOTES

.". KEY WORDS (Conllnue on rflverse .ide If ne,essary and identify by block number)

Fracture toughness 434C steel Stress corrosion Proj ectiles High strength steels Ilumidi ty

'0 ABSTRACT (ContInua on rever.e side It necessary end Identify by block number)

(SEE REVERSE SIDE)

DO FORM I JAN 7] 1473 EDITION OF 1 NOV 65 IS OBSOL.ETE UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE (When Dit/a Ent ~red)

--~

Block No. 20

ABSTRACT

A review was made of the fracture toughness (KIc) and stress corrosion (l&J characteristics of 4340 steel within the 200 to 250 ksi yield strength range. This literature review was conducted in support of a fracture mechanics and environmental investigation of 4340 steel for the control section housing of the Copperhead CLGP (Cannon-Launched Guided Projectile) weapon system. Factors affecting toughness and corrosion cracking characteristics are considered. Also included are data pertaining to the damaging effects of humidity. Fracture toughness and stress corrosion cracking resistance of 4340 steel are usually higher in the alloys possessing lower yield strengths.

Materials Engineer

MILTON LEVY Supervisory Research/Chemist

Research Chemist " '

APPROVED:

E. B. KULA Chief Metals Research Division

UNCLASSIFIED

UNCLASSIFIED I'CU"ITY CLAIIIPlCATION 0' TMII ".G.,. .. Del. &I'I(:t'94)

Block No. 20

ABSTRACT

A review was made of the fracture toughness (K1c) and stress corrosion (K1scc) characteristics of 4340 steel within the 200 to 250 ksi yield strength range. This Ii terature review was conducted in support of a fracture mechanics and environmental investigation of 4340 steel for the control section housing of the Copperhead CLGP (Cannon-Launched Guided Projectile) weapon system . Factors affecting toughness and corrosion cracking characteristics are considered. Also included are data pertaining to the damaging effects of humidity. Fracture toughness and stress corrosion cracking resistance of 4340 steel are usually higher in the alloys possessing lower yield strengths.

APPROVED:

E. B. KULA Chief Metals Research Division

Materials Engineer

MIL TON LEVY I Supervisory Research :emist

UNCLASSIFIED

CONTENTS

Page

INTRODUCTION

Background. ............................. 1

Fracture Toughness Considerations .................. 1

Stress Corrosion Considerations ................... 1

Application ............................. 2

Objective .............................. 2

RESULTS AND DISCUSSION

Requirement for 434C Steel. ..................... 2

Fracture Toughness and Yield Strength ................ 2

Fracture Toughness and Test Specimen Considerations ......... 4

Fracture Toughness - Processing Effects ............... 6

Fracture Toughness Comparison .................... 8

Stress Corrosion Cracking ...................... 10

Stress Corrosion and Yield Strength ................. 10

Stress Corrosion and Temperature. .................. 12

Stress Corrosion and Cther Variables. ................ 12

Environmental Effects ........................ 13

Missile Storage Criteria - Humidity Effects ............. 14

Stress Corrosion Comparison ..................... 14

SUMMARY .................................. 14

LITERATURE CITED. ............................ 15

INTRODUCTION

Background.

CONTENTS

Fracture Toughness Considerations

Stress Corrosion Considerations

Application

Objective .


Requirement for 434C Steel ..... .

Fracture Toughness and Yield Strength

Fracture Toughness and Test Specimen Considerations

Fracture Toughness - Processing Effects

Fracture Toughness Comparison

Stress Corrosion Cracking . .

Stress Corrosion and Yield Strength

Stress Corrosion and Temperature ..

Stress Corrosion and ether Variables.

Environmental Effects . . • . . . .

Missile Storage Criteria - Humidity Effects

Stress Corrosion Comparison

SUMMARY ..

LITERATURE CITED

Page

1

1

1

2

2

2

2

4

6

8

10

10

12

12

13

14

14

14

15

.. . ,

INTRODUCTION

Background

Continued advances in weapons technology reiterate the need for ultrahigh- strength materials. Reliability, minimum weight, and economy are important requirements for guided missile components. These components must be fabricated from materials possessing high strength:weight ratios as well as uniform and reproducible mechanical properties such that unexpected failures will not occur at stresses lower than the design operating conditions. If strength of material was the only limiting design parameter, it would be a simple procedure to select a strong material for application. Unfortunately, many widely used engineering alloys experience failure at nominal stress levels well below their yield strengths when exposed to particular conditions of temperature, loading rate, stress distribution, and surrounding enviornment.


To mitigate these problems, designers are increasingly employing linear elastic fracture mechanics principles and concepts of crack-extension force and stress intensity factor in their utilization of high strength materials. As a consequence of much research activity and rapid development,1’3 fracture toJgh- ness testing, based on fracture mechanics principles, has quickly evolved from the research stage to a standardized procedure.4 Of growing interest at this time is the true material property of plane strain fracture toughness designated as Qc. Failure in a structure can occur when the stress intensity K equals the fracture toughness value.


Since weapon system components are often stored in readiness condition for long periods of time in controlled or uncontrolled environments, stress corrosion cracking susceptibility must be considered. Stress corrosion cracking (see) is the failure of material from the combined effects of a corrosion environment and a static tensile stress. The source of the stress may be from applied loads or “locked-up” residual stresses.

Fracture mechanics can also be employed in the analysis of stress corrosion cracking.%6 The threshold value of stress intensity is designated KIscc. Crack growth should not occur for stress intensities K below KIscc. If an initial value of K is above KISCC, existing cracks can be expected to grow with time until fracture occurs.

1. 2. 3. 4. 5.

6.

Fracture Toughness Testing and Its Applications. ASTM STP 381, 1965. Plane Strain Crack Toughness Testing of High Strength Metallic Materials. ASTM STP 410, 1966. Review of Developments in Plane Strain Fracture Toughness Testing. ASTM STP 463, 1970. ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials: E399-74. SCULLY, J. C., ed. The Theory of Stress Corrosion Cracking in Alloys. NATO Science Committee, Research Evaluation Conference, Brussels, W. S. Maney and Sons, Ltd., Leeds, England, 1971. BROWN, B. F., ed. Stress Corrosion Cracking in High Strength Steel, Titanium, and Aluminum Al1o.w. U. S. Government Printing Office, Stock No. 085 l-0058, 1972.

1

INTRODUCTION

Background

Continued advances in weapons technology reiterate the need for ultrahighstrength materials. Reliability, minimum weight, and economy are important requirements for guided missile components. These components must be fabricated from materials possessing high strength:weight ratios as well as uniform and reproducible mechanical properties such that unexpected failures will not occur at stresses lower than the design operating conditions. If strength of material was the only limiting design parameter, it would be a simple procedure to select a strong material for application. Unfortunately, many widely used engineering alloys experience failure at nominal stress levels well below their yield strengths when exposed to particular conditions of temperature, loading rate, stress distribution, and surrounding enviornment.


To mitigate these problems, designers are increasingly employing linear elastic fracture mechanics principles and concepts of crack-extension force and stress intensity factor in their utilization of high strength materials. As a consequence of much research activity and rapid development,I-3 fracture to~ghness testing, based on fracture mechanics principles, has quickly evolved from the research stage to a standardized procedure. 4 Of growing interest at this time is the true material property of plane strain fracture toughness designated as K1c ' Failure in a structure can occur when the stress intensity K equals the fracture toughness value.


Since weapon system components are often stored in readiness condition for long periods of time in controlled or uncontrolled environments, stress corrosion cracking susceptibility must be considered. Stress corrosion cracking (sec) is the failure of material from the combined effects of a corrosion environment and a static tensile stress. The source of the stress may be from applied loads or "locked-up" residual stresses.

Fracture cracking. 5,6 growth should of K is above ture occurs.

mechanics can also be employed in the analysis of stress corrosion The threshold value of stress intensity is designated KIscc ' Crack not occur for stress intensities K below KIscc ' If an initial value KIscc ' existing cracks can be expected to grow with time until frac-

1. Fracture Toughness Testing and Its Applications. ASTM STP 381, 1965. 2. Plane Strain Crack Toughness Testing of High Strength Metallic Materials. ASTM STP 410,1966. 3. Review of Developments in Plane Strain Fracture T01Ighnrss Testing. ASTM STP 463,1970. 4. ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials: E399·74. 5. SCULLY. J. C., cd. The Theory of Stress Corrosion Cracking in Alloys. NATO Science Committee, Research Evaluation

Conference, Brussels, W. S. Maney and Sons, Ltd" Leeds, England. 1971. 6. BROWN, B. F., ed. Stress Corrosion Cracking in Ili1{h Strength Steel. Titanium, and Alumirumt Alloys. U. S. Government

Printing Office, Stock No. 0851-0058,1972.

I

Application

The Copperhead CLGP (Cannon-Launched Guided Projectile) weapon system is a high-performance 155-mm laser-guided projectile. Its control section housing component is basically the outer skin of the projectile from the warhead to the aft closure and is fabricated from air-melted, vacuum-degassed 4340 steel. This component is eventually heat treated to Rockwell C 53 to C 55 hardness range.

Objective

Fracture mechanics principles are being used to analyze the control section housing, and tests have been initiated to determine the fracture toughness and other mechanical properties of the structural alloy. The object of this report was to survey the technical literature to determine the availability of published fracture toughness (KIc), (I($ and stress corrosion (MI& data pertaining to 4340 steel.


Requirement for 4340 Steel

Structural elements in guided missiles utilize ultrahigh-strength alloys to achieve necessary weight savings. The 4340 steel selected for the Copperhead control section housing is a low-alloy, nickel-chromium-molybdenum steel which possesses a good combination of strength and hardness uniformity in large sections and can be welded. Moreover, the alloy can be readily heat treated to ultimate tensile strength levels ranging from 125 to 300 ksi. The yield strength of the Copperhead housing alloy is in the vicinity of 220 ksi. Table 1 shows the chemical composition limits of AISI 4340.


This alloy is a classical heat-treatable construction metal and is considered a standard against which many other steels are compared. Consequently, 4340 steel has been the subject of investigations since the earliest period of fracture toughness testing.

Much of the past data has been collected by the Metals and Ceramics Informa- tion Center and published in its Damage Tolerant Design Handbook.7 Plane strain

Table 1. CHEMICAL COMPOSITION OF AISI 4340 STEEL (WT. '%)

C 0.38-0.43 Si 0.20-0.35 Mn 0.60-0.80 Ni 1.65-2.00 P 0.035 max Cr 0.70-0.90 S 0.040 max MO 0.20-0.30

7. Damage Tolerant Design Handbook, Metals and Ccramlc December 1972, 2nd Supplement, January 1975.

Information , Air Force Materials Labora tory, MCIC-HB-01,

2

App1 ication

The Copperhead CLGP (Cannon-Launched Guided Projecti le) weapon system is a high-performance ISS-mm laser-guided projec. t ile. Its control section housing component is basically the outer sk in of the projectile from the warhead to the aft closure and is fabricated from air-melted, vacuum-degassed 4340 steel. This component is eventually heat treated to Rockwell C 53 to C 55 hardness range.

Objective

Fracture mechanics principles are bei ng used to analyze the control section housing, and tests have been initiated to determine the fracture toughness and other mechanical propertie s of the structural alloy. The object of this report was to survey the technical literature to determine the availability of published fracture toughness (K1c)' (KQl and stress corrosion (K1scc) data pertaining to 4340 steel.


Requirement for 4340 Steel

Structural elements in guided missiles utilize ultrahigh-strength alloys to achieve necessary weight savings. The 4340 steel selected for the Copperhead control section housing is a low-alloy, nick el - chromium-molybdenum steel which possesses a good combination of strength and hardness uniformity in large sections and can be welded. Moreover, the alloy can be readily heat treated to ultimate tensile strength levels ranging from 125 to 300 ksi. The yield strength of the Copperhead housing alloy is in the vicinit y of 220 ksi. Table I shows the chemical composition limits of AISI 4340.


This alloy is a classical heat-treatable construction metal and is considered a standard against which many other steels are compared. Consequently, 4340 steel has been the subject of investigations since the earliest period of fracture toughness testing.

Much of the past data has been collected by the Metals and Ceramics Information Center and published in its Damage Tolerant Design Handbook.7 Plane strain

Table 1. CHEMICAL COMPOSITION OF AISI 4340 STEEL (WT. %)

C 0.38-0.43 Si 0.20-0.35 Mn 0.60-0.80 Ni 1.65-2.00 P 0.035 max Cr 0.70-0.90 S 0.040 max Me 0.20-0. 30

7. Damage Tolerant Design Handbook, Metals and Ceramic Inforllliltion Co! nter. Air Force Mate rials Laboratory, MClC-HB~l. December 1972, 2nd Supplement , January 1975.

2

fracture toughness (KIc ted as function of yield

or KQ) data from the Handbook are shown in Figure 1, plot- strength of 4340 steel between 200 and 240 ksi. An arbi-

trary reference line has been drawn on the chart to indicate the generally expected decrease in fracture toughness with increasing yield strengths. A precise rate of decrease cannot be established because of the wide scatter in data points. Many authors present data of this type as a wide band or within envelopes. These data also indicate the feasibility of processing 4340 steel to achieve high toughness along with high strength.

The individual data points in the figure represent mixed results from nine different investigations which are referenced in the Design Handbook.7 A variety of heat treatments and other test controls were employed in the investigations. This information may be found in the Handbook and will not be repeated here.

For practical comparison, the fracture toughnesses of 4340 alloy removed from three production Spartan second-stage rocket motor cases8Bg have been incorporated into the chart. In general, the fracture toughness of the motor case material was within the limits expected of 4340 steel. Although the hardnesses

4340 Steel

100 0 Handbook (Ref. 7)

A Spartan Case (Ref. 8)

0 Oregon (Ref. 16)

cl

Figure 1. Fracture toughness of 4340 steel.

I I I I 210 220 230 240

Yield Strength (ksi)

8. WONG, A. K., LEVY, M., and GRENIS, A. Stress Corrosion, Mechanical Properties, and Acoustic Emission of 4340 Steel from a Second-Stage Spartan Missile Motor Case. Army Materials and Mechanics Research Center, report in process.

9. KULA, E. B., and ANCTIL, A. A. Preliminary Metallurgical Evaluation of Proof Test Failure of Spartan Second-Stage Motor Case. Army Materials and Mechanics Research Center, AMMRC SP 73-8, May 1973.

3

fracture toughness (KIc or KQ) data from the Handbook are shown in Figure 1, plotted as function of yield strength of 4340 steel between 200 and 240 ksi. An arbitrary reference line has been drawn on the chart to indicate the generally expected decrease in fracture toughness with increasing yield strengths. A precise rate of decrease cannot be established because of the wide scatter in data points. Many authors present data of this type as a wide band or within envelopes. These data also indicate the feasibility of processing 4340 steel to achieve high toughness along with high strength.

The individual data points in the figure represent mixed results from nine different investigations which are referenced in the Design Handbook.7 A variety of heat treatments and other test controls were employed in the investigations. This information may be found in the Handbook and will not be repeated here.

For practical comparison, the fracture toughnesses of 4340 alloy removed from three production Spartan second-stage rocket motor cases 8,9 have been incorporated into the chart. In general, the fracture toughness of the motor case material was within the limits expected of 4340 steel. Although the hardnesses

100

90

:f

'" ~ '" '" ~ 70 u

,z

~ 0

~ 0 c ~ ~ ~ 0 ~

~

~ 50 t> ~ 0 ~

40

JO 200

4340 steel

o Handbook IRef, II

6. spartan Case (Ref.

o Or~on (Ref. 161 0

0

Arbitrary Reference line ;' 0

0

0

t::. 0 g 0

0

0

210 220 230 Yield Strength (ksi)

8)

o o

240

Figure 1. Fracture toughness of 4340 steel.

8. WONG, A. K., LEVY, M., and GRENIS, A. Stress Corrosion, Mechanical Properties, and Acoustic Emission of 4340 Steel from a Second·Stage Spartan Missile Motor Case. Army Materials and Mechanics Research Center, report in process.

9. KULA, E. B., and ANCTIL, A. A. Preliminary Metallurgical Evaluation of Proof Test Failure of Spartan Second·Stage Motor Case. Army Materials and Mechanics Research Center, AMMRC SP 73-8, May 1973.

3

of the case materials were szmilric (‘:‘W(l 50) + -“\rci~- yield strengths ranged from 212 to 265 ksi and their ultimate ~cni: i 3t st: re:\gths ranged from 243 to 272 ksi. Hardness measurements are often ilsed !iurii\g manufacturing as a quality, assurance tool. Care should be taken to insure that tile hardness criteria designated for quality control is truly representatlvc of t?re dosiri?d mechanical properties. The motor case yield strengths slIclwn in 1: lz~.~rr 1 a-l-e based on longitudinal properties. Transverse yield strengths are h i gher .

Fracture Toughness and Test SpeclmEn tonsld,erat-ions

A host of factors affect tht.: fr:~~?_ur:-, ‘toughness of 4340 alloys of the same strength level. These include testing methodol.ogy, temperature, strain rate, impurities and inclusions, fabricat ion methods, melt -practice, and heat treatments.

Many of the data points in Figure I multiple identical specimens. I+ or

re;~est;nt averaged values from tests of ~>xalrlp i e , one point located at 53 ksi in. 2 was

derived from quantities ranging from 48.6 !_c: 58.6 ksi in.3. On the other hand, the same investigator also reported identical va3.ues of 52.5 ksi in.% for three individual specimens in another t e:;t_ a [jci-ice 3 it appears that the reported fracture toughness data may, at times, var)’ bk more tryan 20 percent, while at other times it may be perfectly reproduc;bI <:. rdcnti ctt 1 specimens and controlled test conditions were used in both WSCS.

An assortment of test speci?.lc>ns of v it LOINS size:< and shapes have been designed and used by the workers in the fie.taI to !+~~.~~~;ure plane strain fracture toughness. The general appearance and classzf; ,c;ftion of some of these specimens are shown in Figure 2. For the sake of uniformity and reproducibility, the ASTM has standard- ized4 the compact tension specimen and th;: three-point-load bend specimen.

Some of the effects of employing :;pea:imcns with different geometries and thicknesses are shown in Figure: 3, iO, 1 3. e\Jidenceci by the scatter in the individual test points. Although the di_;persion in the test results can be attributed to the specimen variabilities, it should bt- note d that it also is typical of the scatter mentioned earlier in tests with identical specimens. Nevertheless, properly designed nonstandard specimens can yield valid data. Figure 3 also exhibits the expected diminution of fracture toughne:;s w;th increases in yield strength of the 4340 steel.

Experiments have also demons crated that fracture toughness of 4340 steel increases with increasing test temperatures o Figure 4 shows the changes between -100 F and +200 F for an alloy with a yield strength of about 220 ksi at room temperature . 1 2 Other data may be found in tile .Ierospace Structural Metals Handbook.

10.

Il.

12.

AMATEAU, M. F., and S~IY,I~~I‘RWAI.D>, 1~. $1. t +YC ::I’(‘ t ‘/ZUW ?C I.P\!/~ :, (‘1 S’~r~~crro.al Metals. TRW, Bureau of Naval Weapons, ER 5937, April 1964.

FITZGIBBON, IX P. Sertzia~~nual Report WI t)w~\:or 1 VA\:‘I 14 >:pjr intc~ua. Swce Technology Laboratories, Inc., Air Force Ballistic Missile Division, TK-S9-(~000-00714 1 Juni I 955, STEIGERWALD, E. A. Plarzc Strain Fracture 7;1~~:‘~1:!~~.\1 ‘)c!; : i t *dildi;ooA r’rt~.~ctritiitiorz. TRW, AFML-TR, June 1967 (AD 821626).

of the case materials \l,lere similar (,""H!'H-: ~;O). 'r-heir yield strengths ranged from 212 to 265 ksi and their ultimate if)W';]( stre'I,gths ranged from 243 to 272 ksi. Hardness measurements are often 11SCG during manufa,ctu-ring as a quality' assurance tool. Care should be tal\en to insure th~tt the hardness criteria designiited for quali ty control is truly represcn tat! vc ur tite desirc.,d mechanical properties. The motor case yield strengths 5],C'''0 in F igUT!' 1 aTe based on longi tudlnal properties. Transverse yield strengths arc Illgr."c:,.

Fracture Toughness and Tes t Speci men Cons i derati ors

A host of factors affect til'. fracture tc,ughness of 4340 alloys of the same strength level. These include t2'3ting methodology, temperature, strain rate, impurities and inclusions, fabrica',ion methods, melt practice, and heat treatments.

Many of the data points in Figure 1 represent averaged values from tests of 1

multiple identical specimens. For example, one point locjlted at 53 ksi in.':! was derived from quantities ranging from 48.b (c S8.il ksi in.':!, On the other hand, the same investigator also reported identical values of 52.5 ksi in.lz for three individual specimens in another tc,t. lie""" it appears that the reported fracture toughness data may, at times ,vary b\ l1li.'re tl~an 20 percent, whi Ie at other times it may be perfectly repruducible:. TdcnticaJ specimens and controlled test conditions were used in both cases.

An assortment of test slwci],wJ1s of VII lOll" size:; and shapes have been designed and used by the workers in the fj cld to ""ed';ure plane strain fracture toughness. The general appearance and classificat:lon of SOniC of these specimens are shown in Figure 2. For the sake of uniformity and reproducibility, the ASTM has standardized4 the compact tension specimen and the' three-point-load bend specimen.

Some of the effects of employing specimens with different geometries and thicknesses are shown in Figure :,.10,11 evidenced by the scatter in the individual test points. Although the di"lwrsion in the test results can be attributed to the specimen variabilities, it shOUld he noted that it also is typical of the scatter mentioned earlier in tests with ident i cal specimens. Nevertheless, properly designed nonstandard specimt'ns can yield valid data. Figure 3 also exhibits the expected diminution of fracture toughness ,,' th increases in yield strength of the 4340 steel.

Experiments have also dernonst rateu that fracture toughness of 4340 steel increases with increasing test temperatures. Figure 4 shows the changes between -100 F and +200 F for an alloy with a yielei strength of about 220 ksi at room temperature. 12 Other data may he fuund ill the Aerospace Structural Metals Handbook.

10. AMATEAU, M. r., and STLICrLRWAJ.D, F. .. \, j ;'Cr,'!!!C (h,;n; "{'Ii,\!h.\ (,', Slrli('tllral .. Uclals. TRW, Bureau ('If Naval Weapons, ER 5937, April 1964.

11. FITZGIBBON, D. P. Semiannual Report 0/1 !'rf\ \ :Ii'( l-;,..:,c! lh '!f:n t_l'ffcriil. Space Technology Liboratories, Inc., Air Force Ballistic Missile Division, TR-59-(\000-00714. Jun~' ]\).'19

12. STEIGERWALD, E. A. Plane Strain FraCTUre li>,::,i/i,'l'S,\ iJ,;'_'il i ;' ,!,'IJhook Prl's('l//urion. TRW, AFr-.lL-TR, June 1967 (All R21626).

loo-

< ti .lj 90- .- ul s v

yr80-

70 -

60-

50 -

SINGLE EDGE NOTCH

SPECIMEN (SEN)

lo 4 01

SURFACE CRACKED

TENSION SPECIMEN (SC)

l-z--l

b I CENTER NOTCHED

SHEET SPECIMEN (CC)

COMPACT TENSION

SPECIMEN (CT)

NOTCHED SLOW

BEND SPECIMEN (NB)

NOTCHED ROUND

SPECIMEN

Figure 2. Common specimen geometries for plane strain fracture toughness testing.

Vacuum Melt - 4340 Steel

l SEN 112 Mn - 0.65 q cc l/8 5 - 0.005

SC l/2 P - 0 0.010

NB 112 Cr- 0.82

A MO - 0.26

A NB 1 Ni - 1.85

Figure 3. Specimen geometry effects on

plane strain fracture toughness of 4340

steel.

401 I I I I I 180 190 200 210 220 230

0.2% Yield Strength (ksi)

Figure 4. Temperature effect on fracture

toughness of 4340 steel.

Temperature (deg F)

5

10 A 01 ~ ~ T

SINGLE EDGE NOTCH SURFACE CRACKED NOTCHED SLOW SPECIMEN (SEN) TENSION SPECIMEN (SC) BEND SPECIMEN (NB)

[0 ~ 0 to 0 ~ CENTER NOTCHED COMPACT TENSION NOTCHED ROUND SHEET SPECIMEN (CC) SPECIMEN (CT) SPECIMEN

Figure 2. Common specimen geometries for plane strain fracture toughness testing.

100 •

u

~80

:;.S

l>

o

•

Consumable Electrode Vacuum Melt - 4340 Steel

0 • •

Geom- Thick-~ ness, in.

o SEN 118

• SEN 111

• CC 118 o SC 111

" NB 111

wt~

C" 0.43 Si - 0.30 Mn-0.65 S - 0.005 P - 0.0\0 Cr - 0.81 Mo - 0.16

'\ L...-""'------'=-----' N i-I. 85 .- NB

~' .~. t

" '1-

O.2'1i Yield Strength (ksi)

Temperature (deg F)

5

Figure 3. Specimen geometry effects on

plane strain fracture toughness of 4340

steel.

Figure 4. Temperature effect on fracture

toughness of 4340 steel.


Melting practice, impurity elements and inclusions, and heat treatment are other factors which strongly influence fracture toughness of 4340 steel. Table 2 lists some toughness data obtained from heats produced by three conventional melting procedures. 1 3 Air-melted material exhibited a fracture toughness level of 40.5 ksi in.%, whereas degassed and vacuum arc remelt (VAR) heats exhibited properties in the ranges of 48.3 to 53.0 and 53.2 to 56.8, respectively.13 Thus, it appears that vacuum melting can upgrade fracture toughness.

A variety of heat treat procedures are used to achieve desired characteristics. Effects of tempering temperature on fracture toughness10,11j14 are shown in Figures 5 and 6. Although the toughness generally increases with increasing tempering temperatures, it should be noted that the final selection of tempering temperatures may be based on the need for certain tensile properties, hence, the requirements for a given tensile strength will govern the fracture toughness of the alloy. Austenitizing is also a critical step. Low austenitizing temperatures are preferred because of the resultant small austenite grain size and best combination of mechanical properties; but investigations15 revealed that the low temperatures did not provide maximum toughness.

Figure 6 also presents the deleterious effect of sulfur-plus-phosphorus content on toughness. Increasing the impurity elements from 0.01% to 0.05% can halve the fracture toughness. Sulfide inclusions as well as undissolved carbide act as crack nuclei which can drastically lower fracture toughness. Additionally, investigators have established that certain microstructural features such as blocky ferrite, upper bainite, and twinned martensite plates are harmful to toughness. On the other hand, other microstructural constituents such as lower bainite, autotempered martensite, and retained austenite can enhance toughness. By controlling the amounts and distributions of the microstructural constituents, the fracture toughness values of 4340 steel can be raised to the level of 18Ni maraging steel of equivalent yield strengths. I5

Table 2. EFFECT OF MELT PRACTICE PLANE STRAIN FRACTURE TOUGHNESS OF 4340 STEEL

Material Plane Strain Yield Fracture

Melt Toughness Practice

SfJ"" (ksi in.%)

Air 241 40.5 Degassed 229 53.0 Degassed 231 48.3

VAR 241 53.2 VAR 240 56.8

13.

14.

15.

HAUSER, J. J., and WELLS, M. G. H. Inclusions in MC@-Strength Steels, Their Dependence on ProcessinK Variables and Their Effect on Engineering Properties. Crucible Steel Corp.. AFML ‘l-R-68-222, August 1968.

KULA, E. B., and ANCTIL, A. A. Tempered Martensite t:‘mhrittlement and Fracture Toughness in SAE 4340 Steel. Journal of

Materials, JMLSA, v. 4, no. 4, December 1969, p. 817-84 1.

PARKER, E. R., and ZACKAY, V. 1:. Microstnrctrrral Ei’atures A fykcting Fracture Toughness of High Strength Steels. Engineer-

ing Fracture Mechanics, v. 7, no. 3, 1975, p. 371-375.


Melting practice, impurity elements and inclusions, and heat treatment are other factors which strongly influence fracture toughness of 4340 steel. Table 2 lists some toughness data obtained from heats produced by three conventional melting procedures. 13 Air-melted material exhibited a fracture toughness level of 40.5 ksi in.~, whereas degassed and vacuum arc remelt (VAR) heats exhibited properties in the ranges of 48.3 to 53.0 and 53.2 to 56.8, respectively.13 Thus, it appears that vacuum me 1 ting can upgrade fracture toughness.

A variety of heat treat procedures are used to achieve desired characteristics. Effects of tempering temperature on fracture toughness IO ,II,14 are shown in Figures 5 and 6. Although the toughness generally increases with increasing tempering temperatures, it should be noted that the final selection of tempering temperatures may be based on the need for certain tensile properties, hence, the requirements for a given tensile strength will govern the fracture toughness of the alloy. Austenitizing is also a critical step. Low austenitizing temperatures are preferred because of the resultant small austenite grain size and best combination of mechanical properties; but investigations I5 revealed that the low temperatures did not provide maximum toughness.

Figure 6 also presents the deleterious effect of SUlfur-pIus-phosphorus content on toughness. Increasing the impurity elements from 0.01% to 0.05% can halve the fracture toughness. Sulfide inclusions as well as undissolved carbide act as crack nuclei which can drastically lower fracture toughness. Additionally, investigators have established that certain microstructural features such as blocky ferrite, upper bainite, and twinned martensite plates are harmful to toughness. On the other hand, other microstructural constituents such as lower bainite, autotempered martensite, and retained austenite can enhance toughness. By controlling the amounts and distributions of the microstructural constituents, the fracture toughness values of 4340 steel can be raised to the level of l8Ni maraging steel of equivalent yield strengths. 15

Table 2. EFFECT OF MELT PRACTICE PLANE STRAIN FRACTURE TOUGHNESS OF 4340 STEEL

Mater; a 1 Plane Strain Yield Fracture

Melt Strength Toughness Practice (ksi) (ksi in.!~)

Air 241 40.5 Degassed 229 53.0 Degassed 231 48.3

VAR 241 53.2 VAR 240 56.8

13. HAUSER, J. J., and WELLS, M. G. H. Inelllsiolls in /liKh·StrenKth Steels, Their Dependence on Processing Variables and Their Effect on Hnl(ineering Properties. Crucible Stcd Corp .. AFML TR-68-222, August 1968.

14. KULA, E. B., and ANCTIL, A. A. Tempered Martcl/sitei:'lIIhritt/ellJent and Fracture Toughness in SAE 4340 Steel. Journal of Materials, JMLSA, v. 4, no. 4, December 1969, p. R 17·841.

15. PARKER, E. R., and ZACKAY, V. F. Microstmcfllral Features Afj'l'ctinx, Fracture Toughness of lligh Strength Steels. Engineering Fracture Mechanics, v. 7, no. 3, 1975, p. 371-375.

6

I I I I I I 400 500 600 700 a00 900

Temper Temperature (deg F)

Figure 5. Effect of tempering temperature on fracture toughness on 4340 steel.

Figure 6.

20- 0 0.01 0.02 0.03 0.04 0.05

Sulfur Plus Phosphorus (Weight 46)

Effect of impurity elements on fracture toughness of 4340 steel.

7

~ ~

-g ~

c .~

V; ~

100

c .,40 "-

Temper Temperature ~deg F)

Figure 5. Effect of tempering temperature on fracture toughness on 4340 steel.

~

.s

.;:;;; (j)

"" u :;z

Temper 700 F

ro~ __ ~ __ ~~~~ __ ~ __ ~_ o 0.01 O. OZ 0.03 0.04 0.05

Sulfur Plus PhosptlOruS cWeight ",LI

Figure 6. Effect of impurity elements on fracture toughness of 4340 steel.

7

Heat treatment parameters have also been developed by other workers for improving the microstructure of 4340 steel such that it is possible to achieve fracture toughness of nearly 90 ksi in. G at ultimate strength levels of over 300 ksi, thereby enhancing the attraction of the alloy for critical applications. The potential of upgrading the toughness of 4340 steel is indicated in Figure 1 by the fracture toughness value of the alloy specially heat treated to the 230 ksi yield strength level. l6 However, other properties such as resistance to dynamic loading are detrimentally affected and should be investigated.


Ultrahigh-strength 4340 steel heat treated to have a yield strength over 200 ksi is usually relatively brittle when cracklike defects are present. Neverthe- less, it has been used with a modicum of success in the wall of solid propellant rocket motor cases.8,g But one noted missile engineer17 states, with reference to airborne pressure vessels, that commercially standardized grades of steel, e.g., SAE and AISI such as 4340, are generally unsuitable for applications at strength levels above 200 ksi because of their susceptibility to temper embrittlement, quench cracking, and other factors that reduce their resistance to brittle fracture. As a consequence, other specially developed steels should be considered for ultrahigh-strength applications.

As stated earlier, 4340 steel is a classical alloy against which many other materials are compared. Consequently 9 the literature shows many comparisons of the fracture toughness of 4340 as a function of strength with other candidate ultrahigh-strength steels. Figures 7a and 7b show two corn arison graphs of fracture toughness plotted against ultimate tensile strength? ! *lg The ultimate tensile strength of the CLGP housing alloy is above 260 ksi. Similar data from other sources, 20-22 shown in Figures 8a and 8b, are plotted as a function of yield strength. The yield strength of the CLGP housing alloy is about 220 ksi. Some of the toughness data are not considered “valid” because the tests did not meet the requirements of ASI?4 E399.4

Because of the vagaries of materials characteristics and fracture toughness testing, these comparison charts should be approached with caution. However, cur - sory review indicates that the more costly HP 9-4 and 18% nickel maraging steels are highly promising candidates as alternate materials. Other candidate materials with practical potential include the D6AC and 3OOM alloys. Table 3 lists the nominal chemical compositions of some ultrahigh-strength steels.

16.

17.

18.

19.

20.

21.

22.

WOOD, W. E. Mechanisms of Enhanced Toughrless in Martensitic AIlo1.s. Oregon Graduate Center, Contract NOOOl9-76-C-0149,

April 1977 (AD-A040 373/3GA).

HURLICH, A. Choice of Materials and Fahricatiojl Techniqurs for J’ress~rre Vessels. Convair-Astronautics, Chapter 6 in Materials

for Missiles and Spacecraft, E. R. Parker, ed., McGraw-Hill Book Co., New York, 1963.

Private communication, Lockheed California Company, 1976.

McEOWEN, L. J. Combining Strength and Fracture Tollghness. Metal Progress, March 1975, p. 52.

AMATEAU, M. F., and STEIGERWALD, E. A. Fracture Characteristics of Structural Metals. TRW, Bureau of Navai Weapons,

ER 5937-1, August 1964. Problems in the Load-Carrying Application of High Strength Steels. DMIC Report 210, October 1964.

MOORE, T. D. Structural Alloys Handbook. Mechanical Proptxties Data Center, Belfour Stulen, Inc., Traverse City, Michigan,

1976.

8

Heat treatment parameters have also been developed by other workers for improving the microstructure of 4340 steel such that it is possible to achieve fracture toughness of nearly 90 ksi in.lz at ultimate strength levels of over 300 ksi, thereby enhancing the attraction of the alloy for critical applications. The potential of upgrading the toughness of 4340 steel is indicated in Figure 1 by the fracture toughness value of the alloy specially heat treated to the 230 ksi yield strength level. 16 However, other properties such as resistance to dynamic loading are detrimentally affected and should be investigated.


Ultrahigh-strength 4340 steel heat treated to have a yield strength over 200 ksi is usually relatively brittle when cracklike defects are present. Nevertheless, it has been used with a modicum of success in the wall of solid propellant rocket motor cases. 8,9 But one noted missile engineer l7 states, with reference to airborne pressure vessels, that commercially standardized grades of steel, e.g., SAE and AISI such as 4340, are generally unsuitable for applications at strength levels above 200 ksi because of their susceptibility to temper embrittlement, quench cracking, and other factors that reduce their resistance to brittle fracture. As a consequence, other specially developed steels should be considered for ultrahigh-strength applications.

As stated earlier, 4340 steel is a classical alloy against which many other materials are compared. Consequently, the literature shows many comparisons of the fracture toughness of 4340 as a function of strength with other candidate ultrahigh-strength steels. Figures 7a and 7b show two com~arison graphs of fracture toughness plotted against ultimate tensile strength. 1 ,19 The ultimate tensile strength of the CLGP housing alloy is above 260 ksi. Similar data from other sources,20-22 shown in Figures 8a and 8b, are plotted as a function of yield strength. The yield strength of the CLGP housing alloy is about 220 ksi. Some of the toughness data are not considered "valid" because the tests did not meet the requirements of ASTM E399. 4

Because of the vagaries of materials characteristics and fracture toughness testing, these comparison charts should be approached with caution. However, cursory review indicates that the more costly HP 9-4 and 18% nickel maraging steels are highly promising candidates as alternate materials. Other candidate materials wi th practical potential include the D6AC and 300M alloys. Table 3 lists the nominal chemical compositions of some ultrahigh-strength steels.

16. WOOD, W. F. Mechanisms of hnhanced Toughncsl' in MarrellSiric Allol's, Oregon Graduate Center, Contract NOOOI9·76-C-{)149, Ap,ii 1977 (AD-A040 373/3GA).

17. HURLICH, A. Choice of Materials and Fahricotioll Techniqucs for Pressure Vessels. Convair-Astronautics, Olapter 6 in Materials for Missiles and Spacecraft, E. R. Parker, cd., McGraw-Hill Book Co .. New York. 1963.

18. Private communication, Lockheed California Company, 1976. 19. McEOWEN, L. J. Combining Strength and Fracture Toughness. Metal Progress, March 1975, p. 52. 20. AMATEAU, M. F., and STEIGERWALD, E. A. Fracture Characteristics of Strnctural Metals. TRW, Bureau of Naval Weapons,

ER 5937-1, August 1964. 21. Problems in the Load-CaTrving Application of lIixh SlrCllgth Srcrls. DMIC' Report 2] 0, October 1964. 22. MOORE, T. D. Stmctural Alloys Handbook. Mechanical Properties Data Center, Belfour Stulen, Inc., Traverse City, Michigan,

1976.

8

Lockheed (Ref. 18)

Ud

I \ ,HP 9-4-30

- \! Republic (Ref. 19)

s- 80 r' .- r

b)

Tensile Strength (ksi) Yield Strength (ksi)

Figure 7. Fracture toughness of ultrahigh-strength

steels versus tensile strength. Figure 8. Fracture toughness of ultrahigh-strength

steels versus yield strength.

Table 3. NOMINAL COMPOSITIONS OF ULTRAHIGH-STRENGTH STEELS (NT. %)

Designation C Mn Si Ni Cr MO v co

Low Alloy

AISI 4340 0.40 0.70 0.30 1.80 0.80 0.25 AISI 4330V 0.30 0.70 0.30 1.80 0.80 0.25 AMS 6434 0.35 0.70 0.30 1.80 0.80 0.35 0.20 D6AC 0.45 0.75 0.25 0.55 1.05 300M

1.00 0.07 0.42 0.75 1.70 1.80 0.80 0.40 0.80

Medium Alloy

AISI Hll 0.35 0.30 1.00 5.20 0.40

Hiqh Allov

HP 9-4-25 0.25 0.10 0.10 8.50 0.50 0.50 HP 9-4-30

0.10 3.75 0.30 0.30 0.14 8.50 1.00 1.00 0.10 4.50

HP 9-4-45 0.45 0.10 0.10 8.50 0.30 0.20 0.10 3.75

Maraging

18Ni (200) 0.03 0.10 0.10 18.0 18Ni (250)

3.25 8.5 0.02 0.10 0.10 18.0

18Ni (300) 4.90 8.0

0.03 0.10 0.10 18.5 4.90 9.0

9

(a )

",-

.5 100 lockheed IRet. 18)

.~

'" O! D6AC

'" 80 ~ ~ ~ ~ ~ ~ ~

~ 60 ~

5 ~ ~ 40 ~

(b)

Republic (Ref. 19)

Figure 7 . Fracture toughness of ultrahigh-strength steels versus tensile strength.

~80 .S

~

~

c

"3- 40 ~

E "

(a)

(b)

DMIC IRel. 2U

~ m~----~----~r---~'-~-rln---~m--~

Yield Strer19th (ks i)

Figure 8 . Fracture toughness o f ultrahigh-strength steels versus yield strength .

Tabl e 3. NOMINAL COMPOS IT IONS OF ULT RAHI GH-STRENGTH STEELS (liT. %)

Desi gnation C Mn Si Hi Cr Mo V Co

Low All oy

AISI 4340 0.40 0.70 0 . 30 1.80 0.80 0 . 25 AISI 4330V 0 .30 0 .70 0 . 30 1. 80 0. 80 0.25 AMS 6434 0.35 0 . 70 0 . 30 1. 80 0.80 0.35 0.20 06AC 0 . 45 0.75 0 . 25 0.55 1. 05 1.00 0. 07 300M 0 .42 0. 75 1. 70 1.80 0 . 80 0 . 40 0 . 80

Medi um Alloy

AISI Hl 1 0.35 0.30 1.00 5.20 0.40

Hi gh Alloy

HP 9-4-25 0.25 0.10 0.10 8 . 50 0.50 0.50 0. 10 3.75 HP 9-4- 30 0 . 30 0.30 0 .1 4 8.50 1. 00 1.00 0. 10 4 . 50 HP 9-4 - 45 0 . 45 0 . 10 0.10 8.50 0.30 0 . 20 0 . 10 3 . 75

Marag; ng

18N i (200 ) 0. 03 0.10 0. 10 18 .0 3.25 8.5 18Ni (250) 0 . 02 0 . 10 0.10 18 . 0 4 . 90 8 . 0 18Ni (300) 0 .03 0. 10 0. 10 18.5 4. 90 9 .0

9

Stress Corrosion Cracking

Stress corrosion cracking of high strength structural alloys was the source of numerous serious problems throughout the Department of Defense during the 1960'~.~ Most of the earlier studies on corrosion cracking were conducted with smooth specimens. However, information of contemporary interest to weapon designers pertains to work with flawed or cracked materials. Fracture mechanics approaches can be used to good advantages in the analysis of stress corrosion cracking of high strength steels.6s23

The combined effects of a corrosive environment and a static tensile stress can cause crack initiation, crack propagation at intensities less than KIT, and eventual failure at stresses below the yield strength of the material. Time-tofailure is strongly influenced by stress intensity. Fracture mechanics plots can be used to display stress corrosion data. Figure 9 shows the effect of initial stress intensity KIi on time-to-failure of a 4340 steel with an ultimate tensile strength of 235 ksi.

Precracked specimens were used in the development of the stress corrosion data because they eliminated the uncertainties associated with the growth of cracks from corrosion pits. Furthermore, the crack provided a flaw geometry for which a stress analysis was available through fracture mechanics. These tests then produced stress corrosion information that was useful for predicting the behavior of large structural components wherein fracture was a critical design factor.

High initial stress intensities encourage subcritical crack growth. The time-to-failure of individual specimens are plotted against the corresponding KIi level and used to construct the type of curve shown in Figure 9. Susceptibility to crack growth decreases with stress intensity. A minimum KIi may be established below which stress corrosion cracking will not occur after an arbitrarily selected time. This minimum test duration time varies with different test materials and is often selected as 100 hours for low alloy steels and up to 1000 hours for high alloy steels. The minimum KIi value is an apparent threshold stress intensity level designated as Klscc. As indicated in the figure the K~scc parameter for this particular heat of 4340 in distilled and salt water (3.5% NaCl) is about 22 ksi in.$.24


Threshold stress intensity factors from eleven investigations' are shown plotted in Figure 10 as a function of yield strength of 4340 steels between 200 and 245 ksi. An arbitrary reference line was drawn through the data to indicate a possible trend. As alluded to by the reference curve, K1scc values appear to decrease in general with increasing yield strength of the alloy. However, they may level off and remain relatively constant at strength levels above $230 ksi. Also included in this chart for comparison is an envelope of KIT fracture toughness data derived from Figure 1.

2 3. Stress Corrosion Testing. ASTM Special Technical Publication 425, 1966. 24. BENJAMIN, W. D., and STEIGERWALD, E. A. Envirorlmerztally /nduced Delayed Failures in Martensitic High-Strength Steels.

TRW, AFML TR 68-80, April 1968.

10

Stress Corrosion Cracking

Stress corrosion cracking of high strength structural alloys was the source of numerous serious problems throughout the Department of Defense during the 1960's.6 Most of the earlier studies on corrosion cracking were conducted with smooth specimens. However, information of contemporary interest to weapon designers pertains to work with flawed or cracked materials. Fracture mechanics approaches can be used to good advantages in the analysis of stress corrosion cracking of high strength steels. 6,23

The combined effects of a corrosive environment and a static tensile stress can cause crack initiation, crack propagation at intensities less than Klc, and eventual failure at stresses below the yield strength of the material. Time-tofailure is strongly influenced by stress intensity. Fracture mechanics plots can be used to display stress corrosion data. Figure 9 shows the effect of initial stress intensity KIi on time-to-failure of a 4340 steel with an ultimate tensile strength of 235 ksi.

Precracked specimens were used in the development of the stress corrosion data because they eliminated the uncertainties associated with the growth of cracks from corrosion pits. Furthermore, the crack provided a flaw geometry for which a stress analysis was available through fracture mechanics. These tests then produced stress corrosion information that was useful for predicting the behavior of large structural components wherein fracture was a critical design factor.

High initial stress intensities encourage subcritical crack growth. The time-to-failure of individual specimens are plotted against the corresponding Kli level and used to construct the type of curve shown in Figure 9. Susceptibility to crack growth decreases with stress intensity. A minimum KIi may be established below which stress corrosion cracking will not occur after an arbitrarily selected time. This minimum test duration time varies with different test materials and is often selected as 100 hours for low alloy steels and up to 1000 hours for high alloy steels. The minimum Kli value is an apparent threshold stress intensity level designated as Klscc. As indicated in the figure the KIscc parameter for this particular heat of 4340 in distilled and salt water (3.5% NaCl) is about 22 ksi in.!j.24


Threshold stress intensity factors from eleven investigations 7 are shown plotted in Figure 10 as a function of yield strength o£ 4340 steels between 200 and 245 ksi. An arbitrary reference line was drawn through the data to indicate a possible trend. As alluded to by the reference curve, KIscc values appear to decrease in general with increasing yield strength of the alloy. However, they may level off and remain relatively constant at strength levels above ~230 ksi. Also included in this chart for comparison is an envelope of KIc fracture toughness data derived from Figure 1.

23. Stress Corrosion Testing. ASTM Special Technical Publication 425, 1966. 24. BENJAMIN, W. D., and STEIGERWALD, E. A. FIIl'ironmclltally Induced Delayed Failures in Martensitic High-Strength Steels.

TRW, AFML TR 68-80, April 1968.

10

80

C! 4 i .-

.- 2 60 .-

57 I

.pl

s? c - 2 2 20 5; i6 .- .Z = - 0

4340 Steel

Notch Bend Specimens

Failure Time (minutes)

Figure 9. Delayed failure of 4340 steel in distilled and salt water.

Distilled md Salt (3.5% NaCI) Water (RT)

I I I

220 230 240 ‘field Strength (ksi)

Figure 10. Stress-corrosion resistance and fracture toughness of 4340 steel.

11

4340 Steel Ftu • 235 ksi

~- Notch Bend Specimens

;g Klscc

c 0 O~~~~~~~~l~O~~UWSr~~~-L~~~

Failure Time Im inutes)

Figure 9 . Delayed failure of 4340 steel in distilled and salt water.

;f .~

~ ~

"" u; c

'" c

~

E U;

40

'IQ 00

20 0

0 10

8

0

4.140 Steel

Distilled and Salt t3.5".1> NaGl) Waler tRT)

Klscc

o

Arbitrary Reference Line

o

O~ ____ ~~ ____ ~ ______ ~ ____ ~~ __ 200 210 m 2'IQ 240

Yield Strength (ksil

Figure 10. Stress-corrosion resistance and fracture toughness of 4340 steel.

11

Stress corrosion tests on 4340 steel from Spartan motor cases8 correlated well with the data shown in Figure 10. From motor case samples with yield strengths of 212 and 219 ksi, KIscc values of 22 and 17 ksi in.%, respectively, were determined.

Stress Corrosion and Temperature

Data shown in Figure 10 are for tests conducted at room temperature. At ele- vated temperatures, the KIscc parameters for steels usually decrease.25r26 This influence of temperature is exhibited in Figure 11 for a 4340 steel exposed to temperatures between 32 and 212 F. Also indicated in the chart is the increase of KIscc at lower test temperatures. The significant decrement in KIscc between 75 and 212 F emphasizes the need to consider the influence of temperature on the long-term storability of missile components.

Stress Corrosion and Other Variables

Inspection of the KIscc behavior in Figure 10 and other review source@ shows divergence in the data points that is indicative of variables other than yield strength. For example, at the yield strength level of about 210 ksi, the KIscc of 4340 steel reportedly ranges from nearly 10 to over 30 ksi in.%

Factors affecting threshold stress intensity parameter measurements include test methodology, 6,23*27 alloying elements, 28~2g fabrication methods, melt practice, 3o and heat treatments. Although stress corrosion cracks generally propagate intergranularly, there appears to be no significant effects of grain size on KIscc in 4340 steel. But crack growth rates have been observed to decrease with decreasing grain size,31,32 a factor which may be important in the selection of heat treatments for 4340 steels destined for long-term storage.

In view of the number of interacting variables capable of influencing the KIscc parameter, general published stress corrosion data pertaining to 4340 steel should not be used in critical designs without distinct knowledge of the background and history of the material. Stress corrosion tests should be carried out on samples possessing properties closely simulating the condition of the final Droduct. I

25.

26. 21.

28.

29.

30.

31.

32.

STEIGLRWAL.D, E. A., and HANNA, G. L. Inflwrlcc oj’ t:‘r~~%w~rrrcrrt O/I Crack Propagation and Delayed Failures in High

Strength Steels. TRW, AFML RTD-TDR-634225, January 1964. KORTOVICH, C. Corrosion Fatigue Behavior of 4340 arld IXiAC Sfccls Below KIscc TRW, Report ER 7717, April 1974. STI’IGERWALD, E. A., and BENJAMIN, W. 1). Stress Cortmior~ Crackiq Mechanisms in Martensitic Nigh Stren,qth Steels.

TRW, Al:ML TR 67-98. April 1967. TINER, N. A., and GILPIN, C. B. Micvwlvmcss~s irt Stress (hrrosim o,f‘Martensitic Steels. Corrosion, V. 22, October 1966, p. 271. SANDOZ, G. The Effects of Alloving t:‘lcmwts m the Sl~swptihilif~* to Stress Corrosion Cracking of Martcnsitic Steels in Salt Water. Met. Trans., v. 2, 1971, p, 1055. CARTER, C. S. The I;,:ffect of Silicon on the Srrcss Corroslotl RcsisIatm of Low-Al1o.v High-Strength Steels, Corrosion, v. 25,

no. 10, October 1969, p. 423. PROCTER, R., and PAXTON, H. The Effect o.f Prior Attstcnirc Gruitl Size on the Stress Corrosion Susceptibility of AISI 4.340

Steel. ASM Trans. Quart., v. 62, no. 4, December 1969, p. 989. WEBSTER, D. Effect of Grain Refvwrnent on the Microstrtrcttrrc and I’ropcrtics of434OM Steel. Boeing Document D6-25220, The Boeing Company, Scattle, Washington, April 1970.

12

Stress corrosion tests on 4340 steel from Spartan motor cases 8 correlated well with the data shown in Figure 10. From motor case samples with yield strengths of 212 and 219 ksi, KIscc values of 22 and 17 ksi in.~, respectively, were determined.

Stress Corrosion and Temperature

Data shown in Figure 10 are for tests conducted at room temperature. At ele vated temperatures, the KIscc parameter s for steels usually decrease. 25 ,26 This influence of temperature is exhibited in Figure 11 for a 4340 steel exposed to temperatures between 32 and 212 F. Also indicated in the chart is the increase of KIscc at lower test temperatures. The significant decrement in KIscc between 75 and 212 F emphasizes the need to consider the influence of temperature on the long-term s torability of missile components.

Stress Corrosion and Other Variables

Inspection of the KIscc behavior in Figure 10 and other review sources6 shows divergence i n the data points that is indicative of variables other than yield strength. For example, at the yield strength level of about 210 ksi, the KIscc of 4340 steel reportedly ranges from nearl y 10 to over 30 ksi in.~.

Factors affecting threshold stress intensity parameter measurements include test methodology,6, 23 , 27 alloying elements, 28,29 fabrication methods, melt practice,30 and heat treatments. Although stress corrosion cracks generally propagate intergranularly, there appears to be no significant effects of grain size on KIscc in 4340 steel. But crack growth rates have been observed to decrease with decreasing grain size, 31,32 a factor which may be important in the selection of heat treatments for 4340 steels destined for long-term storage.

In view of the number of interacting variables capable of influencing the KIscc parameter, general published stress corrosion data pertaining to 4340 steel should not be used in critical designs without distinct knowledge of the background and history of the material. Stress corrosion tests should be carried out on samples possessing properties closely simulating the condition of the final product.

25. STEIGER WALD, E. A., and HANNA. G. L. /nfllu!fIct' o[ i:"lIl'ironmclI( OIl Crack Pro"Q~Qtio/J and De/ayed Failures in HiX" Strength Sleeis. TRW, AFML RTD·TOR~34225. January 1964.

26. KORTOVICH, C. Corrosion Fatigu £' BehoF/or of 4}40 and Dfi .. 1C Steels Be/ow K1sc(; TRW, Report ER 7717, April 1974. 27. STFIGERWALD, E. A., :md BENJAMIN, W. D. Strc>n Cormsirlll Crocki"K Mechanism.~ in Martensitic 1Ii~" StfPnKth Steels.

TRW, AFML TR 67-98 . Apdl 1967 . 28. TINER , N. A" and GILPIN. C. B. MkmprocC'sscs in Slr(,l· .~ Corrosioll of Mart"ns;tic Steds. Corrosion. v. 22. Octobcr 1966,

.,. 271. 29. SANDOZ, C. n,l' I: ffects of AlloyitiX Hll'lll(',lfs "" '"l' SU~"'I'J!'ihjJi1.1· 10 Strl'ss Corrosion CrackinK of MartC!llsitic Steels ill Salt

Water. Mel. Tram., v. 2, 1971. p. 1055. 30. CARTER, C. S. The Effect of Silicon on the Stress Corrosiol/ H(:sisrOlI('(' of Low·AlIoy IliKh·StrenKth Steels. Corrosion, v. 25.

no. 10 , October 1969, p. 423. 31. PROCTER , R., and PAXTON, H. The I:.fj'ect of Prior Alls(('nitr (,'rain Size on rhe Stress Corrosion Susceptibility of A lSI 4340

Steel. ASM Trans. Quart., v. 62. no. 4. December 1969 . p. 989. 32. WEBSTER, D. I:,yf~ct of Grain Re/inemrnl on rill' MicmHrrwflfre O/lfJ /'ropcrtics ('I 4340M Steel. Boeinl! Document 06·25220,

The Doein!! Company. Seattle, Washington, April 1970.

12

01 0

1 I I I I 50 100 150 200 250

Temperature (deq Fl

Environmental Effects

Figure 11. Effect of temperature on

Klscc of 4340 steel.

As mentioned earlier, the stress corrosion behavior shown in Figure 10 is for 4340 steel in both distilled and salt water environments. Several experi- ments24,27,33 h ave demonstrated that stress corrosion tests of high strength steels in 2 % to 4% NaCl solution environment yields KIscc data similar to that derived from tests in distilled water. Furthermore, other laboratory salt water studies have been made 34y35 which reveal good correlation of data with tests in flowing sea water environments. Therefore, it can be generally assumed that tests in either of the three environments will yield similar results.

Other aggressive environments can also motivate stress corrosion in 4340 steels. In a salt water and acetic acid solution saturated with Hz&36 the KIscc values of 4340 steels fall within the lower bounds of the KIscc data shown in Figure 10. On the other hand, the alloy is also susceptible to a methanol environment, but its KIscc value is somewhat higher than that observed in salt water solutions. Similar behavior has been observed in tests with butyl alcohol and acetone.33

Large changes in acidity and salt concentration of aqueous environments do not appreciably affect KIscc. The introduction of H2S appears to lower KIscc to the lowest values reported for a particular type of steel in salt water.37 Thus it

33.

34.

35.

36.

37.

appears that in critical applications, an analysis should be made of all fluids

TANIGUCHI. N., and TROIANO, A. Stress C’orros~otl rrac,krrlg o./ 4340 Steels in Dif:fercnt Environments. Trans. Iron Steel

Inst., Japan, v. 9, no. 4, 1969.

LENNOX, T. J., et al. Marine Corrosiorl Studies: Stress Corrosiorl Cracking Deep Ocean TechnoEogjl Cathodic Protection ou Fatigue. Naval Research Laboratory, NRL Memorandum Report 17 11, May 1966. SANDOZ, G., and NEWBEGIN, R. A Comparison of Laborator!? Salt Water aud flowing Natural Seawater as arl E,‘r?vironment for Tests of Stress Corrosion Cracking Susceptibilit?*. Report of NRL Progress, Naval Research Laboratory, May 1969.

SNAPE, E. Stress-Induced Failure of High Strength Steels in Envlronmcnts Containing ff_vdrogcn Srrlphide. Br. Corrosion J., v. 4, no. 5, September 1969, p. 252.

BUCCI, R., PARIS, P., LOUSHIN, L., and JOHNSON, 1-I. Fructzrrc Mechanics Consideration of H?,drogen Srrl,fide Cracking in High Strength Steels, Stress Analysis and (irowth of‘ Cracks. Proceedings of the 1971 National Symposium on 1:racturc Mechanics,

Part 1, ASTM STP 513, Philadelphia, PA, 1972.

13

25

c

~20

4340 Steel Distilled Water f ty • 211 ksi

O~ __ ~ __ ~~ __ ~ ____ ~ __ -J

o 50 100 150 200 250 Temperature (de:! F)

Environmental Effects

Figure 11. Effect of temperature on

K Isee of 4340 steel.

As mentioned earlier, the stress corros ion behavior shown in Figure 10 is for 4340 steel in both distilled and salt water environments. Several experiments 24 , 27,33 have demonstrated that stress corrosion tests of high strength steels in 2% to 4% NaCI solution environment yields Klscc data similar to that derived from tests in distilled water. Furthermore, other laboratory salt water studies have been made 34 ,35 which reveal good correlation of data with tests in flowing sea water environments. Therefore, it can be generally assumed that tests in either of the three environments will yield similar results.

Other aggressive environments can also motivate stress corrosion in 4340 steels. In a salt water and acetic acid solution saturated with H2S,36 the Kl scc values of 4340 steels fall wi thin the lower bounds of the Klscc data shown in Figure 10. On the other hand, the alloy is also susceptible to a methanol environment, but its Klscc value is somewhat higher than that observed in salt water solutions. Similar behavior has been observed in tests with butyl alcohol and acetone. 33

Large changes in acidity and salt concentration of aqueous environments do not appreciably affect Klscc. The introduction of H2S appears to lower Klscc to the lowest values reported for a particular type of steel in salt water. 37 Thus it appears that in critical applications, an analysis should be made of all fluids

33. TANIGUC HI , N .. Jnd TROIANO, A. Stress Corrmioll f'rack illX oj 4.?40 Sreel.\' ill ni/ferell' l:.'m' irOlJl1Icllts. Tram . Iron Steel lnst. , Japan , v. 9 , no. 4 , 1969.

34. LENNOX. T. J., el al. Marine Corrosion Studie!!i : Stn'ss Corrosion ('rockillg Deep Ocean Tee/Ulolox), Cathodic Pro tec rion 0 1/

Fatigue. Naval Research L:.lbmatory , NRL Memorandum Report 1711 , ~ay 1966. 35. SANDOZ, G. , and NEWBEGIN, R. A Comparison of Laboratory Sal, Water and H owillK Natural Seawater as all /;"lI l'irOllment

for Tests of Stress Corrosion Crackin f( Susceptibility. Report of NRl Progress, Naval R~search Laboratory, May 1969. 36. SNAPE, E. Stress-Induced Failure of /ligh Strel1!(th Sfcd~ ill t:l1l'l ro lil/1/?l/t5 Containillg lIydroflen SlI lphide. Sr. Corrosion J.,

v. 4, no. 5, September 1969, p. 252. 37. BUCCI, R., PARTS, P., LOUSHlN, L., and JOHNSON, H. Fraell/I"{' Mechallies COllSidcrarinn 1)[ Hy drogen Sulfide Crackillg in

High Strenxth Steels, Stress Analysis alld (;mwth of Cracks. Procl~c dinp..~ o f the 1971 National Symposium on I'- racture Mechanics, Part 1 , ASTM STP 5 13. Philadelphia , PA , 1971.

and compounds used in the various steps of processing and packaging to insure the absence of any substance capable of promoting stress corrosion cracking, particularly during long terms of storage in a damp environment.


Experimental data is needed for the establishment of realistic criteria for environmental control during missile storage, It is common practice38 to assume that a maximum allowable relative humidity of 50% and a temperature range of 70 F to 85 F provide an adequate environment for the prevention of corrosion in metal parts. However, limited studies of 4340 steel with yield strengths of about 220 ksi indicate premature failure both in 90% relative humidity at 75 F3g and in 50% relative humidity environments at 90 F and 120 F. In the 50% relative humidity environment under a stress intensity 75% of KIc (KIc = $52 ksi in.%), the 4340 steel in the 90 F surroundings fractured in 31 days and at 120 F fractured in 12 days.38 More information is needed to elucidate the stress corrosion behavior of 4340 steels in humid environments which simulate missile storage conditions. e


Cursory review of mixed stress corrosion cracking data6 indicates that within the 200 to 250 ksi yield strength range, steels with KIscc parameter better than 4340 steel include: HP 9-4 in the 200 ksi region and D6AC in the 200 to 230 ksi range. Otherwise, 4340 steels appear to be as good or better than most steels within the broader 200 to 250 ksi range. Generally, stress corrosion cracking susceptibility decreases in these alloys at lower yield strength levels.

SUMMARY

1. Fracture toughness and stress corrosion data pertaining to 4340 steel are generally available in the technical literature.

2. Many factors affect the data, including test methodology, composition, melt practice, fabrication, heat treatment, and environments.

3. For applications in critical materiel, mechanical properties data must be obtained from material samples treated to incorporate characteristics closely resembling those of the finished product.

4. Data are needed to establish the stress corrosion behavior of 4340 steel to provide a sound basis for specifying missile storage conditions.

5. Higher fracture toughness and stress corrosion cracking resistance may be achieved through the.designation of 4340 steels with lower levels of yield strengths.

38. Private communication: R. G. Britton, C. Austin, U. S. Army Missile R&D Command, Huntsville, Alabama. September 14, 1977.

39. CARTER, C. S. The Effect of Silicon on the Stress Corrosion Resistance of Low-Alloy High-Strength Steels. The Boeing

Company, Research Report D6-23872, ARPA Contract NOO014-66-C-0365, March 1965.

14

and compounds used in the various steps of processing and packaging to insure the absence of any substance capable of promoting stress corrosion cracking, particularly during long terms of storage in a damp environment.


Experimental data is needed for the establishment of realistic criteria for environmental control during missile storage. It is common practice38 to assume that a maximum allowable relative humidity of 50% and a temperature range of 70 F to 85 F provide an adequate environment for the prevention of corrosion in metal parts. However, limited studies of 4340 steel with yield strengths of about 220 ksi indicate premature failure both in 90% relative humidity at 75 F39 and in 50% relative humidity environments at 90 F and 120 F. In the 50% relative humidity environment under a stress intensity 75% of KIc (KIc = ~52 ksi in.~), the 4340 steel in the 90 F surroundings fractured in 31 days and at 120 F fractured in 12 days.38 More information is needed to elucidate the stress corrosion behavior of 4340 steels in humid environments which simulate missile storage conditions.


Cursory review of mixed stress corrosion cracking data6 indicates that within the 200 to 250 ksi yield strength range, steels with KIscc parameter better than 4340 steel include: HP 9-4 in the 200 ksi region and D6AC in the 200 to 230 ksi range. Otherwise, 4340 steels appear to be as good or better than most steels within the broader 200 to 250 ksi range. Generally, stress corrosion cracking susceptibility decreases in these alloys at lower yield strength levels.

SUMMARY

1. Fracture toughness and stress corrosion data pertaining to 4340 steel are generally available in the technical literature.

2. Many factors affect the data, including test methodology, composition, melt practice, fabrication, heat treatment, and environments.

3. For applications in critical materiel, mechanical properties data must be obtained from material samples treated to incorporate characteristics closely resembling those of the finished product.

4. Data are needed to establish the stress corrosion behavior of 4340 steel to provide a sound basis for specifying missile storage conditions.

5. Higher fracture toughness and stress corrosion cracking resistance may be achieved through the ·designation of 4340 steels with lower levels of yield strengths.

38. Private communication: R. G. Britton, C. Austin, U. S. Army Missile R&D Command, Huntsville, Alabama. September 14,1977. 39. CARTER, C. S. The EYfect of Silicon on the Stress Corrosion Resistance of Low-Alloy High-Strength Steels. The Boeing

Company, Research Report D6-23872, ARPA Contract N00014.-66..('-0365, March 1965.

14

LITERATURE CITED

1. Fracture Toughness Testing and Its Applications ASTM STP 381, 1965. 2. Plane Strain Crack Toughness Testing oj High Strength Metallic Materzals. ASTM STP 410, 1966. 3. Review of Developments in Plane Strain Fracture Toughness Testing. ASTM STP 463, 1970. 4. ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials: E399-74. 5. SCULLY, J. C., ed. The Theory of Stress Corrosion Cracking in Alloys. NATO Science Committee, Research Evaluation

Conference, Brussels, W. S. Maney and Sons, Ltd., Leeds, England, 1971. 6. BROWN, B. F., ed. Stress Corrosion Cracking in High Strength Steel, Titanium, and Aluminum Alloys. U. S. Government

Printing Office, Stock No. 0851-0058, 1972. 7. Damage Tolerant Design Handbook, Metals and Ceramic Information Center, Air Force Materials Laboratory, MCIC-HB-Ol,

December 1972, 2nd Supplement, January 1975. 8. WONG, A. K., LEVY, M., and GRENIS, A. Stress Corrosion, Mecharucai Properties, and Acoustic Emission of 4340 Steel from

a Second-Stage Spartan Missile Motor Case. Army Materials and Mechanics Research Center, report in process. 9. KULA, E. B., and ANCTIL, A. A. Preliminary Metallurgical Evaluation of Proof Test Failure of Spartan Second-Stage Motor

Case. Army Materials and Mechanics Research Center, AMMRC SP 73-8, May 1973. 10. AMATEAU, M. I:., and STEIGERWALD, F. A. Cacrure Characteristics o.fStructur~l Metals. TRW, Bureau of Naval Weapons,

ER 5937, April 1964. 11. FITZGIBBON, D. P. Seqiannual Report on Pressure I’essel Deagn Criteria. Space Technology Laboratories, Inc., Air Force

Ballistic Missile Division, TR-59-0000-00714, June 1959. 12. STEIGERWALD, E. A. Plane Strain Fracture Toughness Data for Handbonl- Presentation. TRW, AFML-TR, June 1967

(AD 821626). 13. HAUSER, J. J., and WELLS, M. G. H. Inrlusions zn High-Strength Steris, Their Dependence on Processing Variables and Their

Effect on Engineering Properties. Crucible Steel Corp., AFML TR-68-222, August 1968. 14. KULA, E. B., and ANCTIL, A. A. Tempered Martensite Enrhrittlement and Fracture Toughness in SAE 4340 Steel. Journal of

Materials, JMLSA, v. 4, no. 4, December 1969, p. 817-841. 15. PARKER, E. R., and ZACKAY, V. F. Microstnrctural Features Affecting Fracture Toughness of High Strength Steels. Enginecr-

ing Fracture Mechanics, v. 7, no. 3, 1975, p. 311-375. 16. WOOD, W. E. Mechanisms of Enhanced Toughness in Martensitic Alloys. Oregon Graduate Center, Contract N00019-76-C-0149,

April 1977 (AD-A040 373/3GA). 17. HURLICH, A. Choice of Materials and Fabrication Techniques for Pressure Vesrels. Convair-Astronautics, Chapter 6 in Materials

for Missiles and Spacecraft, E. R. Parker, ed., McGraw-Hill Book Co., New York, 1963. 18. Private communication, Lockheed California Company, 19?6. 19. McEOWEN, L. J. Combining Strength and Fracture Torr&ncss. Metal Progress, March 1975, p. 52. 20. AMATEAU, M. F., and STEIGERWALD, I?. A. Fracture C’liaracteristics of Structural Metals. TRW, Bureau of Naval Weapons,

ER 5937-1, August 1964. 21. Problems in the Load-Carrying Application of High Strength Steels, DMIC Report 210, October 1964. 22. MOORE, T. D. Structural Alloys Handbook. Mechamcal PropertIes Data Center. Belfour Stulen, Inc., Traverse City, Michigan,

1976. 23. Stress Corrosion Testing. ASTM Special Technical PubllcJtion 425, 1966. 24. BENJAMIN, W. D., and STEIGERWALD. E. A. ~tllliror?nfcrztallv Induced Delayed Failures in Martensitic High-Strength Steels.

TRW, AFML TR 68-80, April 1968. 25. STEIGERWALD, E. A., and HANNA, G. L. Influence of Environment on Crack Propagation and Delayed Failures in High

Strength Steels. TRW, AFML RTD-TDR-63-4225, January 1964. 26. KORTOVICH, C. Corrosion Fatigue Behavior of 4340 and LXAC Steels Below Klscc TRW, Report ER 7717, April 1974. 27. STEIGERWALD, E. A., and BENJAMIN, W. D. Stress Corrosion Cracking: Mechanisms in Martensitic High Strength Steels.

TRW, AFML TR 67-98, April 1967. 28. TINER, N. A., and GILPIN, C. B. Microprocesses in Stress Corrosion 01 Martensitic Steels. Corrosion, v. 22, October 1966,

p. 271. 29. SANDOZ, G. The Effects of Allqving Elements on the, SU\C‘ ptzbilrt\* to Strtlss Corrosion Cracking of Martensitic Steels in Salt

Water. Met. Trans., v. 2, 1971, p. 1055. 30. CARTER, C. S. The E,ffect of Silicon on the Stress Corrosion Resistance 01 Low-Allov High-Strength Steels. Corrosion, v. 25,

no. 10, October 1969, p. 423. 31. PROCTER, R., and PAXTON, H. The L’ffect of Prior Austcnite Gain Size on the Stress Corrosion Susceptibility of AISI 4340

Steel. ASM Trans. Quart., v. 62, no. 4, December 1969, p. 989. 32. WEBSTER, D. Effect of Grain Refinerncnt on the Microstructure and Propc,rtics of 434OM Steel. Boeing Document D6-25220,

The Boeing Company, Seattle, Washington, .4pril 1970. 33. TANIGUCHI, N., and TROIANO, A. Stress Corrosiorl Crat~Xr~?,s ~)f 4340 Sfcels in Different Environments. Trans. Iron Steel

Inst.. Japan, v. 9, no. 4, 1969. 34. LENNOX, T. J., et al. Marine Corrosion Studies: Stress Corroston Crackr.l,s Deep Ocean Technology Cathodic Protection on

Fatigue. Naval Research Laboratory, NRL Memorandum Report 171 1, Mzy 1966. 35. SANDOZ, G., and NEWBEGIN, R. A Comparison of Laborator, Salr Water und F7owing Natural Seawater as an Environment

for Tests of Stress Corrosion Cracking Susceptibihty. Report ot NRL Progress, Naval Research Laboratory, May 1969. 36. SNAPE, E. Stress-Induced Failure of High Strength Ste& in b‘trvironments Containing Hydrogen Sulphide. Br. Corrosion J.,

v. 4, no. 5, September 1969, p. 252. 37. BUCCI, R., PARIS, P., LOUSHIN, L., and JOHNSON. I-1. I ~~a~‘turc Mcchanrcs Consideration of Hydrogen Sulfide Cracking in

High Strength Steels, Stress Analysis and Growth of Cracks. Proceedings of the 1971 National Symposium on Fracture Mechanics, Part 1, ASTM STP 513, Philadelphia, PA, 1972.

38. Private communication: R. G. Britton, C. Austin, U. S. Army MisslIe R&D Command, Huntsville, Alabama, September 14, 1977. 39. CARTER, C. S. The Effect of Silicon on the Stress Corrosion Resistance of Low-Alloy High-Strength Steels. The Boeing

Company, Research Report D6-23872, ARPA Contract NO00) 4-66C-0365, Mxc-h 1965.

LITERATURE CITED

1. Fracmre Toughness Testing and Its Applications ASTM STP 381, 1965. 1. Plane Strain Crack TOllghness Testing of High Strength 'Metallic lfateriuls. ASTM STP 410,1966, 3. Review of Developments in Plane Strain Fracll~re Toughness Testing. ASTM STP 463, 1970. 4. ASTM Test for Plane-Strain Fracture Toughne~~ of Metallic Materials: £399-74. 5. SCULLY, J. C, ed. The Theory of Stress Corrosion Cracking in Alloys. NATO Science Committee, Research Evaluation

Conference, Brussels, W. S. Maney and Sons, Ltd., Leeds, England, 1971. 6. BROWN, B. F., ed. Stress Corrosion Cracking in High Strength Steel, 1Ytoflium, and Aluminum Alloys. U. S. Government

Printing Office, Stock No. 0851{)058, 1972. 7. Damage Tolerant Design Handbook, Metal~ and CeramIC Information Ccnter, Air force Materials Laboratory, MCIC-HB-Ol.

December 1972, 2nd Supplement, January 1975. 8. WONG, A. K., LEVY, M., and GRENIS, A. Stress Com)sion, MedulIlicui Pr"pertj('~, and Acoustic Emission of 4340 Steel from

a Second-Stage S{JfJrtan Missile Motor Case Army Matcrials and Mecnanics Research Center, report in process. 9. KULA, E. B., and ANCTIL, A. A. Preliminary Metallurgical Evaluation of Proof Test Failure of Spartan Second-Stage Motor

Case. Army Materials and Mechanics Research Cl'nter. AMMRC SP 73-8, May 1973. 10. AMATEAU, M, F., and STEIGERWALD, F.. A. Fracrur;; Characteristics of Structurr.l Metals. TRW, Bureau of Naval Weapons,

ER 5937, April 1964. II. FITZGIBBON, D. P. Semiannual Report or. PressH."c Vi'ssei De,nln Criteria. Space Technology Laboratories, Inc., Air Force

Ballistic Missile Division, TR-59..o000-00714, June 1959. 12. STEIGERWALD, E. A. Plane Strain Fracture Tou¥hne.\'~ Dato for Handboo! Presentation. TRW, AFML-TR, June 1967

~AD 821626). 13. HAUSER, J. J., and WELLS, M. G. H. inclusions In Hi!(lhS'rrrllf(th Steels, Their Dependence on Processing Variables and Their

njfeet on Engineering Properties. Crucible Steel Corp., AFML TR-68-222, Augusi 1968. 14. KULA, E. B., and ANCTIL, A. A. Tempered Marunsite EmbriUlement and Fracture Toughness in SAE 4340 Steel. Journal of

Materials, JMLSA, v. 4, no. 4, December 1969, p. 817-841. 15. PARKER, E. R., and ZACKAY, V. F. Microstructurol Fcatures A/fecting Fracture Toughness of High Strength Steels. Engineer

ing Fracture Mechanics, v. 7, no. 3, 1975. p. 371-375. 16. WOOD, w. E. Mechanisms of Enhonced Toughness in Martellsiti" AllOY-I. Oregon Graduate Center, Contract N00019-76-C-0149,

April 1977 (AD-A040 373/3GA). 17. IIURLICH, A. Choice of Materials ond fabrication Techniqw's for Pressllre VeHels. Convair-Astronautics, O1apter 6 in Materials

for Missiles and Spacecraft, E. R, Parker, cd., McGraw-Hill Book Co., New York, 1963. 18. Private communication, lockheed California Compllny, 1976. 19. McEOWEN, L. J. Combining Strenf(th and Fracture Toughness. Metal Progre$s, March 1975. p. 52. 20. AMATEAU, M. F .. and STEIGERWALD, E. A. FrocTUrc Choracteri~·tics of Stmctural Metals. TRW, Bureau of Naval Weapons,

ER 5937-}, August 19M. 21. Problems in the Load-Carrying Application of JIigh Strcn!(fh Steels. DMIC Report 210, October 1964. 22. MOORE, T. D. Structural Alloys Handbook. Mech3nica'! Properties Data Center, BeHour Stulen, Inc., Traverse City, Michigan,

1976. 23. Stress Corrosion Testing. ASTM Special Technical Publication 425, 1966. 24. BENJAMIN. W. D., and STEIGERWALD, E. A, FIIl'ironIl!Clltalh' Induced Dc/aycd }'ailures in Martensitic High-Strength Steels.

TRW, AFML TR 68-80, April 1968. 25. STEIGERWALD, E. A., and HANNA, G. L. Influence 0/ Em'ironmcnt all Crack Propagation and Delayed Fai/Me! in High

Strength Steels, TRW, AFML RTD-TDR--63-4225, January 1964. 26. KORTOVICH, C. Corrosion FatiKfle Beltal'ior of 4340 alld D6.4C Steels Below Klscl:' TRW, Report ER 7717, April 1974. 27. STEIGERWALD, E. A., and BENJAMIN, W. D. Stress Corrosion Cracking Mechanisms in Martensitie High Strength Steels.

TRW, AFML TR 67-98, April 1967, 28, TINER, N_ A., and GILPIN, C. B. Microprocesses ill Srrc.u Corrosion 0/ Martellsitic Steels. Corrosion, v, 22, October 1966,

p.271. 29. SANDOZ, G. Thc FIfects of Allo.ving t:lell1ell/s all lire .'lUll", ptihilitl' tr) Stress Corrosion Crackin, of Martensitic Steels in Solt

Water. MeL Trans., v. 2, 1971, p. 1055. 30. CARTER, C. S. The Effect of Silicon on the Stress Corrosion RCIislollce o/l,ow-A!1oy Ih);h-Strenf(fh Steels. Corrosion, v. 25,

no, 10, October 1969, p. 423. 31. PROCTER, R., and PAXTON, H. The E:Ifr.:ct of Prior Austenilc Grain Size Ofl thc Stress Corrosion Susceptibility of A lSI 4340

Steel. ASM Trans. Quart., v. 62, no, 4, December 1969. p. 989

32. WEBSTER, D. EYfect of Crain Refinement on rhe ,~ficroHr(U'turc and Prop"rlies oj" 4340M Steel. Boein): Document D6-25220, The Boeing Company, Seattle, Washington, April 197().

33. TANIGUCHI, N., and TROIANO, A. Stress CorrosiOI1 Cra('king o} 434() Steds ill [)ijfcrclll Em·ironments. Trans. Iron Steel Inst.. Japan, v. 9, no, 4, \969.

34. LENNOX, T. J" et aL Marine Corrosion S!lIdie,,: Slr('ss ('{lrrnsiOIl Crackl.I,~ [)('{'P Ocean Technology Cathodic Protection Oil

Fatigue. Naval Research Laboratory, NRL Memorandum R~por\ 1711. M~y 1966. 35. SANDOZ, G., and NFWBEGIN, R. A Comparisol! of Labnratorr Salr Waler IInJ Rm.AIlr. .. 'lfaltira[ Seawater as an Em'ironment

for Tests of Stress Corrosion Crackillg Susccptibillty. Report III NRL PHl)!,fess. Naval Research Laboratory, May 1969. 36. SNAPE, E. Stress-Induced Failure of lfigh Strcngth Sle!'/s in Frll'ironmCllts ermrailling Hvdrogen Sulphide. fir. Corrosion 1.,

v_ 4, no. 5, September 1969, p. 252. 37. BUCCI, R., PARIS, P., LOUSHIN, L., and JOHNSON. H. fmctwc .I,1cchallin Consideration of HvdTOgen Sulfide Crockillg in

High Strength Steels, Stress Analysis and Growth of Cracks. Proceedings of 'he 1971 National Symposium on Fracture Mechanics. Part I, ASTM STP 513, Philadelphia, PA, 1972,

38. Private communication: R. G, Britton, c:. Au~tin, IT. S. Army Missile R&D Command, Hunt~ville, Alabama, September 14, 1977. 39. CARTER, C. S. Thc f.JfeCf of Silicon on the Stress Corrmion Resistonce of [ow·Alloy Hi/?h-Strength Steels. The Boeing

Company, Research Report D6-23872, ARPA (on!TllC! NUOOI4-66 .. C{l365, March 1965.

1::)

4340 fracture toughness.pdf

Documents

Transcript of 4340 fracture toughness.pdf