S. NAVAL AIR - Defense Technical Information Centerdtic.mil/dtic/tr/fulltext/u2/600727.pdf · o U. S. NAVAL AIR ENGINEERING CENTER ... (IC) 4340 Steel at the ... on the properties

o U. S. NAVAL AIR ENGINEERING CENTERI , P H I L A D E L P ff U A o'P E N N S 'i L V A N I A

AERONAUTICAL MATERIAIS LABORATORY

REPORT NO. NAEC-AML-1947 y DATE 21 May 1964

EVALUATION OF AIR MELTED AND VACUUM MELTEDAISI 4340 STEEL

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NAVAL ATrA ENGINEERING CENTERPHILADELPHIA 12, PENNSYLVANIA

AERONAUTICAL MATERIALS LABORATORY

REPORT NO. NAEC-AML-1947 DATE 21 May 1964


PROBIEM ASSIGNMENT NO. 10-23 UNDER BUREAU OF NAVAL

WEAPONS WEPTASK RRMA 02 018/200 1/R007 05 01..

PREPARED BY: .h..t .- .eWILLIAM H. GOIDING (TPROJECT ENGINEER

APPROVED BY:

WALTERPHYSICAL METALUJRGY BRANCH

7F. S. WILLIAMS, SUPERINTENDENTMETALLURGICAL DIVISION

Qualified requ,3sturs m- y obtain copies of thisr report direct from DDO

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REPORT NO. NAF-AML-1947

TABLE OF CONTENTS

PAGE

ABSTRACT 3INTRODUCTION 4EXPERIMENTAL PROCEDURES 4 to 9RESULTS 9 to 13ANALYSIS OF RESULTS 13 to 17CONCLUSIONS 17, 18RECOMMENDATIONS 18

LIST OF TABES AND PLATES

TABlES

1 - Chemical Composition2 - Jominy Hardness Traverses (Rockwell "C")3 - Unnotched Tensile Properties of Transverse and Longitudinal Tensile

Specimens Heat Treated to the 260-280 ksi Strength level4 - Unnotched Tensile Properties of Transverse and Longitudinal Tensile

Specimens Heat Treated to the 200-220 ksi Strength level5 - Notched Transverse Tensile Strength6 - Impact Test Results for V-Notch Charpy Specimens at the 260-280 ksi

Strength Level7 - Impact Test Results for V-Notch Charpy Specimens at the 200-220 ksi

Strength Level8 - Comparison of Tensile Strength for Plated and Unplated Notched

Transverse Tensile Specimens9 - Fatigue Data for Notched Specimens of AM (1c) 4340 Steel at the

High and Low Strength Levels10 - Fatigue Data for Smooth Specimens of AM (IC) 4340 Steel at the

High and Low Strength levels11 Fatigue Data for Notched Specimens of VAR (2A) 4340 Steel at the

High and low Strength levels12 Fatigue Data for Smooth Specimens of VAR (2A) 4340 Steel at the

High and Low Strength Levels13 - Fatigue Data for Notched Specimens of VIM (2D) 4340 Steel at the

High and Low Strength levels14 - Fatigue Data for Smooth Specimens of VIM (2D) 4340 Steel at the

High and Low Strength levels15 - Fatigue Data for Notched Specimens of VIM (3D) 4340 Steel at the

High and Low Strength Levels16 - Fatigue Data for Smooth Specimens of VIM (3D) 4340 Steel at the

High and Low Strength Levels

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REPORT NO. NAEC-AML-1947 1TABLES (Continued)

17 - Fatigue Data for Notched Specimens of VIR (2E) 4340 Steel at theHigh and Low Strength Levels

18 - Fatigue Data for Smooth Specimens of VIR (2E) 4340 Steel at the VHigh and Low Strength levels

PLATES

1 - Heat Flow Chart2 - Location of Transverse Test Specimens Removed From 4 in. Sq.

Billets of Air and Vacuum Melted 4340 Steel3 - Notched Tensile and Fatigue Specimens Used for Tests4 - Macroetched Top and Bottom Sections of AM (1C) 4340 Steel5 - Macroetched Top and Bottom Sections of VAR (2A) 4340 Steel6 - Macroetched Top and Bottom Sections of VIM (2D) 4340 Steel7 - Macroetched Top and Bottom Sections of VIM (3D) 4340 Steel8 - Macroetched Top and Bottom sections of V3 (aE) 4340 Steel9 - Macroetched Top and Bottom Sections of VIR (2E) 4340 Steel

10 - Typical Inclusion Type Stringers Present in AM and VAR Materials11 - Microstructures Typical of AM, VAR, VIM, and VIE Materials12 - Typical Microstructures of Material Heat Treated to 200-220 ksi

and to 260-280 ksi Strength Ranges13 - Tensile Strength of Vacuum and Air Melted 4340 Steel Heat Treated

to 26o-28o ksi14 - Tensile Strength of Vacuum and Air Melted 4340 Steel Heat Treated

to 200-220 ksi15 - R.A. and Elongation Values for Air and Vacuum Melted 4340 Steel I16 - Results of V-Notch Charpy Impact Tests

17 - Temperature vs Impact Strength 200-220 ksi Strength level18 - Temperature vs Impac* Strength 260-280 ksi Strength Level19 - Results of Static Fatigue, Unplated and Plated Notched Tensile

Strength Tests20 - Static Fatigue Curves for Vacuum and Air Melted 4340 Steel Heat

Treated to 260-280 ksi21 - Fatigue Limit Curves for Air and Vacuum Melted 4340 Notched Steel

Specimens Heat Treated to the 200-220 ksi Strength Range22 - Fatigue Limit Curves for Air and Vacuum Melted 4340 Smooth Steel

Specimens Heat Treated to the 200-220 ksi Strength Range23 - Fatigue Limit Curves for Air and Vacuum Melted 4340 Notched Steel

Specimens Heat Treated to the 260-280 ksi Strength Range24 - Fatigue Limit Curves for Air and Vacuum Melted 4340 Smooth Steel

Specimens Heat Treated to the 260-280 ksi Strength Range

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I REPORT NO. NAEC-AML-1947

ABSTRACTI

Thi report compares the mechanical properties of air-melted versusthree different types of vacuum-melted AISI 4340 steel.

Cleanliness, hardenability, tensile, impact, fatigue properties andfracture toughness characteristics are compared at two strength levels(200-220 ksi and 260-280 ksi). Particular emphasis was placed on trans-verse mechanical properties. Susceptibilities to hydrogen embritclementof the variously different processed materials are also compared.

In general, the data indicate that vacuum melting offers a signifi-cant improvement in mechanical properties over air-melted steel in thetransverse grain direction. In particular, the fracture toughness, impactstrength, fatigue, ductility and resistance to hydrogen embrittlementare significantly enhanced by the vacuum melting process. ( )

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1 , , / ,- ,-,, --7, ' A'z, ,,~.-, ' v, J e . . .,' < d " ,r",,. _. . . , ..

REPORT NO. NAEC-AML-1947

I. INTRODUCTION

A. Background

1. The current concern for very clean, high strength aircraftquality steels has influenced increased production by vacuum meltingtechniques. As a result, vacuum melted steels have entered the steelmarket at substantial increases in price and with purported improvementsin mechanical properties. In view -f this development, the NavalWeapons Plant began an investigation to determine whether the increasedcost of vacuum melted steel is accompanied by a commensurate improvementin mechanical properties.

2. In 1961, following the disestablishment of the Naval WeaponsPlant, the problem assignment was transferred to the Aeronautical Materialslaboratory for completion. Prior to this date, however, a test programof broad scope was initiated by the Naval Weapons Plant. By the timethe problem assignment was transferred to the Aeronautical Materialslaboratory, material shortages and economic considerations necessitateda revision of the original test program. In the revision, emphasis wasshifted from the use of mid-radius longitudinal test specimens to center-of-the-billet transverse type. Consistent with these requirements, thisreport presents the results of transverse tensile, impact, fracturetoughness, fatigue and hydrogen embrittlement studies conducted by theAeronautical Materials laboratory and supplemented by the informationobtained from the U. S. Naval Weapons Plant Report No. Ser. 14J4-722.2and from the literature.

B. Object

To demonstrate the effects of various vacuum melting techniqueson the properties of the 4340 steel and to ascertain the extent of thechanges in the properties affected as compared with the air-melted air-craft quality steel bar stock.

II. EXRIMENTAL PROCEDURE

A. Material

1. Processing History

Three special heats (No. 44085, 05076, and 05233) were pre-pared for the Naval Weapons Plant by the Crucible Steel Company ofAmerica. From these heats, four groups of billets were finished rolledinto 4 inch square cross-sections and cut into 8-foot lengths. Eachbatch having the same pedigree was identified by either of the legendsAM, VAR, VIM, or VIRo These designations are described as follows:

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IIREPORT NO. NAEC-AML-1947I

AM - Electric furnace air melt heat no. 44085

VAR - Part of heat no. 44085 vacuum remelted asconsumable electrodes

VIM - Vacuum induction melted heat nos. 05076 and 05233

VIR - Part of VIM heats 05076 and 05233 vacuum remeltedas consumable electrodes

A flow chart showing the processing history of the test materials ispresented in Plate 1.

2. Chemical Composition

The chemical ccmpositions were determined of each batch of

material by conventional wet analysis, In addition, a gas analysis wasconducted on samples of each group of materials. This included oxygenand nitrogen determinations by vacuum fusion analysis and hydrogendeterminations by the hot extraction method.

3. Cleauliness

The internal cleanliness of the different materials was de-termined on the basis of:

a. Sulphur Distributionb. Inclusion Content - Macroscopicc. Inclusion Content - Microscopic

a. Inclusion Content

(1) Sulphur Distribution

Sulphur prints were made from cross-sections of thedifferent materials using conventional techniques.

(2) Macroscopic Method

Both the ASTM specification E45-51 and the Allisonstep-down methods were used to determine the inclusion ratings of thevarious steel bars macroscopically.

(3) Microscopic Method

Each batch of steel was tested in accordance withASTM Specification E45-51 to determine the average JK inclusion ratings.

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R~EPORT NO. NAEC-AML-1947

4. Microstructure

Metallographic specimens were removed from the center-of-the-bar test specimens of the different materials and prepared formicroscopic examination. Photomicrographs were prepared of typicalmicrostructures representing the upper and lower strength levels.

5. Heat Treatment

All tests were conducted with specimens heat treated to twostrength levels (200-220 ksi and 260-280 ksi). These strength levelswere obtained with a coimmon austenitizing temperature of 1550*F with anoil quench followed by a 775*F or 400Fr tempering temperature.

6. Hardenability

Hardenability determinations were made of the differentmaterials using standard type 2-A test blanks in accordance with Method711.1 of Federal Test Method Standard No. 151.

B. Tensile

1. Smooth Specimens

From each batch of steel a minimum of six standard .505longitudinal mid-radius tensile blanks were removed. In addition tot~hese specimens, an equal number of center-of-the-bar transverse .505"terasile blanks were prepared. A sketch showing the method of samplingthe test bars is presented in Plate 2. Half of the longitudinal andone half of the transverse specimens were heat treated to the 260-280ksi strength range. The remtaining specimens in each group were heattreated to the 200-220 ksi strength level. After heat treatment, allspecimens were finished machined and tested.

2. Notched Specimens

From each bpt.i of steel, six notched transverse center-of-the-bar tensile specimens were prepared. A sketch of the test specimenshowing the notch configuration is presented in Plate 3. Half of thesespecimens were heat treated to the upper strength level and the remainderto the lower strength level.

The notched-unnotched tensile ratios were determined foreach material. The material was considered to be notch sensitive whenthe ratio was less than 1.0.

C. mpact

Thirty transverse grain direction standard V-notch Charpy impactspecimens were prepared from near-center locations of each 4 inch square

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1billet of AM, VAR, VIR, and two heats of VIM steel. Material shortagesprevented tests with both heats of VIR material. One half of thespecimens were heat treated to the 260-280 ksi strength range and theremainder to the 200-220 ksi strength level. Specimens at both strengthlevels were tested in triplicate at room temperature, O'F, -400F, -100°Fand -200 0F. All temperatures below room temperature, with the exceptionof -200*F, were obtained with an acetone-dry ice bath. The -200OF temp-erature was obtained in a controlled cold box using liquid nitrogen asthe refrigerant.

D. Fracture Toughness

Only the VAR material was furnished in sheet form for fracturetoughness tests. However, fracture toughness data on identical VAR, VIR,AM and VIM material was made available by the Crucible Steel Companyof America. This latter data is included in this report.

All fracture toughness data reported was obtained on NRL centernotch type specimens. All specimens were pre-cracked by fatigue priorto testing. The fracture toughness parameter K. was obtained as a func-tion of critical crack length.

E. Hyd2rogen Embrittlement

Ninety-six tensile specimens of the type shown in Plate 2 wererough machined and heat treated to 260-280 ksi strength range prior tofinish machining. Material shortages dictated that these transversespecimens be extracted from near-center-of-the-bar locations rather thanfrom the exact center as originally planned. The 96 test specimens weredivided into six groups of 16 specimens bearing the following processinghistories:

2A iC 2D 3D IE 2EVAR AM VIM VIM VIR VIR

Ht. 44085 Ht. 44085 Ht. 05076 Ht. 05233 Ht. 05233 Ht. 05076

The above materials can be identified by referring to paragraph II.A.l.and the flow chart shown in Plate I. From each of these groups, threesamples were tensile tested as heat treated. The remaining specimenswere cyanide cadmium plated to introduce hydrogen into the surface.Three of the plated specimens from each of the six geoups were tensiletested to compare with the unplated three. All of the remaining platedspecimens were used to establish static fatigue limit curves. Thesecurves were obtained by plotting static load versus time-to-failure.The load was varied until a 500-hour limit was sustained.

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F. Fatigue

Forty rotating beam type fatigue blanks were extracted fromnear-center locations of the transverse grain direction of each group

of 4 inch square billets of AM, VAR, VIR, and each of the two heats ofVIM material. Material shortages did not permit tests with both heatsof VIR steel. Half of each of these groups was used for notched typefatigue specimens shown in Plate 2, while the other half was used forthe smooth type test specimens. Each group selected for unnotched ornotched specimen blanks was again divided into two equal groups forheat treatment to either the 200-220 ksi strength level or to the 260-280 ksi strength range. After heat treatment, the 200 test blanks werefinish machined and tested to establish fatigue limit curves.

III. RESULES

A. Material

1. Chemical Composition

The results of chemical analyses are tabulated in Table 1.Also -shown in Table 1 are the gas content determinations for hydrogen,oxygen and nitrogen. As indicated, all of the test material meets thechemical composition requirements of AMS Specification 6415E for 4340steel. Results show that the sulphur and phosphorus contents are muchlower in the vacuum melted steels than in the air melted steels. Thiscannot be attributed to the vacuum melting process, but instead, it

indicates that the raw materials used in making the vacuum melted steel

contained less sulphur and phosphorus. As would be expected, the vacuumprocessed materials were significantly lower in gas content than the airmelted material.

2. Cleanliness

a. Sulphur Distribution

Examination of sulphur prints and macroetched specimens(see Plates 4 to 9) indicate that the VIR steel is the cleanest material.

The VIM steel was next in order of cleanliness followed by the VAR steel.

The least clean, by comparison, was the AM material.

Normally, the VAR steel would be expected to be cleanerthan the VIM steel. - reversal of this order of cleanliness between

these two steels is bt .ved to be attributable to the use of rawmaterials of higher p. Lty in making the VIM steel.

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REPORT NO. NAEc-AML-1947

~b. Macrosco9pic Method

The AS'.1M ncroscopi! methoe E45-51 indicatea that theAM; VAR, and VIR specim.b.c were essentially free of inclusions. However,iin two Induction mel r ed (Vf,,-' 5: .ecimens., a total of three inclusionswere observed thv.ough tl:,- area iset..e d.

In one s*. . 'rin zclusions ./32-inch and 1/16-inch in

length were observed, while in ;he second specimen, one inclusion 1/32-inch in ?.ngt', -Tas noted. Since the ASTM specification gives weightedvalues on.,y to those ir. _,-qons which are over 1/16-inch in length, all

bers wo,_J ,-e considers' , very clean.

e. Allinon 12tep-Down Meta±od

The Leyi~ o of ,-clusions as computed by the Allisonstep-dotn r . od is i. Cc b',-',':

!, tee] Frequency of Inclusions

AM 0.0081VAR 0VIM 0.0072V 0.0027

The only engineering material specification availablefrom the Allison Division of General Motors Corporation is one forspecial high quality SAE 9310 steel. The maximum frequency rating per-mitte. in this specification is 0.50. Again, by comparison, all bars

• .be classified as very clean.

d. Microscopic Method

Results of tests conducted in accordance with ASTMSpecification E45-51 to determine the average JK inclusion rating forsections removed from mid-radius billet locations of the differents;eels are tabulated below:

Steel Sulfide Alumina Silicate Oxide Total

AM 2.6 1.0 2.1 1.0 6.7VAR 1.4 0.2 0.3 1.4 3.3VIM 0.5 0.1 0.1 1.2 1.9VIR 0.5 0 0.2 0.9 1.6

All of the above JK ratings represent thin type inclusions with thesmaller number indicating the cleaner steel. This method confirms theorder of cleanliness determined macroscopically.

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3. Microstructure

Although spetimens removed from mid-radius locations of thevarious billets were relatively free of non-metallic inclusions, micro-structural examination of center-of-the-billet samples of AM and VARmaterials disclosed the presencue of inclusion stringers of the typeshown in Plate 10. in addition, the AM, VAR, and VLM material exhibitedmicrostructural banding of the type shown in Fig. 1 of Plate 11. TheVIR material was singularly free of both stringer type inclusions andbanding. (See Fig. 2 of Plate 11). After heFat treatment to eitherstrength level, all material exhibited tempered martensitic structurestypical of AISI 4340 steel. Photomicrographs showing typical micro-structures are presented in Plate 12.

4. Hardenability

The Jominy hardenability data is tabulated in Table 2. Asindicated, all test bars complied with the hardenability requirementsof AMS Specification 6415E for 4340 steel which requires Rockwell "C"50 at 20 sixteenths from the quenched end.

B. Tensile Properties

1. Smooth Specimeus

a. The smooth bar tensile properties of the various testmaterials are tabulated in Tables 3 and 4 and are shown graphiically inPlates 13, 14, and 15.

b. longitudinal

A comparison of the longitudinal tensile properties ofthe AM and various vacuum melted materials indicate that the materialsare undistinguishable with respect to longitudinal tensile propertiesat both high and low strength levels.

c. _Nitudinal vs Transverse Tensile Properties

(1) lower Strength Level (200-220 ksi)

Both longitudinal and transverse tensile specimensexhibit similar tensile strengths at the lower strength level. Withrespect to tensile ductility, howe,er, the reduction of area and elonga-tion values for transverse specimens were significantly lower than forlongitudinal specimens of similar processing history.

(2) Higher Strength level (260-280 ksi)

At the higher strength level, the AM and VAR trans-verse tensile properties were markedly inferior to both VIM and VIR

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REPORT NO. NAEc-AML-1947

II

transverse and to AM and VAR longitudinal tensile properties. Furthercomparison reveals that the VIM and VIR transverse tensile properties

II

closely approach the tensile test results obtained with VIM and VIRlongitudinal test specimens.

d. Transverse

In 'oth strength and ductility, the tensile propertiesi rof VIM and VIE transverse materials at the higher strength level were

superior to the AM and VAR material. At the lover strength level, however, the superior tensile properties of VIM and VIR steel over AM andVAR steel is reflected in reduction of area and elongation propertiesonly.

2. Notched Specimens

Notched transverse tensile strength was compared with un-notched transverse strength at both strength levels. The resultsindicated that both air and vacuum melted material were notch sensitiveat the higher strength level with the AM and VAR material possessing

the greater notch sensitivity. At the lower strength level, the AM andVAR material only was notch sensitive. (See Table 5 and Plates 13 and

C. Impact Properties

1. The results of Charpy V-notch impact tests are presentedin tabular form in Tables 6 and 7 and shown graphically in Pletes 16, 17and 18. In general, the test results indicatethat for transverse graindirection, the cleaner the steel, the higher the impact resistance atall test temperatures. Specifically, the VIR material was slightlysuperior to VIM and both VIM and VIR material were markedly superiorto AM and VAR material. AM material exhibited the lowest impact resis-tance of all four materials.

2. It should be noted that the impact values obtained for thehigher tempering temperature (775F) were lower at all test temperatur sthan the values obtained for the lower tempering temperature. Thisfact indicates that the 775F temperin temperature is within the temperbrittle range.

D. Fracture Toughness

Fracture toughness data obtained on the VAR material together

with that furnished by the Crucible Steel Company is tabulated below

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I fact indicate tha te 75*.tmpri*,tmpraur iswthnth eme


AM1 VAR I VAR 2 VIM1 VIR

Kc Kc Kc Kc Kc*1000 psi n. 1000 psi i. 1000 psi . 1000 pSI 4'n. 1000 psi ,.

8o 75.1 115 205 197

*Based on percent shear; all other values based on

critical crack length.

kCrucible Steel Company2Aeronautical Materials Laboratory

As indicated above, with the exception of the VAR material,vacuum melting results in a marked improvement in fracture toughness.The relatively poor performance of the VAR material in the fracturetoughness tests is consistent with its performance in other tests.

E. Hydrogen Embrittlement

1. Results of hydrogen embrittlement tests are presented inTable 8 and are also shown graphically in Plates 19 and 20. As indicatedthe VIR and VIM material was significantly less sensitive to the embritt-ling effects associated with hydrogen adsorption than was the AM andVAR material.

2. It is to be noted that the unplated O.1(O inch diameter notchedtransverse tensile specimens extracted from near-cenxuer-of-the-bar loca-tions (see Plate 2) exhibited significantly less notch sensitivity thandid 0.505 inch diameter notched transverse tensile test specimens extractedfrom the exact center-of-the-billet lccations. An explanation for thisbehavior is offered in the Analysis of Results.

F. Fatigue Properties

The results of fatigue tests are presented in tabular form inTables 9 to 18 and are shown graphically in Plates 21 to 24.

In general, the data indicate that the fatigue limits of the Jvaious test materials is related to the degree of cleanliness; thecleanest material exhibiting the highest fatigue limit in both thenotched and unnotched conditions at both strength levels.

Somewhat erratic behavior was observed in tests of the VARmaterial. Similarly, the VIM-2D and VIM-3D materials exhibited anomalousbehavior. Failures outside the notched gage sections were obtained withthe VIM-2D material, while the unnotched VIM-3D material exhibited anabnormally low fatigue limit. The erratic and anomalous behavior ofthese materials is discussed in the Analysis of Results.

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REPOPT NO. NAEC-AML-1947

IV. ANAIYSIS OF BESULTS

A. Material

The major objectives of vacuum melting techniques are as follows:

1. To lower gas content;2. To control composition more closely;

3. To improve -leanliness;4. To o" '. aigot .tructures free from center porosity

and segregption

The degree to wh: ,- these were accomplished in this study is examined.As a natural consequence of the attainment of the above objectives, cer-tain mechanical properties should be proportionately improved. Thedegree to which this was obtained wi.l also be examined.

The first objective was achieved with the test materials reportedherein. The oxygen content diminishes from 0.006 ppm to 0.0003 ppn andthe nitrogen content from 0.0082 ppm to 0.0005 ppm for the AM and VIRmaterial, respectively. The hydrogen contents for the AM and VAR mat-erials are not significantly different. In this respect, it has beenpointed out that the VAR material was not representative of the clean-liness of material processed by this method. This feature may account

- for the essentially unchanged hydrogen content of the VAR material ascompared with the AM material from which it was processed.

The hydrogen content of the VIM material is not significantlydifferent from the AM or VAR material. However, in this case, it shouldbe noted that this comparison is not valid since the VIM heat was madefrom different material. The VIR material, which is a remelt of the VIM

I material, does however show a reduced hydrogen content.

Since the next three objectives are interrelated, they are dis-cussed together. Original plans called for very close control of theIcomposition variables, but it was learned after receipt of l.the testmaterial that raw materials of higher purity were used to produce theVIM and VIR heats. Nominally, all materials, with the exception of thelow phosphorus and sulphur content for the VIM and VIR heats, were in-distinguishable with respect to chemical composition. However, the effectof the use of raw materials of variant purity became apparent aftermacroscopic examination unexpectedly rated VAR material second to VIMf steel with respect to material cleanliness. Subsequent microscopicinspection before and after heat treatment revealed evidence of micro-structural banding in all but the VIR material. In addition to banding,AM and VAR material possessed stringer type inclusions. Although some-what reduced during remelting by vacuum arc techniques, the stringerswere still present in the VAR remelt of the AM mterial. No stringers

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P ?ORT NO. NAEC-AML-1947

were found in the VIM or VIR material. This observation was a reflectionof the use of higher purity raw materials to produce the VIM and VIRmaterials. The presence of inclusion type stringers and banding undoubt-edly contributed to the erratic and unfavorable performances of AM andVAR material in the mechanical tests. This conclusion was concurred inby the Crucible Steel Company of America, the supplier of the material.On the other hand, the minimal presence of banding-promoting elemeitsas a result of the use of higher purity raw materials had doubtlesslycontributed to the improved mechanical properties performance of VIMand VIR material. The presence of banding in VIM material and its'absence in VIR material is attributable to melting practices.

As was pointed out previously, material shortages prevented

carrying oat all tests from the same locations in the test bars. Con-sequently, the test specimens were extracted from those locations thatwould reflect the poorest properties of the material. In all cases,however, for a given test, all specimens were extracted from the samelocation in each test bar. Therefore, all reported data must be viewedin light of the following:

1. Raw materials used to prepare all test materials were notidentical;

2. Because of limited test material, all specimens were notextracted from the same locations.

B. Mechanical Properties

Although some anomalies were encountered in certain specificmechanical properties tests of the various test materials, in general,the vacuum melting process offers a marked imprcvement in the transversegrain direction for tensile ductility, notched tensile strength, impactstrength, fracture toughness, fatigue limit and resistance to hydrogenembrittlement. More specifically, the vacuum induction remelt (VI)material exhibited an approximate two fold increase in fracture toughness,notched tensile strength and impact resistance over air melted (AM)material. Similarly, transverse tensile ductility was increased 10%and 25%, respectively for elongation and reduction in area measurements.The fatigue limit was increased by a factor of one and a half.

It should be noted, however, that steel with the cleanliness

and microstructure necessary to effect the improvement in properties

noted above was obtained with the use of high purity raw materials incombination with vacuum melting techniques. Vacuum melting alone'cannotbe expected to produce material that is ultra clean if the raw materialsused to process a heat are of sub-standard purity. It cannot be over- J"emphasized, that while vacuum melting significantly reduces the contentof certain gases, it will not significantly lower the inclusion content.In support of this, the VIR material, which was processed from high

15


purity raw materials and subsequently vacuum arc remelted, exhibitedmechanical properties superior to the VAR material which was a vacuumarc remelt of a parent heat made from lower purity raw materials.Summarizing, if the vacuum melting process is to produce materials5 which exhibit superior mechanical properties, then each ste-? in theprepgration of a heat must be carefully oriented toward the prod actionof an ultra clean material.

j The anomalous behavior referred to above, was in each case,found to be directly related to cleanliness and microstructural homo-geneity. For instance, in all but the air melted material, the ultimatestrength of the 0.160 inch diameter unplated notched (hydrogen embrittle-ment tensile type) specimens possessed notched to unnotched strengthratios exceeding unity. In contrast, all of the 0.505 inch diameternotched tensile samples extracted from the exact center-of-the-billetlocations exhibited lower notch tensile ratios than did these 0.160 inchnear-center-of-the-billet (see Plate 2) specimens. The detrimentaleffects of the decreased soundness associated with the center-of-the-billet specimens would account for their lower notched strength.

With respect to the fatigue tests, the unusual behavior of some

of these specimens was also determined to be related to material clean-liness. The cases in point were the VAR, VIM-3D and VIM-2D steels.The VAR and VIM-3D materials exhibited erratic behavior and relativelypoor fatigue properties, whereas several test specimens of the VIM-2Dmaterial failed through the filleted area 4djacent to the shouldersection (see Plate 3) rather than through the notched gage section.Microscopic examination of sections removed from the VAR test specimensin the area of failure revealed a banded structure with a dispersionof fine non-metallic stringers. Sections removed from the parent AMmaterial exhibited a similar microstructure with somewhat thicker in-clusion type stringers. (See Plate 10.) This was the only significantdifference noted between the two materials. Undoubtedly, this condi-tion contributed to the cause of the erratic performance of the AM and

VAR material in fatigue and other tests. Although the inclusion stringerswere absent in the VIM-3D material, the persistence of a banded structurein this material is suspected of causing the relatively poor fatigueproperties.

In the attempt to understand the cause of the premature failureof the VIM-2D notched specimens, the broken samples were sectionedthrough the failed filleted area adjacent to the shoulder section,mounted, and inspected metallographically. Throughout the sectionedarea fine, scattered inclusions were noted. Reexamination of the macro-etched bottom section of the VIM-2D billet from which these specimenswere extracted (see Plate 6) also revealed evidence of fine inclusiontype pits thrcughout the areas which coincided with the filleted areaadjacent to the shoulder section of the extracted fatigue specimens.(lee Plate 2.) It is considered that the presence of this fine dis-

16

REPORT NO, NAEC-AmL-1947

persion of inclusions in combination with the fillcted shoulder areasof these specimens produced a stress concentration greater than thatprovided by the notch. This condition would account for the selectivefailure of these specimens through the filleted shoulder section.

In summary, the erratic behavior of the fatigue and notchedtensile specimens herein discussed ere believed to be associated withthe presence of inclusions and/or banding.

V. CONCLUSIONS

1. The gas content of vacuum melted steel is lower than that ofair melted steel.

2. The vacuum melting process in itself does not insure ultraclean steel.

3. The VIR and VIM steels which were processed from higher purityraw materials were markedly superior to AM and VAR material withrespect to cleanliness and microstructural homogeneity.

4. Hardenability of air and vacuum melted steels of the samencuinal composition are similar.

5. Significant improvements in the mechanical properties in the

transverse grain direction are dependent upon the degree of cleanlinessand microstructural homogeneity. Consistent with this, the followingconclusions related to the mechanical properties in the transverse graindirection are drawn:

a. The unnotched transverse tensile properties of the veryclean VIM and VIR steels closely approach the longitudinal tensileproperties in both strength and ductility at both the upper and lowerstrength levels. At the lower strength level, the ductility of theAM and VAR steels, as mea3ured by percent reduction in area in the trans-verse grain direction, was significantly lower (40%) than in the longi-tudinal direction. At the upper strength level, both strength andductility were significantly lower in the transverse grain direction(14%-32% lower in strength and 32% lower in reduction in area).

b. The notched strength of the VIR and VIM steels is signifi-cantly higher than that of the AM and VAR steels at both strengthlevels. (Approximately 80% higher at both the upper and lower strengthlevels, )

c. At the 260-280 ksi strength level, the VIM and VIR steelsexhibit significantly less susceptibility to hydrogen embrittlementthan the AM and VAR steels. Based on a 500-hour static fatigue limit,

171

A';

REPOT NO. NAEC-AML-1947

!the VIM and VIR steels were approximately similar with respect to sus-ceptibility to hydrogen embrittlement, however, in .,omparing them withAM and VAR steels the static fatigue limits were frcm two to five timeshigher for the VIM and VIR steels.

d. The much cleaner VIM and VJI steels shpwed the most signi-ficant improvement in the fatigue limit, fracturetoughness and impactstrength properties over the AM and VAR material. The VIM and VIR steelsshow a two-fold increase in transverse impact strength and fracturetoughness and a 50% increase in the fatigue limit over the AM and VARsteels.

VI. RECOMMENDATIONS

In view of the significant improvements in mechanical propertiesassociated with vacuum melted steel which possesses ultra clean andhomogeneous microstructures, serious consideration of their use shouldbe given to those applications requiring that transverse grain direc-tion properties closely approach longitudinal grain direction properties.Particular attention is directed to the consideration of their usewhere ductility, fracture toughness and fatigue strength are importantdesign considerations in the transverse grain direction.

1118i

REPfCIT NO. NAEc-AmL-1947

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22

ril TABLE 4


NOTCHED TRANSVERSE TENSILE STRENGTH

Notched Ratio

Material Load (ib) Breaking Strength (psi) Unnotched

200-220 ksi Strength Range

AM-I 25,000 125,0002 28,200 141,700 o.653 30,000 150,000

Avg. 138,900

VAR-I 30,750 153,7002 29,150 146,300 0.713 35,000 175,000

Avg. 158,350

VIM-2D-1 51,200 257,3002 48,800 245,200 1.233 53,500 266,200

Avg. z56,250

VIM-3D-1 49,250 246,200

2 48,1i00 240,500 1.193 48,500 242,500

Avg. 246,400

260-280 ksi Strength Range

AM-i 27,000 135,0002 28,150 14o,700 0.753 30,000 150,000

Avg. 141,900

VAR-i 33,100 165,5002 33,150 165,700 o.663 31,950 158,900

Avg. 163,350 i

VIM-2D-I 50,400 252,0002 51,000 253,700 0.96 " j3 52,300 261,500 j !

Avg. 255,750

TABE SPAGE 10OF 2 PAGES i

II


Notched RatioMaterial Load (ib) Breaking Strength (pi) Unnotched R

260-280 ksi Strength Range (continued)

VIM-3D-i 47,500 238,7002 48,600 243,000 0.893 49,40o 247,000

Avg. 242,900

VIR-i 45,000 225,0002 45,300 226,500 0.823 47,300 236,500

Avg. 229.,350

I

b I.i

L. 24+TABLE 5

PAGE 2 OF 2 PAGES'ii

REPORT. NO * NAEC -AML-194f7

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REPORT O.NAEC-AML.-1947

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FATIGUE DATA FORI NOTlCHED SPECIMENS OF AM (10) 4340STEEL AT THE HIGH AND LOW STRENGTH IMVIS

High Strength (260-280 ksi)

Spcie Srs ksi) yls Remarks

1 50 85,000 Failed2 45 60.,000 Failed

3 40 204,000 Failed

4 35 158,000 Failed

5 30 186,000 Failed

6 20 20,000,000 No Failure

7 25 1,203,000 Failed

8 23 --- Broke on oading

9 23 373,000 Failed

6A* 8o 16,000 Failed

Low Strength (200-220 kat)

1 80 15,.000 Failed

2 50 73,000 Failed

3 4o 139,000 Failed

30 378,000 Failed

5 25 1,218,000 Failed

6 23. 739.,000 Failed

7 21 1,333,000 Failed1*8 19 2,218.,000 Failed9 17 18,439,000 Failed

I-10 16 1,518,000 Fail1ed

*Rerun at higher stress for specimen that didnot fail below 20 million cycles.

TABTE 9 28

mq

REPORT NO, NAEC-AML-1947

FATIGUE DATA FOR SMOOTH SPECIMENS OF AM (IC) 4340STEEL AT THE HIGH AND LOW STRENGTH IEVEIS

High Strength (260-280 ksi)_

Specimen Stress (ksi) Cycles Remarks

1 100 156,000 Failed

2 95 2,951,000 Failed

3 93 95,000 Failed

4 90 7,097,000 Failed

5 88 1,669,000 Failed

6 85 148,000 Failed

7 80 3,095,000 Failed

8 75 20,000,000 No Failure

9 78 20,000,000 No Failure

10 79 8,686,000 Failed

8A* 120 60,000 Failed

9A* 140 20,000 Failed

Low Strength (200-220 ksi)

1 110 49,000 Failed

2 100 49,000 Failed

3 90 131,000 Failed

4 80 81,000 Failed

5 70 1,732,000 Failed

6 68 20,000,000 No Failure

7 69 20,000,000 No Failure

8 75 20,000,000 No Failure

9 75 7,367,000 Failed

7A* 120 19,000 Failed

*Rerun at higher stress for specimen that did notfail below 20 million cycles.

TABLE 10


FATIGUE DATA FOR NOTCHED SPECIMENS OF VAR (2-A) 4340STEEL AT THE HIGH AND LOW STRENGTH lEVElS



1 40 97,000 Failed

2 30 271,000 Failed

3 25 347,000 Failed

4 23 575,000 Failed

5 20 664,000 Failed

6 17 20,000,000 No Failure

7 18 872,000 Failed

8 60 30,000 Failed

6A* 50 66,000 Failed


1 80 18,000 Failed

2 17 4,470,000 Failed

3 15 5,945,000 Failed15 2,719,000 Failed

5 13 30,749,000 Nc Failure

6 14 2,622,000 Failed

7 50 46,000 Failed

8 40 93,000 Failed

9 30 263,000 Failed

10 20 579,000 Failed

*Rerun at higher stress for specimens that didnot fail below 20 million cycles.

TABIZ 11 30


FATIGUE DATA FOR SMOOTH SPECIMENS OF VAR (2A) 4340STEEL AT THE HIGH AND LOW STRENGTH EM..S


Spimen Stress ():si) Cycles Remarks

1 100 1,435,000 Failed

2 95 1,814,000 Failed

3 . 92 628,000 Broke in Shoulder

4 90 25,000 Broke in Shoulder

5 90 704,000 Failed

6 85 20,000,000 No Failure

7 88 2,057,000 Failed

8 86 20,000,000 No Failure

9 110 269,000 Failed

6A* 150 16,000 Failed

8A* 130 24,000 Failed


1 110 26,000 Failed

2 75 514,000 Failed

3 70 21,356,000 Failed

4 72 2,503,000 Failed

5 71 537,000 Failed

6 120 23,000 Failed

7 100 64,000 Failed

8 90 171,000 Failed

9 80 144,000 Failed

10 71 320,000 Failed

Ii

*Rerun at higher stress for speclmens that did

not fail below 20 million cycles.

TAKIE12 i~

I


FATIGUE DATA FOR NOTCHED SPECIMENS OF VIM (2D) 4340STEEL AT THE HIGH AND LOW STRENGTH IEVELS

High Strength (260-280) ksi

J SPecimen Stress (ksi) Cycles R,.narks

1 100 7,000 Failed

2 40 742,000 Broke Outside Notch

3 35 2,038,000 Broke Outside Notch




7 35 195,000 Failed


9 25 600,000 Failed


1 20 20,000,000 No Failure

2 30 430,000 Failed

3 25 20,000,000 No Failure

4 28 20,000,000 No Failure

5 29 1,235,000 Failed

6 70 23,000 Failed

7 35 270,000 Failed

8 40 142,000 Failed

1A* 80 18,000 Failed

3A* 60 36,000 Failed

4A* 50 95,000 Failed

WRerun at higher stress for specimens that did

not fail below 20 million cycles. 32

1. TABE 13

- -'-- --I--


FATIGUE DATA FOR SMOOTH SPECIMENS OF VIM (2])) 4340STEEL AT THE HIGH AND IOW STRENGTH LEVEIS



1 100 684,ooo Failed

2 95 324,ooo Failed3 90 lO,485,000 Failed

4 88 1,745,000 Failed

5 85 5,872,000 Failed

6 82 20,000,000 No Failure

7 83 2,586,000 Failed8 110 239,000 Failed

9 130 26,000 Failed

6A* 150 19,000 Failed


1 80 7,570,000 Failed

2 78 20,000,000 No Failure3 79 579,000 Failed

4 120 58,000 Failed

5 110 48,000 Failed

6 :100 120,000 Failed

7 90 2,236,000 Failed

8 85 369,000 Failed

9 90 429,000 Failed

10 95 936,006 Failed


TABI 14 T

I 'REPORT NO. NAEC-AML-1947

IFATIGUE DATA FOR NOTCHED SPECIMENS OF VIM (3D) 434oSTEEL AT THE HIGH AND LOW STRENGTH IEVEIS

I High Strength (260-280 ksi)

pecimen Stress (ksi) Cycles Remarks

1 40 242,000 Failed

2 38 246,000 Failed

3 35 288,000 Failed

4 30 302,000 Failed

5 25 20,000,000 No Failure

6 27 388,000 Failed

7 26 12,872,000 ]Failed

8 60 43,000 Failed

5A* 8o 15,000 Failed


I 40 215,000 Failed

2 30 337,000 Failed

3 25 20,000,000 No Failure

1 4 27 20,000,000 No Failure

5 28 20,000,000 No Failure

6 29 543,000 Failed

7 50 60,000 Failed

8 35 152,000 Failed

3A* 80 16,000 Failed

4A* 70 24,000 Failed

5A* 60 38,000 Failed

*Rerun at higher stress for specimens that did not fail below 20

million cycles.

TA$3E 15I


FATIGUE DATA FOR SMOOTH SPECIMENS OF VIM (3D) 4340STEEL AT THE HIGH AND lW STRENGTH IZVEIS


ecimen sksi Ccles Remarks

1 100 66,000 Failed

2 90 65,000 Failed

3 90 150,000" Failed4 85 79,000 Failed

5 80 21,997,000 Failed

6 82 34,000 Failed

7 83 942,000 Failed

8 120 175,000 Failed


1 80 83,000 Failed

2 66 456,000 Failed

3 70 162,000 Failed

4 62 31,233,000 No Failure

5 63 453,000 Failed

6 100 32,000 Failed

7 90 132,000 Failed

8 85 142,000 Failed

4A* l10 55,000 Failed


TABLE 16 .1

II


I FATIGUE DATA FOR NOTCHED SPECIMENS OF VIR (2E) 4340STEEL AT THE HIGH AND LOW STRENGTH LEVELS

! High Strength (260.280 ksi)

I §cinn Stress (ksi) Cycles Remarksi 80 14,000 FailedI I2 40 172,000 Failed

3 30 13,241,000 Failed

4 27 4,.01,000 Broke in Shoulder

5 27 3,976,000 Broke in Shoulder

6 25 20,000,000 No Failure

7 27 20,000)000 No Failure

8 28 20,000,000 No Failure

9 35 2,050,000 Broke in Shoulder

6A* 50 87,000 Failed

7A* 60 59,000 Failed8A* 70 26,000 Failed


1 40 183,000 Failed

2 30 20.000,000 No Failure

3 35 20,000,000 No Failure

4 38 948,000 Failed

5 37 20,000,000 No Failure6 50 64,000 Failed

7 60 37,000 Failed

8 45 129,000 Failed9 70 21,000 Failed

2A* 80 17,000 Faile:

3A* 70 22,000 Failed

36*Rerun at higher stress for specimen that did

not fail below 20 million cycles.

I TABLE 17


FATIGUE DATA FOR SMOOTH SPECIMENS OF VIR (2E) 4340STEEL AT THE HIGH AND LOW STRENGTH LEVElS


Specimen Stress (ksi) . Cycles_ Remarks

1 100 20,000,000 No Failure

2 110 20,000,000 No Failure

3 120 5,998,000 Failed

4 115 9,196,000 Failed

5 113 20,000,000 No Failure

6 140 273,000 Failea

7 130 1,931,000 Failed

8 114 l,018,000 Failed

9 125 1,180,000 Failed

10 114 11,346,000 Failed

1A* 150 59,000 Failed

2A* 160 56,000 Failed

5A* 160 35,000 Failed


1 100 569,000 Failed

2 95 20,000,000 No Failure

3 98 32,766,000 Failed

4 99 4,894,000 Failed

5 110 325,000 Failed

6 120 125,000 Failed

7 130 58,000 Failed

8 140 33,000 Failed

9 105 680,000 Failed

2A* 160 ---- Specimen Overheated

but did not break

*Rerun at higher stress for specimen that did 37.not fail below 20 milli:n cycles.

TABLE 18

EPORT NO. NAEC-AML..1947

et 0

0 49t

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38 a

Il V' J iO T

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6 6 7 ()l.

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PHOTO NO: CAN-360678(L)-5-.d4 PLATE No. 2

PZO


NOTE:NOTCH ROOT

.- 250 RADIUS .010 IN.

TAPER .6250 IN. 01 .001 IN.PER FOOT \,so DRILLED & TAPPED FOR

= 0=1 -20 I.W.S. THO.

3 3r

NOTCHED FATIGUE SPECIMEN

24U NOTE:NOTCH ROOT RADIUS

A04~ .0005

r .60 DT-13 THD. T

HYDROGEN EMBRITTLEMENT NOTCHEDTENSILE SPECIMEN

I

NOTCHED TENSILE SPECIMEN

FOR TESTS 05

IPOTO NoN CAOT-369679(L) - 5 - 6 PLATE No. 3

I


"A-

1ETCHED 45 MAIN.MAGNIFICATION: IX TOP 1. 1 HCL AT 1600 F

2. CLEANED 2% NITAL

BOTTOM 4;

MACROETCHED TOP AND BOTTOM BtLLk SECTIONS

PHOTO NO: CAN-36680(L)-5-64 OF AM(IC) 4340 STEELPLATE NO. 4


1. ETCHED 45 MIN.

MAGNIFICATION: IX TOP 1:1 HCL AT 160OF

2.CLEANED 2% NITAL

BOTTOM

MACROETCHED TOP AND BOTTOM BILLET SECTIONSPiOTrO NO: CAN-360681(L)-5-64 OF VAR(2A) 4340 STEEL

PLATE NO. 5

• -- -- -7 tf,

REPORT NO. NAEC-ANL-194/

I

II

TO I. ETOHED 45 MIN.

jMANIFICATION: IX TO i HCL AT1600F

2.CLEANED 2% NITAL

IIII

1 -

BOTTOM

MACROETCHED TOP AND BOTTOM BILLET SECTIONST NOF VIM (2D) 4340 STEEL

PHOTO NO: CAN-360682(L)-5-64 PLATE NO. 6

j REPORT NO. NAEC-AML-1947

giiTOP 1. ETCHED 45 MIN.

MAGNIFICATION: IX 1:1 HOL AT 1600 F2. CLEANED 2% NITAL

BOTTOM

MACROETCHED TOP AND BOTTOM BILLET SECTIONS

PHOTO NO: CAN-360683(L)-5-64 O I(D430SELPLATE NO. 7

---- ~A-


1. ETCHED 45 MIN.MAGNIFICATION! %X TOP 1:i1 HCL AT 1600 F

2.CLEANED 2% NITAL

BOTTOMMACROETCHED TOP AND BOTTOM BILLET SECTIONSI OF VIRU(E) 4340 STEELNO: CAN-360684(L)-5..6

4 PLATE NO. 8

I REPORT NO. NAEC-AML-1~947

1. ETCHED 45 MdIN.

MAGNIFICATION: IX TOP 1: 1 NC. AT 1600 F

2. CLEANED 2% NITAL

BOTTOMMACROETCHED TOP AND BOTTOM BILLET SECTIONSI OF VIR(2E) 4340 STEEL

PiOTrO %,o: CAN-36O685(L)-5-64PLTNO9PLTUO


FIG. I MAT'L: AM

UNETCHED - MAG. IOOX

FIG. 2 MAT'L: VAR

4-11

TYPICAL INCLUSION TYPE STRINGERS PRESENTF IN AM AND VAR MATERIAL

PHOTO No: CAN-360686(L)-5..64 PAEN.1

_PLAT NO 10-

REPORT NO. NAEC-ANL-1947

BANDING - TYPICAL OF

~~ AM, VAR, AND VIM MATERIAL

FIG. I

ETCH: 2% NITAL MAG. 75 X

I UNBANDED VIR MATERIAL

Ff6.2

~48

MICROSTRUCTURES TYPICAL OF AMVARVIM AND VIR MATERIALS

PHOTO NO: CAN-360687(L)-5-64PLTNO I

J, PLT NO. 11..-4,


~~I 2*.1h

FIG. I TEMPERED 400*F

ETCHED: 2% NITAL MAG.250X

FIG. 2 TEMPERED 775* F

TYPICAL MICROSTRUCTURES OF MATERIALS HEAT TREATEDTO THE 260-280 KSI AND 200-220 KSI STRENGTH RANGES

PHOTO NO: CAN-36O688(L)564 PAEN.1


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200-20 $TENTH REPORT NO. NAEC-AML-1947

20-20KSI STEGHLEVEL

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R.A. ELONGATION

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I I

TEMPERATURE vs IMPACT STRENGTH200-220 KSi STRENGTH LEVEL

20'

it-

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9-0-- .: VIM17, 0 0 o VAR

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PHOTO NO: CAN-360693(L)-5-64 PLATE NO. 17


-

TEMPERATURE vs IMPACT STRENGTH260-280 KSI STRENGTH LEVEL

- a " a -" A a A AM

0---- 0----0 VAR XI U f l U ." E3VIM

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14.

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S. NAVAL AIR - Defense Technical Information Centerdtic.mil/dtic/tr/fulltext/u2/600727.pdf · o U. S. NAVAL AIR ENGINEERING CENTER ... (IC) 4340 Steel at the ... on the properties