ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR. MICH. THIRD PROGRESS REPORT TO MATERIALS LABORATORY WRIGHT AIR DEVELOPMENT CENTER ON AN INVESTIGATION OF THREE FERRITIC STEELS FOR HILGH-TEMPERATURE APPLICATION by Ae P0 Coldren JT W. Fr ee ',narn Project 2460 A...: Y.Foe Contract No, AF 33663239 Task No, 73512 f..'., *..te., --.1 1 **/..*. ' *,..., ''._.

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SUMMARY This report describes the progress made in an investigation of the relationship between types of microstructure and the elevated-temperature, creeprupture properties of low-alloy ferritic steels. The work period covered by the report was from March 15, 1956 to June 15, 1956. Considerable tangible progress was made in the general survey of the response of "17-22-A"'V steel to heat treatment. Complete details are presented of the heat treatments which were experimentally determined to produce a total of 17 different microstructures for creep-rupture testing. The heat treatments used in the study of mixed bainitic structures and the study of the effect of a prior homogenization normalize are also presented for the three subject steels ("'t7-22-A"V, "17-22-A"S, and SAE 4340). The program of survey-type creep-rupture testing is well under way, with 65% of the test specimens either completed, in progress, or waiting for the next available testing unlits. Results have been obtained from a number of short-time rupture tests in each of three different studies. These data are too sparse to permit the drawing of any conclusions5 so they are presented in the report without discussion. The observation is made, howevery that the rupture times for the I'17-22-A"V tests seem unexpectedly short. Photomicrographs of many of the structures being tested are also presented with some discussion,

1 INTRODUCTION This progress report, the second report issued under Air Force Contract No, AF 33(616)-3239, covers work done from March 15, 1956 to June 15, 1956. The research work being done on this project is a continuation of a previous investigation done at the University of Michigan for the Wright Air Development Center concerning the fundamental relationships of microstructure of steels to properties at elevated temperatures. The three steels being studied currently include (1) a 1. 25 Cr - 0. 75 Si - 0. 5 Mo - 0. 8 V ("17-22-A"V) steel, (2) a 1.,25 Cr - 0. 75 Si - 0.5 Mo - 0.25 V ("17-22-A"S) steel, and (3) a Ni -Cr - Mo (SAE 4340) steel. The major items presented in this report include: 1. Details of most of the heat treatments used to produce the various microstructures to be creep-rupture tested. 2 Photomicrographs of most of the structures produced to date, 3. Rupture data from the few rupture tests completed thus far in the investigation, The previous work involved surveys of the high-temperature properties of several low-alloy, ferritic steels in the form of forged rotor wheels and in the form of bar stock given various continuous cooling and isothermal heat treatments to produce specific microstructures. The results of these studies are to be found in WADC Technical Reports 53-277-Part I, 53-277-Part II, and 55=388 (References 1, 2, and 3). The phases of research originally planned under this contract included:' i1) completion of work initiated under the previous contract on the effect of hardness level on the haiglh-temperature properties of several typical structures for each of the three steels; (2) a general survey of the relationship between properties and structures of the "1I7-2ZZ-ArVsteel;

2 (3) determination of the influence of transformation over a range of temperature, using stepwise isothermal transformations in the bainitic -r-ange for the three subject steels; (4) an evaluation of the effect of an homogenization normalize prior to the final heat treatment of the three steels; and (5) a study of the effect of various double heat treatments to determine possible prior history effects on response to heat treatment as measured by microstructures and by high-temperature properties, TEST MATERIALS At the completion of the study of the effect of hardness level on creep and rupture properties the supply of SAE 4340 steel was exhausted, Since additional stock from the same heat was unavailable, material from a different heat (No. PD(l14064) was supplied gratis by the tniversal-Cyclops: Steel Corporation. Additional "17-22-A'S and the "17-22.A'lV stock for work under the present contract were both supplied gratis by the Timken Roller Bearing Company, The chemical compositions of the steels were reported by the manufacturers to be as follows: Steel Heat No,, C Mn Si Cr Ni Mo V SAE 4340 19053 0,40 0,70 0.30 0.78 1 75 0.26 SAE 4340 D-14064 0.40 0.80 0 27 0, 82 1, 67 0,32 "17-22-A:'S 10420 0,29 0 6.1 0o 67 1.30 ).,18 0o47 0.26 "17-22 A"V 11833 0.29 0,70 0,71 1.43 0.31 0.51 0.81 PROCEDURE The Procedure, Results, and Discussion sections of this report will each be subdivided under the following headings: (1) General Survey of the Response of "17-22-A"V Steel to Heat Treatment, (2) Mixed Bainitic Structures, and (3) the Effect of a Prior Homogenization Normalize. These correspond to items

3 (2), (3), and (4)9 respectively, listed in the Introduction, The Study of the Effect of Harldness Level was completed for SAE 4340 and "17-22-A'S and was reported in the Second Progress Report (Reference 4), The hardness level study for "l172-2-A"V will be incorporated in the General Survey of the Response of "17-22-A"11 Steel to Heat TreatmentO General- Survey of the Response of "17-22-A"V Steel to Heat Treatment Briefly, the original plan for surveying the response of "17-22-A"V to heat treatment was: (1) to determine the approximate isothermal transformation diagram, (2) to produce typical microstructures by the appropriate isothermal and continuous cooling heat treatments, (3) to determine by survey type creep and rupture tests the relative strengths of these structures in the temperature range of 700" to 11000F, and finally, (4) to correlate the creep and rupture data -with the observed microstructures. The approx:nmate issothermal transformation diagram has been determined and was presented in the Second Progress Report (Reference 4). Based on this diagram9 five isothermal heat treatments were selected so that typical "pure" isothermal structxres could be studied0 The usual treatments of air cooling (normalizing) and oil quenching were also included as basic treatments giving a total of seven basic n.acrr ostructu.res, Modifications of the basic structures were effected by variations in (1) the final tempered hardness, (2) the rate of continuous cooling as controlled by section size, and (3) the austenitizing temperature, The mo d.ifications of the seven basic stri.uctures brought the total number of structures to seventeen. The specific heat treatments for these seventeen structures are considered in the Results section, The basis on which the high-te popeies of the seventeen structures are to be compared is the data obtained from single, survey-type creep-rupture tests run under the following conditions:

4 Testing Temperature ( F) Stress (psi) Type of Test 700 115,000 Creep 900 70,000 Creep 1100 40,000 Short-Time Rupture 1100 19,000 Creep These conditions were selected partly on the basis of previous work done at 1000~ and 1100~F on this'iat of "17-Z2-A"V for a different project, and partly on the assumption that this steel would have strengths at 7000 and 900~F comparable to those of the "117-2iz-A"S steel, The main comparison of data from the creep tests on the various structures is based on the times to reach specified total deformations; whereas, the primary data for comparison from the shorttime rupture tests are the rupture times, Minimum creep rates are also reported. Creep tests are the main basis of comparison at the lower temperature because there is little time depenqceancyfor rupture and because rupture strengths of interest are above the yield strength,, The correlation of the creep and rupture data with the metallographic observations will necessarily be of a qualitative nature beqause the data are so limited for survey purposesO In general the purpose will be to classify various structures accordiing to strength as a function of temperatureo It is planned that three representative metallographic samples shall be prepared for each structureo The first sample shall be of the initial structure prior to tempering; the second shall be of the tempered structure; and the third sample shall be from a completed creep specimen. A comparison of the second and third samples will show any major changes in the microstructure which might have occurred during creep testing, Mixed Bainitic Structures Basically, the interest in the development of microstructures containing

5 a mixture of the upper and lower -temperature forms of bainite resulted from the knowledge that bainitic structures formed during continuous cooling (as in normalizing malall sections of alloys of the type being considered) are made up of an intimate mixture of bainites formed over a range of temperature. It was felt that one step toward an understanding of these structures could be achieved through the development and study of mixed bainitic structures. The suggested type of heat treatment foxu producing mixed bainitic structures was simply to use two or more transformation temperatures in a stepwise, isothermal treatment, The control of the type and amount of bainites would be achieved through control of the temperatures and times of each isothermal step, respectively. Specifically, the sample would be austenitized in the usual way, held until the desired amount of bainite had formed, transferred directly to a second salt bath at a lower bainitic temperature, held until the desired additional amount of bainite had formed9 and so on until the sample contained the desired mixture of bainites, For the sake of simplicity and to avoid excessive losses in time in securing additional equipment, structures containing only two types of bainite were selected for study under this contract. All three.subject steels will be studied in this respecto Effect of a Prior Homogenization Normalize It is common. practice to use a normalizing treatment prior to the final heat treatment, The purpose of the normalize is to minimize or eliminate (1) differences between heats resulting from differences in prior thermal histories and (2) chemical inhomogeneities. The prior normalize is often from an austenitizing temperature 50Q to 100'F above the-austenitizing temperature used for the final heat treatment. The purpose of this part of the investigation is to

6 determine for the three subject steels whether the prior normalizing treatment appreciably affects the elevated-temperature properties as measured by creep and rupture test data. The procedure adopted for this study was simply to repeat the testing of three typical structures for each steel, with everything being held constant except for the insertion of a normalizing treatment prior to the final heat treatment. The three structures selected were the oil-quenched (martensitic), normalized (nonisothermal bainite), and middle bainite (isothermal, medium bainite). The austenitizing temperature for the prior normalize was 100~F above that used for the final heat treatment. RESULTS It is to be emphasized that while the rate of progress of this investigation as measured by the amount of creep and rupture data produced has heretofore been rather slow, the current rate of creep-rupture testing is very high. Since May 15, 1956 30 tests have been completed, At the present time 43 tests are in progress, with 27 specimens ready to be started as soon as creep-rupture testing units become available,. These 100 tests constitute about 65% of the originally planned program of testingo General Survey of the Response of '117-22-A1t'V Steel to Heat Treatment The specific conditions of heat treatment developed for each of the 17 structures are presented in Table I. The results to date are primarily from the short-time rupture tests. The data are too sparse to permit any generalizations to be made at this time, so thefollowing results are presented without commentj other than to note that the strength of the I7-TZZ-A"V material seems abnormally low at 11000F, Checks are in progress to attempt to determine the reason for this.

7 Nominal 'Temp Hardness (BHN) '.(~F) '~~~~~ — w q-i-; 'i - I! Stres s -R upture psi Time (hrs), ~~7 10 -P-.,, Elong. Red, of (%) Area (%) Structure Oil Quenched 300 900 70,000 350 900 70,000 350 1100 40,000 300 1100 30, 000 350 1100 30,000 350 1100 19,000 Normalized 350 1100 40,000 300 1100 30,000 350 1100 30,000 Middle Pearlite 250 1100 40,000 Lower Pearlite 300 700 115,000 300 1100 40,000 350 1100 40,000 Upper Bainite 300 900 70,000 350 900 70,000 300 1100 40,000 350 1100 40,000 Middle Bainite 300 1100 40,000 350 1100 40,000 Lower Bainite 300 700 1 000 350 700 115,00 300 1 100 4C, OG 350 1 10 40,000 Note: The symbol> means 'greater than" and is which the test was discontinuedo 257, 9 >1200 3 43 4 83, 7 177. 5 1491. 6 123. 3 231.0 514 8 93. 3 101. 7 89. 2 138. 8 230. 3 >1138.8 29. 8 59. 6 75. 6 89. 0 239, 5 >9790 7 102, 7 201o 8 29. 0 -1700 27, 5 23. 5 20. 5 12.0 11. 5 19. 5 34.0 17. 0 35, 0 18.0 27. 0 40. 0 250 0 22. 0 35.0 16.0 24. 0 19. 6 71. 1 48. 8 64. 1 47. 8 24.4 23. 5 31.8 19. 9 51 3 59.0 39. 6 21. 8 69. 7 69. 3 39. 7 35, 9 42, 0 60, 5 43. 5 23, 8 used to indicate the time at Photomicrogra}phs of 14 of the structures produced for the "17-22-A"V steel survey are presented in Figures 1 through 7, The following significant facts were revealed by the metallographic examinationss 1o The austenitizing treatment of 1 hor.r at 1850'F left numerous small carbide particles undissolved. The initial fine grain size (ASTM No. 9 - 10) of the hot-rolled bar stock was preserved because of the effectiveness of the carbide particles as grain growth inhibiters, 2, The section size of a nornrrlized part can have a profound influence on the resulting microstructure-and hence, presumably, on the resulting strength

8 properties. For example, the microstructures of air-cooled Oe 8-inch and simulated 3- and 6-inch rounds were 100% bainite, 90%o bain-ite + 10% ferrite, and 5% bainite + 95% ferrite, respectively, (Figures 2 and 3) 3, The bainite in the normalized 0, 8-inch round (Figure 2) appeared to be very similar to the isothermal, middle bainite (Figure 6). Mixed Bainitic Structures The specific heat treating conditions which were experimentally determined for each steel to produce approximately 50-50 mixtures of upper and lower bainite are presented in Table II. There are no test results yet for the 1'1722-A'"S or ''17-22-A'-V steels. Only one rupture result can be reported for SAE 4340: At 1000~F and 31, 000 psi the rupture time was 374. 3 hours. This may be compared to rupture times of 389, 261, and 210 hours for upper middle, and lower bainite, respectively, for exactly similar tests on Heat No. 19053. (The heat being tested currently is No, D-14064.) The "upper bainite"l structure for Heat No. 19053 was actually 70 percent bainite plus 30 percent martensite, The metallographic work is notkquite complete for the mixed bainitic structures, so no photomicrographs are presented, Effect of a Prior Homogenization Normalize The conditions of heat treatment which have been determined for the study of the effect of a normalizing treatment prior to the final heat treatment are presented in Table IIo The only available rupture test:results for this study are for the "'17-22-A"S steel, These results are presented below, along with results from similar tests on material not given a prior normalize:

9 Test Stress Rupture Time (hrs) Structure Temp (~F) (psi No Prior Normno: Prior Norm, Oil Quenched 1100 41,000 52o7 42,8 Normalized 1100 41,000 92,8 106,2 These results were all from Heat No, 10420, and they are obviously too sparse to permit any drawing of conclusions at this time, Photomicrographs for the structures being used in the prior normalize study are shown in Figures 8 and 9. The structures are for the "17-22-A"S and SAE 4340 steels only. The metallographic work on the "17-22-A"V steel is not yet finished. DISCUSSION General Survey of the Response of "17-22-A"V Steel to Heat Treatment The only possible comment which could be offered at this time regarding the few rupture data for 1l17-22A"'V is that lower bainite appears to be the strongest of the structures tested at 1100'F thus far, Previous work of this type on "17-22-A"$ and SAE 4340 (Reference 2} also indicated that the highest strengths were associated with the predominantly bainitic structureso The strength values in general, however, appears to be abnormally low for "17-22-A"V steel, The metallographic studies of the various "17222MA"V structures have thus far revealed two important facts which may be related to the high-temperature properties of this steeLo The first is that for normal.iz-lng treatments the section size of the part has a very important bearing on the resultant microstructure-at least for the heat under consideration, Specifically, part sizes up to those corresponding to a 3- inch round will contain at least 90% bainite after air cooling from 1850~Fy while part sizes up to those corresponding to a 6-inch round will contain up to 95% pro-eutectoid ferrite after air cooling from 1850~F. The

10 rupture data on these structures are not yet availablef but previous work has shown that bainite is superior to free ferrite with respect to high-temperature strength. The second characteristic of this heat of "17-22-A"V which was shown by the metallographic work was that an austenitizing treatment of 1 hour at 1850~F left numerous, small carbide particles undissolved, Supposedly there are two ways in which the lack of complete carbide solution could affect the high-temperature strength of the steqoo (1) the carbides tie up appreciable quantities of vanadium, molybdenum, chromium, and carbon which, if in solution, could strengthen the iron matrix; and (2) the carbide particles act as grain growth inhibiters and thus preserve the initially s pall grain size of the as-rolled stock. The fine grain structure may or may not have an appreciable effect on the high-temperature properties. Tests are planned for the oilquenched and the normalized structures produced with an austenitizing treatment of 1 hour at 2000ZF, and it is believed that the results of these tests will help to show the effect that undis solved carbides have on the strength of this particular steel. The status of the work on the study of Mixed Bainitic Structures and the study of the Effect of a Prior Homogenization Normalize does not warrant any discussion of these studies at this timne FUTURE WORK Future work will consist largely of an analysis of the creep and rupture data which will soon be available. Metallographic work on the mixed bainitic structures remains to be finished, as well as the examination of representative, completed creep specimens,

11 The work on the double heat treatments will be considerably simplified with respect to heat treating because of the experience gained in the investigation up to now, REFERENCES (1) A. Zonder, A. I. Rush, and J. W. Freeman, "High Temperature Properties of Four Low-Alloy Steels for Jet-Engine Turbine Wheels", Wright Air Development Center Technical Report 53-277, Part I (November, 1953). (2) A. I. Rush and J. W. Freeman, "High-Temperature Properties of Four LowAlloy Steels for Jet-Engine Turbine Wheels", Wright Air Development Center Technical Report 53-277, Part II (February, 1955). (3) K, P. MacKay, A. P. -Coldren, A. I. Rush, and J. W. Freeman, "A Survey of the Effect of Austenitizing Temperature and Rate of Continuous Cooling on the Structure and 700~ to 1200'F Properties of Three, Low-Alloyed Steels'", Wright Air Development Center Technical Report 55-388 (September, 1955). (4) A, P, Coldren and J, W, Freeman, "An Investigation of Three-Ferritic Steels for High-Temperature Application," Second Progress Report to Wright Air Development Center, Contract No. AF 33(616)-3239 (March 15, 1956),

Structure Oil Quenched (100% Martensite) Oil Quenched (100% Martensite) Normalized (100% Bainite) Normalized (100% Bainite) Normalized (10% Ferrite + 90% Bainite) Normalized (95% Ferrite + 5% Bainite) Middle Pearlite (5% Pearlite + 95%o Ferrite) Lower Pearlite (5% Pearlite + 95% Ferrite) Upper Bainite (60% Bainite + 40% Martensite) Middle Bainite (100% Bainite) Lower Bainite (100% Bainite) * Timken Heat No. 11833 TABLE I Structures and Heat Treatments Used in the General Survey of the Response of "17-22-A"V Steel* to Heat Treatment Average Hardness Tempering Treatment Initial Heat Treatment Before Tempering (BHN) 300 BHN 350 BHN 1 Hour at 18500F, Oil Quenched (0. 8-in. Round) 476 1 hr at 1300~F 2 hrs at 1250~F 1 Hour at 2000~F, Oil Quenched (0.8-in. Round) 487 4 hrs at 1250~F 1 Hour at 1850~F, Air Cooled (0. 8-in. Round) 374 1.3 hrs at 1300~F 2 hrs at 1250~F 1 Hour at 2000~F, Air Cooled (0. 8-in. Round) 384 4 hrs at 1250~F 1 Hour at 1850~F, Air Cooled (Simulated 3-in. Round) 365 23 hrs at 1200~F Average Final Hardness (BHN) 304 345 348 308 359 349 300 1 Hour at 1850~F, Air Cooled (Simulated 6-in. Round) 1 Hour at 1850~F, Isothermally Transformed at 1275~F for 3.5 Hours, Water Quenched (0.4-in. Round) 1 Hour at 1850~F, Isothermally Transformed at 1200~F for 5 Hours, Water Quenched (0.4-in. Round) 1 Hour at 1850~F, Isothermally Transformed at 850~F for 2 Hours, Water Quenched (0.4-in. Round) 1 Hour at 1850~F, Isothermally Transformed at 750~F for 0.3 Hour, Water Quenched (0.4-in. Round) 1 Hour at 1850~F, Isothermally Transformed at 650~F for 0.2 Hour, Water Quenched (0.4-in. Round) 303 None 303 255 None 255 360 447 364 405 1 hr at 1300~F 1.3 hrs at 1300~F 1 hr at 1300~F 1.5 hrs at 1300~F 1 hr at 12i0~F 4.5 hrs at 1200~F 5 hrs at 1200~F 6 hrs at 1200~F 289 347 290 348 298 338 294 348

TABLE II Structures and Heat Treatments Used in the Study of Mixed Bainites and the Study of the Effect of a Prior Homogenization Normalize for the "17-22-A"V, "17-22-A"S, and SAE 4340 Steels Structure Initial Heat Treatment Average Hardness Tempering Before Tempering (BHN) Treatment Average Final Hardness (BHN) Mixed Bainite (60% Upper Bainite + 40% Lower Bainite) Double Normalize (100% Bainite) Normalize + Oil Quench (100% Martensite) Normalize + Isothermal Transformation (100% Middle Bainite) "17-22-A"V (Heat No. 11833) 1 Hour at 1850~F, Isothermally Transformed Stepwise at 850~F for 5 Min. and at 650~F for 45 Min., Water Quenched 1 Hour at 1950~F, Air Cooled + 1 Hour at 1850~F, Air Cooled 1 Hour at 1950~F, Air Cooled + 1 Hour at 1,850 F, Oil Quenched 1 Hour at 1950~F, Air Cooled + 1 Hour at 1850~F Isothermally Transformed at 750~F for 0. 3 Hour, Water Quenched 397 360 4. 5 hrs at 1200~F 2 hrs at 1250'F 2 hrs at 1250~F 360 348 471 a 348 a a Mixed Bainite (50% Upper Bainite 50% Lower Bainite) Double Normalize (90% Bainite + 10% Martensite) Normalize + Oil Quench (100% Martensite) Normalize + Isothermal Transformation (95% Middle Bainite + 5% Martensite) "17-22-A"S (Heat No. 10420) 1 Hour at 17500F, Isothermally Transformed Stepwise at 900~F for 0. 5 Hour and at 7000F for 1.5 Hours, Water Quenched 1 Hour at 1850~F, Air Cooled + 1 Hour at 1750~F, Air Cooled 1 Hour at 1850~F, Air Cooled + 1 Hour at 1750~F, Oil Quenched 1 Hour at 1850~F, Air Cooled + 1 Hour at 1750~F, Isothermally Transformed at 800~F for 0.5 Hour, Water Quenched 353 335 471 3 82 8 hrs at 1200~F 2.25 hrs at 1200~F 2. 25 hrs at 1200~F 4 hrs at 1200~F 298 351 356 314 Mixed Bainite (60% Upper Bainite 40% Lower Bainite) Normalize + Oil Quench (100% Martensite) Double Normalize (90% Bainite + 10% Martensite) Normalize + Isothermal Transformation (95% Middle Bainite + 5% Martensite) SAE 4340 (Heat No. D-14064) 1 Hour at 1750~F, Isothermally Transformed Stepwise at 850~F for 1 Hour and at 650~F for 1 Hour, Water Quenched 1 Hour at 1850~F, Air Cooled + 1 Hour at 1750~F, Oil Quenched 1 Hour at 1850~F, Air Cooled + 1 Hour at 1750~F, Air Cooled 1 Hour at 1850~F, Air Cooled + 1 Hour at 1750~F, Isothermally Transformed at 750~F for 24 Hours 3 16 506 408 321 None 316 1.75 hrs at 1 200~F 1.5 hrs at 1200~F None 307 307 320 a - Not yet determined Note' All bars which were normalized or oil quenched were 0. 8-inch rounds; all bars which were isothermally transformed were 0.4-inch rounds.

X100 X1000 (a) Oil Quenched from 1850~F (0. 8-inch round). Average BHN - 476 (b) Oil Quenched from 1850~F + Tempered 2 Hours at 1250~F. Average BHN-345 (c) Oil Quenched from 1850~F + Tempered 1 Hour at 1300~F. Average BHN-304 Figure 1 - "17-22-A" V Bar Stock (0.8-inch Round) (a) As Oil Quenched from 1850~F, (b) Tempered to 350 BHN, and (c) Tempered to 300 BHN, 'T ~ ~ ~ ~ ~ L:ai:%~.~r ~ -x~~ A ~~~~~~~IAg A-::x3: ~300 BHN.

V 1 nn lVV"^~~~~ ~X1000 (a) Air Cooled from 1850 ~F (0. 8-inch round). Average BHN 374 (b) Air Cooled from 18500F + Tempered 2 Hours at 1250~F. Average BHN 359 (c) Air Cooled from 1850~F + Tempered 1-1/3 Hours at 1300~F. Average BHN- 308 Figure 2 -" 17-22-A"I V Bar Stock (0.8-inch Round) (a) As Normalized from 1850~F, (b) Tempered to 350 BHN, and (c) Tempered to 300 BHN. Vii ~~~~~~~, ~ ~ ~ ii.iii~i~:iiL-~:-~- -:~; -:i F::: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-~::: —~:::: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:~:: (b) Air Cooled from l8500F + Tempered 2 Hours at 12500F* Average~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:: BEN~~~~~~~~~~~~~' 359i~iiii. l~iiiii 4~(- 4. k~~~~~~~~~~~~~~~~-~-:-:-c —::I /K$. ~ ~ -~:~ 18500?, (b) Tempered to 350 BEN and (c) Tempered to 300 BEN.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Iii —ii~iiii~ii:

X100 Xlooo (a) Air Cooled from 1850~F in Firebrick Jacket to Simulate Cooling Cycle at Center of a 3-inch Round. Average BHN - 365 (b) Air Cooled from 18500F in Firebrick Jacket to Simulate Cooling Cycle at Center of a 6-inch Round. Average BHN - 303 Figure 3 -"17-22-A" V Bar Stock As Normalized in (a) Simulated 3-inch Round, and (b) Simulated 6-inch Round.

X100. O1000 (a) Isothermally Transformed to Lower Pearlite (0.4-inch Round). Average BHN - 360 (b) Isothermally Transformed to Lower Pearlite + Tempered 1 Hour at 1200~F. Average BHN - 347 (c) Isothermally Transformed to Lower Pearlite + Tempered 1 Hour at 1300~F, Average BHN - 289 Figure 4 -"17-22-A" V Bar Stock (a) As Transformed to Lower Pearlite, (b) Tempered to 350 BHN, and (c) Tempered to 300 BHN.

X100 X1000 (a) Isothermally Transformed to Upper Bainite (0 4-inch Round). Average BHN - 447 - ~ ~ ~ A or' S'~ '...... "-~-Ai: "x~ JV.;c... ':" (b) Isothermally Transformed to Upper Bainite + Tempered 4-1/[g Hours at. 1200~F. Average BHN- 348:~...i-:r-':,'" ~-,.~.:,-;.... M" 4-J:.& i -C~~~~R ~,:,:..'.x<i, -* t%.~j ~.~:...;A~?i'..~....:h. t,: -,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~- - 4: 74...~~~~~~~~~~~~~~~~~~~~~~~~~~~~r -r '~ - '* 130~F A v rg -BHN - - 9 '10 4~ ~ A-h#" - -- 1 Mf 11N~li. fCi:~: N, Fe ~ -- V Figure 5- f17-22-A"~V Bar Stock (a) As Transformed to Upper Bainite, (b) Tempered to 350 BHN, and (c) Tempered to 300 BHN. N A'I 4.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~i,: qq 6. ~ ~ ~ ~ ~ ~ ~ ~ ~ X`* I" ~I;~~,~ Fair~~~~~~~~~~~~i". iv V~~~~~~~~~~~~~~~~~~~~~i w'- X 7j(I- ' ".:? ";-~ g V.~~~~~~~~~~~, -" i?~ P 20"f W6 N N.,N -34 R, P"'zY':::; ~ j1. -J.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-rJ*~:i~ Rll,~~~~~~~~~~~~~O WV ~ ~ ~ ~~~~' i l'Ctu "t *'~I~ ~t, M - -YA, — ' -MO.- 1:x.:" 1;~~~~;*~~~t ~~a xA'j, " iq~O.i4 i ~~~~~~~~~~~~~~~~~~~~~~~f~~~~~~~~~24:a~~'4 d; ~~'~~nT~: jlI~~t:t~~::;t ~ ~ z~~~fo* r.~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~~- (c)Isthrmll Tanfome t UperBan'e Tmpre 11/ Hur a (b) Tempered to 350 BHN, and (c) Tempered:S:

X100 X1000 (a) Isothermally Transformed to Middle Bainite (0.4-inch Round). Average BHN - 364,ti,i (b) Isothermally Transformed to Middle Bainite + Tempered 5 Hours at 1200~F. Average BHN - 338 (c) Isothermally Transformed to Middle Bainite + Tempered 1 Hour at 1300~F. Average BHN - 298 Figure 6 -"117-22-A" V Bar Stock (a) As Transformed to Middle Bainite, (b) Tempered to 350 BHN, and (c) Tempered to 300 BHN.

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UNIVERSITY OF MICHIGAN 3 9015 02827 3905 II 3 9015 02827 3905