SEVENTH PROGRESS REPORT TO MATERIALS LABORATORY, WRIGHT AIR DEVELOPMENT CENTER DEPARTMENT OF THE AIR FORCE ON FOUR LOW-ALLOY STEELS FOR ROTOR DISKS OF GAS TURBINES IN JET ENGINES by A. Zonder J.. W. Freeman PROJECT NO. M903 AIR FORCE CONTRACT NO.:AF33(038)-13496 EXPENDITURE ORDER NO.:605-227 SR-7 SEPTEMBER 30, 1952

SEVENTH PROGRESS REPORT ON FOUR LOW-ALLOY STEELS FOR ROTOR DISKS OF GAS TURBINES IN JET ENGINES SUMMARY This report is the Seventh Progress Report on an investigation being carried.. out for the Materials Laboratory, Wright Air Development Center, Department of the Air Force, under Air Force Contract Number: AF 33 (038)-13496 (Expenditure Order Number: 605-227 SR-7) The purpose of this investigation is to determine the effect of heat treatment upon the high temperature properties. of four low-alloy steels, 4340, "17.-22AS, H*40, and C-422, in the form of forged J-33 jet engine disks, and to establish design data for each steel, heat treated to give the best practical properties. A concurrent investigation of the high.temperature properties of the products of isothermal transformation of these four steels was carried out utilizing bar stock in order to define the relationship between. structure and properties. Correlations.involving relative propertiesof disks and bar stock and the results.of the microstructural study were developed. All creep-rupture testing of the normalized 4340 disk at 1000'F has been completed. All three H-40 disks.were retempered for 4 hours..at 1250~F in order to reduce their hardness to 280 to 320 Brinell. A survey of the rupture properties. at the rim of these retempered disk materials was carried.out at 1100~F. The oil-quenched..and.tempered.H-40 disk (No. 3) was selected for determination of design data..at 1000~'.,.1100~, and 1200~F. This testing

is now in progress. Also, the tensile properties of this retempered disk material have been determined at room temperature, 1000,~ 1100~, and 1200~F. The results of the microstructural study, utilizing bar stock, indicate that the best high temperature strengths were exhibited by coarse.bainitic structures for the 4340, "17-22A"'S, and H-40 steels. In the case of a mixed structure of martensite and coarse bainite, increasing amounts of martensite resulted in poorer high temperature properties. Also, the presence of appreciable amounts of clear acicular ferrite (associated with the formation of coarse bainite) resulted in lower elevated temperature properties. The results obtained in the disk investigation were in good agreement with those obtained in the bar stock study for the 4340 and " 17-ZZA"S steels. The variation between the properties of the H-40 disk material and bar stock material could be attributed to differences in microstructure and grain size. Because of the transformation characteristics of C-422 steel, only the normalized and oil-quenched structures were investigated in the bar stock. Both heat treatments yielded similar structures and similar high temperature properties. The results obtained in the disk study were in good agreement with those obtained in the bar stock study. A more complete, detailed analysis of the correlative microstructural study of the bar stock and disk material will be presented in the final report on this investigation.

3 INTRODUCTION This report covers the progress made between 1 July 1952. and 30 September 1952 on an investigation of the high temperature properties of four low-alloy steels, 4340, "17-22A"S, H-40, and C-422, in the form of forged J-33 jet engine disks. The objectives.of this investigation are to determine the effect of heat treatment upon the high temperature properties of each of these four steels and to obtain design d.ta at 1000', 1100~, and 1200~F for the heat treated disk of each steel showing the best practical properties. A concurrent investigation of the high temperature properties of the products of isothermal transformation for each of the four steels was carried out utilizing bar stock. Correlations of the results of the disk study and the bar stock study were made in order to help explain the properties. of the disks after various heat treatments. RESULTS The results obtained to date are presented separately for each steel under (1) disk investigation, and (2) investigation of the properties of the products of isothermal transformation. The latter section includes brief summaries of. the results of the microstructural study of the disk material and bar stock material.

4 Disk.Investigation 4340 STEEL The last creep-rupture test at 1000~F and 24, 000 psi on a surface plane tangential specimen at the rim of the normalized disk was completed with the. following results: Time to Reach Time at Minimum Rupture Elongation Reduction 1-Percent Total Transition to Creep Time in 2 in. of Area Deformation Third..Stage Creep Rate.(Hrs.) (%) (%) (Hrs.) (Hrs. (%/Hour) 635 3.5 2.4 470 320 0.0015 The results. of the. testing of disks 1', 3, and 4 were presented..in the Sixth Progress Report. "1.7.22A"S AND C-422 STEELS Creep-rupture testing of. these two steels was.completed in the 1 April to 30 June period.and.the results were presented in the Sixth Progress Report. H-40.. STEEL The, survey at 1100'F of. the.rupture properties of the three disks retempered 4 hours, at 1250'F has been.completed, and the results.are shown in Table I. and.figures 1 and.2, Disks No. 1 (normalized + tempered) and No. 3 (oil quenched + tempered) had similar high temperature strengths., but the oil-quenched and tempered disk exhibited better rupture-test ductility, Therefore, disk No. 3.was selected for further testing at 10000~, 1100.,: and 1200'F. This.testing is. now in progress,. and the results.obtained to date are shown in Table..I and figures 1 and.2 The high temperature strengths of the.H.-40 bar stock., as-received disk materials, and retempered disk materials at 1100' F are shown in Table II.

5 The tensile properties of retempered (4 hours at 1250~F) disk No. 3 have been determined at room temperature, 10000, 1100', and 1200~F and are shown in Table III and figure 3. Investigation of the Properties of the Products, of Isothermal Transformation, 4340 STEEL The results of the bar stock study show that the best high temperature properties can be obtained at 1000~ and 1100~F with a coarse,upper bainite type of structure. Using the stress to cause 1-percent total deformation in 1000 hours at 1000'F as.a basis.of comparison, the strengths of the various structures were as follows: Strength Heat Treatment and Structure (psi) 1. Austenitize 1750~F + 28 hrs. at 850~F. 70% upper bainite + 30% martensite, 17, 300 2. Austenitize 1750~F + 1-1/2 hrs. at 650~F. 100% lower bainite. Approximately 13, 300 3. Normalize 17500F. 35%o martensite + 65% upper and lower bainite. 13,300 4. Austenitize 1750~F + 10 hrs. at 1240~F. 35% ferrite + 65% medium pearlite. Approximately 14, 000 5. Oil quench 1750~ F. 100% martensite. 11,500 6. Austenitize 1750~F +.1.1 hrs, at 1050OF 10% ferrite + 90% very fine carbide aggregate. Less than 11,500 These structures were tempered to a Brinell hardness of 280 to 320 wherever necessary. before testing. The actual number of structures developed by isothermal treatment were very limited and consequently only outline the influence of microstructure upon high temperature properties. Considering the limited data available, the results obtained in the bar stock study were in good agreement

6 with those obtained in the disk study. The 1000 hour 1-percent total deformation strengths at 1000~F for the three disks were as follows: Disk Strength No. Heat Treatment (psi) 1 (a) Normalize 1750~F + temper 2 hrs. at 1200~F. (b) Normalize 1750~F. (15% martensite + 82% bainite + 3% ferrite) 20, 500 3 (a) Oil quench 1750~F + temper 8 hrs. at 1200~F. (b) Oil quench 1550~F + temper at 1050~F. (85% tempered ground mass of martensite and bainites,+ 15% ferrite) 10, 000 4 Interrupted-quench 1750~F + temper 2 hrs. at 1200~F. -(Tempered ground mass of bainite. Very little evidence of tempered martensite. No free ferrite.) 21, 000 The superiority of the normalized disk over the normalized.and tempered bar stock was attributed to two factors, namely: (1) The disk:test specimens were approximately 20 points Brinell harder than the bar stock test specimens. (2) The disk showed less martensite and lower bainite than the bar stock, The superiority of the disk material over the isothermally transformed upper bainite bar stock was attributed to the fact that the disk showed less martensite than the bar stock. The 1000-hour 1-percent total deformation strengths of the oilquenched and tempered disk specimens and bar stock specimens were similar at 1000~ F even though the structures involved were not similar. Although the structure of the oil-quenched and tempered disk showed, appreciable amounts, of what appeared to be a coarse bainite, it also showed about 15-percent of what appeared to be a supersaturated ferrite. The low strengths and high ductilities in the rupture test may be due to this ferritic structure.

7 The interrupted-quenched.and tempered disk was superior to the isothermally transformed upper bainitic bar stock. The disk exhibited a structure which appeared to.be entirely bainitic. The superiority of the disk material is attributed to the fact that very little martensite, if any, was present. The upper pearlitic structure developed in the bar stock by holding 10 hours at 1240~F showed.a good 1000-hour 1-percent total deformation strength.at 1000~F. It is thought that at the stresses involved, the stability of the structure was the chief factor contributing to the strength exhibited, but that at higher stresses using different criteria for comparison (creep strength or rupture strength), the upper pearlitic structure would not show up as good because of its inherent weak strength. This fact was observed in the case of "-17-22A"S upper pearlitic bar stock material. The lower pearlitic structure developed in the bar stock by holding 111 hours at 1050~F showed very poor high temperature properties. Examinations of the microstructure of this material before and after testing showed that the material spheroidized rapidly during testing at 1000~F. A more complete analysis of the structure-property correlation between the disk and bar stock materials, including photomicrographs, will be presented in the final report. "17-Z2A"S STEEL The results.of the bar stock study indicate that a coarse bainitic structure produces the highest 1 000-hour 1 -percent total deformation strength at 1100~F. Using the 1000-hour 1-percent total deformation strengths at 1100~F as a basis for comparison, the isothermal structures studied had the following strengths:

8 Strength Heat Treatment and Structure (psi) 1o. Normalize 1750'F. 15% martensite + 85% coarse bainite. 19,000 2. Austenitize 1750~F + 1-1/2 hrs. at 1300~F. 55% ferrite + 45% medium pearlite. 16, 000 3. Austenitize 1750~F + 5 min. at 700~F. 95% lower bainite + 5% ferrite. 15, 500 4. Oil quench 1750~F. 98% martensite + 2% ferrite. 15, 000 5. Austenitize 1750~F + 2 hrs. at 900~F. 40% martensite + 60% upper bainite and acicular ferrite. 14,000 6. Austenitize 1750~F + 10 hrs. at 1150~F. 60% ferrite +-40% fine pearlite. Less than 14, 000 These structures were tempered to a Brinell hardness of 280 to 320 before testing where'exr necessary. Considering the behavior of the normalized bar stock, it appears that the poor strength of the upper bainitic bar stock developed by holding for 2 hours at 900~F, results from the large amounts of martensite and clear acicular ferrite present. Although the upper pearlitic structure, developed by holding for 1-1/2 hours at 1300~F, had a fairly high 1000-hour 1-percent total deformation strength (16,000 psi) at 1100~F, subsequent testing at 19, 000 psi and 1100~F showed this structure to have a poorer creep strength and rupture strength than all of the other structures tested except the fine pearlite + ferrite structure. The tempered lower pearlitic structure, developed by holding for 10 hours at 1150~0F, had very poor properties at 1100~F. Testing at 1100~F produced rapid spheroidization of this structure.

9 The 1000-hour 1-percent total deformation strengths of the three disks at 1100~F were as follows: Disk Strength No,. Heat Treatment (psi) 1 Normalize 1750~F + temper 2 hrs. at 1-200F. (Ferrite + medium pearlite + tempered constituent). 14, 000 2 Oil Quench 1750~F + temper 8 hrs. at 1200~F. (Tempered ground mass of martensite and upper and lower bainites), 19, 000 4 Interrupted-quench 1750~F + temper 2 hrs. at 1200~F + temper 2 hrs. at 1200~F. (Tempered ground mass of mostly upper bainite and probably some martensite and lower bainite). 20,500 The normalized and tempered disk showed poorer properties than the normalized and tempered bar stock material. Examination of the disk showed that it did..not harden upon heat treatment. The structure of the disk con-.sisted of free ferrite, medium pearlite, and a tempered constituent. The high temperature properties.of the disk were similar. to those of the upper pearlitic bar. stock, which had been developed by holding for 11/2 hours at 1300~F. The oil-quenched and tempered disk had a higher 1000-hour 1-percent total deformation strength than the. oil-quenched and tempered bar stock. The tempered disk showed large amounts..of what. appeared to be upper or coarse bainite, whereas the oil-quenched..and. tempered bar stock was 98 percent martensite. The interrupted-quenched and tempered disk had the highest 1000 -hour 1-percent total deformation strength at 10'F. It exhibited a structure similar to that of the oil-quenched.and tempered disk, except that it appeared to have somewhat higher.percentages of coarse bainite present.

10 H-40 STEEL The results of the bar stock study show that the highest 1000-hour 1 -percent total deformation strength at 1 1000F can be obtained with a coarse bainitic structure. The structures studied had the following 1000 -hour 1-percent total deformation strengths >at 1100~F: Strength Heat Treatment. and Structure (psi) 1. Normalize 1950~F. 70% bainite + 30% martensite. 27, 750 2. Oil quench 1950~ F. 98% martensite + 2% ferrite. 23, 250 3. Austenitize 1950~F + 10 hrs. at 750~F. 60% martensite + 40% acicular ferrite and bainite. 21, 500 These structures were tempered to a Brinell hardness of 280 to 320 before testing. The H —40 steel behaved similar to the 4340 and "17-22A"S steels. The best properties were obtained with a coarse bainitic structure with as little martensite and clear acicular ferrite present as possible. The 1000-hour rupturestrestrengths and 1-percent total deformation strengths at 1100~F of the three disks before and after tempering 4 hours at 1250~F were as follows: Disk No. Heat Treatment As-Received: 1 Normalize 1950~F + temper 2 hrs. at 1200~F + temper 3 hrs. at 1200~F. (Tempered ground mass of martensite + bainite and acicular ferrite. Grain size was 1/5). 3 Oil quench 1950~F + temper 8 hrs. at 1200~F + temper 3 hrs. at 1200~F. (Tempered ground mass of martensite + bainite and acicular ferrite. Grain size was 1/4). Rupture Strength BHN (psi) About 340 35, 000 1 -Percent Strength (psi) 29, 750 About 345 37,000 35,000

11 Rupture 1-Percent Disk Strength Strength Noo Heat Treatment BHN (psi) (psi) 4 Interrupted-quench 1950~F + temper 2 hrs. at 1200~F + temper 3 hrs. at 1200~F. (Tempered ground mass of martensite + bainite and acicular ferrite. Grain size was 1/4). About 350 34,000 33,000 After Re-tempering 4 hours at 1250~F: 1 -. 287/303 32,250 32,250 3 -- 295/315 32,000 30,000 4 287/311 32,250 29,000 The structures, hardnesses, and high temperature strengths of the three as4-received disks were somewhat similar. The structures of the disk specimens and bar stock specimens. were not comparable, and it was not possible to get a complete correlation of their respective properties. The superiority of the as-received disks as compared to the bar stock materials could be partially explained on the basis of two factors, namely: (1) The disk specimens were 25 to 40 points Brinell harder than the bar stock specimens. (2) The as-received disks exhibited a coarser grain size than the bar stock specimens. Retempering the disks for 4 hours at 1250'F produced the following effects: (1) Reduced the hardness of all three disks to 280 to 320 Brinell, (2) Reduced the 1000.-hour rupture strengths at 1100~F for all three disks. (3) Reduced the 1000-hour 1-percent total deformation strengths at 1 100'F of disks Nos. 3 and 4, but increased this strength of disk No. 1.

12 (4) Improved the rupture test ductility of all three disks. The elongation values obtained in rupture testing at 1100~F before and after tempering at 1250~F were as follows: Elongation in 2 -inches Disk No, Before Tempering After Tempering 1 1.3%- 8. 3% 2. 3%- 10. 5% 3 1. 0%- 3. 1% 4. 5% - 17. 0% 4 1. 3%- 5. 6% 2o 5% - 10. 5% C-422 STEEL Because of the transformation characteristics of this steel, only the normalized and the oil-quenched structures were tested in the bar stock study. The structures developed were very similar, and the l000-hour 1-percent total deformation strengths at 1100 ~F were as follows: Strength Heat Treatment and Structure (psi) 1. Normalize 1900~ F. 98% martensite + 2% white etching spheroids. 28, 750 2. Oil quench 1900O~F. 98% martensite + 2% white etching spheroids. 30, 000 Both structures were tempered to a Brinell hardness of 280 to 320 before testing o The 1000-hour 1-percent total deformation strengths at 1100~F of the two C-422 disks were as follows: Disk Strength No. Heat Treatment (psi) 1 (a) Normalize 1900~F + temper 2 hrs. at 1200~F. (b) Full anneal 6 hrs. at 1600~F Normalize 1900~F + temper 2 + 2 hrs. at 12000F. 4 (a) Oil quench 1900~F + temper 8 hrs. at 1200~F. (b) Full anneal 6 hrso at 1600~F. Oil quench 1900~F + temper 2 + 2 hrs. at 12000F. 29,000 30,000

13 The structures of these two disks differed somewhat. The structure of the normalized and tempered disk exhibited a heavy carbide network in a martensite matrix, whereas,the oil quenched and tempered disk-exhibited.a more uniform martensite structure. The results obtained in the disk investigation were in very good. agreement with those obtained.in the bar stock-study. FUTURE WORK Thecreep-rupture testing of.H-40 disk.No. 3 at 1000~, 1100~, and 1200~F will be continued in order to accumulate the additional required design data. When the testing of the H-40 disk is completed, a final report covering this..investigation will be issued.. This report will include a more complete analysis, including photomicrographs, of the structure-property correlation between the disk- and the bar stock materials.

TABLE I Creep-Rupture Test Data for the Retempered H-40 Disks at 1000~, 1100~, and 1200~F Spec. Specimen No. Location. ) Disk 9W 9X 9Y 9Z No. 1. Heat SRR CRR CRR SRR T J [ Test Stress Rupture Elongation Reduction Temp. Time in 2 in. of Area a,, I~F) (pMi) (hrs.) (S) A) 0. 1% Treatment: N. 1950~F + T. 2 hrs. at 1200'F + T. 3 hrs. 1100 60, 000 2. 7 10. 5 37.4 (d) 1100 50.000(b 43 3*0 7.8 (d) 1100 451,000 81 2.7 6.2 (d) 1100 34,000(C) 735 2.3 4.3 (d) irne to Reach Specif Total Deformations I. —. hrs. ) 0.2% 0.5% at 1200~F A (d) (d) {d) 1. f T. 4 hrs. at 1250'F. BHN=287/303 0.04 0.5 - 0.3 10.7 25 0. 5 53 68 0. 219 652 520 0. lied Ti'me at Start a of Third Stage Creep 1.0%o (hrs,) Minimum Creep Rate f//hour) o026 0096 001 Disk No. 3. Heat 8W SRR Treatment: 0. Q. 1950F + T. 8 hrs. at 1200~F + T. 3 hrs. at 1200~F + T. 4 hrs. at 1250F. 1000 65 000 9W 9y 9X 5Aef) 9A(f) 9Z 14Z lOY 10Z SRR CRR CRR SRR SRC SRR STR CRR SRR 1100 1100 1100 1100 1100 1100 1 100 1100 1100 60, 000 50,000 42, 000) 40, 000 39,350 36, 000 33,000 28,000 20,OO0 (e) 10 80 175 313 (e) 514 <e) (h) (h) 17.0 8. 0 5.0 2. 0 50. 0 (d) 22. 0 (d) 8. 8 (d) 7. 0 (d) i- (d) 10. 0 (d) _o (d).f (d) _o 1 4. 5 (d) (d) (d) (d) {d) 2 2 16 256 O.1 1. 5 13 94 19 71 1 4 23 84 304(g) 280 30 100 282 280 BHN=293/335 0. 285 0~ 020 0.0066 0.0016 0. 0024 7W SRR 7X CRR 1200 1200 35,000 30, 000 36 (e) 5. 5 8.1 (d) up(d) (d) 0. 1 5.5 12 18 0. 039 Disk No. 4.Heat Treatment: I. Q. 1950~F + T. Z hrs. at 9W 9X 9Y 9Z SRR CRR CRR SRR 1100 1100 1100 1100 60, 000 50,000 45, 000 3 9. 000 2* 9 70 144 273 10. 5. 5 6.5 1200~F + 40.2 8.2 7. 4 -12.6 T. 3 hrs. (d) (d) (d) (d) at 1200~F (d) (d) (d) (d) 0.03 1. 5 1 3 14 0.8 26 94 100 + T. 4 hrs at 1250~F. 0. 55 44 100 7 0. 38 0 020 0. 0084 0. 0056 BHN287 / 311. (a) SRR Surface plane radial specimen at rim of disk CRR Central plane radial specimen at rim of disk SRC - Surface plane radial specimen at center of disk STR - Surface plane tangential specimen at rim of disk (b) Broke in gage mark (c) Broke in fillet (d) Specimen reached this deformation on loading (e) Rupture test in progress (f) 0. 250-inch specimen (g) Extrapolated value (h) Creep test in progress

TABLE II High Temperature Strengths of H-40 Bar Stock, As-Received Disk Materials, and Retempered Disk Materials At 1100OF Material Heat Treatment BHN Rupture Strengths.(p 'i) ____ 1hr. 10 hr. 100 hr. 1000 hr. ~ * ~ _1 * __,,..-...-, _ 1, I Stress to Cause 1-Percent Total Deformation at Indicated Times (psi) 1 hr. 10 hr 1 00 hr. 500axr 100O.. hr _ -. *,.. As. Received Disks, Disk No. 1 N. 1950~F + T. 2 hrs. at 1200~F + T. 3 hrs. at 1200~F. About 340 _ 65,000 48,000 35,500 72,000 46,000 34,000 29, 750 Disk No. 3 0O.. 1950~F + T. 8 hrs. at 1200~F + T. 3 hrs. at 1200~F. About 345 73,000 51,500- 37,000 70,000 49,250 37,500 35,000 Disk No. 4 I.Q. 1950~F + T Zhrs. at 1200~F + T. 3 hrs. at 1200~F. About 350 73,500 50,000 34,000 72,000 49,000 37,000 33,000 Retempered Disk Materials. Disk No.. 1 N. 1950~F + T. 2 hrs. atl200'F + T. 3hrs. at 1200~F +T. 4hrs. at 1250~F.. 287/303 64,500 55,000 44,000 32,Z50 57,000 49,500 41,500 35,000 32,950 Disk No. 3 Disk No. 4 O. Q.. 1950~F + T. 8hrs. at 1200~F + T. 3 hrs. at.l200~F+T. 4 hrs. at 1250~F..295/315 73,000 60,000.1Q. 1950~0F+T. 2 hrs. atl200'~F +T. 3 hrs. at 1200:~F +T. 4 hrs. at 1250~F. 48,500 47, 500 32,000 62,000 53, 00.. 41,000 33,000 30,000 33,000* 29,000* 2871311 63,500 56,000 32,250 59,500 52,000 42,500 Continued on next page

T able II.(continued) Material Heat Treatment BHN Rupture Strengths (psi) -_ 1 hr. 10 hr. 10 0 hr. 100 0 hr. _. Stress to Cause l-Percent Total Deformation at Indicated Times (psi. 1 hr. 10 hr 100 hr. - 500 hr. 1000 hr. Bar Stock Bar Stock N. 1950~F+T. 18 hrs. at I200~F O.Q. 1950~F +T. 12 hrs. at 1200~F. 312/320 - 30, 000 33,000 27,750 - 27, 000 23, 250 322 29,000* Bar Stock Aust. 1950 F + 10 hrs. at 750~F + T. 1 hr. at 1300~F. 308/313 - - 31,000* - 27,500 21,500 * Extrapolated value.

TABLE III Short Time Tensile Properties of Retempered H-40 Disk No. 3 Heat Treatment: O.Q. 1950~F+T. 8Hrs.at 1200~F + T. 3 Hrs. at 1200~F + T. 4 Hrs. at 1250~F, BHN=295/333 Specimen Specimen Location Number (a) 3W SRR 3X CRR 1Z SRR 1Y 14W CRR STR Test Temp. (~F) Room Room Room 1000 1000 1100 1100 1200 1200 Tensile Strength (psi) 146,500 145,250 155, 000 99, 750 96,750 80, 250 80, 000 65, 500 63,750 U. U7o 113, 500 113,000 120,000 68, 500 70, 000 54,500 54, 000 39, 000 39, 750 U. 17uo 126, 500 125,500 133,500 87, 000 86, 500 68, 500 68, 500 50, 500 52, 000 Offset Yield Strengths (psi) 0. Z~/o 130, 000 129, 000 139, 000 94,000 92, 250 74, 500 74, 500 55,500 58, 000 Proportional Limit (psi) 90, 000 98, 000 102, 5 00 47,000 50, 000 37, 000 34,000 26, 000 25, 000 3Y 14X Elongation Reduction in 2 in. of Area,(%) (%) 15.5 50.5 16.5 51.5 13.5 44..0 CRR CTR 15.0 19. 0 21.0 16.5 15. 0 16. 0 50. 5 61. 0 61.0 48. 8 53. 5 47. 8 3Z 14Y SRR. CTR (a) SRR - Surface plane radial specimen at rim of disk CRR- Central plane radial specimen at rim of disk STR- Surface plane tangential specimen at rim of disk CTR - Central plane tangential specimen at rim of disk

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UNIVERSITY OF MICHIGAN 4050352 3302