NINTH 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 A. I. Rush J. W. Freeman PROJECT M903 AIR FORCE CONTRACT NUMBER: AF33(038)-13496 SUPPLEMENTAL AGREEMENT NUMBER: S4(53-534) EXPENDITURE ORDER NUMBERS: 605-227 SR-7 and R6.15-13 SR-3a March 31, 1953

INTRODUCTION The Materials Laboratory, Wright Air Development Center, is sponsoring an investigation of the high temperature properties of low alloy steels for use as forged wheels for the gas turbines of jet engines. This progress report covers the period between January 1, 1953 and March 31, 1953. The work is being carried out under Contract Number: AF 33(038)13496 (Expenditure Order Number: 605-227 SR-7) and Supplemental Agreement Number: S4 (53-534) (Expenditure Order Number: R615-13 SR-3a). Previous reports have presented the results of a study of the properties of forged wheels of 4340, "17-22A"S, H-40 and C-422 alloys. The data obtained. on wheels are now being incorporated in a final report on this phase of the work. A concurrent, limited investigation was carried out on the relationship between structure.and properties of these types of alloys. This phase of the work has been extended and is now in progress. RESULTS During the period covered by this report, an extensive metallographic examination of the forged wheels was carried out. The problems of correlating properties and structures of the wheels with the results of the heat treatment studies on the alloys have, however, been greater than anticipated. It was originally expected that a final report on the wheels would have been submitted during this period. It has not been possible to do so.

2 Influence of Heat Treatment on High Temperature Properties of Low Alloyed Steels The objective of the heat treatment studies is to provide information relating the varying microstructures obtainable in low-alloyed steels with their properties at high temperatures. Work previously carried out was very limited in scope. Attempts were made to establish the stress for one-per cent total deformation at 1100~F for four isothermally transformed structures and for oil quenched and normalized structures. The present program was undertaken to extend the range of structures; to extend the range of stresses to include rupture tests and the temperature range from 700~ to 1200~F; to include continuous cooling, as well as isothermal types treatment; and to include additional compositional variations. 1. Structures to be Investigated The structures and treatments to be tested are outlined in Tables I through III. By reference to time - temperature - transformation diagrams previously outlined and reported, certain idealized structures were selected to cover the range of structures possible. The names of the idealized structures constitute a convenient way of identifying the treatments used for discussion purposes. It is very important, however, to recognize, as is outlined in the tables, that the actual structures deviated from the idealized structures in many cases. The major reason for the variations between idealized aim structures and the actual structures was that the times for complete transformation were too long. Partial transformation to the desired structure could be obtained, but the time to complete the transformation would have

3 been very long. For example, "upper bainite" in 4340 steel was only 70 per cent upper bainite and 30 per cent martensite. The 70 per cent of upper bainite was obtained in 28 hours at 850~F. The time - temperature, transformation diagram, however, indicates that transformation would not be complete for time periods considerably longer than a week. It was not considered desirable in such cases to attempt to produce complete transformation, but rather to obtain a predominance of the aim structure. The transformation temperatures were chosen in the following manner: 4340 and "17-22A"S The highest transformation temperature was chosen in the upper limit of the pearlite nose of the curve such that transformation would occur in a reasonable time. The resulting structure is called upper pearlite. The lower temperature limit beneath the pearlite nose of the curve where only pearlite would form was chosen for the lower pearlite structure. The middle pearlite structurewas obtained by transforming in an intermediate temperature range between these two limits, The same procedure was used for choosing transformation temperatures around the bainitic nose of the curve. H-40 All transformations in the upper nose of the H-40 curve result in a fine carbide precipitate. Therefore, only one temperature was chosen and the resulting structure referred to as pearlite. The bainitic region of the curvewas restricted to one temperature, since at other temperatures, the transformation times were unreasonably long. Hence, only one transformation temperature was used, and the resulting structure referred to as bainite. In general, these treatments include those previously considered,

4 together with the addition, where the transformation characteristics permit, of "middle pearlite" and "middle bainite. " Where the initial hardness exceeds 320 Brinell, tempering was used to reduce.the hardness to about 300 BHN. 2. Evaluation of the High Temperature Properties of the Various Structures The general objective of the tests will be to determine the relative strengths of the various structures by survey type tests as outlined in the following sections: (a) At 700~ and 900~F base comparisons on one stress. The stress should, in general, be one which will give total deformations in 1000 hours around one-per cent. Rupture tests are, in general, of little value at these temperatures because the rupture curve would be expected to be nearly horizontal from the tensile strength for the time periods considered, and the stresses would all have to be well above the yield strength. The properties of 4340 may be an exception to this in that its strength is so low at high temperatures that rupture properties would be useful. (b) 4340 steel will also be tested at 10000 and 1100~F. At these temperatures, the new structures (middle pearlite and middle bainite) will be tested under 13, 000 and 4, 500 psi, respectively, the same stresses as were used in.previous work. In addition, rupture tests will be run. The first survey of rupture properties will be based on single tests, using a stress which should cause fracture between 100 and 1000 hours for all structures. (c) t17-22A"S and H-40 steels will also be tested at 1100' and 1200~F. The new structures will be tested under the survey stresses used in previous work at 1100~F. In addition, rupture tests under one stress aimed to fracture in time periods between 100 and 1000 hours will be run.

5 At 1200~F, the survey will be confined to rupture tests aimed to rupture between 100 and 1000 hours. (d) On completion of the survey tests, consideration will be given to more extensive testing of the more useful structures. (e) No definite program has yet been laid out for other phases of the work. 3. Progress to Date The necessary 4340 and "17-22A"S bar stock were received during March. It was furnished gratis by the Timken Roller Bearing Company, which supplied the following chemical analysis: Type Heat Steel C Mn P S Si Cr Ni Mo V Number 4340.40.70.020.019.30.78 1.75.26 - 19053 "17-.22A"S.29.61.016.016.67 1.30.18.47.26 10420 Specimens aimed to produce "middle bainite" and "middle pearlite" as previously outlined for 4340 and "17-22A"S were heat treated from stock from the heats previously used. The "pearlite" samples of H-40 were also heat treated. Tempering data for the 4340 and "17-22A"S structures are included as Figures 1 through 4. The actual tempering conditions used and the hardness values obtained are included in the tabulation of treatments. In addition, a number of samples for the heat treatments previously used were prepared for testing and tests started. During the next period, effort will be concentrated on accumulating the survey tests outlined previously. Additional information on tempering characteristics will also be accumulated for all the structures to enable a future survey of the structures tempered under other conditions than those previously used to a hardness of 300 BHN,

TABLE I Type Structures, Heat Treatments and Actual Structures for 4340 Steel (All 4340 bar stock au.stenitized at 1750~F for 1 hour) Aim Structure Upper Pearlite Middle Pearlite Lower Pearlite Upper Bainite Middle Bainite Lower Bainite Normalized Oil T ransformation Conditions Temp-~F Time-hrs 1240 10 Approximate Structure Obtained 1150 14 1050 111 65% medium pearlite + 35% ferrite 85% fine pearlite and fine carbide-ferrite aggregate + 15o ferrite 90% very fine carbide-ferrite aggregate + 10%o ferrite 70% upper bainite + 30% martensite 100% medium acicular bainite BHN 212/221 199/233 260/275 319/324 302/313 430 385 585 Tempering Temp-~ F Time-hrs None - None None 199/233 BHN 212/221 260/275 850 28 750 24 None None 1100 319/324 302/313 277/301 650 1-1/2 100% lower bainite Air Cooled from 1750 35% martensite + 65% bainite Oil Quenched from 100% martensite 1750 1100 1100 1 10 300/311 304/309

St: Ur Pe M: Pe Lc Pe Ur Ba Mi Ba Lc Ba Nc Oi Qu TABLE II Type Structures, Heat Treatment and Actual Structure for 1.25 Cr-Mo-Si-V ("17-22A'"S) Steel (All "17-22A"S bar stock austenitized at 1750~F for 1 hour) Transformation Tempet Aim Conditions BHN ructure Temp —F Time-Ohrs Approximate Structure Obtained Temp ~F T >per 1300 1-1/2 55% ferrite + 45% medium 309 None.arlite pearlite iddle 1225 1-1/2 60% ferrite + 40% medium fine 267/285 None zarlite pearlite -wer 1150 10 60% ferrite + 40% fine pearlite 375 1200.arlite >per 900 2 40% martensite + 60% upper 465 1200 tinite bainite and acicular ferrite iddle 800 1/2 100% fine acicular bainite 360 1200 linite )wer 700 1/12 95% lower bainite + 5% ferrite 365 1200 Linite )rmalized Air Cooled from 15% martensite + 85% coarse 355 1200 1750 bainite 1 Oil Quenched from 98%a martensite + 2% ferrite 525 1300 ienched 1750 ring 'ime-hrs 12 16 4 12 10 1 BHN 309 267/285 293/313 284/327 307/310 273/302 302/313 272/310

TABLE III Type Structure, Heat Treatment and Actual Structure for 3 Cr-Mo-W-V (H-40) Steel (All H-40 stock austenitized at 1950~F for 1 hour) Transformation Aim Conditions Structure Temp.- A F T ime hr s Pearlite 1300 24 Bainite. 750 10 Normalized Air Cooled from 1950 Oil Oil Quenched from Quenched 1950 Approximate Structure Obtained fine carbide precipitate 60% martensite + 40% bainite and acicular ferrite 70% bainite + 30% martensite 98% martensite + 2% ferrite BHN 190/199 480 435 523 Tempering Temp-~F Time-hrs None 1300 1 BHN 190/199 293/312 312/320 290/.323 1200 1200 18 12

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