REPORT ON RUPTURE PROPERTIES AT 1200~ AND 13000~F OF A TURBINE DISC FORGING FROM A286 STEEL By R. Jackowski A. I. Rush J. W. Freeman PROJECT 842 J 3 REPORT 203 June 30, 1954 REPORT 203 THE TIMKEN ROLLER BEARING COMPANY STEEL AND TUBE DIVISION CANTON, OHIO

INTRODUCTION This investigation was undertaken to determine the rupture strength at 1200~ and 1300~F of A.286 steel taken from a turbine disc forging. This steel is used generally in the form of bars and forging stock for turbine rotors, shafts, buckets or blades and other uses requiring high strength up to 1300~F. This report presents the stress-rupture properties estabished for the material taken both radially and tangentially from the forged turbine disc.. SUMMARY AND CONCLUSION Appraisal of the data obtained on the turbine disc forging from A.286 steel led to the following conclusions: 1. The 1000-hour rupture strength at 1200~ and 1300~F were approximately 50, 000 psi and 31,000 psi, respectively, for both radial and tangential direction. 2. The elongation to rupture in 1000 hours at 1200~F was approximately 2 to 4 percent. At 1300~F, the ductility was somewhat higher. Radial specimens near the rim exhibited the lowest elongations, about 5 percent, whereas the radial specimens from the center of the disc gave elongations as high as 10 percent. 3,. The position of the specimen in the disc appeared to have very little effect on the rupture strength at 1000 hours,

2 4. The migration to and growth at the grain boundaries of the carbides indicate the minor structural instability at the temperatures tested. TEST MATERIALS A number of tensile specimens, machined to a diameter of 0. 357 inches, were submitted from a turbine disc forging of A286 steel having the following chemical composition: Heat No. C Mn P S Si Cr Ni Mo V Ti 02395 0.047 1.54 0.017 0.011 0.68 14.15 25.44 1.28 0.27 2. 12 The forged disc was oil quenched from 1800~F and tempered for 16 hours at 1325~F to a hardness range of 248/262 Brinell. The direction and location of the specimens within the disc and the code numbers used for identification were as follows: Code Direction of Test R Radial (near outer diameter of disc) T Tangential (near outer diameter of disc) RC Radial (from center of disc) RESULTS AND DISCUSSION Tests were carried out to establish the rupture characteristics at 1200~ and 1300~F of both the tangential and the radial specimens from the A286 forging described above. The results of the stress-rupture tests are presented in Table I and Figure 1.

The stress - rupture time curves, Figure 1, were established initially at both temperatures for time periods out to 1000 hours from radial specimens. Check tests at both temperatures were then run on the tangential specimens taken from the outer diamter of the disc and the radial specimens taken from the center of the disc. The rupture strengths at both temperatures for 100 and 1000 hours are shown by the following tabulation: Specimen Temp Rupture Strength (psi) Elongation (%) Direction (~F) 100-hour 1000-hour 100-hour 1000-hour R 1200 60,000 50,000 3 2 T 1200 (64,000) 49,000 -- 4 RC 1200 -- (47,000) -- 3 R 1300 45,000 31,000 5 5 T 1300 (48,000) 31,000 -- 7 RC 1300 -- (32,000) - 10 ( ) Figures enclosed in brackets are estimated values based on extrapolations. The rupture data indicate that there is very little variation in the 1000-hour rupture strength between specimens taken from different locations in the disc. The two tests run at each temperature on the tangential material show a slight tendency toward higher short-time strengths and lower strengths beyond 1000 hours because of the steeper slope of the stress - rupture time curve s,. There was no observable difference in microstructure between the tangential and radial specimens. The original structure of the A.286 steel from this heat is shown in Plate No. 1.. The 1800~F treatment of this

4 material resulted in ASTM grain size of 3 to 5. The structure consisted of an austenitic matrix of carbides and nitrides (or carbonitrides) distributed rather uniformly throughout the structure, both in the grains and in the grain boundaries. The structure of the radial specimen fractured after 2156 hours at 47, 000 psi and 1200~F is shown in Plate No. 2. There appeared to be lesser amounts of carbides in the grains than were observed prior to testing. However, the grain boundaries were clearly outlined by a discontinuous precipitate. These were probably formed by migration of the carbides to the grain boundary during rupture testing. Intergranular cracks are present both at the fractured surface and in the side adjacent to the fracture. The radial specimen fractured after 738 hours under a stress of 32, 500 psi at 1300~F showed the presence of larger grain boundary precipitates than were obtained for the material tested at 1200~F. Other than this, the microstructure of the specimens tested at 1200~ and 1300~F were similar. There were a lesser number of intergranular cracks both at the fracture and at the surface adjacent to the fracture. There was some evidence of transgranular fracture, as may be seen in the micrograph of the fracture at 1300~F, Plate No. 3.

TABLE I Stress-Rupture Data for a Turbine Disc Forging from A286 Alloy (Heat 02395) (Oil Quenched from 1800~F + 16 hours at 13250F - 248/262 Brinell) Code Stress Rupture Time Elongation Reduction of Area No. (psi) (hours) (% in 1 in.) (%) Rupture Test at 1200~F R 60,000 113 2.5 5.5 R 57,000 237 2.0 2.0 R 50,000 641 2.0 2.0 R 47,000 2156 (a) (b) T 57,000 406 4.0 (a) 4.0 T 47,000 1437 4.0 4.5 RC 47,000 881 3.5 3.0 Rupture Test at 1300~F R 55,000 11 3.0 5.0 R 45,000 101 5.5 6.5 R 36,000 470 6.0 10.5 R 32,500 738 5,0 7.5 T 45,000 208 3.0 4.0 T 32,500 745 7.0 12.0 RC 32,500 837 10.0 11.0 (a) Broke in gage mark. (b) Broke in fillet.

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Three mounted picture pages follow here. See E.R.I. file copy.