REPORT ON RUPTURE CHARACTERISTICS OF 12 Cr, 2-1/4 Mo, 1/4 V (LAPALOY) STEEL AT 1100* AND 1200'F By R. Jackowski J. Wo Freeman PROJECT 842 November 15, 1954 REPORT 208 THE TIMKEN ROLLER BEARING COMPANY STEEL AND TUBE DIVISION CANTON, OHIO

RUPTURE CHARACTERISTICS OF 12 Cr, 2-1/4 Mo, 1/4 V (LAPALOY) STEEL AT 1100~ AND 1200~F The purpose of this investigation was to determine the rupture characteristics at 1100. and 1200F of a heat of 12 Cr - 2 1/4 Mo - 1/4 V steel (Lapaloy) made by the Timken Roller Bearing Company. Lapaloy is a Mo + V modification of the 12 Cr martensitic steel proposed for use in the steam-power and gas-turbine industries. In addition to determining the rupture strength, metallographic examinations were made of the original and of the most prolonged rupture specimens. SUMMARY The Lapaloy tested had the following rupture properties at 100 and 1000 hours: Temp Rupture Strength (psi) Rupture Elongation (%) ( F) 100-hr 1 000-hr 10-2hr -1. 000-hr 1100 41,500 (29,000) 25 20 1200 22,000 13,000 30 (45) The heat of Lapaloy tested at 1100'F was not much better in 100-hours rupture strength than 12 Cr 3 Mo oil-quenched material and slightly weaker at 1000 hours. There appeared to be no difference in ductility. It did have higher ductility and about equal strength to the 12 Cr 3 Mo steel normalized from 1900 ~F

2 The rupture strength values at 1100'F of the Timken made heat of Lapaloy were on or below the low side of the range of values reported in literature for the alloy. The 1000-hour strength at 1200'F fell below the reported range. The structure of this heat consisted essentially of tempered martensite and of a small amount of delta ferrite in the form of stringers. TEST MATERIALS Machined 0. 505-inch-diameter specimens were supplied from rolled bar stock from a one-ton heat of Lapaloy reported to have the following composition: Heat No. C Mn P S Si Cr Ni Mo V 02449.26 1.12.015.019,68 12.17.19 2.25.30 The material for the specimens was heat treated as follows: 1750~F, 1 hour at heat, air cool - 341/352 BHN 1900'F, 1 hour at heat, air cool - 555 BHN 1300'F temper for 4 hours, air cooled - 285 BHN For rupture testing at stresses over 40,000 psi, the specimens were remachined to 0. 400-inch diameter to bring the load requirements within the capacity of the stress-rupture units. RESULTS The stress-rupture data obtained for this investigation are listed in Table I and the established stress-rupture time curves are shown in Figure 1. The 100-hour and 1000-hour rupture strengths and rupture

3 elongation values obtained from the data are as follows: Temperature Rupture Strength (psi) Rupture Elongation (%) ('F) 10 00r-hr 1 0 00-hr 100-hr- OO -hr 1100 41,500 (29,000) 25 20 1200 22,000 13,000 30 (45) The structure of the original material and of the fractured specimens taken from the longest time rupture tests at 1100. and 1200'F were examined microscopically. The original structure is shown in Plate 1. The appearance of the fracture, the surface adjacent to the fracture, and the structure of the interior after testing at 1100' and 1200'F are shown in Plates 2 and 3 respectively. DISCUSSION The rupture strength and elongation of Lapaloy, Heat 02449, are compared with those of 12 Cr 3 Mo steel, previously investigated in Figure 2 and with data reported in literature in the following tabulation: Steel Heat Heat Treatment BHN Rupture Strength (psi) Rupture Elong. (o%) No. i______0-hr 10o0-hr i'00-hr I00r Rupture Strength at 1100 F (a) Lap- 02449 N 1750' + N 1900F 285 41,500 (29,000) 25 (20) aloy + Temper 1300'F 12 Cr 02718(b)N 1900F + 6 hrs 321/ 44,500 28,000 20 15 3 Mo at 1150'F 352 12 Cr 02718(b OQ 2115F + 6 hrs 286/ 37,500 31,000 24 3 Mo at 1200'F 302 Lap- (c) OQ 2000'F + - -- 25,000/ aloy Temper 43,000

4 Steel Heat Heat Treatment BHN Rupture Strength (psi) Rupture Elong. (%) No. 100 -hr - -000,hr 100-hr 1000,-hr.*~i ~ i' I. i.. *,. -.. i.... Rupture Strength at 1200~F Lap- 02449 N 1750' + N 1900' 285 22,000 13,000 30 (45) aloy + Temper 1300'F Lap- (c) OQ 2000F + -- 19,000/ 15,700/ aloy Temper 29,000 20,000 (a) Figures in brackets indicate extrapolation of the stress-rupture time curve s. (b) Data for the 12 Cr 3 Mo steel taken from Report No. 197. (c) Range of values found in literature based on the Larson Miller parameter, T (25 + log t. ). The rupture strength of Lapaloy at 1100*F is higher at 100 hours and lower at 1000 hours than that of the 2115'F oil-quenched 12 Cr 3 Mo steel. The available data do not show any difference in ductility. Comparison with the 12 Cr 3 Mo steel normalized from 1900 F indicates that the.strength of Lapaloy is about equal for 1000 hours, but lower for 100 hours. The ductility of the Lapaloy was slightly higher. Only one rupture test at 1200*F for the normalized 12 Cr 3 Mo material was available for comparison. The two materials gave identical results at the same stress as may be seen f-rom the following tabulation: Material Stress (psi) Rupture Time (hours) Elongation (%) Reduction of Area (%) Lapaloy 27,000 41.3 29.0 81.0 12 Cr 3 Mo 27,000 40.0 34.0 78.5 The rupture strength of the heat of Lapaloy tested at 1100'F falls on the low side of the range of values reported for Lapaloy in literature. The 1000-hour strength.at 1200F was below that of the reported range.

5 Microscopic examination of the original material indicated that the structure consisted of tempered martensite and delta ferrite. The final normalizing temperature of 1900~F resulted in a rather fine-grained structure. The ruptured specimens showed a transgranular type of failure at the fracture at both 1100~ and 1200~F. The surface adjacent to the fracture gave no indications of intergranular oxidation. The only change observed in the structure after testing was an increase in the tempering of martensite.

TABLE I Rupture Data for Lapaloy at 1100' and 1200~F (Heat 02449, Air Cooled from 1750'F, Air Cooled from 1900~F and Tempered 4 Hours at 1300F - 285 Brinell.) Stress Rupture Time Elongation Reduction of Area (psi.) (hours) (% in 2 in.) (%) 1100'F 50,000 11 9 27.0 73.0 46,000 31.3 26.0 74.5 39,000 350 23.5 72.0 36,000 399 28.5 72.0 33,000 543 21.5 71.0 1200'F 33,000 15.6 32.0 82.0 27,000 41.3 29.0 81.0 16,000 423 47.5 82.5

liissing Figures 1 and 2, also Plates?Ko. 1,2,3 refer to file copy