The University of Michigan ~ Office of Research Administration Ann Arbor, Michigan "17-22-A"V STEEL MODIFIED WITH COLUMBIUM OR ALUMINUM by R. Jackowski J. W. Freeman Project 04603-52-T Report 244 July 15, 1964 THE TIMKEN ROLLER BER ING COMPANY STEEL AND TUBE DIVISION CANTON, OHIO

"17-22.-A"V STEEL MODIFIED WITH COLUMBIUM OR ALUMINUM Timken "17-22-A"V steel has excellent creep-rupture properties at temperatures up to 1100~F. Higher creep-rupture strengths, retention of strength to higher temperatures, increased ductility and wider latitudes in heat treatment could, however, be useful enhancements of the properties of this steel. In this investigation Timken supplied specimens from a heat with an addition of 0. 44 percent Cb and from three heats with Al contents varying from 0.21 to 0.63 percent. These materials in a number of different conditions of heat treatment were evaluated by rupture tests at 1100~F and.for the Cb bearing heat at 1200'F as well. Experimental induction furnace heats rolled to barstock were used in this investigation. Some bars were heat treated in massive blocks to simulate the heat treatment of rotor forgings for gas turbines. The base "17-22-A"V composition used was the nominal 0. 3 percent C and 0. 8 percent Mn adopted by Timken for adequate hardenability when rotor forgings are normalized and tempered. SUMMARY AND CONCLUSIONS The addition of 0. 44 percent Cb to- "17-22-A'V steel resulted in rupture strengths at 1100~ and 1200 F which were on the high side of the range for the steel when normalized from 1850~ to 1950~F. The ductility of the alloy was low, however. The results from adding Cb were difficult to understand and as a consequence additional research might be warranted. Adding Al in the range of 0. 21 to 0. 63 percent was of no benefit except to increase ductility when the temperature of heat treatment was 1750 or 1800~F. Even then one heat did not show the improved ductility. 1

The data again demonstrate the lower strength and ductility which seem to be associated With C contents of 0. 30 percent and Mn levels at about 0.8 percent. These levels were used to obtain hardenability adequate for forged discs. MATERIAL Tensile specimens were supplied from four heats of 117-22-A"V steel. Columbium had been added to one heat while the other three contained varying amounts of Al. Two of the heats, Heats 2759 and 2760, were 30 pound induction heats. The other two were 300 pound laboratory induction furnace heats. The composition (Weight percent) of the heats as reported by The Timken Roller Bearing Company were as follows: Heat No. C Mn P S Si Cr Ni Mo V Cb Al A165.295.65.018.036.79 1.31.18.51.80.44 A173.32.85.015.018.70 1.30.07.49.87 -.21 2759.32.85.013. 041..78 1.33 19'.72.73 - 32 2760.31.83.016..039.78 1.37.19*.70 75 -.63 - Ni + Cu The specimens supplied were machines from heat treated 7/8-inch diameter barstock. The bars for Heat A165 and for one treatment of Heat A173 were enclosed in 9-inch by 91/2-inch by 4-inch thick blocks to simulate the heat treatment of forgings. Specimens were also supplied from directly heat treated barstock from Heat A173. The treatments and hardness were as follows: Heat No. Heat Treatment BHN 7/8-inch diameter bars sealed in blocks A165 Normalized from 1850~F and tempered for 6 hours at 1250~F 302/311 A165 Normalized from 1900"F and tempered for 6 hours at 1250~F 302/321 A165 Normalized from 1950~F and tempered for 6 hours at 1250~F 311/321 A173 Normalized from 1850~F and tempered for 6 hours at 1250~F 311/321 2

Heat No. Heat Treatment 7/8-inch diameter barstock A173 Normalized from 1750 F and tempered for 6 hours at 1225 F 293/302 A173 Normalized from 1800~F and tempered for 6 hours at 1225~F 311/321 A173 Normalized from 1850~F and tempered for 6 hours at 1225~F 321/331 Barstock from the other two heats, Heat 2759 and 2760, was normalized from 1800~F followed by a 6 hour temper at 1225~F, resulting in Brinell hardness values of 311 and 285, respectively. RESULTS The rupture properties were surveyed using two tests (Table I) for all but Heat A173 which was more completely evaluated, These tests defined the rupture strengths (Figure 1 and Table II) for 100 and 500 hours, Table II does, however, include estimated values for 1000 hours because rupture strengths for 1000 hours are widely used for evaluating alloys of the type under consideration. Columbium Modification The stresses for rupture in 100 hours at 1100~F were similar to those characteristic of experimental heats of "17-22-A"V steel. The estimated strengths at 1000 hours were within the range for'17-22-A"V steel, Ductility values in the rupture tests were low. Increasing the normalizing temperature from 1850'F to 1950'F only slightly increased the stress at 1100~F for rupture in 100 hours, Lower strengths at longer time periods were indicated since the slope of the stress-rupture time curve was somewhat steeper. The indicated rupture strengths at 1200~F would apparently be somewhat higher than those for 117-22-A"V steel at the longer time periods. Ductilities were again very low. The microstructure (Plate 1) appeared to be a mixture of very fine and quite coarse "grained" tempered bainite when normalized at 1850 0F, Normalizing at 1900~F removed all fine grains (Plate 2) and 1950~F 3

resulted in marked coarsening (Plate 3). The comparisons based on experimental heats may not be correctly evaluating the effect of Cb. The barstock was heat treated by being placed in holes in blocks 9-inch by 9 1/2-inch by 4-inch thick to simulate forgings. The comparative data for experimental heats of "17-22-A"V steel were obtained from barstock heat treated directly. The difference in cooling rate then could be altering comparative properties. Data previously obtained has generally indicated lower properties for 117-22-A"V steel when the C was about 0 3 percent and the Mn about 0. 8 percent. These levels of C and Mn were needed to obtain hardenability sufficient for disc forgings. The Cb may therefore have helped to raise the strength since the values are slightly higher than the range for production material, The poor rupture ductility, however, would handicap the Cb modification as a potentially useful alloy. It is difficult to understand the microstructures. Columbium would be expected to be a grain growth restrainer. Secondly, it srhould require higher than usual temperatures of heat treatment to dissolve CbC and obtain effective increases in strength. The slight increase in strength accompanying the upper temperature of normalizing (1950'F) is therefore not surprising. However, the apparently coarse grained austenite, adequate hardening and low ductility are surprising. Titanium (Report 243) had the expected effects and was very effective in increasing strength and ductility when heat treated at 19500F and higher. Possibly the Cb only reduced the effective C content of the alloy and thus raised strengths. There would seem to be sufficient reason to investigate the role of Cb more than was done for this investigation with emphasis on solution of CbC and avoiding the apparent coarsening of the austenite during heat treatment. Aluminum Additions Heat A173 with 0,21 percent Al had rupture strengths on the low side of the range for production heats of "17-22-A"V steel when normalized from 1750~ and 1800~F (See Tables I and II and Figure 1). Ductility was high 4

after these treatments. Raising the normalizing temperature from 1800~ to 1850~F, however, reduced ductility to very low values with some increase in strength. This emphasized the sensitivity of the alloy to small changes in temperature of heat treatment in that temperature range. To simulate the heat treatment of disc forgings, barstock from this heat was also normalized from 1850 F and tempered at 1250eF while sealed in a block which measured 9 by 9 1/2 by 4 inches. There appeared to be little difference in rupture strength and ductility between the barstock heat treated in the block and the barstock heat treated directly. Plates 4, 5 and 6 show a fine tempered bainitic structure when the normalizing temperature was 1750~, 18000 or 1850~F. Considerable coarsening occurred during heat treatment in a block at 1850'F, although it may not have been uniform (Plate 7). Heat 2759 with 0. 32 percent Al had slightly higher 100-hour strengths than Heat A173 when normalized from 1800~F. Ductility was, however, lower. The 0. 63 percent level of Heat 2760 resulted in ductilities similar to Heat A173, but with lower long time strengths. There were no observed differences in microstructure (Plates 8 and 9). There does not appear to be an obvious reason for the low ductility and somewhat higher strength of Heat 2759 with 0. 30 percent Al. The data suggest that Al additions might be useful for improving ductility in rupture tests when temperatures of normalizing are kept at 1800~F or lower. 5

TABLE I Stress-Rupture Time Data at 1100~ and 1200~F for Columbium and Aluminum Modified "17-22-A"V Steel Heat Treatment Rupture Austenitized Tempered Stress Time Elongation Reduction (~F) (~F) BHN (psi) (Hours) (% in 2 in.) of Area (%) Rupture Tests at 1100~F "17-22-A"V + 0. 44% Cb (Heat A165) (A) 1850 1250 302/311 55,000 61 5.0 14, 5 45, 000 217 2 0 7. 0 (A) 1900 1250 302/321 55,000 118 2,.5 4.5 48,000 210 1.5 5.0 (A) 1950 1250 311/321 55,000 85 2.0 4.0 "17-22 —A"V t 0.21% Al (Heat A173) (B) 1750 1225 293/302 45,000 21 19.0 61.5 37,000 129 17.5 39.0 29,000 398 20.0 28.5 (B) 1800 1225 311/321 45,000 42 11.5 35.5 37,000 170 18.5 30.0 29,000 526 14.0 22.5 (B) 1850 1225 321/331 32,000 544 2.0 (c) (A) 1850 1250 311/321 50,000 28.5 4.5 12.5 37,000 233 1. 1.5 32,000 330 2.0 (c) "17-22-A"V + 0. 32% Al (Heat 2759) (B) 1800 1225 36,000 231 2.5 7.0 30,000 522 4.0 5.0 "17-22-A"1V + 0.63% Al (Heat 2760) (B) 1800 1225 40,000 144 10.0 13.0 30,000 322 13.0 15.0 Rupture Tests at 1200~F "17-22-A"V + 0.44% Cb (Heat A165) (A) 1850 1250 302/311 30,000 120 2.5 8.0 22,000 361 1.5 6.0 (A) 1900 1250 302/321 30,000 88.5 3.0 5.0 22,000 434 3,0 3.5 (A) Barstock sealed in a block (B) Barstock (C) Broke in fillet.

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