The University of Michigan ~ Office of Research Administration Ann Arbor, Michigan PROGRESS REPORT ON HIGH TEMPERATURE METALLURGICAL CHARACTERISTICS OF 2 1/4 Cr 1 Mo STEEL TUBES MADE BY THE MICHIGAN SEAMLESS TUBE COMPANY by P. D. Goodell J. W. ireeman Project 08043-32-P April 10, 1967 Prepared for: MICHIGAN SEAMLESS TUBE COMPANY 400 WEST AVENUE SOUTH LYON, MICHIGAN

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PROGRESS REPORT ON HIGH TEMPERATURE METALLURGICAL CHARACTERISTICS OF 2 1/2 Cr 1 Mo STEEL TUBES MADE BY THE MICHIGAN SEAMLESS TUBE COMPANY The Michigan Seamless Tube Company produces seamless tubing which is used at high temperatures in applications under the jurisdiction of the Codes of the ASME Power and Pressure Vessel Committee. An investigation is in progress to determine if the tubing as produced by the Michigan Seamless Tubing Company has the creep-rupture properties expected for the stresses allowed by the Codes for such tubing. The creep-rupture properties of 2 1/4 Cr 1 Mo steel are known to vary over a considerable range. The reasons for the range are not understood. Presently specified chemical composition alone will not determine the level of the properties. ASTM Specification A-213 attempts to insure at least a minimum level of strength by restricting heat treatment. The matter is sufficiently uncertain, however, so that users of the tubing, particularly in superheaters, can be concerned that the production procedures of each supplier will not result in unexpectedly low properties. It is just as important to the Michigan Seamless Tube Company to know.that their production procedures do not result in low properties as it is to their advantage to know if the properties developed by their procedures are at high levels. The research currently in progress extends the information resulting from a survey of tubing made and heat treated several ways as presented in The University of Michigan Report No. 05007-30-T, entitled:'A. Survey of Creep Rupture Properties at 11000F of 2 1/4 Cr 1 Mo Steel Tubes Made by Michigan Seamless Tube Company, " and dated July 31, 1964. The following are the specific objectives: 1.o Extend the creep-rupture data from the July 31, 1964 Report on selected tubes to time periods approaching 10, 000 hours in order to satisfy the presently widely held view that tests of this duration are necessary to establish reliable creep-rupture strengths.

2 Determine the creep-rupture properties of tubes heat treated by a new modified isothermal" process. 3. Make laboratory heats with low and high nitrogen to determine if there is an affect of nitrogen on creep-rupture properties. Materials Investigated The compositions of the tubes being considered in this investigation are given in Table 1. This Table was made up by simply adding the information to Table 1 of the July 31, 1964 Report for Tube No. 15. Tube No. 15 is the new tube with the modified isothermal treatment. Extension of Creep-Rupture Testing at 1100~F on Selected Tubes Surveyed for Report No. 05007-30-T Tube No. 12 (Special Anneal at 14500F) Tube No. 12 had the highest extrapolated 100, 000-hour rupture strength at 1100~F (9,600 psi) of all those investigated for Report 05007-30-T. A specimen was machined and a test was started at 11, 800 psi to check this high strength with the expectation that it would have a rupture time of 6000-7000 hours if the original stress-rupture time curve was correct. The following test results were obtained: Temperature 100~F Stress 11,800 psi Rupture Time 2443. 6 hours Elongation 32. 5% Reduction of Area 62. 8% This test result is. included in Table 2 along with the results previously obtained. The specimen used was of full wall thickness and 0. 5-inch wide. The rupture time was much shorter than the stress-rupture time curve of Figure 2 of Report No. 05007-30-T predicted. Experience with stress rupture testing indicates that the stress-rupture time curve increases in slope * Figures 2 and 3 from Report No. 05007-30-T were reproduced and the data from the current research added in red to show the results of the research in progress. 2

at about 1000 hours and probably extrapolates to about 7000 psi at 100, 000 hours. It will be noted that, as drawn, the slope of the curve after the increase in slope is similar to that for the other tubes, lending support to the extrapolation of the curve as now shown. The specimen was examined microscopically and no unusual features were observed. The ductility dropped from the previous test. Both observations tend to support the increase in slope of the stress-rupture time curve as characteristic of the material. There has been discussion of conducting a test on a 0. 250-inch diameter specimen to check the slope of the curve. This should receive further consideration before conducting the test. Long Time Rupture Test on a Full Sized Specimen After the test on Tube No. 12 at 11,800 psi ruptured, it was decided to start another full wall specimen for a long duration (5000-10, 000 hours) test. A specimen was machined from Tube No. 14 for this purpose. The status of this test is: 12, 000 psi In Progress 646 hours (as of 4-10-67) Modified Isothermal Treatment (Tube No. 15) Four full wall rupture specimens were machined and two rupture tests have been started at 11000F: 19, 000 psi In Progress 142 hours (as of 4-10-67) 16, 000 psi In Progress 646 hours (as of 4-10-67) These points have been added to a copy of Figures 2 and 3 taken from Report No. 05007-30-T. The tests have been in progress longer than the tests previously conducted on material annealed at 1750'F or normalized plus tempered. The rupture times are approaching the longest of any obtained to date after the special 1450~F anneal (Tube No. 14). 3

Creep Test on Tube No. 13 Both rupture and creep strengths are used in evaluating steels for Code use. Because annealing at 1450"F is a somewhat unusual heat treatment, it was deemed necessary to be sure that it does not result in abnormally low creep strength. The tube (No. 13) with the apparently lowest rupture strength with the special 1450"F anneal was selected on the basis that if its creep strength was adequate, there would be no question about the creep strength of the tubes with higher rupture strengths. The test was run at a stress of 4, 200 psi, the current Code stress, at 1100~F. The creep curve (Fig. 2) indicates a creep rate of 0.02 per cent per 1000 hours. This would extrapolate to a stress of 3600 to 3800 psi for a creep rate of 0. 01 per cent per 1000 hours. This creep strength is at the low side of the range for heat treatment "above or near top of critical range" —one interpretation of the heat treatment clause of the present A-213 Specification and the treatments used for setting the Code stress. Because Tube No. 1 also had a creep strength of about 3800 psi, there seems to be an indication that treatment at 14500F might not develop as high creep strengths as treatment at higher temperatures. While the creep rate now appears to be fairly constant, it is suggested that the test be continued for another 1000 to 1500 hours in order to check whether or not it might not still decrease to a lower rate. Tests on 2 1/4 Cr 1 Mo steel often require rather long time periods before attaining minimum creep rate. Effect of Nitrogen In accordance with previous agreement, laboratory heats have been made with low and normal or high nitrogen content. The heats have been made, rolled to bar stock and heat treated. The aim compositions were as follows: 4

Carbon 0. 12 per cent Manganese 0. 45 per cent Silicon 0. 30 per cent Chromium 2. 25 per cent Molybdenum 1. 00 per cent Nitrogen low (none added), 0. 01 and 0.02 per cent The heats were melting in a vacuum induction furnace and carbon deoxidized. Experience has indicated that this procedure provides material with properties similar to production furnace heats by avoiding the oxygennitrogen reactions of air melting in small induction furnaces with the accompanying complications from the need for excessive use of solid deoxidizers. Nitrogen was added as chrome nitride. Split heats were used, the first half with no added nitrogen and the second half with added nitrogen, so that the nitrogen effect would not be influenced by other heat-to-heat effects, if any. The heats were hot rolled, cold reduced 40 per cent and heat treated. Samples have been sent to a commercial laboratory for chemical analysis. Stock sufficient for 3 or 4 specimens were given the following heat tr eatments: a) Heated 1/2 hour at 1450~F, air cooled. b) Heated 1/2 hour at 17500F, cooled at 500F per hour to 1100~F, and furnace cooled to room temperature. Currently it is planned to machine 0. 250-inch diameter specimens and to conduct tests on the material with no nitrogen added and then with an addition of 0. 02 per cent. The material heat treated at 14500F will be used. Note: A student melted, rolled, and heat treated the heats with MST support only for materials and as technicians assistance. 5

Table 1 DESCRIPTION OF SAMPLES OF TUBES SUBMITTED Chemical Composition Reported Tube Heat Tube Size C Mn Si Cr Mo P S No. No. Dia. (in,) Wall(in. ) Heat Treatment (%) (%) (%) (%) (%) (%) (%) 1 3341384 2 0.404 Annealed 1450~F(a).13.44.28 2.22 1.02.010.017 2 3341384 2 0.404 Norm. 1650~+Temp..13.44.28 2. 22 1.02.010.017 1375 OF(b) 3? 2 3/8 0.404 Annealed 1450~F(a). 4 3320643 2 1/8 0.471 Annealed 1450~F(a).11.44.31 2.25 1.02.010.008 5 27218(e) 2 1/8 0.471 Annealed 1450~F(a).11.46.30 2.31 0.94.013.025 6 27218(e) 2 1/8 0.471 Annealed 1750~F(c) Same as Tube No. 5 7 3341339 2 1/8 0.450 Cold drawn+1450~F(a).11.42.29 2.23 0.95.008.013 8 3341339 2 1/8 0.450 Tube reduced+1450~F(a).11.42.29 2.23 0.95.008.013 9 3341339 2 1/8 0.440 Cold drawn+Annealed+.11.42.29 2.23 0.95.008.013 1750~F(c) 10 3341339 2 1/8 0.450 Cold drawn+Norm. and.11.42.29 2.23 0.95.008.013 Temper.(d) 11 3341339 2 1/8 0.450 Cold drawn+Water.11.42.29 2.23 0.95.008.013 quench. 17000F+ temper. 1450~F 12 3342219 2 1/8 0.452 Duplicates No. 7.105.47.30 2.27 0.96.008.012 13 332108 2 1/8 0.452 Duplicates No. 12.105.45.33 2.29 0.98.008.016 14 30558(e) 2 1/8 0.452 Duplicates No. 12.11.45.32 2.25 0.90.013.025 15 3322242 2 1/8 0.452 Modified isothermal(f).115.45. 29 2. 10 0.97.010.007 (a) Cold worked tube was heated to 1450~F, 1 hour at heat and air cooled. (b) Tubing heat treated at 14500F from the same lot as Tube No. 1 was reheated to 1650~F for 1 hour and air cooled plus tempered at 1375~F for 1 hour, air cooled. (c) Cooled at 500F per hour from 1750~F. (d) Fast cooled from 17500F+tempered at 1375~F for 1 hour. (e) Tubes 5, 6 and 14 were made from steel from a different steel producer than the other tubes. (f) Cold draw before modified isothermal anneal.

Table 1 (continued) Ultimate Yield Heat Treatment Prior to Tube Strength Strength Elongation Hardness Piercing Cold Working to Size No. (psi) (psi) (% in 2") Rockwell "B" and Rolling (~F) (hours) (cooling) 1 67,600 34,700 57 72 >1800~F 1650 3 50~F/hr to 1100~F 2 69,300 46,600 65.6 76/77 Same as 1 except reheat treated 3 68,700 40, 100 64.8 75/77 >1800~F 1450 1 Air cooled 4(a) 69,000 50,800 57 74/75 to 2 7/8" 1450 1 Air cooled x 9/16" 5(a) 70, 000 48,700 54.6 77/78 to 2 7/8" 1450 1 Air cooled x 9/16" 6 Same as Tube No. 5 except final heat treatment 7-10 84,400(b) 58,700 53.1 72/76 11 78,200 63,200 53.9 85 12 72,100 41,000 56.2 72/74 13 84,200 61,600 48.4 85 Same as Tube No. 12 14 84,000 56,600 53.9 85 Same as Tube No. 12 15 80,600 63,400 51.5 81/82 (a) To compare tubes of steel from two suppliers, made the same way. (b) May be heat certification properties.

Table 2 STRESS RUPTURE TIME DATA AT 11 00F FOR MICHIGAN SEAMLESS TUBE COMPANY 2 1/4 Cr - 1 Mo STEEL TUBING Rupture Elongation Reduction of Tube No. Stress (psi) Time (hrs) (% in 2 in.) Area (%) Heated for one hour at 1450~F, air cooled 1 20,000 25.9 63.5 87. 0 17,000 63 72. 0 84 5 15,000 155 71. 0 84 5 13,000 560 74.5 81. 0 11,000 1664 62.5 77.0 3 17,000 86.2 47.0 83.0 15,500 174 71. 0 84.0 14, 000 562 52.5 81.0 12,500 1187 69.5 83.5 4 16, 000 106 54. 0 59.0 14,800 151 45.5 60.0 13,000 401 39,0 55.5 5 16,000 187 38.5 53.5 14, 500 280 33. 5 46. 5 13,500 410 35.5 49.5 12,000 974 38.5 50. 0 7 19,000 238 49.0 80. 0 17,000 384 68.5 81.0 15,500 814 55.5 77. 5 8 17,000 79.4 67. 0 87.5 14,000 265 59.0 86.5 12, 000 1005 68.5 86.5 12 16,000 123 51.0 55. 5 14,500 449 50. 0 70. 0 13,500 1063 56. 0 62.5 11,800 2443.6 32.5 62.8

Table 2 (continued) Rupture Elongation Reduction of Tube No. Stress (psi) Time (hrs) (% in 2 in. ) Area (%) 13 16,500 369 59.5 65.5 14,500 905 41. 0 66. 0 13,500 1516 45.0 61.5 14 16,500 864 43.5 63.5 14,500 1575 43.5 67.5 13,500 3225 36.5 56. 0 12, 000 In Progress 646 hours (4-10-67) Heated for one hour at 1650~F, air cooled and tempered for one hour at 1375~F, air cooled 2 17,000 180 55.0 81.0 15,000 393 58.0 82.5 12, 000 1924 55.0 74.0 Heated for one hour at 17500F, air cooled and tempered for one hour at 1375~F 10 17,000 299 60.5 85.0 15,000 726 49.0 82.5 14,000 1181 50.5 83.0 Furnace cooled 50~/hour from 1750~F 6 17, 000 70.5 85. 0 76.5 14, 000 335 59.5 70.5 12,500 799 60.0 61. 0 9 17,000 62.2 76.5 91.5 14, 000 305 72. 0 89. 0 12,500 697 62.5 90. 0 Modified Isothermal treatment 15 19, 000 In Progress 142 hours (4-10-67) 16, 000 In Progress 646 hours (4-10-67)

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