Effect of aluminum content on low temperature tensile properties in cryogenic Fe/Mn/AI/Nb/C steels
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and 25 pct, respectively. A typical microstructure of the controlled rolled materials is shown in Figure l(a). Grain size of the controlled rolled materials was about ASTM 11. In the determination of the effect of A1 content on the tensile ductilities of the alloys, the controlled rolled materials were subjected to a recrystallization heat treatment of 850 ~ for 1 hour. Figure l(b) shows an optical microstructure of the recrystallized alloy (5AI). The grain size of the recrystallized material was similar to that of the controlled rolled material. Tensile tests were performed at RT, - 4 0 ~ -100 ~ and -196 ~ Figure 2 shows yield stresses v s test temperatures as a function of aluminum content for the controlled materials. The yield strength of the 5AI alloy at -196 ~ was 1022 MPa, while that of the Al-free alloy (0A1) was 810 MPa at - 196 ~ The addition of 5 wt pct AI to the M-free alloy (0A1) produced about 25 pct increase in the yield strength in the controlled rolled state. It is also noted that the yield strength of this controlled rolled alloy, 1022 MPa at - 196 ~ in this work was about 10 pct higher than that of the same alloy reported in our previous study, l The increase of the yield strength in this work is most likely
Effect of Aluminum Content on Low Temperature Tensile Properties in Cryogenic Fe/Mn/AI/Nb/C Steels YOUNG G. KIM, JAE K. HAN, and EUN W. LEE We have recently reported the development of high strength-high toughness cryogenic Fe-30Mn-5A1-0.1Nb0.3C steel produced by a hot controlled rolling process. ~The controlled rolled cryogenic steel exhibited an excellent impact energy, 177 joules at - 196 ~ with a yield strength of 944 MPa at - 196 ~ A particularly interesting observation for the alloy was the increase in elongation with decreasing test temperature. The alloy showed 29 pct elongation at room temperature, compared to 57 pct at - 1 9 6 ~ The inverse ductility behavior is ideal for cryogenic material requirements. The inverse ductility behavior was not observed in the non-ausformed Fe-25Mn steel by Tomota and Morris. 2 This paper reports the effect of varying aluminum content on the tensile properties in the composition (wt pct) of Fe-30Mn-A1-0.1Nb-0.3C steels. The aluminum amounts (wt pct) added to the steel were 0, 1, 2, 3, 4, and 5, respectively. The six alloys (0A1, 1AI, 2A1, 3A1, 4A1, 5AI) were air-induction melted and were subjected to hot controlled rolling after soaking at 1250 ~ for 2 hours. The final rolling temperature and rolling reduction ratio were 780 ~ YOUNG G. KIM, Professor/Chairman, and JAE K. HAN, Graduate Student, are with the Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), P. O. Box 131 Cheongrang, Seoul, Korea. EUN W. LEE, formerly Graduate Student at KAIST, is with Hyndai Heavy Industries, Ulsan, Korea. Manuscript submitted November 15, 1985. METALLURGICALTRANSACTIONS A
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(b) Fig. 1--Optical micrographs of Fe-30Mn-5AI-0. INb-0.3C (etched with 2 pct nital): (a) controlled rolled and (b) recrystallized at
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