EFFECT OF COBALT ON THE TRANSFORMATION CHARACTERISTICS OF 5NI-CR-MO STEELS.
UNITED STATES STEEL CORP MONROEVILLE PA
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Studies were initiated to determine 1 whether the addition of cobalt to raise the M sub s temperature would increase self tempering in a 5Ni-Cr-Mo steel without deleteriously reducing hardenability and 2 whether cobalt additions would reduce the susceptibility of a 5Ni-Cr-Mo steel to heat-affected-zone cracking. The results of high-speed dilatometric measurements on specimens heat treated to simulate the cooling of 12- through 4-12-in.-thick water-quenched plates indicated that the addition of cobalt raised the M sub s temperature of the 5Ni-Cr-Mo steel about 17 F per 1.0 cobalt in the range 0 to 5 cobalt, and also increased self tempering of the martensite. However, the addition of 8 cobalt reduced the hardenability so that an undesirable amount of coarse bainite was formed. Author