Changes in the structure of refractory alloys during prolonged heating at 600�C

Abstract

1. The type of preliminary heat treatment does not affect the phase compositions of 12Kh1MF and 15Kh1M1F steels resulting from 3000 h heating at 600°C. However, the type of preliminary heat treatment determines the time necessary to reach relative equilibrium. This time decreases with increasing temperature and time of preliminary tempering. 2. During heating at 600°C the solid solution becomes impoverished in alloyed elements. In 12Kh1MF steel all the vanadium in the steel (0.20–0.25%), one-quarter to one-fifth of the chromium (0.20–0.25%), and about one-third of the molybdenum (0.08–0.10%) are used in the formation of the three carbide phases (Fe3C, VC, and M7C3). In 15Kh1M1F steel all the vanadium in the steel (0.20%), about one-fifth of the chromium (0.20%), and about one-half of the molybdenum (0.50–0.55%) are spent on the formation of the four carbide phases (VC, Mo2C, M23C6, and M6C). There are reasons for believing that the phase composition we determined is not an equilibrium composition, since we found a tendency for the amount of M23C6 carbide to decrease with increasing heating times between 1000 and 3000 h. 3. In 12Kh1MF steel the most stable values of the hardness during heating at 600°C occur after preliminary normalizing and subsequent tempering at 740°C. 4. In 15Kh1M1F steel the most stable values of hardness during heating at 600°C occur for annealed samples (cooled at the rate of 30°/h). The change in the hardness after tempering at 740°C is relatively small.