Effect of Prior Heat Treatments on the Rate of Sigma Transformation

Abstract

The effect of prior heat treatments on sigma transformation of high chromium steels which contained 35∼60% chromium, was investigated by hardness, intensity of magnetization and microstructure. The prior heat treatments were of the following three kinds: (1) Annealing at 500° for 500 hours, (2) furnace cooling from 1000° and (3) water quenching from 900°. Annealing temperatures were 650°, 700° and 750° and annealing time was up to 300 hours. In general, the rate of sigma transformation of the specimens heat-treated as (1) was most rapid, and that of specimen heat treated as (3) was slowest. The reason of this difference was not ascertained, but the nuclei of sigma phase which resulted in annealing at 500° for 500 hours seemed to play an important roll.