Yoshiyuki Miwa1 and Hidetaka Ono1
1Graduate School, Waseda University, Tokyo
The Ac3 ( α→γ ) transformation behavior on super-rapid heating up to 106°C/sec and the isothermal transformation on heating at various temperatures over Ae3 were investigated for a high purity iron using newly designed apparatuses.
The main results obtained are as follows:
(1) The Ac3 transformation temperature at a rate of 106°C/sec in a vacuum of 10-6 Torr and in air was determined by a PbS cell heat radiator. It was detected that the Ac3 point at each heating rate in vacuum is higher than in air.
(2) The Ac3 transformation temperature rises above the equilibrium temperature with increasing heating rate up to 106°C/sec. The Ac3s (transformation start) temperature is almost independent of the heating rate, whereas the Ac3f (transformation finish) temperature rises up to around 1350°C in vacuum at the heating rate of the order of 105°C/sec.
(3) The α - γ isothermal transformation process was continuously observed by measuring the change in electric resistance. It was considered that α→γ transformation in high purity iron might proceed intermittently by a diffusionless mechanism.
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