On the Transformation of Pure Iron by Super-Rapid Heating

Abstract

The formation of austenite by rapid heating has influence on the transformation characteristics on cooling and offers substantial problems concerning the hardenability of steels. And the transformation on rapid heating has been keeping deserving its importance in the field of strengthening of steels. However, it has not been established so far whether the α→γ transformation occurs in a diffusion or diffusionless mode.
In the present study the test specimen (thickness of 0.1 mm) was heated by 85 kVA electric power of spot welder, and A_c3 points by various heating rates up to the order of 10⁷°C/sec were measured by a PbS cell heat radiater.
The main results obtained are as follows:
(1) The heating cycle under the speed of 10⁷°C/sec was recorded by the PbS cell heat radiater.
(2) The PbS cell heat radiater was sufficient to detect the α→γ transformation temperature on super-rapid heating.
(3) The increments of transformation temperature from the equilibrium point (A_c3) in pure iron with increasing heating rate (0∼10⁷°C/sec) were determined. As one of the results, A_c3f was around 1100°C at the heating rate of 10⁷°C/sec. This means that the α→γ transformation is not intercepted by super-rapid heating.