Effect of starting microstructure on refining potency of electro-pulsing on reverse austenite grain

The influence of starting microstructure on the austenite grain refining potency in Electro-Pulsing (EP) was investigated by microstructure observation and hardness testing. Results indicate that the mechanism of austenite formation from the starting tempered martensite during Electro-Pulsing Treatment (EPT) is occurred by the α + Fe₃C → γ diffusional transformation, and austenite grains are ultra-refined (d_γ < 5 μm). This verifies the analysis that the austenite nucleation rate can be increased by EPT. However, the reverse transformation from martensite during EPT occurs by the α'→ γ displacive transformation process. The prior austenite grain boundaries of the starting martensite are not changed during the reverse transformation, leading to the formation of coarse grained Displacive Reverse Austenite (DRA). Martensite transformed from DRA after quenching is strengthened. As the peak temperature is increased during EPT, the recrystallization of DRA is occurred. The nucleation recrystallization is started at the boundaries of DRA, where the high angle microstructure is only reversed after displacive reverse transformation. The mean size of the austenite grains is 11 μm after recrystallization.