A model for rapid austenitization in steel with ferrite and pearlite microstructure under electropulsing

Besides the chemical gradient, electropulsing treatment (EPT) produces a temperature gradient and an electric field to drive the austenitization, making it difficult for the traditional model to illustrate the transformation during EPT. Thus, for establishing a suitable rapid austenitization model of EPT, this experiment studies the electropulsing-induced microstructure evolution from ferrite and pearlite to austenite. The results show that EPT induces the transformation to be completed within 500 ms. During the evolution, the pearlite parallel to the current is more difficult to transform due to the weakening of the athermal effect of EPT, and the ferrite is divided into several parts before the complete transformation owing to the distributary effect of current. Moreover, the new model illustrates that both of diffusion rates in pearlite and ferrite increase significantly under EPT. Therein, EPT accelerates the diffusion in ferrite so that the diffusion rate driven by the chemical gradient has little effect on the austenitization of ferrite. This greatly reduces the difference in the diffusion rate of carbon between ferrite and pearlite. Thus, the austenitization process under EPT is less sensitive to the initial microstructure than other processes, but is related to the resistivity of bulk samples.