Non-isothermal phase-transformation kinetics model for evaluating the austenization of 55CrMo steel based on Johnson–Mehl–Avrami equation

Abstract

In order to attain the distribution of hardness and austenite volume fraction in the induction hardening by the numerical simulation, the dilatometric curves of phase-transformation for 55CrMo steel were tested by the Gleeble-1500D thermal–mechanical simulator at the different heating rates. The volume fraction of austenite was evaluated using the level principle according to these curves. The regression analysis is performed to evaluate some parameters in the non-isothermal Johnson–Mehl–Avrami (JMA) equation. For 55CrMo steel, the phase-transformation activation energy Q=7.264×105J/mol, the phase-transformation kinetic parameters n=1.2303, lnk0=78.7087. Using the JMA equation and the user subroutine developed in the paper, the distribution of austenite volume fraction and the hardness in the surface of the ball screw were obtained by the numerical simulation. The comparison of the calculation results and the experiment results shows that, the simulation results are consistent with the experiment results, the JMA equation and the user subroutine are valid, and the JMA equation can well describe the austenitization of 55CrMo steel.