Improvement of prediction accuracy of phase transformation in steel during induction hardening by considering autocatalysis

Residual stress that is mainly caused by heat treatment is one of the important factors in mechanical products such as internal combustion engines, since it affects the maintenance of peak performance and operational durability in competitive scenarios. In this paper, a phase transformation analysis method, in which volume fraction of 4 phases (Ferrite, Pearlite, Bainite and Martensite) during heat treatment process can be individually taken into account, is constructed for the prediction of residual stress caused by heat treatment such as induction hardening. First, phase transformation problem, considering the history of time and temperature, is formulated with the volume fraction of 4 phases, based on the idea of the autocatalysis nucleation. Next, material parameters of heat-treated steel SCM440 and non-heat-treated steel S50C in the evolution equations are identified by comparing the model with the measured and literature data. Finally, the proposed method is applied to SCM440 and S50C under the condition of induction hardening, in which different grain size is considered, and the validity of the proposed method is confirmed.