Measurement of Transformation Plasticity during Heating of Bearing Steel

Abstract

Transformation plasticity is known to play an important role during heat treatment processes of steels. It has been considered that the distortion during heating is less significant than that during cooling and thus the heating process was often neglected in the heat treatment simulations such as quenching. The recent study, however, revealed the significance of heating process to the final shape and dimension of the heat treating materials. This study thereby aims at identifying transformation plasticity during heating of a bearing steel (SUJ2 in Japanese industrial standard). The major difficulty when measuring transformation plasticity during heating is to eliminate the creep effect from the obtained dilatation curves. A temperature dependent creep equation is defined and each parameter appear in the equation was identified from the dilatation curves. In this way, transformation plastic strain can be separated from the creep effect. The obtained transformation plasticity coefficient of SUJ2 during heating was well identified to be 1.38×10^-4 MPa^-1 which appears to be much larger from what is estimated by Leblond’s mathematical model.