Effect of applied stress on bainite transformation, microstructure, and properties of 15CrMo steel

Abstract

The effect of external stress on the isothermal bainite transformation kinetics and microstructure of 15CrMo steel was studied using dilatometer, optical microscopes (OM), electron back-scatter diffraction (EBSD), scanning electron microscopes (SEM) and X-ray diffraction (XRD). The results show that the additional mechanical driving force provided by the external stress promotes the transformation of bainite, resulting an increase volume fraction of bainite-ferrite (BF) and causing the BF laths to become slender. The application of external stress can also induce selective orientation during the bainite transformation process, and the orientation relationship between the prior austenite and the BF under stress is closer to the Kurdjumov-Sachs (K-S) relationship. There is also an incomplete transformation of bainite transformation under stress. At the same time, the Vickers hardness of 15CrMo steel would increase after applying external stress. The mechanical driving forces calculations demonstrate that when tensile stress and compressive stress are of similar magnitudes, they provide comparable mechanical driving forces. As a result, they exert similar effects on the kinetics of bainite transformation, leading to no discernible differences in the resulting bainite microstructure.