Abstract: By conducting singlepass compression test in MMS300 thermomechanical simulator and optical microstructural observation， the hot deformation behavior of S38MnSiV microalloyed forging steel was investigated at temperature of 1173~1423K and strain rate of 001~10s-1. The effect law of strain rate and deformation temperature on dynamic recrystallization(DRX)behavior and microstructural evolution was gained， and the activation energy and the constitutive equation were established for hot deformation according to hyperbolic sine method. The results show that DRX is easier to occur at higher deformation temperature and lower strain rate. With the process of DRX， the average austenite grain size decreases with the increasing strain. When steady state stress is achieved， the austenite grain size remains almost the same，independent of the strain.

Key words: microalloyed forging steel, S38MnSiV, hot deformation behavior, dynamic recrystallization, microstructural evolution