Reconsideration of the dislocation arrest model for dynamic strain aging in C-bearing high Mn steel with low stacking fault energy

Abstract

In the present study, we investigated the behavior of type A serration in the tensile flow curves measured at temperatures ranging from 273 K to 323 K with a strain rate of 1 × 10−3 /s, using high Mn steels with varying N contents. As a result, it was found that the critical engineering strain for the onset of type A serrations (ecA) increased with an increase in the N content at a given tensile temperature. This finding could not be explained by the conventional dislocation arrest model, which has been used to account for type A serrations occurring in C-bearing high Mn steels without N. Therefore, we attempted to explain the result by introducing the dynamic formation of obstacles to dislocation slip, such as mechanical twins and Lomer-Cottrell locks, during tensile deformation, a factor not considered in the conventional dislocation arrest model. However, the specific reason for the increase in the ecA value due to the addition of N was not elucidated. Therefore, we modified the dislocation arrest model based on the concept that the combination and cross-slip of screw partial dislocations, which accumulate at the obstacles, become more favorable due to an increase in stacking fault energy resulting from the addition of N. The modified dislocation arrest model successfully explained the influences of not only N content but also strain rate and tensile temperature on the ecA value in both C-bearing high Mn steels with and without N.