Effect of microstructure and strain rate on hydrogen-induced microcrack initiation in high-Mn TWIP/TRIP steels

In this work, the relationships between the microstructure and hydrogen-induced crack (HIC) initiation and propagation of three kinds of high-Mn steels were studied, as well as the effect of strain rate. Firstly, the hydrogen-induced delayed fracture performance was studied by slow strain rate tensile. The results show that all of the hydrogen embrittlement susceptibility (Eloss) of the three kinds of specimen at 1×10-6 s-1 strain rate was significantly greater than at 1×10-5 s-1. And the Eloss increases with the increase of the volume fractions of ε-martensite (PVFM) at 1×10-5 s-1 strain rate. However, at 1×10-6 s-1 strain rate, the Eloss decreases first and then increases with the increase of PVFM. Secondly, EBSD and TEM results show that there are a large number of persistent slip bands formed by the dislocation planar slip in the specimens with 10% PVFM at strain rate of 1×10-6 s-1. However, the interaction between deformation twins and trigeminal boundaries may promote hydrogen-induced intergranular crack initiation at 1×10-5 s-1. For the specimens with 45% PVFM, the microcracks induced by hydrogen initiated at grain boundary at both 1×10-6 s-1 and 1×10-5 s-1. Most importantly, thirdly, it was found that the γ/ε phase interface with N-W orientation relationship, i.e, (111)γ||(0001)ε and [110]γ||[2-1-10]ε, could hinder the propagation of HIC, just like the Σ3 grain boundary.

Posted by: Jinxu Li, Prof, University of Science and Technology Beijing, China (05-Mar-2020)
Follow Us
F Twt Li YT