Enhancing hydrogen embrittlement resistance of TRIP-rich medium Mn steel by morphology optimization

The transformation-induced plasticity (TRIP) effect in medium Mn steel generally provides a considerable enhancement to its work hardening capability and therefore an excellent combination of strength and ductility. However, the resultant fresh martensite formed during deformation is highly susceptible to hydrogen embrittlement (HE). Here, we propose an elongated, banded morphology (EBM) to mitigate HE caused by fresh martensite. EBM produced by warm rolling possesses a comparably high work hardening rate, but a better resistance to HE than the equiaxed grain morphology (EGM) produced via conventional intercritical annealing. For the EGM, hydrogen-induced crack (HIC) can propagate rapidly due to insignificant obstacles for crack propagation. On the contrary, for the EBM, HIC can be stopped or deflected at elongated grain or phase boundaries. The EBM morphology design may improve HE resistance in other steels and alloys with intensive TRIP effect.