Unravelling the effect of hydrogen on microstructure evolution under low-cycle fatigue in a high-manganese austenitic TWIP steel

Abstract

We systematically investigated the effect of hydrogen on the low-cycle fatigue (LCF) behaviour of a Fe–28Mn-0.3C (wt.%) twinning-induced plasticity (TWIP) steel by comparing the fatigue microstructure of samples with and without hydrogen pre-charging using electron channelling contrast imaging (ECCI) and cross-correlation electron backscatter diffraction (CC-EBSD). The results reveal that a complex interplay of several hydrogen-microstructure interaction mechanisms is involved in the observed LCF behaviour of the studied TWIP steel with hydrogen pre-charging; first, hydrogen assists the nucleation of stacking faults (SFs) and deformation-induced ε-martensite in the studied TWIP steel by reduction of local stacking fault energy (Suzuki effect) and stabilization of the hexagonal close-packed (hcp) ε-phase. The evolution of fatigue dislocation pattern is strongly retarded in the presence of hydrogen. The rapid formation of ε-martensite leads to a stronger cyclic hardening. Meanwhile, the impingement of ε-martensite plates at GBs causes high local stress concentration, which plays a dominant role in the observed fatigue cracking. The crack opening angle indicates that the exact associated hydrogen embrittlement mechanism is the hydrogen-enhanced decohesion (HEDE) mechanism instead of the hydrogen-enhanced localized plasticity (HELP) mechanism. Among different GB types, annealing twin boundary shows the highest immunity to hydrogen-related fatigue cracking.