Mitigation Effect of Internal Hydrogen on External Hydrogen‐Induced Embrittlement in Austenitic Lightweight Steel

The influence of various hydrogen environments on the hydrogen embrittlement behavior of Fe‐30Mn‐8.6Al‐C austenitic lightweight steel was investigated using slow strain rate tensile tests. Under the experimental conditions adopted in this work, external hydrogen induces the most severe hydrogen embrittlement. In the combined internal‐external hydrogen environment, internal hydrogen can mitigate the damage to mechanical properties caused by external hydrogen, showing an approximately 50% relative reduction in hydrogen embrittlement susceptibility compared with the sole external hydrogen condition. Postmortem analysis shows that in the external hydrogen environment, relatively few intergranular cracks are dominant, and these cracks induce hydrogen accumulation and cause significant ductility loss. In contrast, in the combined internal‐external hydrogen environment, numerous intergranular and transgranular cracks initiate and release stress, which slows the propagation of cracks. In the presence of external hydrogen, the hydrogen embrittlement of lightweight steel is dominated by grain boundary decohesion based on the hydrogen‐enhanced decohesion mechanism, accompanied by localized plastic deformation around the cracks.