Effect of inclusions on the hydrogen embrittlement of martensitic medium-Mn steel

In this study, we investigated the hydrogen embrittlement (HE) of martensitic medium-Mn steels with varying levels of S and Ti contents using thermal desorption analysis, silver decoration, slow strain rate tensile testing, and fractography. The S or S–Ti added specimens demonstrated higher HE resistance compared to the S-free specimens. This is because the S or S–Ti added specimens had a large volume fraction of fine MnS or Ti(C,N)–MnS complex inclusions with a size less than ∼1 μm, which provide strong irreversible H trap sites. However, coarse elongated inclusions were found to be detrimental to HE resistance. Therefore, we concluded that to improve the HE resistance of martensitic medium-Mn steel, it is important to distribute a large volume fraction of fine MnS or Ti(C,N)–MnS complex inclusions without coarse elongated ones