Improving hydrogen embrittlement resistance of martensitic steel via interface B segregation

In this work, we find that the engineering grain boundary boron (B) segregation can effectively enhance the resistance to hydrogen embrittlement (HE) of a low-carbon lath martensitic steel. The B segregation in prior austenite grain boundaries (PAGBs) strongly suppresses H-induced intergranular cracking. Such a beneficial role, associated with B segregation, is interpreted as the suppression of H-trapping at PAGBs and the enhancement of the atomic bonding strength of grain boundaries. Despite the improvement in HE resistance, an H-induced quasi-cleavage fracture still occurs in the B-doped samples. Further detailed fractography analysis, conducted using electron backscatter diffraction and transmission electron microscopy, reveals that the primary H-induced damage mode in the B-doped samples is {110} plane cracking, resulting from a combined effect of H-enhanced decohesion and H-enhanced localized plasticity. The obtained results advance the understanding of HE in lath martensitic steel with solute segregation and provide a strategy for mitigating such an issue. • Boron segregation improves hydrogen embrittlement resistance of martensitic steel. • Boron segregation in grain boundaries inhibits H-induced intergranular cracking. • H-induced quasi-cleavage fracture of B-doped lath martensitic steel is observed. • A combined H-enhanced decohesion and H-enhanced plasticity mechanism is proposed.