Improving hydrogen embrittlement resistance in high-strength martensitic steels via thermomechanical processing

This study proposes a novel approach for architecting dual-phase heterostructure to enhance hydrogen embrittlement resistance in high-strength martensitic steels while maintaining a tensile strength above 1200 MPa. Through thermomechanical processing, a unique dual-phase structure was achieved, characterized by a refined martensitic substructure and dynamically transformed ferrite grains along the prior austenite grain boundaries (PAGBs). Lowering the deformation temperature increased the ferrite volume fraction and the coverage of PAGBs by fine ferrite grains, which consequently reduced the area fraction of hydrogen-related intergranular fracture. Notably, 60 % compression at 700 °C completely suppressed hydrogen-related intergranular fracture, demonstrating an exceptional combination of strength and ductility even in hydrogen-charged state. The coverage of PAGBs by dynamically transformed ferrite was a critical factor in enhancing the hydrogen embrittlement resistance, with higher coverage correlating with improved hydrogen embrittlement resistance. These findings provide valuable microstructure design concepts for high-strength martensitic steels with superior hydrogen embrittlement resistance.