Hydrogen embrittlement sensitivity of a novel cast high-strength multiphase stainless steel

This study explores the hydrogen embrittlement (HE) sensitivity of a novel cast high-strength multiphase stainless steel subjected to solution treatment and tempering at 610 °C and 650 °C. Tensile testing, scanning electron microscopy (SEM) /electron backscatter diffraction (EBSD) observations, and thermal desorption spectroscopy (TDS) were combined to clarify how microstructural features influence hydrogen absorption, cracking, and fracture. The reduction in ductility and area loss shows a clear ranking of HE susceptibility: S1050 sample > T610 sample > T650 sample. Fractographic and surface observations reveal that cracks formed during hydrogen charging originate mainly along δ-ferrite/martensite interfaces. TDS analysis identifies these interfaces as the trapping sites associated with Peak 2, and the Peak-2 intensity follows the same order as the measured HE sensitivity, confirming the dominant role of interphase boundaries in hydrogen accumulation and crack initiation. T650 sample exhibits the lowest HE sensitivity because its higher reverted-austenite fraction and reduced Laves-phase precipitation suppress interfacial hydrogen enrichment, resulting in a weaker Peak-2 response. During charging, hydrogen segregation at δ/α′ boundaries is associated with interfacial microcrack initiation. During subsequent tensile deformation, strain-induced transformation of austenite affects hydrogen redistribution, while enhanced local plastic deformation is observed near the phase boundaries in the presence of hydrogen. These effects facilitate crack propagation and result in mixed intergranular and quasi-cleavage fracture features. The results highlight the role of phase constitution and hydrogen trapping in controlling hydrogen embrittlement behavior of cast multiphase stainless steels.