Hydrogen-induced ductility loss of 17-4 PH stainless steel with internal hydrogen

Hydrogen-induced ductility loss of two precipitation-hardened martensitic stainless steels, 17-4 PH, were investigated via tensile tests with internal hydrogen. The tensile-ductility loss was more enhanced at higher hydrogen content or tensile strength. Quasi-cleavage fracture accompanied with large plastic strain was observed at lower hydrogen content and tensile strength, suggesting hydrogen-dislocation interaction contributed to the ductility loss. When hydrogen content or tensile strength was increased, intergranular or cleavage surface was incorporated into the quasi-cleavage surface, implying the contribution of the hydrogen-induced reduction of cohesive strength. Such a reduction was confirmed via impact tests at cryogenic temperature, revealing that some mechanisms were responsible for the ductility loss.