Hydrogen embrittlement fracture mechanism of 430 ferritic stainless steel: The significant role of carbides and dislocations

Abstract The effect of electrochemical hydrogen charging on the mechanical properties and the fracture mechanism of AISI430 ferritic stainless steel were studied by tensile test. Electrochemical hydrogenation experiments of 2, 4, 8 and 12 h on the tensile specimen with a current density of 50 mA/cm2. Hydrogen has a significant impact on the mechanical properties of the material: the elongation of the material is reduced from 27.8% to 13.0%, the yield strength is increased from 325 MPa to 380 MPa, and the tensile strength is increased from 500 MPa to 575 MPa. The obvious increase in tensile strength is attributed to two aspects: (1) the hydrogen-induced dislocations pinning; (2) the influence of the second phase carbide particles on the critical shear stress of dislocation glide. As the hydrogen outgassing time increases, the hardness measurement proves the softening effect of hydrogen. Since the reduction of the binding energy of the carbide and ferrite matrix interface is attributed to the HEDE mechanism, the crack nucleation in the vicinity of the carbide leads to the generation of the cleavage (C) region. Under low diffusible hydrogen content, the samples are mainly C mode and F-MVC mode guided by the synergistic effect of hydrogen-enhanced decohesion (HEDE), hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced strain-induced vacancies (HESIV) mechanisms and under high diffusible hydrogen content, the transgranular (TG) mode replaces the F-MVC mode, and the HEDE mechanism is more dominant than the HELP mechanism.