The Tensile Ductility of Austenitic Steels in Air and Hydrogen

An empirical correlation of yield strength with reduction-in-area at fracture was demonstrated for austenitic stainless steel. The correlation is consistent with an existing fracture model that involves microvoid nucleation at isolated inclusions. Hydrogen effects on tensile ductility are also consistent with this model, if one assumes that hydrogen is transported by glide dislocations and that localized hydrogen accumulations lower the stress necessary to initiate fracture at particle-matrix interfaces. Smooth-bar tensile specimens of fourteen austenitic stainless steels were tested at room temperature in air, in 69-M Pa He, and in 69-M Pa H₂. Macroscopic reductions-in-area at fracture varied between 12 and 82 percent, and yield strengths were between 179 and 1069 MN/m². The resulting empirical correlation suggests that the ductility of austenitic stainless steels is limited by the interfacial stress required for microvoid nucleation and coalescence. For low strength steels, the required interfacial stress is reached only after extensive plastic deformation. However, as steel strength is increased, fracture occurs at lower strains.