Test environment effect on the mechanical properties of austenitic stainless steels

Properties of a 316 type austenitic stainless steel were investigated as a function of test temperature in two test environments: (a) vacuum and (b) air. It was observed that the number of serrations per unit strain is higher for specimens strained in air. On the other hand, the flow stress and ultimate tensile strength were systematically higher for the specimens strained in vacuum. Observations on the sections of the specimens revealed three areas: (a) a cracked layer of oxide scale (OS); (b) a near-surface zone (NSZ) characterized by chromium depletion, grain boundary oxidation and sensitization; and (c) core material. During tensile deformation, cracks in the OS and oxidized/sensitized grain boundaries act as stress concentrators. A hypothesis is put forward which links these concentrators with the environmental effect on the mechanical properties of the material.