Role of Local Oxidation on Grain Boundary Sliding and Transgranular Slip in Low-cycle Fatigue Crack Initiation at 700.DEG.C..

Low-cycle fatigue crack initiation process of Austenitic stainless steel SUS316 have been studied at 700°C in air and vacuum with an attention to the role of local oxidation on grain boundary sliding and transgranular slip. In vacuum, local cumulative displacements at grain boundary due to sliding saturates in an early stage of fatigue life, while local cumulative displacements due to transgranular slip develops proportionally to the number of strain cycles and results in slip bands crack initiation. In air, local oxidation attack on the newly originated surface due to grain boundary sliding can be a primary reason for the intergranular crack initiation. Intergranular oxidized cracking is induced by wedge shaped oxide with micro-cavities in the process of grain boundary sliding, while transgranular slip bands simply cause small steps on the surface and this oxidized transgranular slip steps do not develop into transgranular cracking in air.