Nanoindentation characterization on competing propagation between the transgranular and intergranular cracking of 316H steel under creep‐fatigue loading

Abstract

316H austenitic stainless is regarded as an excellent candidate in the most advanced generation of nuclear reactor at elevated temperature. The effects of dwell times and strain amplitudes on the creep-fatigue (CF) fracture mechanism of 316H steel were studied by using nanoindentation. The cyclic lives are observed to decrease with increasing strain amplitudes, while they are insensitive to the variation in dwell times. In comparison to the as-received specimen, the nano-hardness was evidently enhanced in both the fracture and interior regions for the CF-tested one, whereas elastic modulus was little changed. As related to the creep resistance, creep flow could be suppressed with increasing strain amplitudes and dwell times, especially for the fracture edge. And the correlation between strain rate sensitivity (m) during creep flow and CF testing conditions was obtained. Based on the morphologies of fracture surface and variation in H, E, and m, a normalized damage indicator ln(H/E)/m is proposed to characterize the competing propagation of the transgranular (fatigue damage) and intergranular (creep damage) cracking in the CF fracture.