Cyclic plastic response and damage in superaustenitic steel in high temperature cycling with dwells and in thermomechanical cycling

Abstract

The cyclic plastic response and damage evolution in high temperature cycling with dwells and during thermomechanical fatigue of superaustenitic steel Sanicro 25 has been studied. Fatigue hardening/softening curves in cycling with dwells have been compared with those in constant strain rate cycling. Rapid hardening and early saturation has been found in cycling with dwells. Study of the surface evolution using SEM observations and FIB cutting revealed the preferential oxidation of grain boundaries which were perpendicular to the stress axis. Introduction of dwells in maximum tension lead to the opening of the early cracks, their sliding and formation wedge cracks. Fatigue hardening/softening curves in thermomechanical in-phase cycling do not exhibit saturation and the hardening is higher than in constant strain rate cycling. Damage mechanism was similar to that in isothermal cycling and even more damaging as found by plotting Manson-Coffin curves.