Damage Mechanism of Low Cycle Fatigue in an Advanced Heat Resistant Austenitic Stainless Steel at High Temperature

Abstract

Sandvik Sanicro 25 is a newly developed heat resistant austenitic stainless steel grade for the next generation of coal fired advanced ultra-super critical (AUSC) power plants. In this paper, low cycle fatigue behavior and damage mechanisms of the material were studied. The low cycle fatigue test was performed in air at room temperature, 600°C to 700°C. The microstructures were studied using electron back scatter diffraction and electron channeling contrast image techniques. At room temperature, the material shows a conventional hardening and softening behavior as most metal materials. At high temperatures, however, it shows only a cyclic hardening behavior. Dynamic strain ageing is found to be one of the mechanisms. The damage and fatigue crack initiation mechanisms due to cyclic loading at different temperatures and loading conditions have been identified. The interactions between dislocations or slip bands with grain boundary or twin boundary are the main damage mechanism at low temperature or at high temperature with large strain amplitudes. Strain localization due to dislocation slipping is the main mechanism for the fatigue damage in grains.