Analysis of creep deformation and damage behaviour of 304HCu austenitic stainless steel

Abstract

Creep deformation, damage and rupture behaviour of 304HCu austenitic stainless steel have been studied at temperatures 923, 973 and 1023 K over the stress range 100–240 MPa. The material exhibited relatively short primary stage of creep deformation followed by secondary (steady-state creep) stage and relatively extensive tertiary stage of creep deformation. The transient creep deformation is analysed based on the Garofalo relationship, ε= ε0+εT1−exp−r′.t+ε˙s.t. The variations of (i) rate of exhaustion of transient creep (r′)withsteadystate creep rate ε˙s and time to onset of secondary creep and (ii) initial creep rate with ε˙s were found to obey power-law relationship with powers close to unity, thereby facilitating the development of master transient creep curve. The variation of ε˙s with stress and temperature obeyed Dorn’s equation modified with back stress concept. The time to onset of tertiary creep is found to be proportional to rupture life (tr) while the damage tolerance factor λ=εfε˙s.tr decreased with increase in tr. In view of the prolonged tertiary creep, associated with microstructural change and intergranular creep cavitation, Kachanov–Rabotnov model has been used to assess the creep damage behaviour of the steel. The damage assessment coupled with finite-element analysis closely predicted the creep deformation and rupture life of the steel.