Creep Properties of Grade T91 Steam Generator tube steel at 923 K

Abstract

Creep-rupture properties of T91 steam generator (SG) tube steel have been examined at 923 K in normalised and tempered condition in the stress range 55-150 MPa. At all stress conditions, the creep deformation was characterised by a decrease in creep rate in the transient creep followed by a minimum creep rate in secondary creep and a rapid increase in creep rate in tertiary creep stage. A systematic decrease in creep rate with decreasing stress was observed in transient, secondary and tertiary creep. Stress dependence of minimum creep rate and rupture life obeyed power law creep. Both minimum creep rate and rupture life exhibited deviations in terms of lower respective stress exponent values at low stresses than those obtained at high stresses. A decrease in creep ductility was observed with increase in rupture life. The fracture mode remained transgranular at all test conditions. Creep-rupture strength of SG tube steel has been found to be comparable to those reported in literature as well as specified in French Nuclear Design Code, RCC-MR for the steel.