Creep properties of aged duplex stainless steels containing σ phase

The creep properties of a cast of duplex stainless steel were characterized at temperatures 550–800°C under different loading conditions. For fully aged specimens containing σ, the stress exponent for creep was close to 3 and the activation energy was 281±9 kJ mol−1. The results suggested that the creep mechanism in the samples in this investigation was controlled by dislocation movement. Extensive σ/γ2 interfaces introduced during ageing improved the creep resistance of the material and related to a reduction of the creep rate in Stage II creep and an increase in the creep rupture strength of the material. Microstructural studies revealed the dependence of the creep properties on the morphology of the microstructure. Among the aged specimens containing σ, the creep strength and ductility were higher for specimens having larger γ grain thickness measured on the longitudinal plane. This characteristic was related to the crack propagation and interconnection of voids within γ matrix during tertiary creep. With appropriate solution treatment, the creep strength of σ-containing steels can be improved to a value exceeding that of type 316 steels.