Creep and creep-fatigue behaviour of 316 stainless steel

The austenitic stainless steel 316 is of current interest as structural material for the future Gen IV nuclear power plants operating at high temperatures. Although 316 steel grades have been studied for the service conditions of current nuclear and other conventional applications, improved data and models for the long term high temperature properties are needed, especially regarding the primary to tertiary creep strain and creep-fatigue response. The Gen IV technology will need an update for predicting safe life to given strain and rupture in the temperature range of 500-750 °C, and to facilitate FEA for complex product forms. Modelling the stress dependence of creep strain and strain rate is particularly challenging due to the need for long term extrapolation and limited (public domain) data. Large variation in mechanical propertiessuch as high temperature yield strength between casts and product forms also need to be addressed for design and life prediction. In the present work, new creep models have been established for predicting creep strain and rupture of 316L and316L(N), using the Wilshire equations and logistic creep strain modelling for improved accuracy. The models have been extended to creep- fatigue and applied to characterize the steels 316FR and 316L in terms of the linear life fraction rule.