Lifetime prediction of 9-12%Cr martensitic steels subjected to creep-fatigue at high temperature

A physically-based model has been proposed in a previous study to predict the creep-fatigue lifetime of P91 steel which is of the 9-12%Cr steels family (Fournier et al., 2008) [1]. The present study applies this model to three other different 9-12%Cr martensitic steels P92, Ti1, and VY2. All these materials were tested under pure fatigue conditions. Whereas for a P92 steel, the experimental lifetimes are very close to those of the P91 steel, the two other steels present a significantly shorter fatigue and creep-fatigue lifetime. First the damage mechanisms were observed on these three materials and compared to those identified on P91. Taking into account the increased cracks density and the grain size effect on crack initiation, the model is able to account quite accurately for these different fatigue and creep-fatigue lifetimes.