Thermo-Mechanical Fatigue Life Evaluation for Ni-23Cr-7W Alloy by Strain Range Partitioning Method

This study focuses on a thermo-mechanical fatigue (TMF) life evaluation method for Ni-23Cr-7W alloy for boiler pipes and tubes. The inelastic strain range applied in the TMF test was partitioned into the creep strain and the plastic strain components by using the steady-state creep rate obtained from the creep tests and the cyclic stress-strain curve obtained from the fatigue tests. The TMF life was then predicted by the strain range partitioning method (SRP). The predicted lives based on the SRP method with the creep strain obtained by using the cyclic stress-strain curve at maximum temperature of the TMF loading showed good agreement with the actual lives within a factor of 2 scatter bands. This life prediction method could be applied to other heat of the Ni-23Cr-7W alloy and other thermal cycle of TMF loading. All material data required for the life prediction can be obtained by the isothermal fatigue tests. Therefore, the TMF life of the Ni-23Cr-7W alloy can be predicted from the results of the isothermal fatigue test by using this method.