Study of Life Prediction and Damage Mechanism for Modified 9Cr 1Mo Steel Under Creep Fatigue Interaction

Abstract

Creepfatigue interaction is a principal cause of failures of many engineering components under high temperature and cyclic loading. In this work, stress controlled creepfatigue interaction tests are carried out for modified 9Cr1Mo (P91) steel. In order to study the damage mechanism of P91 steel under creepfatigue interaction, Scanning Electron Microscopy (SEM) of specimen fracture morphology and insitu observation experiments were conducted. Based on the ductility exhaustion theory and creepfatigue interaction tests data, the modified ductility exhaustion life prediction model was developed. The predicted results are in a good agreement with the experiment. By comparison with frequency separation model, the life predicted by ductility exhaustion model is better than frequency separation model obviously. The results show that different stress amplitude and mean stress have great effect on the fracture damage mechanism when the hold time is invariable. By the SEM analysis of fracture morphology, the damage characters of creep, creepfatigue interaction and fatigue can be partitioned. The specimen crack initiation source is the modified 9Cr1Mo steel inclusion. Therefore, this work can provide a reference of life prediction and design for high temperature materials and components.