Research on high-temperature fatigue process

It is a general case that in high-temperature low cycle fatigue, materials show the deformation behavior of hardening or softening due to repeated plastic deformation, and through the generation and propagation of cracks, they cause breaking. Especially at high temperature, complicated deformation behavior is shown due to precipitation and restoration during testing, and the features such as the generation and propagation of grain boundary cracking appear under some condition. In this reasearch, high-temperature low cycle fatique was examined by the observation of cross section and fractured surface, considering the correspondence of repeated deformation behavior with the change of metal structure and the relation of the behavior of crack generation and propagation to the dependence on strain wave form. In SUS316-HP steel and SB49 steel causing repetition hardening, the initial dislocation density was low, but the dislocation density increased due to the repeated deformation, and the cell size became small. In SCMV4-NT steel causing repetition softening, a large quantity of dislocations were introduced due to the bainite transformation, but the restoration progressed due to the repeated deformation, and the dislocation density decreased. The cell size became large. (Kako, I.)