Microstructural changes in a service exposed CrMoV rotor steel subjected to high temperature low cycle fatigue

Abstract

The influence of low cycle fatigue (LCF) deformation on the microstructure of a CrMoV rotor steel service exposed at 510°C for 23 years has been investigated by conducting transmission electron microscopy studies on thin foils made from shoulder and gage sections of the fatigue specimens tested at 538°C using different strain ranges with or without 1 h hold period. The LCF deformation has led to the spheroidisation of coarse cementite present along the grain boundaries as well as within the bainitic ferrite, a slight coarsening of vanadium-rich MC type carbide and profuse precipitation of molybdenum rich M2C type carbide as fine platelets. Increasing strain range or superimposing hold period at the peak tensile load during LCF testing has accelerated these changes.