Damage mechanism in weldment of 2.25Cr–1Mo steel under creep–fatigue loading

The purpose of this study is to clarify damage process of “Type IV cracking” in weldment of a 2.25Cr–1Mo steel and to propose a micro damage prediction method. From continuous observation under a creep–fatigue test, it was found that spherical shape voids initiated and grew on grain boundaries in fine grain region and these voids grow continuously by changing their shape to crack-like. Both spherical and crack-like void growth rate equations were derived from the proposed void growth model. It was indicated that measured void growth rate under the creep–fatigue loading was well predicted by the growth rate equations.