Failure mechanisms and design of dissimilar welds of 9%Cr and CrMoV steels up to very high cycle fatigue regime

Cross-weld and pure base metal specimens machined from dissimilar welded joints of 9%Cr and CrMoV steels were cyclically loaded up to very high cycle fatigue at 500 °C under load ratio of zero. Results showed fatigue strength of the welds was greatly weakened, lower than base metals. A transition of failure mechanisms from geometrical soft zone in heat-affected zone of CrMoV steel to micro-defects induced cracking at weld metal was responsible for decreasing fatigue strength reduction factor with the increasing of fatigue lifetime. A sound fatigue design requires careful selection of filler metal and consideration of soft zone and micro-defects.