Microstructural analysis of notched fatigue strength and fatigue notch sensitivity of welded part of steels

Abstract

The fatigue notch sensitivity of steel has been reported to be raised by welding, though lowered value has also been appeared in another investigation. The present study was therefore undertaken in attempt to resolve the apparently paradoxical behavior.
Considering the mean size of carbide, L', and its mean spacing, 2L, to be the main structural factors which influence the fatigue strength of steels, the authors has previously showed correlation between microstructure and fatigue behavior of quenched and tempered steels with and without notch. On this basis, the effect of microstructural change caused by welding on notched fatigue strength of welded steel was investigated.
It is found that the notch sensitivity can be raised or lowered according to the metallurgical change at welded part. That is for a given steel with lowere value of Lb (Suffix b refers to base metal), the fatigue notch sensitivity is generally raised by welding. On the other hand, the notch sensitivity of welded part is not so affected by welding in case the value of Lb is small such as high strength steels. Moreover, it is expected to be lower notch sensitivity of welded part if Lw (Suffix w refers to weld part) is larger than Lb.