Factors Affecting Fatigue Strength of Welds in High Tensile Steels

Abstract

Fatigue limits under rotating bending of transverse manual arc butt-welds in high tensile steels are examined by varying welding heat input in a wide range. A fatigue crack initiates almost at the softened zone of heat-affected zone (HAZ), but those fatigue limits are not lower than those of base metals. Influence of hardness change in welds or fatigue was also examined by using high tensile steels heat treated by a synthetic apparatus for weld thermal cycle, or steels heat treated by TIG arc process. The fatigue limit of the specimen having hardness change of Hv 100 shows just a little lower value than that of the specimen having no hardness change. Notched fatigue strengths in HAZ of welds of various microstructures in high tensile steels are investigated in detail. Those fatigue limits are almost equal to those of base metals, the notch sensitivities of HAZ's are not high compared with those of base metals.
It is discussed that there are essentially little metallurgical factors affecting fatigue strengths of welds and a low fatigue strength of welds in high tensile steel may be due to a stress concentration of about 4 near a toe of reinforcement of welded joint.