Relationship between Residual Stress and Net Strain in Low-Temperature Transformation Weldments Considering Microstructure

Abstract

Weldments inevitably shrink during cooling from the melt pool. Residual stresses then occur owing to surrounding constraints. Tensile residual stresses in weldments cause various problems, such as deformation and reduction of fatigue strength. Low-temperature transformation (LTT) welding consumables can reduce the tensile residual stress through volume expansion, which accompanies a phase transformation from austenite to martensite. In this study, the relationship between residual stress and net strain was examined, mainly by controlling the martensite start (Ms) temperature, and the result was related to the weld’s microstructure. The Ms temperature and the expansion accompanying the phase transformation were analyzed by the dilatometric method. A hole drilling test was carried out to measure the residual stress in the weldments. The highest compressive stress was observed in the most expanded weldment at room temperature, and a linear relationship between the net strain and residual stress was derived. This linear relationship was analyzed with a microstructural approach.