Deformation Behaviour of Welded Joints at Low Temperature

Abstract

The temperature dependence of deformation properties of welded joints was investigated by means of the photoelastic coating technique. A smooth tensile specimen with a buttwelded joint was used to study the micro-structural dependence of plastic behaviour of a mild steel. From successive developments of photoelastic fringe patterns obtained in tension tests at various low temperatures, the structural and temperature dependence of yield strength of such parts as parentmetal, heat-affected zone and weld metal was determined. It was found also that the yield strength of the heat-affected zone was higher than that of the parent metal or the weld metal in the range from room temperature to -196°C. The existence of such a harder metal as the heat-affected zone produces a plastic constraint in a softer metal, on which the former borders, and then it hinders the trarsverse contraction of the latter and leads to the embrittlement in theconstrained regions. The temperature dependence of plastic constraint was also discussed.