The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in weldments. Welding distortion and residual stress in welded structures can result in problems such as dimensional inaccuracies during assembly and raise concerns regarding safety during service. Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment. In the present paper a new method of analysis is proposed to predict welding residual stress by considering solid phase transformations during the welding process. This method is applied to two cases, involving medium carbon steel and low carbon steel respectively. The analysis of medium carbon steel revealed the presence of compressive residual stress due to martensite formation when phase transformation was considered. However, in low carbon steel the residual stress obtained considering the effect of phase transformation did not differ significantly from that obtained when phase transformation was ignored.
Computer simulation of three-dimensional heat transfer and fluid flow in gas metal arc (GMA) welding has been studied by considering the three driving forces for weld pool convection, that is the electromagnetic force, the buoyancy force, and the surface tension force at the weld pool surface. Molten surface deformation, particularly in the case of GMA welding, plays a significant part in the actual weld size and should be considered in order to accurately evaluate the weld pool convection. The size and profile of the weld pool are strongly influenced by the volume of molten electrode wire, impinging force of the arc plasma, and surface tension of molten metal. In the numerical simulation, difficulties associated with the irregular shape of the weld bead have been successfully overcome by adopting a boundary-filled coordinate system that eliminates the analytical complexity at the weld pool and bead surface boundary. The method used in this paper has the capacity to determine the weld bead and penetration profile by solving the surface equation and convection equations simultaneously.
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