Importance of Thermophysical Properties of Materials in Thermal Modelling of Welds

During the process of welding, the intense heat source leads to rapid heating, melting of the material and vigorous circulation of the molten metal. The circulation in the molten metal is driven by the forces of buoyancy, surface tension and in addition, by electromagnetic forces (if electric current is utilised for welding). In fusion welding process, the temperature of molten weld pool ranges from near the boiling point on the top surface to liquidus- solidus transformation temperature at the edge of fusion boundary. The resulting heat transfer and the fluid flow determine the microstructure, size and shape of the weld region, the properties of weld metal and the base metal, and the residual stress distribution, The evolving microstructure and the residual stress distribution can significantly affect the strength and performance of the welded component. Experimental determination of the temperature distribution, microstructure and the residual stress distribution is not always feasible, and is expensive even if it is feasible. Theoretical models taking into account the various parameters involved in the welding processes are developed to predict the temperature distribution, evolution of microstructure and the residual stresses in the welded joint. Using validated computer models, allowable design loads and consequent inservice behaviour of the welded joint under different environmental conditions can be predicted.