Heat conduction analysis of bidirectional multipass welding with short bead lengths

A heat conduction analysis is considered for multipass welding conducted in a forward–reverse manner. When the welding is conducted continuously and the bead is short, the interpass temperature sometimes exceeds 500°C. To predict the thermal histories, a heat conduction model is examined using the analytical solution of a moving point heat source in a wide plate of finite thickness. In the model, point heat sources, some of which are moving in one direction and others in the opposite direction, are considered. Comparison of the calculated and experimental results reveals that the proposed model can predict the thermal histories fairly well. This is followed by calculation of the equivalent arc energy, defined as the apparent arc energy which gives either the same cooling time from 800 to 500°C or the same kinetic strength of the heat cycles with no preheating (the concept of kinetic strength has been developed to estimate austenite grain growth in the heat affected zone region), and examination of the effect of maximum interpass temperatures on the equivalent arc energy. When the interpass temperature is greater than 500°C, its effect can be to increase the equivalent arc energy from 2.5 kJ mm^-1 to between 6 and 14 kJ mm^-1.