Modelling of Welding in Low Alloy Steels

Modelling the welding of steels, particularly in the heat affected zone (HAZ) has been considered by several investigators. The analytical solution by Rosenthal, generally recognised as the earliest attempt, does not predict the real situation close to the heat source; the numerical solutions, notably FDM, are quite powerful, but do consume a long computation time since traditionally, the entire system is taken for discretization. The development of a mixed boundary model (MBM) that, while incorporating the virtues of the numerical and analytical techniques, manages to reduce the computation time drastically while predicting the time--temperature behaviour at different positions in the HAZ is presented. A different model based on a modified Kirkaldy approach, predicts the CCT behaviour. The composite model then predicts the micro-structure and, finally, the hardness is also predicted. The models have been validated against actual micro-structural and hardness behaviour in a few low alloy steels (TISTEN 55 and LPG). Gaps in the predictions while dealing with very large grain-sizes and acicular ferritic formation are pointed out.