Prediction of cooling rate and microstructure in laser spot welds

Theoretical and experimental investigations have been carried out to examine the influence of laser power and on time on the weld thermal cycle and weld metal microstructure and hardness during laser spot welding of low alloy steel. A transient heat transfer model that takes into account the temperature dependence of material properties and latent heat of phase transformation is employed to simulate thermal cycles and cooling rates experienced by the material under various combinations of power and on times. Two models for predicting the microstructure and hardness of the weld pool metal from the cooling rates are used to evaluate the results