Hardness distribution in welds of Ultra-Narrow Gap GMA welding has been evaluated with numerical simulation. Estimation of hardness distribution has been performed considering weld thermal cycle and microstructure in welds. In order to investigate temperature profile of welds precisely, detailed measurement has been performed. Welding wire is oscillated vertically in the Ultra-Narrow Gap GMA welding process, however, temperature profile in heat affected zone during cooling has not been affected by the oscillation. Therefore the finite element heat conduction analysis has been possible to perform without considering the effect of oscillation of welding wire. Changes in microstructure have also been calculated based on the continuous cooling transformation diagram of the material. Hardness distribution in welds has been estimated based on the calculated weld thermal cycle and fraction of microstructure with the rule of mixture. Estimated distribution of hardness in welds was in good agreement with measured result. The method is applicable to evaluation of performance of welded joint.
