Measurement and numerical simulation of angular distortion of fillet welded T-joints-Welding angular distortion control by transformation expansion of weld metals (Report 1)

摘要

In this report, an investigation has been carried out, firstly, to confirm that transformation expansion at the weld metal has the effect of reducing angular distortion, and secondly, to establish the numerical simulation method used for examining the effect of transformation expansion characteristic on the angular distortion of the joint. At first, by fabricating fillet welded T-joints using low transformation temperature welding consumables, an experiment for measuring transitional angular distortion has been conducted, and it has been made clear that; Whilst, with conventional welding consumables, angular distortion produced during welding remains as it is even after the end of welding, with low transformation temperature welding consumables, the amount of angular distortion decreases after it has shown maximum value. Then, by inserting thermocouples into the weld metal immediately after the welding torch has passed, the thermal hysteresis during the cooling period has been measured to examine the relationship between the transformation start temperature of the weld metal and the transitional angular distortion behaviour of the joint, and it has been shown that: When one of the cross sections in the weld line direction is focused on, around the area where the weld metal reaches the transformation start temperature, the amount of angular distortion of the joint starts to decrease, and, when the weld metal reaches the transformation finish temperature, the amount of angular distortion starts to show nearly constant values. Also, the chemical composition and the transformation start and finish temperatures of the weld metal have been measured, and it has confirmed that: The chemical composition of the weld metal of the fillet welded T-joint fabricated with low transformation temperature welding consumables was affected by the dilution by the base material, and the contents of Ni and Cr that are additions for lowering the temperature to start the transformation to martensitic phase become lower than that of the joint fabricated only with welding wire, and as a result, the transformation start and finish temperatures of the weld metal become higher than those with welding wire. Following these, with the fabricated fillet welded joints, the numerical simulation of welding distortion with consideration given to the phase transformation accompanying the welding hysteresis has been carried out. It has shown that: The numerical simulation enables the calculation, with sufficient precision, of the angular distortion of the fillet welded T-joint including the transitional occurrence behaviour of angular distortion during welding and the decrease of angular distortion owing to transformation expansion of the weld metal during cooling.