Influence of the interpass temperature on t8/5 and the mechanical properties of submerged arc welded pipe

Abstract

In submerged arc welding (SAW) process, t8/5 is critical in determining the microstructure, dimensions and mechanical properties of weld metal (WM) and heat affected zone (HAZ) and it depends on the heat input developed depending on the welding parameters and the temperature of the base metal (BM) and is extremely sensitive to any change therein.When t8/5 values are identical in the case of identical welding heat inputs gained, although all the welding parameters are different, the notch impact toughness and hardness values of the welded construction are very approximate to each other. Although all welding parameters are identical, t8/5 and consequently the notch impact toughness and hardness values are different from each other because of the difference of interpass temperature between internal and external welding. The interpass temperature of weld area can be changed by stopping the welding machine for a while after the internal welding or by shifting the external weld head from internal welding. While the improvement of notch impact toughness at −20°C is 24.5% by stopping the welding machine after the internal welding, this value is 17.7% by shifting the external weld point. This work shows the importance of the interpass temperature and cooling rate being defined with t8/5 in order to improve the mechanical properties of steel welds.