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For the automation of butt welding, it has been considered to introduce tack welds instead of out-of-plane restraint jigs to perform welding with large heat input. However, the occurrence of hot cracking has been a significant issue in large heat input welding. In the previous report, the authors have developed a prediction method of hot cracking that can investigate the influence of not only the high-temperature strain generated in the weld metal but also the phenomena related to solidification, such as solidification shrinkage, latent heat of solidification, and crystals growth direction. In this study, the conditions for the prevention of hot cracking were investigated by numerical analysis and experiments by controlling the temperature gradient at solidification temperature using a trailing torch in tandem welding. As a result, it was confirmed that the large strain existing position predicted using the proposed hot cracking analysis has a good agreement with the cracking position observed experimentally in tandem butt weld. It was also found that with increasing the electrode distance, both the columnar crystals' associate angle became larger and the local strain became smaller. It can be concluded that the hot cracking can be successfully prevented in the practical experiments using the proposed large electrode distance.

Study on prevention method of hot cracking under butt welding