Prevention of Solidification Cracking in Narrow Gap Welding of Carbon Steel

Pear-shaped bead cracking occurs in carbon steel when P/W, the ratio of penetration depth to bead width, increases. Pear-shaped bead cracking is a type of solidification cracking. In a previous study, we achieved the reduction of BTR in carbon steel by appropriate Ti addition. However, there are very few studies that pear-shaped bead cracking of carbon steel was prevented by reducing BTR. In this study, the effect of BTR reduction by Ti addition on the prevention of pear-shaped bead cracking was investigated. Narrow gap GMA welding was carried out using 0.15% C as the standard material and 0.15% C - 0.95% Ti as the countermeasure material. In the weld metal microstructure of 0.15% C - 0.95% Ti, there was a formation phase at dendrite boundaries and columnar grain boundaries. According to the EPMA analysis results, Ti-based oxides and MnS were formed in 0.15% C and in addition to these, TiC was formed in 0.15% C - 0.95% Ti. The results of the theoretical investigation of BTR indicated that BTR was significantly reduced by Ti addition when Ti content was reduced to 0.74% in 0.15% C - 0.95% Ti. Weld cracking was observed in the center of the weld metal in 0.15% C, but not in 0.15% C - 0.95% Ti. Observation of the fracture surface of 0.15% C indicated that the cracking was solidification cracking. The occurrence of solidification cracking was determined by the weld shape ratio (P/W ratio). The solidification cracking at 0.15% C can be uniformly determined by the P/W ratio, and the cracking occurs when the P/W ratio exceeds 1.0. On the other hand, in 0.15% C - 0.95% Ti, no solidification cracking occurred even when the P/W ratio exceeded 1.0. In other words, it was found that pear-shaped bead cracking (solidification cracking) of carbon steel can be prevented by reducing BTR. © 2024 Japan Welding Society. All rights reserved.