Evaluation of solidification cracking susceptibility factors in carbon steel and availability of Ti addition based on theoretical analysis

This study conducted a basic investigation to improve the solidification cracking susceptibility of carbon steel. BTR is one of the susceptibilities to solidification cracking, and it is said that solidification cracking susceptibility is reduced when BTR is smaller. BTR of three commercial filler metals was evaluated by using Trans-Varestraint test. EPMA and EDS analysis of the weld metal microstructure revealed two compounds. The white structure was composed of silicon, manganese, and sulphur, and the black structure was Ti-based compound.Theoretical analysis of BTR was conducted by applying a two-phase peritectic solidification model in FA mode and considering MnS crystallization during solidification segregation. The analysis results indicated that BTR of carbon steel is attributed to the difference in solidification completion temperatures, and carbon is the most deleterious element. Also, MX compound (Ti, C, N) crystallized in addition to MnS at the end of solidification. Theoretical analysis was conducted for Ti virtual addition materials because MX compound (Ti, C, N) crystallization by Ti addition may lead to BTR reduction by trapping C in the liquid phase. The results showed that Ti addition reduced BTR. The amount of C in the residual liquid phase was reduced by an increase in MX compound (Ti, C, N) crystallization due to Ti addition. Based on theoretical considerations, it can be concluded that Ti addition to carbon steel is effective in reducing BTR.