To clarify the mechanism of the ductility-dip cracking formed under the weld bead during multi-pass welding, the thermal-elastic-plastic analysis is performed in this study. Thermal-elastic-plastic analysis is included in a widely used FEM commercial software. By using this method, the influence of the increment of plastic strain in DTR (DTR plastic strain) and staying time in DTR (DTR time) on crack formation are closely examined. Both are considered as index of the crack formation. From the results of serial computation, it is found that these parameters tend to be larger near under the weld bead. Furthermore, the same tendency is observed in the results computed by FEM using temperature dependent interface element developed by the authors. This indicates that ductility-dip cracking is considered to be possibly analyzed by using either thermal-elastic-plastic FEM or FEM using temperature dependent interface element. However, FEM using temperature dependent interface element is necessary to analyze the crack extension problem.
