To suppress welding cracks when ultrahigh tensile strength steel sheets are subjected to flash butt welding.
The invention refers to a method where ultrahigh tensile strength steel sheets 1 are subjected to flash butt welding. After the completion of upset, in post-heat treatment where direct electric conduction is performed in which a weld zone is repeatedly subjected to electric conduction and non-electric conduction using a welding power source, previously, based on the objective values of the heating arrival temperature in a temperature rising stage, and the respective objective values of the cooling arrival temperature and cooling velocity in a cooling stage, the conditions of the respective direct electric conduction in the temperature rising stage and the cooling stage are decided. Then, the post-heat treatment is performed according to the decided conditions. In this way, the quality of the weld zone in the flash butt welding of the ultrahigh tensile strength steel sheets improves, and its fracture upon cold rolling can be effectively prevented.
MATSUDA HIDEKI
Tetsuya Mizogami
Yoshinori Iwahara