2020 年 38 巻 1 号 p. 41-51
Cold cracking sensibility is severe problem in the welding fabrication of large-scale steel structures. It is well-known that diffusible hydrogen content in the weld metal strongly influences this cracking. In the recent years, a novel welding process using special welding torch was researched and developed. By using this process, amount of hydrogen content in the weld metal can be highly reduced than the conventional process. In this study, the effect of cold cracking prevention and required preheating temperature reduction by new welding process were confirmed. The window type restraint weld cracking test was applied. Both base metal and welding material were 780MPa class high-tensile steel. During the test, the preheat and interpass temperatures were controlled strictly. Moreover, the temperatures level was changed from 50 to 0℃. As a result, the cold cracking (transverse crack) was occurred with the conventional method under 50℃ temperature controlling. In contrast, there is no crack with the developed one under 50 and 25℃. When the controlled temperature was lowered to 0℃, many cracks were observed with the developed process. From the above, the effect of cold cracking prevention by the novel welding process for reducing diffusible hydrogen were confirmed and about 50℃ preheating temperature reduction effect were demonstrated. These test results were confirmed the consistency with past research results. A very good agreement was obtained when comparing the test results and the past research results of cold cracking control indexes in terms of root cracking and multi-pass weld transverse cracking. Therefore, the validity of this study was demonstrated.
