Prevention of cold cracking by the welding process for reducing diffusible hydrogen in high-tensile thick plate welding

Abstract

ABSTRACT Cold cracking sensibility is a 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 recent years, a novel welding process using a special welding torch was researched and developed. By using this process, the amount of hydrogen content in the weld metal can be greatly 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 780 MPa class high-tensile steel. During the test, the preheat and interpass temperatures were controlled strictly. Moreover, the temperature level was changed from 50°C to 0°C. As a result, cold cracking (transverse crack) occurred with the conventional method in which the temperature was kept under 50°C. In contrast, there is no crack with the developed one under 50°C and 25°C. When the controlled temperature was lowered to 0°C, 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 was confirmed and about 50°C preheating temperature reduction effect was demonstrated. These test results 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.