The Effect of Cold Cracking Prevention of FCAW by the Welding Process for Reducing Diffusible Hydrogen

Abstract

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. Generally, it is said that there are two ways to prevent the cracking. One is to control the heat input by pre/post heating process and interpass temperature. The other is to select low hydrogen welding materials. However, in 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 in FCAW by new low hydrogen process was confirmed. The y-groove weld cracking test was applied. High-tensile steel of 490 MPa was selected to both base metal and welding materials for the test. The preheat temperature level was changed from 75 to 0℃. From the result of the test, the cold cracking (root cracking) was occurred with the conventional method under 25 and 0℃ preheating. On the other hand, there was no cracking with using the developed process even in the 0℃ preheating condition. From the above result, the effect of cold cracking prevention by the novel welding process for reducing diffusible hydrogen were confirmed and 50℃ or more preheating temperature reduction effect were demonstrated. It has been clarified that the reduction effect is appropriate as the result of applying the cold crack control index reported in the past research. This test result has proved that the reduction of the hydrogen in weld metal leads to preventing the cold crack that is reported in the past research.