Report No. 1: investigation on high-temperature properties of weld metals of stainless steel flux-cored wires and the effect of bismuth report of the Japan welding engineering society

摘要

Among the welding consumables for austenitic stainless steel, represented by Type 308, consumption of flux-cored wires has increased since the 1980s because of high welding efficiency that reduces production costs, and flux cored arc welding (FCAW) of austenitic stainless steel is expanding its application remarkably. In the first half of 1992, many cases of cracking were observed in the Type 308 weld joints of austenitic stainless steel adopted for the equipment used at high temperatures over 700℃ of the fluid catalytic cracking(FCC) units. At first, these cracks were considered to have been caused by creep damage in the areas of high stress concentration. However, because most of the cracks were observed in FCAW weld metals, it was thought that the welding process was an important factor. As a result of investigation, it was concluded that the cracks initiated caused by reheat cracking and propagated caused by reheat cracking and creep. Among many factors that may have caused the cracks, a small amount of Bi contained in the weld metals was considered to be the most predominant factor that deteriorated creep ductility and increased reheat cracking susceptibility of the weld metals. Bi in the weld metals was a residue from the flux component that was added for improving slag detachability. In comparison with Bi-bearing FCAW weld metals, Bi-free FCAW weld metals have showed better creep ductility and reheat cracking resistance comparable to SMAW weld metals. Based on the results of this investigation and research, it is recommended to use Bi-free welding consumables (Bi<=0 OOlwt%) to prevent reheat cracking for the constructions of austenitic stainless steel used at a high temperature or subjected to heat treatment in fabrication.