鋼材の溶接遅れ割れの研究(第3報)

Abstract

In the previous reports, the authors studied the effects of various factors on the occurence of cold cracks including root cracks, toe cracks and under-bead cracks in the heat-affected zones of base metals. They proposed the preheating temperatures necessary for the prevention of these cold cracks as a function of the chemical composition of steel, the groove shape, the restraint and the hydrogen content in weld metal.There have arised cases where not only base metal cracking but also weld metal cracking must be considered in the selection of the preheating temperature, especially for the welding of steels with lower carbon contents. A number of cold cracking tests have thus been conducted in order to find the necessary preheating and inter-pass temperature, θpr*, for preventing cold cracking in multi-run weld metals.The θph* is given by the following empirical equation as:θph*(°C)=120+120 log (HJIS/3.5)+5(hω-20)+8(σB-83)where, HJIS is the diffusible hydrogen content in weld metal by the JIS method (0.1 to 40 ml/100gr), hw the weld metal thickness (15 to 40 mm) and σB the tensile strength of weld metal (60 to 90 kgf/mm2).