鋼材溶接性に及ぼす外気温度の影響

Abstract

It is well known that there are four main factors for cold cracking probability in a heat affected zone (HAZ), i.e., carbon equivalent, diffusible hydrogen content, welding thermal history and residual stress. Using these four factors, several criteria have been presented to avoid cold crack-ng. At low ambient temperaturel welding without prehaeting is sometimes preculded, because the surface of a welded plate might be frozen. On the other hand, high tensile strength modern steels have low carbon equivalent owing to such newly developed processes as thermomechanical control, which means that steeleweldability is much higher than that of the old days. And because of this tendency, reducing carbon equivalent, many opportunities will occur that welding, sometimes without preheating, is condicted at low ambient temperature. However, there are few research reports which examine the effect of ambient temperature on steel weldability. The authors examined the eqect of ambient temperature on cold cracking susceptibility. Temperatures chosen were 20°C, -10°C and -30°C. The Tekken test method was applied to steels, and five macro sections were machined from every tets piece to observe cold cracking in hte HAZ. From the experimental results, it is concluded that it must be considered as an additional independent factor for cold cracking susceptibility. To assess this effect, the modified carbon equivalent is introduced.