溶接金属の連続冷却変態挙動におよぼす酸素の影響 : 溶接金属の組織と靭性に関する研究(第 1 報)

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The effect of oxygen on the transformation of low carbon ferritic weld metal prepared by the MIG welding process has been investigated by means of dilatometry and microstructural observations. The Continuous-Cooling-Transformation (CCT) diagrams for the Si-Mn, Si-Mn-Ti and Si-Mn-Ti-B weld metal austenitized at 1350℃ show that the region of ferrite formation was shifted to the faster cooling rate at high oxygen levels, and higher oxygen weld metals transformed from the austenite at significantly higher temperature. These observations suggest that the non-metallic inclusions promote the ferrite formation in weld metal. At sufficiently high oxygen levels the primary ferrite and the side plate ferrite were formed predominantly at the higher temperature range, and the coarse grained ferrite structures were formed. The bainitic structures were apt to form at the low oxygen levels. The notch toughness of the weld metal, therefore, was low at both low and high oxygen levels, and was high at the intermediate oxygen levels because of fine acicular ferrite structures. The inclusion volume fractions in the high oxygen weld metal were larger than in the low oxygen weld metal, and these non-metallic inclusions act as the nucleants for ferrite. In the Si-Mn-Ti-B weld metals the grain boundary segregation of boron suppresses the formation of the primary ferrite at the austenite grain boundary and it leads to the uniform microstructure. The notch toughness of Si-Mn-Ti-B weld metal, therefore, was affected largely by the oxygen levels. On the other hand, the Si-Mn weld metals made primary ferrite formation more likely, and the notch toughness of these depended less on the oxygen content even if the cooling rate is significantly high. It is concluded that the effect of oxygen on the notch toughness of the weld metal can be understood by the transformation characteristics.
社団法人溶接学会の論文
1981-12-05

溶接金属の連続冷却変態挙動におよぼす酸素の影響 : 溶接金属の組織と靭性に関する研究(第 1 報)

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