低炭素鋼板の溶接熱影響部の変態挙動に及ぼす加熱・冷却速度の影響

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Effects of welding thermal cycle pattern and microstructure of a low carbon base steel on transformation behavior of heat affected zone (HAZ) were investigated in order to know the relationship between microstructure and the deterioration in toughness of HAZ of high heat input welding. Thermal dilatation and microstructural observations showed that the reverse transformation from ferrite to austenite and from austenite to δ-ferrite occurred displacively at rapid heating. A_<c1> temperature was decreased by heating rate of 200℃/s in TMCP steel, but it was not decreased in normalized steel. This meaned that reaustenitization was accelerated in non-equilibrium microstructure. Austenite and δ-ferrite transformed displacively were characterized by inner stress and substructure with defects, which promote the formation of grain boundary ferrite (GBF) and acicular ferrite (AF) in cooling. Slow cooling in stable austenite region above 900℃ caused the relaxation of inner stress and the restoration of substructure, which were followed by the retardation of the formation of GBF and AF. GBF related to the precipitation of pearlite bordering on GBF. It was already reported by authors that the lowering toughness of HAZ was attributed by the precipitation of degenerate pearlite. These results indicate that it is important to simulate thermal cycle accurately in order to evaluate toughness of HAZ of high heat input welding.
社団法人日本鉄鋼協会の論文
1998-02-01

低炭素鋼板の溶接熱影響部の変態挙動に及ぼす加熱・冷却速度の影響

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