初晶フェライトで凝固するオーステナイト系ステンレス鋼溶接金属の凝固・変態挙動

Cr-Ni系ステンレス鋼溶接金属の凝固・変態に関する研究(第2報)

抄録

Weld metals solidified with ferritic-austenitic solidification mode (FAmode) have dual phases of ferrite and austenite in an as-solidified condition, where ferrite exhibits different morphologies, depending on chemical composition and welding condition. The effect of solidification and transformation sequence on the formation of the final morphologies of ferrite was investigated in the present study. Austenite is formed through either eutectic reaction or peritectic reaction at dendrite boundaries after the primary formation of ferrite. In the case of the eutectic formation of austenite, ‹100›_δ direction of the primary ferrite and ‹100›_r direction of the eutectic austenite are parallel each other, and lie along the growth direction of primary dendrites. However, any specific relationship is not identified as to lattice planes between the two phases. Durng cooling after the solidification, austenite extends into the primary ferrite via. solid state transformation, and the final morphology of ferrite becomes vermicular without the coherent orientation relationship between the primary ferrite and the eutectic austenite. In the case of the peritectic formation of austenite, the Kurdjumov-Sachs orientation relationship is present between the primary ferrite and the peritectic austenite, while ‹100›_r direction of the peritectic austenite is not parallel with the growth direction of primary dendrites. During cooling after the solidification, the primary ferrite transforms to austenite and the final morphology of ferrite becomes lathy since the primary ferrite and the peritectic austenite have the favorable coherent orientation.