鉄-炭素系包晶凝固中のγ相成長速度に及ぼす初期炭素濃度と冷却速度の影響

抄録

Changes in fractions of δ-ferrite, austenite and liquid phases during peritectic solidification in iron-carbon system are calculated. The peritectic solidification, δ+L→γ, is divided into δ→γ transformation at δ/γ interface and L→γ solidification at γ/L interface. Both the transformation and solidification proceed by (1) carbon diffusion from liquid through austenite into δ-ferrite and (2) precipitation of austenite from δ-ferrite and crystallization of it from liquid due to cooling. Approximately 80% of the austenite formed during the peritectic solidification is the product of δ→γ transformation, which may lead to the generation of tensile stress in the solidification shell because of the difference in density between the two solids. The amount of the δ→γ transformation is largest, when the initial carbon content is 0.17 mass%. However, when the transformation in a well-developed dendrite network is focused on, the carbon content for the largest amount of the transformation decreases to 0.14-0.16 mass%, which corresponds to the carbon content at which surface cracking of continuously cast slabs is reported to be most frequent.