含ボ口ン 25 % Cr 白鋳鉄の共晶凝固にともなう組織形成および溶質元素の挙動

抄録

  To clarify the fomation processes of eutectic structure unidirectional solidification of 25 % Cr white cast irons containing 1-2 % B, the distribution of solute elements in liquidus region at solid / liquid interface zone and the composition of eutectic compounds formed were examined mainly by means of EPMA technique. Eutectic solidification of the 25 % Cr alloys occurred through two step processes with the primary and secondary eutectics as well as that of the 15 % Cr alloy which was reported in the previous paper. In the low B alloys, both of the eutectics were γ+M₂₃(C, B)₆, though they had different composition. They solidified in a rod-like three-dimensional dendritic structure. In the high B alloys, the primary eutectic was γ+M₂B which grew in network structure, while the secondary eutectic was γ+M₂₃(C, B)₆, which grew in rod-like structure as well as that in low B alloys. Front position of the secondary eutectic was revealed by a discontinuous point on the fraction of solid-distance curve in solid / liquid zone. A one-to-one correspondence was confirmed between solute concentration profile in the liquid region of solid / liquid zone and change in composition of the eutectic compounds formed.