Fe-0.8 mass%C-0.1 mass%B合金におけるセメンタイトの析出挙動

抄録

The microstructure and precipitation behavior of cementite in Fe-0.8 mass%C-0.1 mass%B alloy were investigated to reveal the influence of B on the precipitation behavior of cementite.
Two types of coarse cementite were observed in the specimen heated at (γ+cementite) equilibrium temperature of 1100°C. The one was Fe₃(C_0.33B_0.67) that precipitated from the liquid phase enriched with B through the partitioning of solutions during solidification. The other was Fe₃C that precipitated from the early liquid phase.
The composition of Fe₃(C_0.33B_0.67) remained unchanged even after the subsequent heat treatment due to its high thermodynamic stability. The Fe₃(C_0.33B_0.67) precipitate was effective as a nucleation site of cementite in the (α+cementite) equilibrium region because Fe₃(C_0.33B_0.67) provided a cementite nucleus with B and thermodynamically enhanced its nucleation. The cementite nucleated on the coarse Fe₃(C_0.33B_0.67) precipitate abnormally coarsened due to its size effect.