J. Japan Inst. Metals, Vol. 63, No. 6 (1999),
pp. 708-716

Precipitation Behaviors of Cementite in Fe-0.8 mass%C-0.1 mass%B Alloy

Takako Yamashita¹, Akihiro Matsuzaki¹,Shigeaki Takajo¹ and Mitsuhiro Hasebe²

Abstract:

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.

(Received December 22, 1998; In Final Form March 26, 1999)

Keywords:

high carbon steel, precipitation, thermodynamics property, surface analysis, spheroidizing annealing

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