Takako Yamashita1, Akihiro Matsuzaki1,Shigeaki Takajo1 and Mitsuhiro Hasebe2
1Technical Research Laboratories, Kawasaki Steel Corporation, Chiba 260-0835
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(C0.33B0.67) 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(C0.33B0.67) remained unchanged even after the subsequent heat treatment due to its high thermodynamic stability. The Fe3(C0.33B0.67) precipitate was effective as a nucleation site of cementite in the (α+cementite) equilibrium region because Fe3(C0.33B0.67) provided a cementite nucleus with B and thermodynamically enhanced its nucleation. The cementite nucleated on the coarse Fe3(C0.33B0.67) precipitate abnormally coarsened due to its size effect.
(Received December 22, 1998; In Final Form March 26, 1999)
high carbon steel, precipitation, thermodynamics property, surface analysis, spheroidizing annealing
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