The purpose of this investigation is to determine the liquidus surface phase diagram of the Fe-5%Cr-C-B system and solute concentration of each compounds. Liquidus surface phase diagrams were determined from the thermal analyses and micrographs of 42 kinds of alloys containing 5%Cr, 0∼5.5%C and 0∼4%B. Thermal analysis of each specimen was carried out at a cooling rate of 0.08∼0.25 K·s
−1 after melting in an Al
2O
3 crucible at about 1673 K under argon atmosphere. Chemical composition of each alloy and solute concentration of each phase were analyzed by EPMA.
Six types of phases, i. e., δ, γ, M
2B, M
3(C, B), M
7(C, B)
3 and graphite, existed on liquidus surfaces of the Fe-5%Cr-C-B system. In addition, two types of pseudo-binary eutectic reaction, i. e., L→γ+M
2B and L→γ+M
3(C, B), and two types of peritectic reaction, i. e., L+M
2B→+M
3(C, B) and L+M
7(C, B)
3→M
3(C, B), occurred on each liquidus surface boundary. The lowest temperature on the liquidus surface (≈1414 K) existed on the pseudo-binary eutectic line in the composition range from 1.5%C, and 1.8%B to 2.0%C, and 1.4%B. The C and B concentrations in the M
3 (C, B) and M
7 (C, B )
3 phases changed in a linear relationship with the alloy composition, while satisfying the stoichiometric relationships. The maximam B solubility of the M
3(C, B) phase was about 4.6% and that of the M
7(C, B)
3 phase was about 2.9%.
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