Abstract
The liquidus surface phase diagram of the quaternary Fe-25%Cr-C-B system has been experimentally determined by using a thermal analysis technique, optical microscopy and X-ray diffraction. The liquidus surface for this system was constructed from five phases of M2B, M23(C, B)6, M7(C, B)3, γ and δ. Each phase formed four kinds of eutectic structures, that is, γ+M2B, γ+M23(C, B)6, γ+M7(C, B)3 and γ+M3(C, B), and three kinds of peritectic structures, that is, M2B+M23(C, B)6, M7(C, B)3+M23(C, B)6 and γ+δ. Additionally, M2B and M7(C, B)3 also solidified in a eutectic manner near the liquidus boundary between M2B and M7(C, B)3. The borides contain 7.0∼9.5 mass% boron and less than 0.3 mass% carbon. The stoichiometric boron concentration of M2B was about 8.9∼9.4 mass%, so it suggested the existence of lower boron boride than that of M2B. Carbon and boron concentrations of three types boro-carbides changed linearly, the maximum boron content of each boro-carbide was about 2.4 mass% in M7(C, B)3, about 2.2 mass% in M23(C, B)6 and about 3.3 mass% in M3(C, B). The microstructures along the pseudo-binary eutectic composition were constructed from one or two kinds of eutectic structures. That is, in the lower carbon content (higher boron content) side from the composition at a minimum temperature (1460 K) on the pseudo-binary eutectic line, γ+M2B solidified singly or together with γ+M23(C, B)6, while in the higher carbon side three eutectic types of γ+M23(C, B)6, γ+M2B and γ+M7(C, B)3 solidified separately or together with others.
