High-Temperature Phases in the Fe–Mo–Cr–C System

Abstract

Phase equilibria involving the stable high-temperature quaternary χ_Fe,Cr,Mo,С phase were established in the Fe–Mo–Cr–C phase diagram. The arc-melted alloys were annealed at subsolidus temperatures for 52 h and then quenched in liquid gallium. The solidus temperature of the alloys was determined with the Pirani–Alterthum method. The sequence of changes in the alloy phase composition with temperature was monitored with high-temperature X-ray diffractometry from room temperature to the solidus temperature. The χ + η + α, χ + η, and χ + σ phase equilibria were directly observed at 973 K < T < 1373 K, 1273 K < T < 1530 K, and 1523 К < T < 1530 K, respectively, in the Fe_52.5Mo_23.5Cr_18.7C_5.3 (at.%) alloy. The χ + M₂₃C₆ + + α and χ + α phase equilibria were directly observed at 973 K ≤ T < 1523 K and 1473 К < < T < 1525 K in the Fe_55.5Mo_11.8Cr_28.2C_4.5 (at.%) alloy. It was shown that the two-phase χ + σ equilibrium could be preceded by three-phase χ + η + σ equilibria or single-phase χ_Fe,Cr,Mo,С equilibrium region (for the Fe_52.5Mo_23.5Cr_18.7C_5.3 alloy in the 1523 K < T < 1530 K temperature range). The quaternary χ_Fe,Cr,Mo,С phase was found in the (51.9–64.9) Fe, (5.4–23.5) Мо, (14.5–35.4) Cr, and (1–10.7) С аt.% composition ranges. Primary crystallization regions of the σ_Fe,Cr,Mo,С and α_Fe,Cr,Mo,С phases with the solidus temperature being about 1530 K (for the Fe_52.5Mo_23.5Cr_18.7C_5.3 alloy) and 1525 K (for the Fe_55.5Mo_11.8Cr_28.2C_4.5 alloy) were revealed. The linear thermal expansion coefficients for the χ_Fe,Cr,Mo,С, η_Fe,Cr,Mo,С, and α_Fe,Cr,Mo,С phases of different composition observed for different temperature ranges were determined.