Stability of the β-Mn Structure in Rapidly Quenched Fe–Mo–Cr–C Alloys at High Temperatures

Abstract

High-temperature x-ray diffraction (HT-XRD) is used to study the evolution of phase states of cast and spinning 51.9Fe11.1Mo26.3Cr10.7C at.% alloys in the temperature range 293–1573 К. It is established that α- and β- Mn-like phases (χ and π, respectively) and solid solutions based on α- and γ-Fe identified by HT-XRD in the temperature range 293–978 К are metastable. A diffusion-free method of mutual transformations of the Mn-like phases in the temperature range 873–978 К is proposed. It is shown that increase in temperature in HT-XRD conditions stabilizes the metastable Mn-like phases. It is experimentally established, for the first time, that a stable β-Mn-like phase exists near the solidus in the Fe–Mo–Cr–C system. It is concluded that congruent crystallization is a way of forming the stable π-phase with Fe5MoCr2.5C composition. It is demonstrated that the stable χ-phase and equilibria with its participation, α + η + М₂₃С₆ + χ and χ + α + π + L, exist in the temperature range 1473–1523 К in the Fe–Mo–Cr–C system. It is determined that decomposition and/or mutual transformations of the metastable Mn-like phases in 51.9Fe11.1Mo26.3Cr10.7C alloys occur at Т ≈ 978 К, which is close to the temperature of the polymorphic transformation α-Mn ⇄ β-Mn in pure manganese.