STABILITY OF THE β-Mn STRUCTURE IN RAPIDLY QUENCHED Fe-Mo-Cr-C ALLOYS AT HIGH TEMPERATURES

High-temperature x-ray diffraction (HT-XRD) is used to study the evolution of phase states of arc-melted and spinning 51.9Fe11.1Mo26.3Cr10.7C (at.%) alloys in the temperature range 293-1573 K. It is established that alpha- and beta-Mn-like phases (chi and pi, respectively) and solid solutions based on alpha- and gamma-Fe identified by HT-XRD in the temperature range 293-978 K are metastable. A diffusion-free method for mutual transformations of Mn-like phases in the temperature range 873-978 K is proposed. It is shown that increase in temperature in HT-XRD conditions stabilizes metastable Mn-like phases. It is experimentally established, for the first time, that a stable beta-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 a stable pi-phase of composition Fe(5)MoCr(2.5)C. It is found out that a stable.-phase and equilibria with its participation, alpha + eta + M(23)C(6) + chi and chi + alpha + pi + L, exist in the temperature range 1473-1523 K in the Fe-Mo-Cr-C system. It is determined that decomposition and/or mutual transformations of metastable Mn-like phases in 51.9Fe11.1Mo26.3Cr10.7C alloys occur at T approximate to 978 K, which is close to the temperature of alpha-Mn double left right arrow beta-Mn polymorphic transformation in pure manganese.