Phase transformations and precipitation behavior in FeCrAl stainless steel during equilibrium solidification

The phase transformations and precipitation behavior were investigated by using Thermo-Calc software in the Fe-(18-21)Cr-(3-5)Al-(0-0.03)C-(0-0.2)Si-(0-0.2)Mn multicomponent system relevant to FeCrAl stainless steel during solidification. The vertical sections of this system were calculated by using the TCFE7 database. Based on these vertical sections, the influence of different elements was analyzed in the phase transformations during solidification and a diagram of the phase-transformation path of FeCrAl stainless steel was obtained during equilibrium solidification. The results indicate that the full-phase transformation path of FeCrAl stainless steel during the cooling process from 1600℃ to 300℃ is as follows:L→AlN+αδFe→AlN+αδFe+Cr₇C₃→AlN+αδFe+Cr₇C₃+Cr₂₃C₆→AlN+αδFe+Cr₂₃C₆→AlN+αδFe+Cr₂₃C₆+σ→AlN+αδFe+Cr₂₃C₆+σ+α'→AlN+αδFe+Cr₂₃C₆+α'. The precipitation of Cr₇C₃ and σ, during the solidification process mainly depends on the carbon and silicon contents in the system, respectively. Increasing the aluminum content can enlarge the stable region of αδFe+Cr₇C₃, lower the precipitation temperature of α', and restrain σ precipitation. Increasing the chromium content can reduce the stable region of αδFe+Cr₇C₃ and enlarge the stable region of σ and α'.