The Formation of Widmanstätten Side-Plate Precipitates Comprising Duplex FCC and L12 Phases in an As-Air-Cooled Fe-Mn-Al Steel

Understanding the constituent phases and their corresponding phase transformations are crucial for the determination of the performance and application characteristics of the alloy systems. The methodology in the Fe-0.8 C-8.3 Mn-16.9 Al (at.%) alloy included the annealing at and air cooling from 1100°C. This study investigates the minor Widmanstätten side-plate precipitates (ppts) distributed uniformly in the major body-centered cubic (BCC) matrix. During air-cooling, a face centered cubic (FCC) phase precipitated in the BCC matrix in the form of the Widmanstätten side-plates through a precipitation transformation. Upon further cooling, the high-temperature FCC phase underwent the spinodal decomposition and decomposed into two low-temperature FCC phases, that is, solute-lean FCC′ and solute-enriched FCC′′. The FCCꞌꞌ phase in the form of nanosized particles precipitated homogeneously in the FCCꞌ matrix. For the alloy after further cooling, an ordering reaction occurred, and the solute-enriched FCC′′ phase transformed into the L12 phase. Therefore, The Widmanstätten side-plate ppt consists of duplex FCC and L12 phases. The nanosized L12 particles precipitated homogeneously in the FCC matrix. The insights gained from this study contribute to deeper understandings of phase stability and transformation mechanisms in Fe-Mn-Al alloys, which can inform their future design.