Leveraging chemical heterogeneity in steels heat treated to retain metastable austenite

The assumption of chemical homogeneity simplifies heat treatment design, particularly for processes like quenching and partitioning (Q & P) aimed at retaining metastable phases in advanced high strength steels. However, real microstructures contain chemical heterogeneities (e.g., banding from solidification or phase partitioning); these effects on final microstructures are not well understood. To investigate the role of chemical heterogeneity, inter-band and intra-band chemical heterogeneities were measured across starting ferrite/pearlite microstructures to predictively model final Q & P microstructures produced by heat treatment. Two models were developed to investigate effects across chemical bands and within prior pearlite regions, supported by experimental measurements of solute distributions. These models quantify the impact of initial microstructural condition on final microstructures with heat treatment, are applicable to other alloys and heat treatments where retaining metastable phases and solute profiles is desirable, and could be used to intentionally design heat treatment processes to exploit chemical heterogeneities and create otherwise unobtainable microstructures.