Effect of Bainite Transformation Sequence on Microstructure, Hardness, and Wear Behavior of Medium‐Carbon Quenching and Partitioning Steel

To explore the influence of bainitic transformation sequence on the microstructure, hardness, impact toughness, and wear behavior of a medium‐carbon Q&P steel, two modified Q&P treatments were systematically investigated. The results reveal that reversing the transformation sequence enables effective tailoring of the multiphase microstructure. Compared with the reverse sequence of bainite followed by martensite (B‐Q&P process), the transformation sequence of martensite followed by bainite (Q&P‐B process) generates a finer multiphase microstructure consisting of martensite, bainitic ferrite (BF), and retained austenite (RA). This refinement arises from the geometrical constraint imposed by the primary martensitic framework on subsequent transformation, while the higher carbon content (1.28 wt.%) of RA originates from the dual‐source carbon partitioning mechanism involving both primary martensite and secondary bainite. The Q&P‐B specimen exhibits a slightly increased hardness (510 HV1) and impact toughness (15.7 J), as well as slightly lower wear coefficient and wear volume. These property differences are primarily attributed to the strengthening effect from grain refinement, increased phase boundaries, and the mechanical stability of RA. Nevertheless, the bainitic transformation sequence exerts a more pronounced influence on microstructural refinement than on mechanical performance, and the two routes yield multiphase microstructures with largely comparable overall properties.