Microstructural Evolution of a Low-Carbon Steel during Application of Quenching and Partitioning Heat Treatments after Partial Austenitization

The “quenching and partitioning” (Q&P) process has been studied in a low-carbon steel containing 1.1 wt pct aluminum by heat treatments consisting of partial austenitization at 900 °C and subsequent rapid cooling to a quenching temperature in the range between 125 °C and 175 °C, followed by an isothermal treatment (partitioning step) at 250 °C and 350 °C for different times. Characterization by means of optical and scanning electron microscopy, electron backscattered diffraction (EBSD), magnetization measurements, and X-ray diffraction (XRD) has shown a multiphase microstructure formed by intercritical ferrite, epitaxial ferrite, retained austenite, bainite, and martensite after different stages of tempering. A considerable amount of retained austenite has been obtained in the specimens partitioned at 350 °C for 100 seconds. Experimental results have been interpreted based on concepts of the martensite tempering, bainite transformation, and kinetics calculations of the carbon partitioning from martensite to austeniteMaterials Science and EngineeringMechanical, Maritime and Materials Engineerin