Microstructural characterization of the C–Mn multiphase high strength cold rolled steel

The multiphase steels have microstructures containing, ferrite, martensite, bainite, carbide particles and a small amount of retained austenite. This microstructure, according to the volume fraction of each constituent, provides the steel with a high mechanical strength and good ductility. Different thermal cycles were simulated in the laboratory to attempt to create microstructures with improved mechanical properties. The samples were heated to 750 °C for 300 s, and then quickly cooled to 500 °C, soaked for another 300 s and then submitted to the accelerated cooling process, with rates of 2–100 °C/s. The microstructure was examined at the end of each different thermal cycle. The mechanical behavior evaluation was made by microindentation hardness testing. The microstructural characterization involved Optical Microscopy (OM), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and the identification of phases was made using the Electron Backscatter Diffraction technique (EBSD).