Microstructure and mechanical properties of high strength and high toughness micro-laminated dual phase steels

A series of steels with the micro-laminated dual phase microstructure were produced by hot rolling and air cooling processes in this study. Different volume fractions and morphology of the ferrite and martensite phases were obtained by adding different carbon contents in the steels containing 3 wt% aluminum. The microstructure of the dual phase steels was examined by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). It was shown that the microstructure was composed of large ferrite and martensite lamellae. Small martensite laths and a miniscule amount of residual austenite were also found in the martensite phase. The tensile, impact and hardness tests revealed that the dual phase steels had an excellent combination of mechanical properties. The mechanical properties had a great relationship with the martensite volume fraction and the micro-laminated microstructure. The fractography of impact specimens was examined to explore the toughening mechanism of the micro-laminated dual phase steels.