Precipitation behavior and mechanical properties of a hot rolled Ti-bearing dual phase steel

We have studied here the microstructure, precipitate evolution and mechanical properties in a Fe-Mn-Cr-Ti dual phase steel processed by thermo-mechanical control processing. When the deformed austenite was treated in the temperature range of 640-760 °C, the microstructure consisted of ferrite and 7-80% martensite. Both random and interphase precipitation of nanoscale TiC particles occurred in the ferrite matrix. With decrease in temperature, the average size of precipitates was reduced from 5.4 nm to 2.2 nm, and the morphology of interphase precipitation was altered from curved to planar because of the change in the mechanism of TiC interphase precipitation. Hot rolling inhibited interphase precipitation but promoted precipitation on dislocations. Given that the ferrite matrix was significantly strengthened by nanoscale TiC particles, the hardness difference between the ferrite matrix and martensite was significantly decreased, and the strength of hot rolled Ti-bearing dual phase steels was less dependent on the martensite content compared to the conventional dual phase steels. The strength of hot rolled Ti-bearing dual phase steels was derived from a number of strengthening mechanisms, namely phase transformation, precipitation and grain refinement strengthening.