Effect of cooling process on mechanical properties of thin-gauge hot-rolled dual-phase steel

The high strength hot-rolled dual-phase steel suitable for a thin slab continuous casting and rolling (TSCR) process was developed by a low C and Nb micro-alloyed design with the controlled rolling and cooling technology. The effect of the isothermal temperature and holding time on the microstructure and mechanical properties of the dual-phase steel was studied using a uniaxial tensile test and optical microscope (OM). The results showed that with the decrease of the isothermal temperature in the ferrite phase transformation region, the thermodynamic conditions of the ferrite transformation were enhanced. The proportion of the ferrite increased while that of martensite decreased, resulting in the reduction of the yield strength and tensile strength and the increase of elongation. With the rise in the isothermal time, the kinetic conditions of the ferrite transformation were enhanced and the proportion of the ferrite increased. The ferrite transformation has completed after 8 seconds of the isothermal holding time, and it was not apparent for increased amount of the transformed ferrite to increase the isothermal time.