Experimental Research on Development of Hot-strip High Strength Steel by Using Ultra-fast Cooling Technology

In the laboratory, taking a kind of ordinary Nb micro alloyed steel as raw material, hot-strip high strength steel was developed by an ultra-fast cooling technology. The microstructure of hot rolled high strength strip was observed and analyzed with LEICA image analyzer, and mechanical properties of the specimens, such as yield strength, tensile strength, total elongation, were detected with INSTRON tensile machine. Results show that two new steel grades with high strength and high elongation were obtained. One is of dual-phase steel, whose composition are polygonal ferrite with volume fraction of 82% and island martensite with volume fraction of 18%. Its yield strength is 516 MPa, tensile strength is 795 MPa, and total elongation is 23%. The other is of multiphase steel, whose composition are granular bainite with volume fraction of 95% and island martensite with volume fraction of 5%. Its yield strength is 538 MPa, tensile strength is 790 MPa, and total elongation is 25%.