Effect of Finishing Rolling Temperature on the Microstructure and Mechanical Properties of Low Si-Mn-Nb Hot Rolled Dual-phase Steel Strip

The effect of finishing rolling temperature on the microstructure and mechanical properties of Si-Mn-Nb hot-rolled dual-phase steel were investigated by using TEM,SEM technology and optical microscopy.The results showed that with finishing rolling temperature decreasing,the size of ferrite grains decreased and the size differences increased,the volume fraction of martensite decreased and the volume fraction of bainite increased.When the finishing temperature was 860 ℃,the microstructure of strengthening phase was mainly martensite,the tensile strength was higher and the yield ratio was lower,the second phase was mainly composed of Nb（C,N） and its size was larger.When the finishing temperature was 743℃,the microstructure of strengthening phase was mainly bainite,the yield strength was higher and the plasticity was good,the second phase was mainly composed of Nb（Ti） CN carbonitride compound and its size was smaller. Comprehensive analysis shows that the different proportions of the strengthening phase and the second phase of different components was obtained through reasonable control of the final rolling temperature,thus the controlling of mechanical properties can be obtained as well.