（1. Research Center, Tangshan Iron and Steel Company， Tangshan 063002， Hebei， China 2. The State Key Laboratory of Rolling and Automation， Northeastern University， Shenyang 110819， Liaoning， China 3. Technology and Research Institute， HBIS Group, Shijiazhuang 050023， Hebei， China）
Abstract：In order to meet the requirements of high strength and high toughness of Q420qD bridge steel, the low carbon steel microalloyed with Nb, V and Ti was adopted. The hot metal pretreatment and automatic steelmaking were applied to control the molten steel purity, the cast slab quality was guaranteed by electromagnetic stirring and heavy reduction, the new generation of TMCP technology was used to refine and homogenize the microstructure, then the mechanical property of steel was guaranteed. The mechanical property test and microstructure determination of the developed steel were carried out, and the results showed that the yield strength was about 450- 510 MPa, the tensile strength was about 560- 640 MPa, the elongation was about 21%- 25%, the impact energy was above 200 J at －20 ℃, the yield ratio was below 0.85, and II class crack detection was qualified. In order to provide the fundamental basis for controlling rolling and cooling processes, the dynamic state CCT curve of steel was measured by Gleeble 3500. The analysis of precipitates by transmission electron microscope indicated that the contribution of precipitation strengthening was below 15% of the total strength, the main strengthening mechanisms were solution strengthening, refinement strengthening and phase transformation strengthening by bainite.
2018, Vol. 28 
