高韧性桥梁钢Q420qD的开发

Development of Q420qD bridge steel with high toughness

为了满足桥梁钢Q420qD高强、高韧性的要求,采用低碳、铌、钒、钛微合金化成分设计方案,应用铁水预处理、自动化炼钢控制钢水洁净度,采用电磁搅拌及重压下等工艺手段保证铸坯质量,利用新一代TMCP工艺,控制钢板的组织细化和均匀,保证产品的综合力学性能。通过力学性能的测试和组织检测,开发钢种屈服强度在450~510 MPa,抗拉强度在560-640 MPa,伸长率在21%-25%,-20℃冲击功全部在200J以上,屈强比全部小于0.85,Ⅱ级探伤全部合格;在Gleeble3500试验机上测定了钢种的动态CCT曲线,为制定控轧控冷工艺提供理论基础;应用透射对析出物的分析表明,析出强化贡献量占全部强度的15%以下,强化机制以固溶强化、细晶强化和贝氏体相变强化为主。

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 450-510MPa,the tensile strength was about 560-640MPa,the elongation was about 21%-25%,the impact energy was above200 Jat-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.