铁路货车铸造车钩用钢相变转变动力学研究

Kinetic study of the phase transition of cast steel for couplers of rail freight cars

通过物理模拟试验,对两种综合力学性能表现较好的新型车钩用铸钢及传统E+级铸钢进行相变点测量,并绘制相应过冷奥氏体连续冷却转变曲线。结合各不同冷却速度曲线下金相组织特征,对比分析两种铸钢的相变转变动力学机理,研究其性能优化理论。通过曲线对比发现新型铸钢A C1=755℃、A C3=831℃,传统小范围成分控制的E+级铸钢A C1=728℃、A C3=786℃,较E+钢,新钢种具有奥氏体相变温度提高、淬火组织区扩大,C曲线整体左移,马氏体临界冷却速度降低,珠光体区扩大等优势特征。通过组织对比分析发现,两种铸钢的淬火组织均为片状马氏体,新型铸钢马氏体组织针状结构细长,网带状偏析倾向小,贝氏体区可见独立下贝氏体区,E+级铸钢则以混合组织为主。近平衡组织区E+级钢组织以等轴状分布,新型铸钢中的铁素体团块体积更大,更加细小的珠光体则以分散形态分布,在更大尺度上将软硬相分散排列。

Two kinds of coupler cast steel with high and comprehensive mechanical properties are measured at phase change point for a new coupler cast steel and a traditional grade E+cast steel,and corresponding continuous cooling transformation curves of supercooled austenite are drawn through physical simulation.Based on the metallographic structure characteristics under different cooling velocity curves,the dynamic mechanism of phase transition of the two kinds of cast steels is compared and their performance optimization theory is studied.By comparing the curves,it is found that the new cast steel A C1=755℃,A C3=831℃,and the traditional Grade E+cast steel A C1=728℃,A C3=786℃.Compared with Grade E+steel,the new steel has the austenitic phase transformation temperature increased,the quenched microstructure area expanded,and the overall curve C shifted to the left,and the critical cooling rate of martensite decreases and the pearlite region expands.It is found that the quenched structures of the two kinds of cast steel are lamellar martensite,the martensite structure of the new cast steel is thin and long,the tendency of net band segregation is small,the independent lower bainite zone can be seen in the bainite zone,and Grade E+cast steel is mainly a mixed structure.In the near equilibrium structure zone,Grade E+is in equiaxial distribution,the volume of ferrite cluster in the new cast steel is bigger,the finer pearlite distributes in a dispersed form,keeping the soft and hard phases in dispersed arrangement at a larger scale.The research results of this paper can provide reference for the future development of cast steel materials.