含铌55CrV钢连铸坯的高温热塑性研究

Research on High-temperature Thermoplastic of Nb Microalloyed 55CrV Steel Continuous Casting Billet

利用Gleeble-3500热模拟机研究了含铌55CrV钢连铸坯的高温热塑性能,结合OM和SEM扫描电镜观察拉伸断口形貌及其附近组织,通过Thermo-calc软件模拟第二相的析出情况,分析了其高温塑性机理。结果表明:含铌55CrV钢存在两个脆性温度区间,分别是:第Ⅰ脆性区温度范围1300~1245℃和第Ⅲ脆性区温度范围849~600℃。微细的铌钒复合析出物延缓了高温时动态再结晶的发生;而在850℃以下,碳化钒、碳化铌与渗碳体等大量析出降低了钢的塑性。为避免0.05%Nb连铸坯裂纹的产生,在过矫直点时,温度应控制在850℃以上。

The high temperature ductility of Nb microalloyed 55CrV steel was determined by using Gleeble-3500 thermal simulation testing machine.The morphology of the fracture and the microstructure near the fracture was observed by OM and SEM.The precipitation of the second phase was simulated by Thermo-calc software to analyze the high temperature plasticity mechanism.The results show that there are two brittle intervals for the Nb alloyed 55CrV steel and the temperature of first brittle zone is 1300-1245℃and the third brittle zone is 849-600℃.The precipitation of fine niobium-vanadium composite precipitate retards the occurrence of dynamic recrystallization at high temperatures.At 850℃below,the precipitation of vanadium carbide,niobium carbide and cementite reduces the thermoplasticity of the steel.In order to avoid the occurrence of cracks in the continuous casting billet,the temperature should be controlled above 850℃at straightening point.