钒-氮微合金化超低碳贝氏体钢的连续冷却转变特性

Continuous Cooling Transformation Characteristics of V-N Microalloyed Ultra-low Carbon Bainite Steels

研究N含量不同的2种超低碳Fe-Mn-Mo贝氏体钢的连续冷却转变特性。采用热膨胀法测试试验钢不同冷速下的连续冷却转变曲线,用40MAT型激光显微镜观察相应的显微组织转变特征,并进行硬度及强度测试。试验结果表明,Fe-Mn-Mo系超低碳贝氏体钢中添加V和N对贝氏体相变具有显著的影响。贝氏体相区明显扩大。其中高氮钢的贝氏体转变区更宽,晶粒大小为相同冷速下低氮钢的1/3左右,维氏硬度值高出低氮钢40 HV,强度高出100 MPa。V-N微合金化超低碳贝氏体钢中析出的V(C,N)粒子促进了贝氏体转变、扩大了贝氏体相区。

The continuous cool transformation （CCT） characteristics of two ultra-low carbon bainite steels（ULCB） with different nitrogen content were studied. The CCT curves of two kinds of steels were tested with heat dilatometer at different cooling rate. Corresponding microstructures were observed with LASER microscope. Vickers- hardness and Strength were tested. The ,asults show that V and N have marked effect on bainite phase transformation of ULCB stee Bainite phase area is expanded. Bainite phase area of higher nitrogen steel is broader than low nitrogen steel. Grain size of the high nitrogen steel are only 1/3 of the low nitrogen steel. Vickers-hardness is about 40 HV and strength about 100 MPa higher than that of the low nitrogen steel. Precipitatioi, of V （C,N） particles in V-N bainite steels promote bainite phase transformation and enlarge bainite phase area.