中碳Cr-Mo-V钢连续冷却时的组织转变规律

Microstructure Transformation Law of Medium Carbon Cr-Mo-V Steel During Continuous Cooling Process

采用Formastor-FⅡ全自动相变仪实现不同冷却速度,利用金相显微镜、扫描电子显微镜和透射电子显微镜,研究了45CrMoV钢在不同冷却速度下的组织转变规律以及回火温度对组织的影响。结果表明,随着冷却速度的变慢,45CrMoV钢的组织由马氏体变为马氏体、先共析铁素体、下贝氏体和粒状贝氏体的混合物。冷却速度进一步变慢,先共析铁素体数量增多,下贝氏体和粒状贝氏体总量减少,材料硬度不断下降;45CrMoV钢中的粒状贝氏体为岛状、颗粒状,也有不规则形状,下贝氏体铁素体板条比低碳钢和超低碳钢中的板条更宽,分布更分散,板条形态不规则;随着回火温度的升高,45CrMoV钢中的渗碳体由细针状变为细条状,最后长大为椭球状,材料强度下降,韧性上升。

Formastor-FⅡ full automatic phase transformation device was adopted for continuous cooling.Microstructure transformation law of 45 CrMoV steel with different cooling rates and effect of tempering temperature on microstructure were investigated by optical microscope,scanning electron microscope and transmission electron microscope.The results show that with reducing cooling rate,the microstructure changes from martensite to a mixture of martensite,proeutectoid ferrite,granular bainite and lower bainite.With further reducing cooing rate,the amount of proeutectoid ferrite increases and that of lower bainite and granular bainite decreases,which induces lower hardness.The shapes of granular bainite in 45 CrMoV Steel are island,particle and irregular shape,and the ferrite laths of lower bainite are wider than that of low carbon or ultra low carbon steels.The ferrite laths with irregular shape distribute more dispersively.With increasing tempering temperature,the cementites in 45 CrMoV steel grow from needle-like shape to stripe shape,and ellipsoid shape at last,which causes the reducing of strength and the increasing of impact toughness of 45 CrMoV steel.