冷却速度对钒微合金钢的组织和析出相的影响

采用光学显微镜和透射电镜研究了不同冷却速度下钒微合金钢的微观组织和析出相变化规律。结果表明:当冷却速度小于或等于5℃/s时,钢的组织均为铁素体+珠光体,且随着冷却速度的增加,铁素体的晶粒尺寸明显变细。当冷却速度达到10℃/s时,钢的组织变为马氏体+少量铁素体。透射电镜研究显示:平衡态时析出相包含大量弥散分布的尺寸主要为45~100 nm的不规则形V(C,N)相和(V,Ti)(C,N)复合相,当冷却速度小于或等于5℃/s时,析出相数量无明显改变,但颗粒尺寸随冷却速度的增加不断减小;但当冷速达到10℃/s时,析出相的数量显著下降,尺寸变小。对含钒微合金钢而言,调整适当的冷却速度,不仅可以细化铁素体晶粒,还可以提高析出强化效果,从而提高钢材的强韧性。

Influence of Cooling Rate on the Microstructure and Precipitates of Vanadium Microalloyed Steel

The variation rules of microstructure and precipitates in vanadium microalloyed steel under different cooling rates were investigated by optical microscope(OM) and transmission electron microscope(TEM).The results showed that when cooling rate was less than or equal to 5℃/s,the microstructures of the tested steel were all composed of ferrite and pearlite,and the grain size of ferrite descended obviously with the increase of cooling rate;When cooling rate reached to 10℃/s,the microstructure was made up of martensite and ferrite.TEM results appeared that the precipitates included a large amount of 45~100nm dispersion distribution irregular V(C,N) and(V,Ti)(C,N) phases in equilibrium state;When cooling rate was less than or equal to 5℃/s,there was almost no change in value,however,the particle size decreased gradually with the increase of cooling rate.But,the number of precipitates decreased significantly when cooling rate reached to 10℃/s.The above results indicate that a suitable cooling rate may not only refine grain size of ferrite but also improve precipitation strength effect,and further improve the properties of the vanadium microalloyed steel.