汽车大梁钢中第二相粒子析出行为

运用热动力学理论和Oswald熟化理论研究了不同氮含量汽车大梁钢中第二相粒子的析出和熟化行为.研究发现钢中N含量的增加会促进V(C,N)在奥氏体中析出从而细化铁素体晶粒,当氮的质量分数增至4.2×10^-4时铁素体晶粒尺寸能细化至4.7μm.形核率–温度曲线和析出–温度–时间曲线表明氮含量的增加可以扩大奥氏体区中最大形核率的温度范围,氮的质量分数由5.5×10^-5增至4.2×10^-4时其最快析出的鼻点温度由840℃上升至968℃.透射电镜观察显示氮含量的增加明显降低析出V(C,N)粒子的尺寸.VN在奥氏体中的Oswald熟化速率计算表明熟化速率随温度的降低不断减少,同时增加N含量还可以有效降低析出粒子的熟化速率,从而抑制沉淀析出的第二相粒子的熟化长大过程.

Precipitation behavior of secondary phases in automobile beam steel

The precipitation and ripening behavior of secondary phases in automobile beam steel with different nitrogen contents were investigated by the thermo-kinetic theory and the Ostwald ripening theory. It is found that increasing the content of nitrogen in the steel can promote the precipitation of V(C,N) in austenite, thus the ferrite grains are greatly refined, and the ferrite grain size is decreased to 4.7μm when the content of nitrogen increases to 4.2×10-4. The curve of nucleation rate to temperature calculated by the thermodynamic theory shows that nitrogen can effectively expand the temperature zone of the biggest nucleation rate, and the precipitation-temperature-time curve demonstrates that the shortest incubation temperature can rise from 840℃ to 968℃ when the content of nitrogen increases from 5.5×10-5 to 4.2×10-4. Transmission electron microscopy observations reveal that the size of precipitated V(C,N) is effectively decreased with the increasing content of nitrogen. The calculated Ostwald ripening rate of VN in austenite indicates that the ripening rate weakens with the temperature dropping, and moreover increasing the content of nitrogen also can decrease the ripening rate to inhibit the ripening growth of the precipitated secondary phases.