直轧条件下含Nb钢筋中Nb(C,N)的析出强化机理及控冷工艺优化

Strengthening mechanism of Nb(C,N)precipitation and controlled cooling process optimization of Nb-containing steel bars under direct rolling condition

为了解决方坯直轧工艺生产含Nb钢筋出现的强化效果不显著问题,通过经典形核理论计算了Nb(C,N)在奥氏体中沉淀析出动力学行为特点,并通过现场控冷工艺试验验证了理论计算的结果。结果表明,加热炉轧制生产含Nb钢筋过程中Nb(C,N)的沉淀析出以晶界形核为主,方坯直轧工艺生产含Nb钢筋过程中Nb(C,N)的沉淀析出以位错形核为主;在含Nb钢筋的成分体系下,Nb(C,N)在奥氏体中沉淀析出过程中的晶界形核和位错形核C曲线鼻尖点温度分别约为1000℃和900℃;方坯直轧工艺生产含Nb钢筋可以在精轧机架间设置多段预穿水,以保证足够低的终轧温度,来获得Nb(C,N)沉淀析出的最佳强化效果。

In order to improve the problem of insignificant strengthening effect of Nb-containing steel bars when produced by billet direct rolling process,the kinetic behavior of Nb(C,N)precipitation in austenite was calculated through classical nucleation theory,then verified through field controlled cooling process experiments.The results show that the main precipitation modes of Nb(C,N)in austenite are grain boundary nucleation for rolling by using heating furnace and dislocation nucleation for billet direct rolling,and for the composition of tested Nb-containing steel bars,the corresponding nose tip temperature of PTT curves for grain boundary nucleation and dislocation nucleation is about 1000℃and 900℃,respectively.The optimum strengthening effect of Nb(C,N)precipitation in direct rolling process can be obtained by setting multi-stage pre-penetrating water between finishing stands to ensure low-enough final rolling temperature.