Nb-Ti处理超低碳烘烤硬化钢的析出行为

Precipitation behavior in Nb and Ti treated ultra low carbon bake hardening steel

通过物理化学相分析试验和热力学平衡计算,分析了Ti、N原子比大于1、等于1、小于1的3种Nb-Ti处理ULC-BH钢板的第二相析出规律。相分析和热力学计算结果表明,3种成分钢板析出相主要为(Ti,Nb)(C,N)、MnS,试验钢中未发现Ti4C2S2和TiS相;Ti、Nb元素的氮化物主要在A1温度以上析出,而碳化物主要在铁素体相区析出。在热轧板经卷取保温后,Nb、Ti元素接近完全析出形成M(C,N);短时退火后,M(C,N)相有少量回溶。当Ti、N原子比接近1时,N主要与Ti结合,C单独由Nb固定,有利于预估钢中固溶C含量。钢中增加酸溶铝含量有利于避免形成Al2O3夹杂。

The precipitation behavior in Nb and Ti treated ultra low carbon bake hardening（ULC-BH）steel was analyzed by using phase analysis experiment and thermodynamic calculation,whose Ti/N atomic ratios are1,=1 and1 respectively.The main precipitation phases in hot rolled bands and annealed sheets of experimental steels are（Ti,Nb）（C,N）,MnS;Ti4C2S2 and TiS phases are not found.The precipitation temperature of niobium-titanium nitrides is above A1temperature and the carbides mainly precipitate in ferrite phase region.After hot rolling and coiling,the elements Nb and Ti are almost completely precipitated and the M（C,N）phase is formed.A small amount of carbides dissolve during short time annealing.When the Ti/N atomic ratio is close to 1,N is almost fully combined with Ti and C is onlystabilizedby Nb,so the solute carbon content of the steel is easy to estimate.Increasing dissolved aluminum content is beneficial to avert the formation of Al2O3inclusion.