超低碳BH钢的应变时效行为和烘烤硬化规律

Strain aging behaviors and bake hardening laws of ultra-low carbon BH steels

采用MTS拉伸试验机和低频内耗仪对Ti处理和Ti+Nb+B复合处理的超低碳BH钢退火钢板的BH值随预应变量、烘烤温度和烘烤时间的变化规律以及Snoek峰高和间隙固溶C原子含量进行研究。结果表明:对Ti处理的超低碳BH钢,在其它条件相同时,预变形量增加,BH值逐渐增加;随着烘烤时间延长,BH值先增加后下降;烘烤温度升高,BH值增加,烘烤温度升高到250℃,扩散到位错处钉扎位错形成柯氏气团的间隙固溶C原子已经接近饱和,对BH值影响幅度并不会太大。对于Ti+Nb+B复合处理的超低碳高强度BH钢,存在Nb C第二相粒子溶解和晶粒长大机制以及基体晶格中的间隙固溶C原子向晶界处扩散偏聚机制,两种作用机制中固溶C原子向晶界处扩散偏聚占主导地位,从而使得退火温度较高和退火时间延长的情况下,超低碳高强度BH钢退火板的BH值和Snoek峰高并没有升高反而略有降低。

The BH value variations with the prestrain,baking temperature and baking time,Snoek peak heights and the interstitial solid solution C atom concentrations for Ti bearing and Ti + Nb + B stabilized ULC-BH annealed steels were studied by MTS tensile test machine and low frequency internal friction instrument. The results show that when other conditions are the same for Ti bearing ULC-BH steels,the BH values increase gradually with the increase of prestain amount,increase first and then decrease with the prolonged baking time,increases with the increase of baking temperature. When the baking temperature rises to 250 ℃,the interstitial solid solution C atoms which diffuse to pin dislocations to form Cottrell atmosphere are close to saturation,therefore the BH value is not affected significantly. For the Ti + Nb + B stabilized high strength ULC-BH steel,there exist Nb C second phase particle dissolution and grain growth mechanism and the diffusion segregation mechanism of the interstitial solid solution C atoms in the matrix lattice to the grain boundary;the diffusion segregation mechanism of solid solution C atoms to the grain boundary is dominant in the two mechanisms,which makes the BH value and Snoek peak height of the high strength ULC-BH annealed steel do not increase but decrease slightly with the increase of annealing temperature and the prolonged annealing time.