低碳含硼钢中BN的析出行为

Precipitation behavior of BN in low carbon boron-bearing steel

以硼质量分数为0.0045%、氮质量分数为0.0039%的低碳含硼钢为研究对象,通过对实验钢在凝固过程中BN析出和长大的热力学与动力学进行分析,并结合实验研究了冷却条件对BN析出与长大行为的影响.结果表明:由于溶质元素B和N在凝固前沿的微观偏析,只有当凝固前沿的固相率大于临界值0.981时,BN才能在凝固前沿析出;在凝固前沿随着固相率的增加,B和N均具有明显的偏析.当固相率接近于1时,硼在剩余液相中的实际含量远高于氮元素的含量,氮的扩散是BN长大的限制性环节;钢液冷却速率的变化对B和N元素的偏析无显著影响,而生成BN的尺寸随着钢液冷速的增加而显著减小.

The low carbon boron-bearing steel with 0. 0045% boron and 0. 0039% nitrogen was investigated, the thermodynamics and kinetics of precipitation and growth of BN during liquid steel solidification were studied. The effect of cooling conditions on the precipitation and growth of BN was experimentally investigated. The results show that BN can only precipitate at the solidifying front where the solid fraction is greater than the calculated critical value of 0. 981 due to the segregation of boron and nitrogen. There is a serious segregation of boron and nitrogen with the increase of the solid fraction at the solidifying front. The diffusion of nitrogen in liquid steel is the rate-controlling step of BN growth because the boron content in the remaining liquid steel is much higher than that of nitro-gen when the solid fraction is close to 1. The change in cooling rate of liquid steel has negligible effect on the segregation of boron and nitrogen. However, the size of BN precipitates decreases greatly with increasing the cooling rate.