含硼钢中硼的存在形式及控制研究

Study and control of boron existing forms in boron-bearing steel

南京钢铁股份有限公司在生产含硼钢S355J-3-B过程中,铸坯裂纹发生率较高。根据钢种成分,采用化学分析、拉曼光谱和场发射透射电镜等手段研究了含硼钢S355J-3-B中硼的存在形式。全硼质量分数为15×10-6,酸溶硼质量分数为9×10-6。拉曼光谱和透射电镜观察下发现了BN析出物。热力学计算表明:含硼钢的冶炼应先加Al充分脱氧后,再加入Ti脱氮,最后加入B。连铸的矫直阶段,细小的BN粒子钉扎奥氏体晶界,是铸坯表面微裂纹产生的重要原因,而Ti元素的加入对提高含硼钢的高温热塑性有利。而且提高Ti含量后,S355J-3-B铸坯裂纹发生率由10%降低到3%。

The crack rate of S355J-3-B steel slab produced by Nanjing Iron and Steel Co. ,Ltd. was high in the production process. Based on the component of S355J-3-B steel, the existing forms of boron in S355J-3-B steel were investigated using the chemical analysis, raman spectrum and field-emission transmission electron microscope （TEM）. The results of chemical analysis showed that when the total boron mass fraction was 15×10^-6 and the acid soluble boron was 9×10^-6 in S355J-3-B steel,BN precipitates were found using raman spectrum and TEM. The thermodynamic calculation indicated that aluminum should be added in liquid steel firstly for sufficient deoxidation in steelmaking; then titanium was added for nitrogen fixation; finally, boron was added into liquid steel. In the straightening stage of continuous casting process, the pinning effect caused by fine BN precipitates on austenite grain boundaries is the significant reason resulted in the occurrence of surface crack on the slab. However, it is favorable for improving the hot ductility of boron-bearing steel with titanium addition. The crack rate of S355J-3-B steel slab decreased from 10 0% to 3 % with increasing the titanium content.