含硼钢铸坯表面裂纹缺陷控制

利用扫描电镜和金相分析等对含硼钢铸坯表面典型裂纹进行了观察,结合裂纹产生的机理,从结晶器铜管、二冷区冷却、保护渣理化性能3方面对芜湖新兴10B21含硼钢铸坯表面裂纹的产生进行了分析。分析结果显示,优化结晶器铜管材质和锥度、调整二冷区比水量与分配比以及协调保护渣润滑与传热效果均有利于减少含硼钢铸坯的表面裂纹缺陷。生产实践表明,通过将结晶器铜管由普通镀硬Cr改为Ni-Cr复合电镀,总锥度由优化前2.0%/m降低至1.8%/m;二冷区比水量由0.6 L/kg降至0.5 L/kg,分配比由34∶34∶20∶10∶2调整至31∶26∶20∶13∶10;保护渣黏度由1.358 Pa·s降低至1.169 Pa·s,碱度由0.75提高至0.98。最终铸坯表面裂纹率由原来的最高达17.4%降低至2.3%,同时铸坯表面光滑,振痕较为平整、有规则,轧材的成材率也由原来的86%提高至95%。

Control of surface cracks in boron containing steel billet

The surface cracks of boron containing steel billet were observed by scanning electron microscope and metallographic analysis. Combined with the mechanism of cracks formation, the surface cracks of Wuhu Xinxing 10B21 boron containing steel billet were analyzed from three aspects: mold copper pipe, secondary cooling zone cooling and physical and chemical properties of mold slag. The results show that optimizing the material and taper of mold copper tube, adjusting the specific water content and distribution ratio in the secondary cooling zone and coordinating the lubrication and heat transfer effect of mold flux are conducive to reduce the surface crack defects of boron containing steel billets. The conducted production practices were as following. The total taper was reduced from 2.0%/m to 1.8%/m by changing the common hard Cr plating to Ni-Cr composite plating. The specific water volume in the secondary cooling zone was reduced from 0.6 L/kg to 0.5 L/kg, and the distribution ratio was adjusted from 34∶34∶20∶10∶2 to 31∶26∶20∶13∶10. The viscosity of mold flux decreased from 1.358 Pa·s to 1.169 Pa·s, and the alkalinity increased from 0.75 to 0.98. By applying the above measures, the surface crack rate of the final slab is reduced from 17.4% to 2.3%, the billet surfaces were smooth, the vibration marks were flat and regular, and the yield of rolled products was also increased from 86% to 95%.