低碳钢薄板坯高速连铸保护渣研究与优化

 针对低碳钢薄板坯高速连铸过程中保护渣液渣层过薄、黏结报警频发、铸坯表面纵裂纹过多等问题,在充分考虑高拉速下低碳钢凝固收缩特性的基础上,确定了保护渣润滑与传热性能的优化方向并开展了工业试验。将保护渣碱度从1.10提高到1.30,Li₂O质量分数从0.57%提高到1.06%,Na₂O质量分数从5.48%提高到8.16%,碳质量分数由7.71%降低到6.72%。对2种保护渣的流变性能和渣膜3层结构进行了深入研究,发现优化后保护渣渣膜中的液渣层比例增加,渣膜润滑系数α增大;同时,渣膜中的结晶层比例也有一定程度的提高,渣膜热阻系数β增大,从而使保护渣的润滑性能和控制传热能力均得到改善。从矿相分析结果看出,保护渣碱度的提高在一定程度上会促进硅灰石的析出,导致渣膜结晶率提高、热阻增大,进而起到控制传热的目的。生产实践表明,在拉速提高后,使用新型保护渣基本避免了黏结和裂纹的产生,生产效率和铸坯质量均得到显著提高。

Research and optimization of mold flux for high speed continuous casting of low carbon steel thin slab

In view of the problems such as too thin slag layer,frequent bond alarm and too many longitudinal cracks on the surface of slab during high speed continuous casting of low carbon steel thin slab,the optimization direction of the lubrication and heat transfer performance of the mold flux is determined based on the fully consideration of the solidification shrinkage characteristics of low carbon steel at high casting speed,and industrial experiments are carried out. The basicity of the mold flux is increased from 1.10 to 1.30,the mass fraction of Li₂O is increased from 0.57% to 1.06%,the mass fraction of Na₂O is increased from 5.48% to 8.16%,and the mass fraction of Carbon is reduced from 7.71% to 6.72%. The rheological properties of two kinds of mold flux and the three-layer structure of slag film are further studied. It is found that after optimization,the proportion of liquid slag layer in the slag film increases,and the lubrication coefficient(α) of the slag film increases;at the same time,the proportion of crystal layer in the slag film also increases to a certain extent,and the thermal resistance coefficient(β) of the slag film increases,so that the lubrication performance and the control heat transfer capacity of the mold flux are improved. From the results of mineral phase analysis,it can be seen that the increase of basicity of the mold flux will promote the precipitation of wollastonite to a certain extent,leading to the increase of crystallization rate and thermal resistance of slag film,thus controlling the heat transfer. The production practice shows that after the increase of casting speed,the use of the new type of mold flux can basically avoid the generation of bond and crack,and the production efficiency and slab quality are significantly improved. It has a certain guiding significance for the production and application of the low carbon steel thin slab high speed mold flux in the enterprise in the future.