复合渣芯线处理高铝钢中多元夹杂物行为特征及控制机理研究

The nozzle clogging and inclusion control of high Al steels are the key common problems in the continuous casting process, calcium treatment is the main technology for solving the castability of molten steel for ordinary Al-containing steels ([Al]≤0.070%), due to the limitation of the saturated calcium solubility under normal pressure, calcium treatment is difficult to satisfy the modification and removal of inclusions in high Al-containing steels ([Al]≥1.0%), and there are also some serious shortcomings in the actual production, for example: secondary oxidation of molten steel is serious, the metal yield of calcium is low and so on. Therefore，the harmless control and efficient removal technology of inclusions in high aluminum steels is unresolved problem. A new controlling method for inclusion would be presented in this research, on the basis of inhibiting the reaction of the slag and metal, the composite slag cored-wire was fed into the steel and penetrated the slag layer in the end of refining or casting process, for capturing and removal inclusions from the liquid steel, small Al2O3 inclusions could be attached and adsorbed by the components of slag cored-wire, and then the clusters would be formed gradually by the collision or aggregation between the inclusions, so that the inclusions floated to remove more easily, in order to increase the removal efficiency of inclusions. Therefore, the following research conclusions should be drawn in this project: the reaction characteristics and control method of composite slag cored-wire and high aluminum molten steel, the generating mechanism of multiple inclusions in steel treated with slag cored-wire and behavioral characteristics of different inclusions in molten steel, establishing the interaction dynamics model of the inclusions and slag cored-wire, a multiscale change rule of micro-inclusions until macro-inclusions in high Al steel should be got finally.

高铝钢连铸过程中夹杂物控制和水口堵塞是冶金行业面临的关键共性问题，钢中喂入钙包芯线可保证含铝钢液（[Al]≤0.070%）的可浇性，由于常压下钙饱和溶解值的限制，该工艺难以满足高铝钢种（[Al]≥1.0%）夹杂物改性和去除要求，且存在钢水二次氧化严重、金属收得率低等不足。因此，高铝钢中夹杂物无害化控制及高效去除技术亟待解决。本研究针对性提出新的夹杂物控制理论：在抑制渣金反应的基础上，拟在精炼结束或浇注时喂入复合包芯线，穿透渣层进入钢液内部捕集并去除夹杂物，利用芯粉中渣组元与Al2O3类细小夹杂物之间的润湿吸附反应，通过相互碰撞聚合形成夹杂物簇群，更容易上浮，以此来提升夹杂物的去除效率。因此，本项目通过研究复合渣芯线与高铝钢液的反应特性及控制方法；渣芯线处理钢中多元夹杂物的生成机理及其在钢液中的行为特征；建立渣芯线与夹杂物相互作用的动力学模型；最终得到钢中夹杂物由微观到宏观的多尺度变化规律。

高铝钢夹杂物超标和水口堵塞是连铸过程中的关键共性问题，由于常压下钙饱和溶解度的限制，钢中喂入钙包芯线工艺难以满足高铝钢夹杂物改性和去除要求，因此开发复合渣芯线处理高铝钢具有非常好的应用前景。本研究旨为其提供基础数据，研究结果主要如下：.通过热力学计算可得，高铝钢液中存在的夹杂物主要是Al2O3和MgO•Al2O3，浇铸降温过程中析出的夹杂物主要是Al2O3和MnS，为了控制钢中夹杂物形态，须严格控制熔渣中SiO2质量分数低于5%，若能控制在1%以下则效果最好。综合对熔渣物理性能的要求，研究选用包芯粉的主要成分范围是：w(CaO)=48%~56%，w(Al2O3)=30%~37%，w(SiO2)≤5%。.喂入不同规格复合钙铝酸盐包芯线的温度场数值分析表明，调整线皮的厚度对熔化时间影响不大；芯线半径每增加1mm，熔化时间增加0.1s~0.2s；而且芯线内径越大，芯线内径的增加对熔化时间影响越大。钢液中喂入线皮厚度0.6mm、芯粉直径14mm的复合钙铝酸盐包芯线，其完全熔化的时间在0.9s左右。通过分析吹氩条件下钢包内混合相温度场和钙铝酸盐熔体流场分布，得出钢液在氩气泡的驱动下做环流运动，运动的轨迹与氩气泡上升的路线相切；当吹氩孔直径为40mm，吹氩速度为3m/s时，钢液的混匀时间小于300s；喂入的钙铝酸盐熔化为液相后，越靠近芯线的钢液中钙铝酸盐的含量就越高且其流场与钢液的流场基本一致。.通过高铝钢中夹杂物在熔渣中溶解行为的高温试验研究发现，熔渣组元含量受夹杂物溶解反应的影响较小。夹杂物在不同熔渣中的溶解速度不同，夹杂物的溶解时间随着夹杂物熔点的升高而延长，经过比较Al2O3，Al2O3·TiN，Al2O3·MgO，CaO·2Al2O3四种夹杂物的溶解过程，发现不含SiO2的熔渣中夹杂物溶解速度更快，复合夹杂物的溶解时间略短于简单夹杂物。