板坯凝固过程夹杂物运动行为

 本文使用离散相模型，利用数值模拟的方法对结晶器中的钢液流动、传热、凝固以及夹杂物的运动进行了耦合计算。通过追踪夹杂物的运动轨迹，并在钢渣界面处对夹杂物进行采样分析，最终计算出夹杂物在结晶器中的上浮率。研究表明，夹杂物在结晶器中的上浮率与其尺寸及拉速的大小均有关系，但受夹杂物密度的影响很小。夹杂物越大、拉速越小，越有利于夹杂物上浮至自由液面。小颗粒夹杂在结晶器中并不能被有效去除。对于粒径为50μm的夹杂物，当拉速为1m/min时其上浮率仅为46%，有37%的夹杂物被凝固坯壳捕捉，主要分布在铸坯表皮下10~25mm处。夹杂物被宽面坯壳捕捉的位置多集中在宽面靠近窄面处，在水口下方被捕捉的夹杂物较少。以往的研究认为只要夹杂物上浮至钢渣界面就能够被保护渣吸收，J.Strandh等的研究表明，夹杂物能否被吸收还取决于保护渣的粘度和润湿性等因素。因此，对于粒径较小的夹杂物，必须在精炼后的软吹氩过程中适当增大钢液的静置时间，尽量减少钢液中小颗粒夹杂的数量。另外，结晶器保护渣的选用对钢液中夹杂物的去除也很重要，不仅要满足其对钢液的保温润滑作用，还要考虑其对夹杂物吸附的影响。

Inclusion Behavior During Slab Solidification

A numerical simulation method was used in this article to study the turbulent flow and heat transfer coupled with the liquid steel solidification and the inclusion movement in mold by using the discrete phase model. By tracing inclusion trajectory in mold and sampling inclusions which pass through the free surface, the inclusion removal rate can be got. As results shown, inclusion removal rate has a close relationship with the casting speed and the inclusion size, but has little relationship with the inclusion density. Inclusions tend to float up to the free surface at low casting speeds and with big sizes. Small inclusions can not be removed effectively in mold. For inclusions whose diameters are 50μm, the removal rate is 46% at 1m/min casting speed, and 37% of inclusions are trapped in the solid shell, which mainly distribute in the region 10~20mm beneath the strand surface. Most of the inclusions trapped in the solid shell at the wide face locate near the narrow face, and few inclusions are trapped under the nozzle. Inclusions which flow up to the slag-steel interface are always thought to be absolutely absorbed by the slag in the former studies. But in J.Strandh’ s study, whether the inclusions can pass through the slag-steel interface depends on many factors, such as the slag viscosity and the overall wettability. So for small inclusions, more time must be taken to stew the liquid steel after the refining process to reduce the amount of small inclusions. In addition, the selection of slag is also important for the inclusion removal in mold. The heat-insulating property, the lubricating ability, and the ability to absorb inclusions are all important factors to be considered when choosing the slag