多元组分夹杂物在钢渣界面运动行为对其分布影响的基础研究

The amount and size of inclusions in the steel have a direct influence on the quality of steel products. They must be strictly controlled during the actual production processes. For the study of the motion of inclusions in the molten steel, the style of inclusions considered is only single component inclusions (e.g. Al2O3). But in fact, the composition of inclusions is usually the multicomponent phases. Meanwhile, the effect of the flow of the molten steel on the separation and removal of inclusions at the interface between the molten steel and slag is neglected. In order to solve the above problems, the continuous casting tundish and tire cord steel are investigated in the current project. Firstly, the removal models of inclusions at the interface between the molten steel and slag are developed by considering the properties of inclusions, the slag and molten steel, such as the contact angle, density, size, viscosity, surface tension, etc.. Secondly, the coupled models of the collision and growth of CaO-MnO-SiO2-Al2O3 inclusions in tire cord steel, its removal at the interface between the molten steel and slag, and the macro-scale flow of the molten steel are developed by combining the authors’ user-defined subroutines with the commercial CFD software (FLUENT 14.0). The amount and size distribution of inclusions in the molten steel in the tundish can be predicted according to the calculation of the above models. The purpose of the current study is to improve the theory of collision, growth and removal of inclusions in the published literature and to clarify the critical factors influencing the amount and size distribution of inclusions in the molten steel. Furthermore, it will lay theoretical basis for the production of high quality clean steels.

钢中夹杂物的数量和尺寸直接影响钢铁产品的质量，在生产过程中必须严格控制。目前对于高温钢水中夹杂物运动的研究，考虑的仅为单一成分夹杂物（如Al2O3），而实际钢中夹杂物成分多为复合相，同时将钢渣界面处夹杂物的分离和去除与钢水的流动脱离开来。针对上述难题，本项目以连铸中间包为研究对象、以帘线钢为目标钢种，首先建立钢渣界面处夹杂物去除模型，综合考虑夹杂物接触角、密度、尺寸、渣相的粘度、表面张力、密度、钢水粘度和密度等因素的影响；其次，使用流体流动商业软件FLUENT，通过自主开发子程序，建立帘线钢中CaO-MnO-SiO2-Al2O3四元组分夹杂物碰撞长大、钢渣界面去除与钢水流动耦合模型。根据模型的计算预测钢水中夹杂物在三维空间内的数量分布和尺寸分布。通过本项目的开展，将完善现有研究中夹杂物碰撞长大和去除理论，明确影响钢水中夹杂物数量分布和尺寸分布的关键因素，为高品质洁净钢的生产奠定理论基础。

钢中夹杂物的运动行为直接影响洁净钢产品的质量。为提升钢水的洁净度，在公开发表的文献中已开展了大量的研究工作，但仍然存在一些突出的问题尚未解决，主要为考虑的仅为单一成分的Al2O3夹杂物，同时将夹杂物碰撞长大过程与在钢-渣界面处的分离和去除过程独立开来，这也限制了理论上的进一步发展。为解决以上问题，本项目首先开发了钢-渣界面处夹杂物去除模型，系统地评价了钢水、渣相、夹杂物等物性参数对其在钢-渣界面处运动行为的影响，明确了各个物性参数影响的先后顺序，为提升钢水洁净度提供了指导方向。其次，以钢-渣界面处夹杂物去除模型为基础，开发了帘线钢中CaO-SiO2-MnO-Al2O3系夹杂物碰撞长大、钢-渣界面去除与钢水宏观流动耦合模型，模型计算结果能够准确地预测夹杂物在中间包三维空间内的数量分布和尺寸分布。具体研究结果如下：.（1）夹杂物在渣-钢界面处主要有三种运动形式：保留在渣-钢界面处、在渣-钢界面处振荡以及穿过渣层被吸附去除。对比可知，降低渣相粘度、提高夹杂物在渣-钢界面处的润湿性、降低渣-钢界面张力均有利于促进夹杂物在渣-钢界面处的运动去除；随着夹杂物直径增大，其突破渣-钢界面进入渣相中的能力增加；而夹杂物密度、钢水密度、钢水粘度和渣相密度的变化对夹杂物在渣-钢界面处的运动行为基本没有影响。.（2）影响夹杂物在渣-钢界面处运动行为的顺序关系为：夹杂物尺寸>渣相粘度>夹杂物在渣-钢界面处的润湿性>渣-钢间的界面张力。通过热力学计算确定的渣相成分范围显著提升了冶炼过程中钢水的洁净度。.（3）中间包内夹杂物颗粒间的碰撞机理主要为Stokes碰撞和湍流碰撞。随着浇注过程的进行，小尺寸夹杂物逐渐碰撞形成大尺寸夹杂物，在注入区两侧包底和挡墙开孔位置处夹杂物数密度变化速率较快，原因为上述区域内存在激烈的湍流运动为夹杂物颗粒间的碰撞长大创造了良好条件。.以上研究成果不仅完善了钢中夹杂物碰撞长大和去除理论，也为高品质洁净钢的生产奠定了理论基础。