高拉速薄板坯连铸保护渣剪切变稀性质

 针对高拉速薄板坯连铸保护渣现场使用过程中卷渣风险加剧、黏结报警频发等问题,通过使保护渣产生非牛顿流体行为,从而有效解决上述问题。该种新型保护渣具有剪切变稀的特性,即在较低剪切速率下具有较高黏度、在较高剪切速率下具有较低黏度。基于现场数据,计算出高拉速薄板坯结晶器钢液面表面区域的剪切速率为10~90 s-1,结晶器弯月面及以下区域的剪切速率可达120~1 600 s-1。采用旋转圆筒法研究了Al₂O₃对保护渣剪切变稀性质的影响。采用Oswald-De Waele幂律模型对剪切变稀行为进行了定量分析。结果表明,随着Al₂O₃含量的增加,保护渣剪切变稀性质先增强后减弱,Al₂O₃质量分数为8.61%的试样剪切变稀性质最强,其流动性指数最低达到0.764 4。研究发现,非牛顿流体保护渣具有的剪切变稀性质能够满足在结晶器钢液面表面区域和弯月面及以下区域内对保护渣黏度的要求。基于高拉速薄板坯连铸的具体工艺参数,建立结晶器内多相耦合模型,通过模型计算发现,保护渣的剪切变稀性质增强不仅会明显降低剪切卷渣的风险,提高结晶器弯月面区域液渣流入的均匀性,而且在结晶器弯月面及以下区域具有更厚的液态渣膜,更容易实现全程液态润滑,同时提高了渣耗量,进一步剖析了保护渣剪切变稀性质的作用效果。本研究为开发非牛顿流体高拉速薄板坯连铸保护渣提供了理论依据。

Shear-thinning property of mold flux for thin slab continuous casting with high casting speed

To solve the problems of slag entrapment risk and frequent bond alarm in the field application of mold flux for high-speed thin slab continuous casting,the above problems can be effectively solved by making the mold flux generate non-Newtonian fluid behavior. The new mold flux has the characteristics of shear-thinning,that is,it has a higher viscosity at lower shear rates and vice versa. Based on the field data,it is calculated that the shear rate of the steel surface area of the thin slab mold with high casting speed is between 10-90 s-1,and the shear rate of the meniscus and below of the mold can reach 120-1 600 s-1. The effect of Al₂O₃ on the shear-thinning property of mold flux was studied by rotating cylinder method. The shear-thinning behavior is quantitatively analyzed by Oswald-De Waele power law model. It was found that with an increase in the Al₂O₃ content,the shear-thinning behavior of the mold flux first increased and then decreased. The sample with 8.61% Al₂O₃ content had the strongest shear-thinning property and the lowest fluidity index, which reached 0.764 4. It is found that the shear-thinning property of non-Newtonian fluid mold flux can meet the requirements of mold flux viscosity in the surface area of the mold steel level and the meniscus and below. Based on the specific process parameters of thin slab continuous casting with high casting speed,a multiphase coupling model in the mold is established. Through model calculation, it is found that the enhanced shear-thinning property of mold flux will not only significantly reduce the risk of shear slag curling and improve the uniformity of liquid slag inflow in the meniscus area of the mold,but also have a thicker liquid slag film in the meniscus and below of the mold,which makes it easier to realize full range liquid lubrication. At the same time,the slag consumption is increased,and the effect of shear-thinning property of mold flux is further analyzed. This research provides a theoretical basis for the development of non-Newtonian fluid high casting speed thin slab continuous casting mold flux.