吹氩结晶器内氩气泡对液态保护渣传热及流动行为的影响

To prevent reoxidation of molten steel and the nozzle clogging and promote the floating of inclusions in the mold, the argon gas is generally blown into the mold through submerged nozzle. When the argon gas enters into liquid mold flux from liquid steel, it can bring changing of the heat transfer and fluidity of the liquid mold flux, furthermore, it may cause slag entrapment or surface defects of strand. What is the movement and distribution behavior of argon bubbles in liquid mold flux, How is the heat transfer and fluid flow behavior of liquid mold flux influenced by argon bubbles? What is the influence of these changing on interfacial behavior between liquid mold flux and liquid steel? Metallurgists have rarely studied these problems, these problems need to be deeply studied. The goal of this project application is to resolve above problems, the movement and distribution behavior of argon bubbles will be measured by the resistance probe in liquid mold flux, the fludity of liquid mold flux will be studied by viscometry, the heat transfer behavior of liquid slag will be studied by the thermocouple method and the hot wire method. Then, the influence roles of argon bubbles on the fluidity and heat transfer behavior of liquid slag can be revealed combined with theoretical analysis and mathematical modeling, the influence rules of interface behavior between liquid steel and slag can be explained reliably. Based on these studies, then, we can propose the optimization method for process parameters of blowing argon gas and mold flux performance, which can provide a theoretical basis and operational guidance for production of high quality strand.

为防止水口堵塞和钢水二次氧化，促进结晶器内夹杂物上浮，连铸中一般从水口吹入一定量的氩气，氩气从钢液进入液态保护渣时，会导致液渣出现乳化现象，液渣的流动性和传热性发生改变，可带来钢液卷渣或铸坯表面缺陷问题。吹氩结晶器中，氩气泡在液态保护渣内的运动形式、分布状态是什么？氩气泡运动、分布状态如何影响液渣的流动及传热行为？液渣流动性和传热性的改变对结晶器内钢渣界面行为有何影响？这些问题前人研究很少，需要进一步探索。本申请项目将以解决这些问题为目标，通过电阻探针法测量液态保护渣内气泡的运动、分布行为；利用黏度测定法研究液渣的流动行为；利用瞬态热线法、热电偶法研究液渣的传热行为；结合理论分析和数学模型，从根本上理解吹氩结晶器内气泡对液渣流动和传热行为影响的机理，探寻其对钢渣界面波动及卷渣行为的影响规律，基于这些研究，提出优化吹氩工艺参数及保护渣性能的方法，为生产高质量的连铸坯提供理论依据和操作指导。

中间包水口吹氩有利于防止水口堵塞，促进结晶器内夹杂物上浮，但是，上浮进入保护渣中的氩气泡可导致液渣乳化，液渣流动性和传热性发生改变，可带来钢液卷渣或铸坯表面缺陷问题。利用物理模拟和数学模型的研究方法，本项目研究了钢渣界面氩气泡大小、数量、上浮速度分布及钢渣界面波动行为。发现增加吹氩量，结晶器内氩气泡尺寸增大，增大拉坯速度，氩气泡尺寸减小；随吹氩量和拉速增加，钢渣界面水口附近气泡直径先减小后增大，窄面气泡直径先增大后减小；增大吹氩量，钢渣界面气泡数量增多，水口附近气泡上浮速度先增加后减小，进入保护渣的气泡体积增加，窄面附近上浮速度增加，气泡体积较小；拉速增大，窄面附近气泡上浮速度明显增大，窄边气泡体积有所增大，水口附近则减小；吹氩有利于降低结晶器窄面附近钢液波高，但会导致水口附近波动加剧。保护渣内氩气泡上浮行为及其对液渣流动性影响研究表明，液渣内氩气泡上浮有大气泡通道上浮式、小气泡自由曲线上浮式两种方式，保护渣内气泡上浮速度比钢液内气泡上浮速度小一个数量级，处于0.02m/s到0.07m/s之间；吹氩量从2L/min增加到6L/min，保护渣乳化程度增加，流动性增强，进一步增加吹氩量，液渣乳化程度略微减小。液渣流动和传热行为研究表明，在吹氩结晶器1/2厚度纵向剖面上，水口附近和结晶器窄面附近存在小环流、中间区域存在大环流；吹氩使液态保护渣整体温度升高，分布更均匀，有利于保护渣熔化；增大吹氩量，可以提高结晶器1/2厚度处沿结晶器宽度方向的液渣流速和温度，但过大的吹氩量会降低结晶器1/2宽度处与水口外壁之间区域液渣温度和流速，造成该处结冷钢；较高拉坯速度下，适度吹氩可以改善液渣流动和温度分布的均匀性，降低钢渣界面液渣流动速度峰值；吹氩条件下，增加水口倾角和浸入深度，液态保护渣速度和温度不断降低，结晶器宽面附近液渣温度分布均匀性增强。研究结果可为优化吹氩工艺参数及保护渣性能提供新的思路和方法，为生产高质量的连铸坯提供理论依据和操作指导。