【作者】 周海斌；

【导师】 朱苗勇；

【作者基本信息】 东北大学 ， 钢铁冶金， 2009， 博士

【摘要】 宽厚板产品在油气输送、船舶制造、桥梁工程、电站锅炉、压力容器、重型机械、海洋石油及军事工业中应用广泛。连铸过程的夹杂物控制已成为高品质宽厚板生产的关键环节。中间包内钢液流动的合理控制对其内夹杂物的去除至关重要,而结晶器内钢渣界面波动与卷混行为的控制则是该连铸过程顺行与夹杂物控制的关键。因此,开展宽厚板中间包内去夹杂控流技术及结晶器内流场特性及界面行为研究具有重要的科学意义和现实指导意义。本论文结合国内某厂宽厚板生产线的实际,采用物理模拟和数学模拟相结合的方法对连铸中间包和结晶器内的过程进行了研究,提出了有效净化中间包钢液的控流方案和结晶器卷渣控制的水口参数并实施了现场应用研究。主要研究内容和研究结果如下：(1)结合宽厚板连铸中间包的实际,基于相似原理,选择模型与原形的弗鲁德准数相等建立了几何比1：2.5的中间包物理模型研究体系。结合该物理模拟系统,对修正前后的组合模型的流动特性分析结果进行对比研究,找出了最优的流动特性分析模型。结果表明：传统的组合模型在死区体积分数的计算上存在较大差异,用此来分析中间包流动特性会造成很大的偏差；而Sahai的修正组合模型能准确的计算死区体积分数,能较合理分析中间包内的流动特性。(2)利用Sahai的修正组合模型考察了不同控流装置对中间包内钢液流场以及夹杂物去除效果的影响规律。结果表明：带顶缘和不带顶缘的抑湍器均能明显提高活塞区的体积分数,且死区体积分数也有不同程度的降低；与带顶缘的抑湍器组合的中间包出口附近的挡坝设计参数对中间包内钢液的流动特性有影响；与带顶缘的抑湍器组合的墙坝间距有一个控制钢液流动特性的最佳值。并利用计算机模拟对典型控流方案下中间包内的流场特性作出描述。在水模型研究和检验数学模型的基础上,进行综合分析研究,最终提出了有效提高钢水纯净度的中间包内控流装置。(3)结合宽厚板连铸结晶器的实际,利用数学模拟和物理模拟相结合的方法考察不同工艺参数对结晶器内界面波动行为和内部流场的影响,并对结晶器内的钢渣卷混机理进行了探索。(4)吹氩宽厚板坯结晶器内存在两种新的卷渣机理,即气泡群冲击卷渣和类旋涡卷渣,且在实验拉速范围内没有发现弯月面附近的剪切卷渣。在各铸坯宽度及对应的拉速范围内,吹气量小于4L/min时基本都不会发生卷渣。(5)对于2200×280mm2断面宽厚板坯结晶器控制液面波动的最佳工艺参数如下：4L/min的吹氩量、-15°的水口侧孔倾角、140mm的水口浸入深度。(6)宽厚板连铸的现场应用研究表明：连铸工艺参数改进后其夹杂物控制效果要明显好于改进前。改进后,中间包与铸坯中的夹杂物含量比改进前分别降低8%和20%；中间包和铸坯内典型夹杂物尺寸由改进前的30μm和15μm分别降至改进后的10μm和5μm。更多还原

【Abstract】 Heavy plate products are widely used in the realms of oil and gas transmission, ship building, bridge engineering, boiler of power station, pressure vessels, heavy equipment, offshore oil, and military industry. The inclusion control in continuous casting process is a key for the high-quality heavy plate production.The reasonable control of molten steel flow is crucial for the inclusion removal in the tundish, and the control of the steel/slag interface and slag entrapment behavior in the mold is a key for guaranteeing the smooth operation of continuous casting process and controlling the macro inclusions. Therefore, it has important scientific and practical guidance significances for developing the tundish flow control technology and understanding the flow characteristics and interfacial behavior in the mold. In this paper, the transport phenomena in the tundish and mold were studied by using mathematical and physical simulations according to the heavy plate practical production process in one domestic steel corporation, and one scheme of flow control devices for cleaning the molten steel in the tundish and the optimum submerged entry nozzle (SEN) parameters for restraining the slag entrapment effectively in the mold were proposed. In addition, the effectiveness of applying the optimal flow control devices and SEN to the actual performance was investigated. The main contents and results obtained are as follows:(1) With the combination of the wide and thick slab continuous casting tundish practical process, a physical model with the scale 1:2.5 was established based on the Froude similarity. By means of the measured results of the physical model, two combined models for characterizing the melt flow were compared and the optimal combined model was found out. The results show that the traditional model may make mistakes both in the estimation on the melt flow characterization and in the choice of optimal flow control devices. As a reasonable modification has been made on the calculation of dead volume fraction, the modified combined model is suitable for characterizing the melt flow in single-strand tundish.(2) The effect of different control devices on the characteristics of melt flow in the tundish was analyzed by the above-mentioned modified combined model presented by Sahai. The results show that the turbulence inhibitors with and without top extending lip both can improve obviously the plug flow volume and decrease the dead volume to some extent. The design parameters of the dam nearby the outlet combined with turbulence inhibitor with top extending lip have some effect on the melt flow in tundish. And the distance between the weir and dam combined with turbulence inhibitor with top extending lip has an optimal value for the melt flow. And a three-dimensional mathematical model to simulate the flow of molten steel in the tundish was developed to analyze the melt flow in tundish with typical control devices. One proposal for the best inclusion removal is presented based on the physical modeling and mathematical modelling.(3) With the combination of the wide and thick slab continuous casting mold practical process, the effects of different operation parameters on the fluid flow, interface fluctuation behaviour as well as the mechanism of mold powder entrapment in the mold were investigated by combining the water model experiments and mathematical simulations.(4) There are two new mechanisms of mold powder entrapment in wide and thick slab mold with argon blowing, viz. powder entrapment caused by the attack of bubbles stream and the vortex, and a flow reversing from the narrow face of the mold give rise to the powder entrapment was not found in the experimental casting speed range. With different slab widths and correspondent casting speed, the powder entrapment will not occure in the mold if the gas flowrate blowing into the SEN is less than 4 L/min.(5) The optimum process parameters for controlling the surface fluctuation in the mold with the section of 2200×280mm2 are that the argon gas flow rate of 4L/min, the nozzle side port angle of-15°and the nozzle submergence depth of 140 mm.(6) The results of application of continuous casting process parameters in practice shows that the presented process parameters are better than the original ones on the control of non-metallic incusions. With the presented process parameters, the inclusion content in the tundish and slab are decreased by 8% and 20% than those under the original process parameters, respectively. And the typical inclusion sizes in tundish and slab is 10μm and 5μm with the presented process parameters, wihle it is 30μm and 15μm with the original ones.更多还原