Centerline Segregation in Continuous Casting Billets

Centerline segregation is of practical significance since it affects the material properties. Centerline segregation in continuous casting billets was studied by solving the fluid flow, solidification, and solute transport equations from the initially liquid steel to the completely solid state using the finite difference method with the SIMPLER algorithm. The results show that the centerline segregation is induced by both the fluid flow in the mushy zone and the accumulation of solute-rich liquid near the solidification front. The species concentration in the center of the strand rises quickly in the mushy region to a maximum at the end of solidification. The most serious segregation occurs along the billet centerline.     

基于反算热流的结晶器内流动--传热--凝固耦合模拟

基于Navier-Stokes动量方程和湍流低雷诺数k-ε方程,综合考虑能量守恒和钢液凝固与糊状区对流动过程的影响,建立了描述结晶器内钢液流动、传热及凝固过程的三维耦合数学模型。以实测温度和结晶器反问题模型计算出的热流为边界条件,模拟计算了结晶器内钢水的流动、传热和凝固行为。钢液流动决定结晶器内的温度和热流分布,铸坯凝固受钢液流动和结晶器热流双重因素的影响。建立的模型以及由此得到的铸坯凝固非均匀特征可为进一步考察浇铸过程中纵裂和其他表面缺陷提供借鉴和参考。     

CSP结晶器内钢液流动及凝固的数值模拟

应用数值模拟方法,建立CSP漏斗型结晶器内钢液流动及凝固传热耦合模型。针对结晶器内铸坯角部受到强冷的特点,对结晶器内热流密度采用修正方程进行计算,分析热流密度修正系数对铸坯凝固坯壳表面温度计算精度的影响。通过比较不同拉坯速率下结晶器内钢液凝固的特点,研究凝固坯壳对结晶器内钢液流动行为的影响。结果表明,采用热流密度修正系数后,铸坯凝固坯壳角部温度的计算值与实际情况更相符;提高拉坯速率可使铸坯凝固坯壳厚度减小;拉坯速率较大时凝固坯壳厚度随铸坯距弯月面距离的增大基本呈线性增长,拉坯速率为3m/min时,凝固坯壳在生长过程中厚度的增长有短暂的停滞现象;凝固坯壳对钢液流动的影响较大,主要是由钢液有效流动区域减少及两相区额外动量阻损造成的。     

双带式薄板连铸数值模拟

建立了双带式薄板连铸凝固过程流动与热交换的数学模型。该模型适用于铸造合金凝固各区即液相区域，固相区和糊状区，能量方程和流动方程在车式错列钢格上离散成有限差分方程后用迭代法求解。计算出ＡＩＳＩ１０２０钢薄板连铸过程流场，温度场和凝固区的形貌，并模拟了浇嘴高板坯厚度对凝固过程的影响。     

马钢大圆坯连铸结晶器内钢水流动与凝固过程的数学模拟

建立了大圆坯连铸过程中结晶器内钢水流动、传热及凝固过程的数学模型,对马钢车轮轮箍钢连铸过程中钢水宏观凝固过程进行数值模拟分析,数值模拟的结果与射钉试验和铸坯表面温度测定的结果很相近,说明该模型具有很高的可靠性与准确性,对连铸工艺有很大的指导作用.     

高碳钢连铸坯凝固过程溶质宏观偏析的数值模型

采用FeC二元合金的紊流、凝固传热及溶质传输三维耦合模型,针对铸坯不同碳质量分数对凝固过程溶质分布的影响进行数值模拟,凝固过程以柱状晶生长方式进行,遵循局部热力学平衡·研究发现,与低碳钢相比,高碳钢的凝固坯壳较薄,等温曲线较为光滑,糊状区范围较大·碳质量分数较高的钢种,偏析较轻;而低碳钢,偏析较为严重     

连铸结晶器中坯壳生长有限元分析

为了预测结晶器出口铸坯坯壳的厚度与均匀性,考虑气隙对连铸坯的边界换热条件的影响,建立了铸坯传热凝固有限元计算分析的数学模型。采用热通量系数法反映实际的坯壳角部凝固特征现象。在方坯结果验证基础上,通过对新型H型连铸坯凝固过程进行模拟,计算得出了结晶器出口处坯壳的厚度。计算结果表明:H型铸坯坯壳的厚度随着拉速的增加而变小;铸坯在腹板和翼板交接处最薄,应适当增加水量,以保证坯壳在结晶器出口处具有足够的厚度。     

热型连铸工艺凝固过程的数值模拟

采用直接差分的方法对热型连铸工艺凝固过程的稳定温度场进行了模拟,绘制了热型连铸工艺凝固过程的温度曲线,分析了铸型出口温度、冷却条件、连铸速度和型内金属液温度对凝固温度曲线的影响．铸型出口温度、冷却条件、连铸速度依次为影响液固界面的主要因素,型内金属液温度对液固界面的影响很小．     

方坯连铸凝固末端电磁搅拌工艺优化的数值模拟

利用ANSYS和CFX软件建立了描述160mm×160mm方坯连铸凝固末端电磁搅拌过程的数学模型.通过确立钢液黏度与温度的定量关系,考虑凝固时钢液黏度的重要影响,研究了方坯凝固末端糊状区磁场和流场的分布,以及电流强度对凝固前沿钢液最大搅拌速度的影响规律.结果表明:搅拌电流强度每增加100A,铸坯中心磁感应强度增加250×10-4T,切向电磁力增加1933N/m3,最大流速增加69cm/s.现场实验检验结果表明:60#钢凝固末端电磁搅拌器安装位置处液芯半径为344mm,最佳电磁搅拌频率为6Hz,最佳搅拌电流为380A,此时凝固前沿最大流速为165cm/s,铸坯中心碳偏析得到明显改善,中心碳偏析指数为104.     

电磁制动下板坯连铸结晶器内金属流场三维模拟的基本流态与主流场分析

在物理模拟实验的基础上, 采用基于标准k-ε 湍流模型的三维稳态流动与磁场耦合模型, 对电磁制动(electromagnetic braking, EMBr)条件下板坯连铸结晶器中的金属流场进行数值模拟, 研究了磁场强度及其分布对结晶器内金属流动的影响, 并与物理模拟结果进行了对比, 进一步揭示了在物理模拟中受传感器数量等限制所无法观察到的一些细微现象或局部流态及流动行为. 结果表明, 在流动控制结晶器(flow control mold, FC Mold) 电磁制动方式下,结晶器内流场具有复杂的三维特性. 此时必须注意结晶器液面流速过慢所导致的表面夹杂、横裂等问题. 合适、有效的电磁制动也应与连铸工艺相匹配.     

连铸坯截面尺寸对流动、凝固及溶质分布的影响

采用方坯连铸过程三维紊流、凝固传热及溶质传输的耦合模型,在其他模拟条件相同的情况下,研究铸坯截面尺寸对连铸过程的影响·结果表明,截面尺寸大者,入流速度大,更深浸入铸坯内部,带动较多钢液随之流动,在结晶器上部的紊流程度较高·对于FeC二元合金,由温度和溶质浓度共同决定了凝固坯壳的分布·小截面尺寸铸坯,溶质在各截面上偏析更为严重·其凝固坯壳也较薄,为防止拉漏,应采用长结晶器     

Characteristics of shell thickness in a slab continuous casting mold

The key to reduce shell breakout in the continuous casting process is to control shell thickness in the mold. A numerical simulation on the turbulent flow and heat transfer coupled with solidification in the slab mold using the volume of fluid (VOF) model and the enthalpy-porosity scheme was conducted and the emphasis was put upon the flow effect on the shell thickness profiles in longitudinal and transverse directions. The results show that the jet acts a stronger impingement on the shell of narrow face, which causes a zero-increase of shell thickness in a certain range near the impingement point. The thinnest shell on the slab cross-section locates primarily in the center of the narrow face, and secondly near the comer of the wide face. Nozzle optimization can obviously increase the shell thickness and make it more uniform.     

基于 PIV 技术的板坯连铸结晶器内钢水流动行为研究

利用粒子图像测速技术,以200 mm×2040 mm板坯连铸结晶器为原型,建立1：4水模型进行实验,对结晶器内钢液流动形态、流速及各流态所占比例、液面波动、以水口为中心结晶器两侧对称点速度随时间的变化、水口两侧液面水平流速、水口两侧对称位置液面至结晶器底部垂直方向速度和钢液对两侧窄面的冲击深度进行系统地研究和分析,并对比拉速的影响.研究表明,粒子图像测速技术不仅可以测量结晶器内流场流速,还可以对流场对称性进行全方位、多角度定量分析,为研究连铸参数变化,比如拉速、水口结构和水口浸入深度,对板坯连铸结晶器内钢液流动及对称性的影响提供一种较为精确的方法和思路.通过分析得出,在本实验条件下拉速0.5 m·min-1优于0.6 m·min-1.     

板坯连铸结晶器内非对称流动现象的数值模拟

基于流体力学基本原理,采用Fluent软件建立板坯连铸结晶器及浸入式水口的三维有限元体积模型,模拟研究了水口不对中和水口单孔结瘤条件下结晶器内流体的流动特征和温度场分布状况.结果表明:水口对中不良时,结晶器两侧回流明显不对称,液面会产生旋涡,水口偏向侧温度高于水口偏离侧;水口出口单孔结瘤时,未结瘤侧流股增强,液面流速增大,并且液面有涡流产生,结瘤侧新鲜钢液减少,温度偏低.     

旋转磁场对Zn-7Cu-0.25Mn合金水平连铸坯组织性能的影响

对Zn-7Cu-0.25Mn合金在有无旋转磁场下水平连铸坯横截面宏观组织、微观组织的形貌及铜元素的分布进行比较分析,探讨旋转磁场对Zn-7Cu-0.25Mn合金水平连铸坯组织和性能的影响。结果表明,当拉坯速度保持为53.3mm/min时,施加频率为30Hz、电流强度为100A的旋转磁场,可以消除铸坯因为重力作用导致下部凝固速度大于上部凝固速度、最终凝固位置偏离中心线上移的现象;旋转磁场对水平连铸坯的凝固组织具有明显的细化作用,并且使铸坯的铜偏析现象得到明显改善;施加旋转磁场后铸坯的平均硬度较施加前略有提高。     

Solidification and crystallization properties of CaO-SiO2-Na2O based mold fluxes

Crystallization properties play an important role in keeping a smooth running of continuous casting process and high surface quality of cast strands. To reduce fluorine pollution in slag, a new type of CaO-SiO₂-Na₂O (CSN) based mold flux was studied. The solidification and crystallization properties, including crystallization temperature, crystallization ratio and solidification mineragraphy, were measured, which were compared with the CaO-SiO₂-CaF₂ (GF) mold flux. The results show that the crystallization performance is equal to the high fluoride mold powder and CSN can be used for peritectic steel grades sensitive to longitudinal cracking in continuous casting.     

Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method

A new method called mixed Lagrangian and Eulerian (MiLE) method was used to simulate the continuous casting process in a mold of free-cutting steel 38MnVS. The simulation results are basically in agreement with experimental data in the literature, achieving the three-dimensional visualization of temperature distribution, melt flow, shell thickness, and stress distribution of blooms in a mold. It is shown that the flow velocity of steel melt becomes smaller gradually as the casting proceeds. When the flow reaches a certain depth, two types of flow patterns can be observed in the upper zone of the mold. The first flow pattern is to flow downwards, and the second one is to flow upwards to the meniscus. The corner temperature is higher, and the thickness is thinner than those in the mid-face. The effective stress in the corner area is much bigger than that in the mid-face, indicating that the corner area is the dangerous zone of cracking.     

恒稳磁场控制连铸结晶器内钢液流场热模拟实验

采用BiPbSn低熔点合金和硅油分别模拟钢液和保护渣,在实验连铸机上,对全幅双条恒稳磁场作用下的连铸结晶器水口区域的流场进行了热模拟实验研究·结果表明:电磁场对结晶器水口区域流场和水口出流流股的控制能力取决于磁感应强度和拉坯速度·磁感应强度大,拉坯速度高,控制效果好;反之,控制效果差·因此,结晶器流动控制技术更适合于高拉速的场合,而且磁感应强度不应低于某一定值     

连铸小方坯的组织与性能研究

The hot cracking of the continuous casting bullit is connected with its macrostructure and mechanical property burnt. The macrostructure and the mechanical property of 0. 13 wt- %C continuous casting bullit was investigated. The results are as follows: 1) the classical representation of the casting bullit shows three distinct zones, a peripherial region of small equiaxed grains, a columnar zone, and a central equiaxed zone. The rapid increase of the under cooling layer thickness is the criterion of the transformation from the columnar zone to central equiaxed zone; 2) The hardness decreases with the reducing of the solidification speed; 3) The tensile strength decreases gradually from the peripherial equiaxed maximum principal strain zone to central equiaxed zone ,and increases with the drop of the temperature.     

结晶器内连铸坯凝固过程的有限元数值模拟

建立了结晶器内连铸坯凝固过程的有限元数学模型，在坯壳面表面边界条件中引入与气隙相关的传热模型修正平均热流量方程，研究了铸坯角部气隙对坯壳凝固行为的影响，模拟结果表明，铸坯角部形成的气隙流量显著地长低了坯壳表面的换热，使得铸坯偏角区成的为热节区，此热节区是铸坯凹陷，裂纹等缺陷乃至漏钢事故发生的诱因。