大方坯凝固过程鼓肚应变及内裂纹形成的研究

通过建立大方坯凝固过程的传热模型,获得大方坯冷却传热过程的主要凝固参数,在此基础上建立了凝固前沿坯壳所承受的应变模型,讨论了大方坯凝固过程的主要应变及其主要影响因素,并针对实际铸机的设备和工艺状况,计算大方坯凝固过程的鼓肚应变,讨论了具体钢种产生裂纹的可能性.     

板坯连铸三维鼓肚变形仿真研究

通过建立板坯连铸凝固过程的传热模型,获得板坯冷却传热过程的坯壳生长情况,在此基础上利用有限单元法建立了坯壳三维鼓肚变形仿真分析模型。针对实际铸机的设备和工艺状况,计算了板坯凝固过程的鼓肚变形情况,并就三维仿真分析的特点进行了分析。     

板坯连铸结晶器温度场计算模型的应用

针对中厚板卷厂板坯连铸机,建立了板坯二维非稳态凝固传热模型,利用各铸机典型拉速下实际生产过程数据验证所建立板坯凝固传热模型的准确性。基于所建立的板坯凝固传热模型,分析了现行结晶器水量下调的可能性,并对结晶器冷却制度进行优化,控制铸坯表面裂纹。     

热送热装工艺中板坯连铸过程传热的数学模型

建立了板坯连铸过程传热数学模型，并用实测数据对计算结果进行了验证，证明该模型可用于预报不同操作条件下板坯凝固过程中温度的变化和凝固状态。应用该模型分析了影响板坯出连铸机温度的主要因素：板坯尺寸、拉速、二冷水量及冷却方式等。适当提高拉速、改善二冷制度能提高铸坯出连铸机温度。     

基于连续模型的板坯连铸凝固过程的数值模拟

结合实际测量数据，建立了基于连续模型的板坯连铸过程流场、温度场和凝固的三维耦合数学模型。计算结果表明：该模型可用于描述连铸板坯结晶器和整个二冷喷水区的凝固进程；凝固坯壳的生长限制了流体流动的空间，加快了水口出口钢流的动量衰减；流体流动加快了铸坯内部传热机制由对流向热传导传热的转变进程，控制了两相区的发展。     

连铸板坯凝固的传热模型

依据武钢板坯连铸机的生产条件，建立了板坯凝固过程传热模型，分析了影响板坯出连铸机温度的主要因素，得出适当提高拉速、控制二冷喷水量和关掉二冷末端冷却水能提高铸坯温度、降低能耗。     

基于有限元法优化低碳钢板坯连铸机结晶器锥度的设计

钢厂1^#连铸机以0.95 m/min拉速生产SS400,D36和X70钢150~180 mm连铸板坯时,易产生角部纵裂纹,发生率最高可达5%。利用商业有限元软件ANSYS,建立了板坯连铸结晶器二维切片式凝固传热数学模型,并采用传热和应力/应变直接耦合的方法对连铸过程结晶器内凝固传热进行计算,分析了各钢种在0.95~1.05m/min拉速下铸坯温度分布以及温度分布不均引起的热应力。工业试验结果表明,根据优化计算结果,将板坯结晶器窄面的锥度系数由原来的1.00%改进为1.10%后,有效地消除了1^#连铸机板坯的角部纵裂纹。     

钢种差异性对板坯连铸自由线收缩的影响规律研究

建立了连铸板坯凝固传热与自由线收缩计算模型.揭示了板坯连铸凝固与冷却过程线收缩的一般规律.针对304不锈钢和Q235B板坯连铸,结合实际生产冷却条件的计算分析表明:连铸过程板坯厚度的自由线收缩在二冷初期较为平缓,二冷后期铸坯凝固末端附近为快速线收缩阶段;相同目标表面温度下,304不锈钢板坯在铸机各位置处的厚度方向自由线收缩量均小于Q235B,且随距弯月面距离的增加,两者的差距先逐渐增加后趋于稳定.     

宝钢3号板坯连铸结晶器传热行为的模拟研究

通过建立传热模型,研究了板坯结晶器的传热行为.模型的建立考虑到结晶器内湍流运动对过热度分布的影响,提出了耦合流场和温度场求解坯壳热流密度,并将其导入传热模型计算的方法.模型包括凝固坯壳,结晶器缝隙和铜板的传热,其中计算结晶器缝隙间热量传递过程中,综合考虑了振痕、固渣层、液渣层和气隙对传热的影响,并做了相应处理.模型能根据不同的生产工艺(不同断面形状和尺寸、拉速等),对凝固坯壳厚度,表面温度,结晶器铜板温度,冷却水温差,以及结晶器理想锥度等进行计算.结合宝钢3号连铸机结晶器生产数据,对模型进行了验证,所得计算结果符合实际测量值.     

板坯连铸二冷计算机仿真软件的应用

在建立板坯连铸凝固传热数学模型的基础上，应用面向对象的编程语言Visual Basic 6．0开发了板坯连铸二冷计算机仿真软件，并针对国内某板坯连铸机应用仿真软件对其进行凝固过程的进行了模拟、对其二冷凝固过程进行工艺优化．     

Modelling of heat flow and interdendritic crack formation in twin-roll strip casting of aluminium alloys

Preliminary mathematical analyses of different interdendritic cracks associated with variation of heat transfer and generation of interdendritic strain in horizontal twin-roll strip casting have been investigated. A 1-D transient finite difference model of heat flow, dendritic solidification and interdendritic thermo-metallurgical strain has been developed. The model contains two cracking criteria to predict qualitatively and quantitatively the tendency of interdendritic crack formation during dendritic solidification of pure aluminium and 6022 aluminium alloy. The model predictions are compared to available analytical methods and previous measurements. This is to verify and calibrate the model where good and reasonable agreements are obtained, respectively. The variations of heat transfer modes during different contact cooling zones and their effects on the generation of interdendritic thermo-metallurgical strain at the surface and central strip locations have been analysed. The model predictions point out that the different contact cooling zones of strip surface and surroundings control the stages of interdendritic crack formation in different mushy regions. The mechanism of interdendritic crack formation in twin-roll strip casting process with previous and present cracking criteria have been explained and discussed. These discussions show the importance of selection of mathematical treatment to predict the stages of interdendritic crack formation.     

Analysis of bulging for high speed continuous casting

In order to research the temperature distribution and mechanical deformation of slab bulging during high speed continuous casting,mathematical models have been developed to analyze the thermal and mechanical behavior of the slab.The thermal history of the slab has been predicted by a two-dimensional transient finite element heat transfer model,whose results serve as the input to the stress model.The stress model has been formulated for a two-dimensional longitudinal plane.In this case,the maximum tensile strain during the bulging process is located at the solidification front just past the top of the upstream roll,which may contribute to crack formation.The maximum tensile stresses are located at the cold surface in the middle of the two back-up rolls,just at the point of the maximum bulging.Stresses near the solidification front are small because of the high temperatures which produce lower elastic modulus values.Finally,the effect of the casting speed on the bulging deformation is discussed.     

Advanced Solute Conservation Equations for Dendritic Solidification Processes Part I: Experiments and Theory

The macrosegregation formed in dendritic equiaxed structure during early stages of solidification of Al‐4.5%Cu alloy has been studied by experimental work and by metallurgical study of cast samples taken from the experimental work. An experimental work was conducted to study the coupled effect of natural convection streams, interdendritic strain and mushy permeability of Al‐4.5%Cu aluminum alloy solidified in horizontal rectangular parallelepiped cavity at different superheats. The metallurgical study includes macro‐microstructure evaluation, measurements of grain size of equiaxed crystals and macrosegregation analysis. This study shows that the level of surface segregation exhibiting as positive segregation varies with superheat whereas the rest of inner ingot areas show the light fluctuation in segregation values. In addition to experimental work, there is a mathematical study which contains a complete derivation of local solute redistribution equations based on Fleming's approach under different solute diffusion mechanisms in the dendritic solid. This derivation includes also the effects of interdendritic strain and mushy permeability on the local solute redistribution distribution. Owing to the length of the study, it is presented in two parts. The first part describes the experimental work and its results as well as a detail derivation of solute conservation equations. This part also involves comparison and discussion between existing and proposed solute conservation equations. The second part contains the mathematical analyses of a two dimensional mathematical model of fluid flow, heat flow, solidification, interdendritic strain and macrosegregation. Also, this part also contains the numerical simulations by using finite difference technique “FDT” to create convection patterns, heat transfer, interdendritic strain, and macrosegregation distributions. This part also includes comparisons between the available measurements and model predications as well as full discussion of different model simulations. The mechanism of interdendritic strain generation and macrosegregation formation during solidification of dendritic equiaxed structure under different diffusion mechanisms in dendritic solid has also been explained and discussed.     

大方坯在连铸过程中传热及凝固规律的数学模拟

结晶器和二冷区传热对大方坯产品质量和铸机的生产率有重要影响。讨论了包头钢铁集团公司引进的大方坯连铸机在拉坯时结晶器和二冷区的传热、坏壳凝固生长和铸坯温度的变化规律。着重讨论了电磁搅拌、过热度和拉速对坏壳凝固和生长规律的影响。指出影响铸坯凝固的主要因素是凝固潜热，影响凝固末端位置的最主要工艺参数是拉坯速度，而电磁搅拌对其影响区内的传热、坯壳生长和铸坯温度亦有较大影响。     

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.      

天钢连铸板坯中心裂纹的成因分析

针对天钢炼钢厂在连铸生产中出现的中心裂纹,结合VAI动态辊缝模拟软件、铸坯凝固过程应变理论及天钢炼钢厂的生产实践,分析了产生铸坯中心裂纹的影响因素.在设备方面,辊缝超差,特别是凝固末端辊缝超差是造成中心线裂纹的主要原因.在工艺方面,铸坯在冷却过程中,由钢水成分、浇注温度以及拉速变化引起的相变降低了钢的高温塑性.在外力作用下,坯壳承受的应力之和超过了钢的允许强度和应力时,铸坯就会产生裂纹.     

内配碳球团热风穿流干燥的数值模拟

在对内配碳球团热风穿流干燥过程中热湿迁移机制研究的基础上。利用质量、能量平衡方程和传热方程。建立了单个球团干燥过程热质传递的数学模型，采用全隐式有限差分方法对模型进行了数值计算。根据模拟结果对影响干燥速率的主要因素进行了讨论。比较球团热质变化的模拟值与实验值，相对误差均小于5％，证明此数学模型能够用来指导和预测实际的工业操作，具有广泛的适用性。     

Heat transfer-solidification kinetics modeling of solidification of castings

A close examination of the recent developments in the field of computer simulation of solidification process reveals that a combination of both macroscopic and microscopic models is necessary in order to accurately describe the solidification of castings. Currently available macroscopic models include models that describe heat transfer from metal to mold, fluid flow of liquid metal during mold filling, and stress field in the casting. At the microscopic level, the models should include more intricate issues such as solidification kinetics and fluid flow in the mushy zone. Although significant progress has been accomplished over the years in each field, the task of including all of these models into a comprehensive package is far from being complete. This paper describes the state of the art on coupling the macroscopic heat transfer (HT) and microscopic solidification kinetics (SK) models and introduces thelatent heat method as a more accurate method for solving the heat source term in the heat conduction equation. A new method for calculation of fraction of solid evolved during solidification based on computer-aided cooling curve analysis (CA-CCA), as well as a method based on nucleation and growth kinetics laws, is discussed. A new nucleation model based on the concept of instantaneous nucleation, which is used to describe equiaxed eutectic solidification of commercial alloys, has been introduced. It is demonstrated that the instantaneous nucleation model agrees well with the experimental results in terms of cooling curves and of evolution of the fraction of solid during solidification. Validation results are also shown for SK models that are based on CA-CCA coupled with HT models for eutectic Al-Si and gray cast iron alloys.     

矩形坯连铸凝固传热的数学模型

根据连铸矩形坯凝固传热特点，在上海浦东钢铁有限公司１号连铸机二冷系统改造中，动用直接差分法建立了二维非稳态矩形坯凝固传热数学模型，已应用于连铸凝固过程的模拟计算，在分析拉速、浇注温度等在数对钢水凝固过程的影响后，为提高拉速找到了理论依据。