反向凝固结晶器中流动与传热的数值模拟

文中根据连续统一模型建立了描述反向凝固结晶器中的流动与传热的数学模型。研究结果表明了反向凝固工艺母带增长的三阶段规律。即快速增长。平衡相持和快速回熔^[1,3,5]。通过母带厚度的实验值和模拟值的比较。验证了模型的正确性。     

反向凝固法凝固层厚度的变化规律研究

讨论了反向凝固钢带凝固层厚度的变化规律，分析了一些因素对凝固厚度的影响，结果表明，母带厚度，钢液过热度及浸入时间对凝固层厚度均有不同影响。     

反向凝固连铸碳素钢带中复合层的凝固生长规律

在实验室条件下,用市售碳素钢板作为母带,用08Al低碳钢作为复合层材料,对反向凝固连铸薄带生产过程中复合层在母带表面的凝固生长规律进行了研究,研究结果表明,母带在钢水中的浸渍时间、母带厚度和钢水过热度对复合层厚度有显影响,而且这些工艺参数之间存在交互作的浸渍时间、母带厚度和钢水过热度对复合层厚度有显影响,而且这些工艺参数之存在交互作用;复合层的变化经历了“快速生长”、“平衡相持”和“迅速回熔”三个阶段,这三个阶段在复合层厚度－浸渍时间图上共同组成具有较长平台 的反向凝固“∩”形特征曲线;较低的钢水温度和较厚的母带有利于增加复合层厚度。     

反向凝固—生产带钢新技术

本文介绍德国曼内斯曼－德马克公司开发的一种反向凝固方法生产薄带钢的新技术。它将母带从凝固器内的钢水中穿过，使母带厚度增加５倍，并获得优良性能的带钢产品。我国已开始对此项技术进行研究，目前在实验室研究以获得可靠的基本工艺参数，为半工业试验提供依据。     

反向凝固连铸碳素钢铸带中新相层的凝固生长规律

在实验室条件下,采用碳素钢板为母带,以08Al低碳钢为新相层材料,对反向凝固连铸薄带工艺过程中新相层在母带表面上凝固生长的规律进行了详细研究。研究表明,母带在钢液中的浸渍时间、母带厚度、钢液过热度对新相层厚度有显著影响,各个工艺参数间存在交互作用;新相层的变化经历“快速生长”、“平衡相持”和“迅速回熔”三个阶段,这三个阶段在新相层厚度－浸渍时间图上显示出“∩”形特征曲线;较低的钢液温度和较厚的母带可促使新相层厚度增加。     

反向凝固复合不锈钢带界面结构的研究

借助光学显微镜,扫描电镜和电子探针,分析了反向凝固轧制后的不锈钢带的熔合区及碳的扩散,并研究了铬元素和铁元素沿横截面的分布情况,试验结果表明,母带和凝固层靠相互扩散形成固溶体而实现良好的冶金结合。     

反向凝固复合不锈钢带界面结合的研究

借助光学显微镜、扫描电镜和电子探针,分析了反向凝固轧制后的不锈钢带的熔合区及碳的扩散,并研究了铬元素和铁元素沿横截面的分布情况.试验结果表明,母带和凝固层靠相互扩散形成固溶体而实现良好的冶金结合.     

反向凝固复合奥氏体不锈钢薄带的实验研究

采用１．２ｍｍ厚的１５Ｆ热轧板为母带，以奥氏体不锈钢１Ｃｒ１８Ｎｉ９作为覆层材料，在实验室条件下研究了反向凝固法生产复合奥氏体不锈钢带的可行性。实验表明，随着母带在钢液中浸渍时间的增加，新相层的生长经历“快速生长”、“平衡相持”和“迅速回熔”三个阶段；新相层厚度则随着钢液过热度的增加而近似线性地减少。此外，母带表面状态、母带在钢液中的浸渍时间及钢液过热度对铸带质量均有显著的影响，但通过控制合格的工     

反向凝固0Cr13／15复合铸带的界面剪切强度及断口分析

在实验室条件下，按照反向凝固工艺原理并控制合适的工艺参数制成了0Cr13/15不锈钢复合铸带。对不同工艺条件下获得的复合铸带进行了界面剪切强度测试，测试结果表明复合铸带获得了良好的界面结合质量。试样断口的X射线衍射和SEM分析证实，剪切断口发生在母带区内，0Cr13复合层内的断口表现为韧窝断裂，而母带区由于过热晶粒长大而发生脆性解理断裂。     

反向凝固复合不锈钢带的轧制工艺及界面结合

针对用反向凝固法生产不锈钢复合带的工艺，研究了轧制温度、轧制速度及轧制变形率对母带与凝固层间结合的影响。结果表明：轧制温度为１２５０℃、两道次的轧制变形率为５０％时，界面结合较好，轧制速度对界面结合的影响不明显。经分析得知 喧与凝固层的界面结合是靠元素相互扩散形成过渡区实现的。     

Vibration Method to Detect Liquid–Solid Fraction and Final Solidifying End for Continuous Casting Slab

Accurate measurement of liquid–solid fraction of casting slab in the secondary cooling zone and precise prediction of final solidifying end of casting slab have momentous significances for internal defects improvement of continuous casting slabs, such as the segregation and shrinkage porosity etc. However, the on‐line detection of slab solidification processing and final solidifying end haven't accomplished, which have been acknowledged as metallurgy problem all over the world. The paper presents a novel method, which called vibration method, to detect the liquid fraction and locate the final solidifying end of continuous casting slab. A physical simulation device using the materials of organic glass and water has been set up according to the similarity theory. Basing on theoretical deduction, physical experiment and numerical simulation, the research results provide guidance and reference for the on‐line detection of liquid–solid fraction and final solidifying end of the slab.     

连铸板坯凝固末端位置的研究

 连铸坯凝固末端位置的确定方法有实验测定法和数学模型法。针对鞍钢厚板坯连铸机,采用有效比热容法建立板坯连铸二冷凝固传热数学模型来预报凝固末端的位置,用实验测定值验证了模型的可靠性。应用数学模型分析拉速对厚板坯凝固末端位置的影响,将计算结果回归得到了X65管线钢和船板钢在不同拉速范围内凝固末段位置和拉速的数学关系式,可为现场控制连铸凝固终点提供参考。     

Motion of Fine Particles under Interfacial Tension Gradient in Relation to Continuous Casting Process

In front of the solidifying interface of a water solution, in the case of NaCl water solution, fine bubbles (10~100 μm in diameter) were just moving upward, no matter how close they were from the solidifying interface. However, in front of the solidifying interface of C₈H₁₇SO₃Na water solution, once the distance between the bubbles and the solidifying interface became less than 90~100 μm, rising bubbles were found to move horizontally toward the solidifying interface quickly, and then to be engulfed by the interface. This effect can be attributed to the surface tension gradient around the bubbles induced by the concentration gradient in the boundary layer formed in front of the solidifying interface. The phenomenon is taken as a kind of the Marangoni effect in a broad sense. The movement of fine particles driven by the interfacial tension gradient is found to have a close relationship to certain phenomena in continuous casting processes, such as the occurrence of bubble or inclusion‐related defects in steel and nozzle clogging.     

连铸数学模型研究新进展

迄今文献研究连铸含铸锭）的数学模型均基于单元系相变过程；事实上，钢铁生产中熔化与凝固乃是多元系相变过程。由此出发，建立了连铸的新数学模型，并且构造了相应的算法以进行数字仿真与生产过程自动控制应用。     

Analysis of thermomechanical behaviour in billet casting with different mould corner radii

Abstract

A finite element thermal stress model to compute the thermomechanical state of the solidifying shell during continuous casting of steel in a square billet casting mould has been applied to investigate longitudinal cracks. A two-dimensional thermoelastoviscoplastic analysis was carried out within a horizontal slice of the solidifying strand which moves vertically within and just below the mould. The model calculates the temperature distributions, the stresses, the strains in the solidifying shell, and the intermittent air gap between the casting mould and the solidifying strand. Model predictions were verified with both an analytical solution and a plant trial. The model was then applied to study the effect of mould corner radius on longitudinal crack formation for casting in a typical 0·75%/m tapered mould with both oil and mould powder lubrication. With this inadequate linear taper, a gap forms between the shell and the mould in the corner region. As the corner radius of the billet increases from 4 to 15 mm, this gap spreads further around the corner towards the centre of the strand and becomes larger. This leads to more temperature non-uniformity around the billet perimeter as solidification proceeds. Longitudinal corner surface cracks are predicted to form only in the large corner radius billet, owing to tension in the hotter and thinner shell along the corner during solidification in the mould. Off corner internal cracks form more readily in the small corner radius billet. They are caused by bulging below the mould, which bends the thin, weak shell around the corner, creating tensile strain on the solidification front where these longitudinal cracks are ultimately observed.     

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

 The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product. The multiphase flow phenomena of molten steel, steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation, and the effect of electromagnetic brake (EMBR) and argon gas blowing on the process were investigated. The relationship between wavy fluctuation height near meniscus and the level fluctuation index F, which reflects the situation of mold flux entrapment, was clarified. Moreover, based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification, the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux, temperature and stress of shell in slab continuous casting mold were described.     

Optimization of Thermal Performance of CCM Mold

Metallurgist - A physical simulation technique was used to study the processes of heat transfer between solidifying metal and CCM mold during continuous casting of steel. Variation trends have been...     

Compensation Control Model of Superheat and Cooling Water Temperature for Secondary Cooling of Continuous Casting

In this paper, a compensation control model of secondary cooling process of billet continuous casting for quality steel has been presented. The effects on the spray control of the various parameters such as steel superheat, casting speed, cooling water temperature and chemical component of steel were considered. The parameters of control model were determined to associate with the two‐dimensional heat transfer equation and solved by finite‐difference method. Effects of steel superheat and cooling water temperature on surface temperature, solidification structure and solidifying end point were discussed. Results indicate that steel superheat significantly affects solidification structure and solidifying end point but has a little effect on slab surface temperature. Moreover, secondary cooling water temperature affects surface temperature and solidifying end point but has a little effect on solidification structure. The surface temperature and solidifying end point can be maintain stabilized through applying the compensation control model when steel superheat and cooling water temperature vary. The models have been validated by industrial measurements. The results show that the simulations are in very good agreement with the real casting situation.     

Simulation of thermal behavior during peritectic steel solidification in slab continuous casting mold

Thermal behavior of the solidifying shell in continuous casting mold is very important to final steel products.In the present work,one two-dimension transient thermal-mechanical finite element model was developed to simulate the thermal behavior of peritectic steel solidifying in slab continuous casting mold by using the sequential coupling method.In this model,the steel physical properties at high temperature was gotten from the micro-segregation model withδ/γtransformation in mushy zone,and the heat flux was obtained according to the displacement between the surface of solidifying shell and the hot face of mold as solidification contraction,the liquid-solid structure and distribution of mold flux,and the temperature distribution of slab surface and mold hot face,in addition,the rate-dependent elastic-viscoplastic constitutive equation was applied to account for the evolution of shell stress in the mold.With this model,the variation characteristics of surface temperature,heat flux, and growth of the solidifying shell corner,as well as the thickness distribution of the liquid flux,solidified flux,air gap and the corresponding thermal resistance were described.     

Simulation of slab formation in a continuous-casting machine

A discrete analog of the differential heat-conduction equation permits the use of nonuniform calculation grids in the simulation of continuous casting. That allows the distribution of the temperature gradients in the model to be taken into account, with corresponding increase in the accuracy of the approximation and the results. A mathematical model is developed for the solidification and shrinkage of continuous-cast slab in the mold. The adoption of a nonuniform grid permits the use of elements measuring 1–2 mm in the simulation. This model is used to study the distortion of the slab cross section at the mold walls. Calculation of the geometric profile permits refinement of the thermal and mechanical interaction of the solidifying shell and the mold walls and determination of the optimal mold taper so as to reduce the risk of surface and subsurface cracking in the slabs.