气隙对连铸坯凝固影响的有限元数值模拟

以连铸坯凝固传热有限元数学模型研究了铸坯角部形状和气隙对坯壳凝固行为的影响研究结果表明：采用有限元法离散铸坯圆角能更合理地反映铸坯角部的几何和换热条件，从而可以更准确地研究角部换热条件对铸坯凝固行为的影响。角部气隙显著地降低了坯壳表面的换热，使铸坯偏角区成为热节区。此热节区是铸坯凹陷、皮下裂纹等缺陷和漏钢事故发生的诱因。     

气隙对连铸坯凝固影响的有限元数据模拟

以连铸坯凝固传热有限元数学模型研究了铸坯角部形状和气隙对坯壳凝固行为的影响，研究结果表明，采用有限元法离散铸坯圆角能更合理地反映铸坯角部的几何和换热条件，从而可以更准确地研究角部换热条件对铸坯凝固行为的影响，角部气隙显著地降低了坯壳表面的换热，使铸坯偏角区成为热节区。此热节区是铸坯凹陷，皮下裂纹等裂陷和漏钢事故发生的诱因。     

连铸结晶器内大方坯的热力耦合分析

针对攀钢大方坯连铸机投产初期铸坯表面角部纵裂缺陷,建立了大方坯连铸结晶器内铜板与铸坯问的热力耦合模型,应用模型分析了大方坯连铸结晶器内的传热过程和坯壳的应力分布.在传热模型中,以稳态模型分析结晶器的传热过程,以瞬态模型分析铸坯的传热过程;在力学模型中,考虑铸坯和结晶器的接触边界以处理结晶器角部的气隙,以热弹塑性模型分析铸坯的变形和应力场.2种结构的连铸结晶器中大方坯温度场和应力场计算结果表明,结晶器倒角从25 mm×45°变为12 mm×45°时,可改善铸坯角部的传热条件,降低凝固坯壳角部温度,增加凝固坯壳厚度,有利于减轻和防止铸坯角部裂纹.     

连铸结晶器内矩形坯的温度场模拟

利用有限元法建立了结晶器内轴承钢矩形坯温度场数学模型.采用了随温度变化的热物性参数,并且在边界条件中采用平均热流、瞬时热流及角部气隙等对比分析,研究了不同边界条件下矩形坯的温度场和坯壳厚度.模拟结果表明:不考虑角部气隙时,采用平均热流边界条件时矩形坯的温度范围要比采用瞬时热流时范围大;考虑角部气隙时,温度范围相差不大;角部气隙只对角部区域的温度有影响,而对芯部、宽面中心、窄面中心等区域基本没有影响;气隙降低了坯壳表面的换热,使得角部坯壳厚度要比不考虑角部气隙时平均小6～7mm左右,在距离角部30mm处出现热节区.     

301不锈钢板坯结晶器出口热力耦合数学模型

针对某厂301不锈钢连铸坯表面裂纹缺陷发生率高的生产问题,建立了301不锈钢板坯连铸结晶器内凝固坯壳形成及应力和变形的热力耦合模型。该模型考虑了包晶钢高温相变特征及其结晶器内的凝固特点。利用有限元软件ANSYS,采用三维瞬态热传导有限元、生死单元技术及三维热弹塑性接触有限元算法进行求解,对301不锈钢板坯结晶器内凝固过程进行了研究。结果表明,结晶器出口处铸坯宽面中心温度最低,距角部40 mm处温度最高,坯壳最薄,随δ-Fe转变量增加,出口处坯壳温度升高,坯壳厚度变薄。铸坯宽面中心位移变形最小,角部最大,窄面位移量大于宽面。随δ-Fe转变量增加,出口处应力水平下降,热点区附近成裂指数增加,发生纹裂机率增大。     

方坯结晶器内气隙分布的数值分析

基于连铸坯壳应力遗传特性建立二维方坯热力耦合模型,利用有限元分析软件ANSYS多载荷步法进行求解。模拟并对比了三种不同结晶器锥度值下的铸坯气隙生成及其分布规律。结果表明：离弯月面60~72mm角部首先出现气隙,随后向铸坯表面中心逐渐扩展,在结晶器出口处仅铸坯表面中心区域坯壳与结晶器存在接触。在结晶器上部300mm内气隙生长速度较快。随着离开弯月面距离增加,气隙生长速度逐渐降低。气隙宽度沿结晶器高度方向分布基本符合抛物线规律。随着锥度增加,气隙出现时机逐渐推迟,气隙宽度和存在范围也相应缩小。     

1500×70断面的CSP板坯静态弹性应力数值计算与验证

文章研究了薄板坯连铸结晶器内凝固坯壳的静态弹性应力分布,并分别计算了有否结晶器支撑的凝固坯壳所受到的等效应力。针对凝固前沿复杂的几何结构,使用Auto CAD.NET技术建立凝固坯壳的物理模型。为捕捉凝固前沿,使用数值模拟的方法计算了CSP结晶器内的钢液流动、传热和凝固。结果表明,由于结晶器内的流动冲刷,凝固壳的分布不均匀。若凝固坯壳与结晶器间存在较大的气隙,则在漏斗区存在应力集中现象,与实际生产中常出现横向表面裂纹的区域一致。     

特大断面连铸方坯结晶器出口的安全坯壳厚度

 连铸结晶器出口处坯壳的安全坯壳厚度对连铸生产的安全顺行、铸坯产品的质量及结晶器长度的设计都有很重要的影响。以特大断面700mm×700mm连铸方坯为基础,通过建立坯壳的三维计算模型对结晶器出口处坯壳厚度进行研究,应用有限元模型计算了不同厚度坯壳的应力分布情况,通过铸坯表面应力分布与材料屈服极限来判断不同厚度坯壳模型是否处于安全生产状态,确定保证安全生产的坯壳厚度的极限值。研究结果表明,坯壳厚度在26mm时表面应力达到屈服极限,随着坯壳厚度增加,铸坯表面应力减小并逐渐远离屈服极限,考虑坯壳生长的不均匀性,讨论了用来修正安全坯壳厚度的安全系数,对于本模型安全系数适用1.46,修正后坯壳的安全平均厚度38mm。     

超宽板坯包晶钢连铸初生坯壳应力的数值模拟

利用商业软件计算了超宽包晶钢连铸过程中初生坯壳所受应力.研究结果表明,由于包晶反应引起的体积收缩,包晶成分钢种的凝固坯壳表面应力显著大于非包晶钢成分钢种,在距铸坯中心约200 ～400 mm处应力出现极大值;随板坯宽度的增加,坯壳表面应力增大,应力极值点向坯壳中心方向移动;连铸工艺参数直接影响包晶钢表面应力大小,随过热...     

高频磁场作用下软接触电磁连铸初生坯壳的变形行为

结晶器内初生坯壳的变形行为直接决定着连铸坯的表面质量。笔者运用Reynold润滑方程推导出渣膜内的动压力分布,建立了初生坯壳的二维弹塑性变形有限元模型,研究了施加电磁场前、后坯壳的变形行为。研究结果表明：高频磁场(20kHz)下的感应加热作用会降低保护渣的粘度;电磁压力将增加渣缝的宽度,使施加电磁场后连铸坯初生坯壳的变形行为受到影响,进一步解释了软接触电磁连铸技术改善坯壳表面振痕的机理。     

中碳钢连铸方坯内部角裂机制研究与优化

 分别选取西钢某厂实际生产中易发生内部角裂缺陷的40Cr和45钢连铸坯为研究对象,通过对缺陷采用热酸浸低倍试验、金相法和探针能谱分析,发现缺陷处不存在明显的组织异常和质点沉淀。运用ANSYS软件对连铸结晶器凝固过程进行热模拟。研究结果表明,缺陷形成于结晶器内的凝固过程,根本原因是铸坯在结晶器中凝固传热不均导致出现铸坯偏角区热节区效应,从而诱导产生热应力,致使沿柱状晶晶间铁素体开裂,并伴随一定量的铸坯鼓肚现象。通过重新设定结晶器铜管圆角半径和优化生产部分工艺后,最终使连铸坯内部角裂评级在10级以上的比例下降到1042%。     

Heat Transfer and Deformation Behavior of Shell Solidification in Wide and Thick Slab Continuous Casting Mold

With the considerations of the behaviors of shell deformation, mold flux film and air gap dynamic distribution in shell/mold gap, a two dimensional slice-travel transient thermo-mechanical coupled model of simulation shell solidification in wide and thick slab continuous casting mold was developed by using the commercial program ANSYS. The evolutions of strand-mold system thermal behaviors, including the air gap formation and the mold flux film dynamical distribution in shell/mold gap and shell temperature field, and the evolutions of shell deformation and stress distribution of peritectic steel solidified in a 2120 mm wide and 266 mm thick slab continuous casting mold were analyzed. The results show that the air gap formation and the thick mold flux film distribution mainly concentrate in the regions 0–21 mm and 0–7 mm, 0–120 mm and 0–100 mm off the shell wide and narrow faces corners, and thus the hot spots are given rise to form in the regions 15–55 mm and 15–50 mm off the shell wide and narrow face corners. The shell server deformation occurs in the off-corners in the middle and lower parts of the mold. The stress evolution in shell surface is tensile stress, while that in shell solidification front is compressive stress.     

方坯结晶器多锥度分析

基于坯壳应力遗传特性建立铸坯热力耦合模型,利用ANSYS对结晶器内铸坯进行铸坯传热及应力分析。依据最小气隙原则对结晶器锥度进行优化,分析了单锥度和多锥度对坯壳凝固行为的影响。结果表明:采用两种锥度形式的结晶器,铸坯角部凝固行为存在明显差异,而表面中心区域基本一致。单锥度结晶器内气隙分布较广,角部热流明显降低,在偏离角部12～22 mm处存在"热点"。多锥度结晶器内气隙宽度和存在范围显著减少,"热点"消失,多锥度结晶器更符合坯壳凝固收缩规律。     

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.     

连铸结晶器温度场及热变形的数值模拟

利用MARC有限元软件建立了圆坯结晶器的三维温度场与应力场耦合的热弹性模型，并在此基础上研究了结晶器厚度、冷却水流速以及拉坯速度对结晶器温度场和铜管变形的影响规律．模拟结果表明：拉速提高时，结晶器的温度和变形量都增大，但影响不显著；结晶器厚度增大时，铜管冷面温度降低，热面温度升高，同时变形增大；冷却水流速对铜管温度分布和变形量有较大影响，增大冷却水流速，铜管温度和变形量均下降．     

连铸圆坯结晶器锥度优化设计研究

基于圆坯轴对称性和坯壳应力遗传特性,建立二维纵向切片热力耦合模型,利用有限元软件ANSYS对结晶器内铸坯传热及应力进行分析。根据结晶器内坯壳的收缩以及气隙的分布,依据最小气隙原则对结晶器锥度进行优化。经过三次优化计算,得到Q195钢圆坯结晶器锥度曲线。优化后的圆坯结晶器内腔呈抛物线形状,总锥度1.88%/m。在分析工艺条件下,使最大气隙降低为0.021 mm。     

Thermomechanical finite-element model of shell behavior in continuous casting of steel

A coupled finite-element model, CON2D, has been developed to simulate temperature, stress, and shape development during the continuous casting of steel, both in and below the mold. The model simulates a transverse section of the strand in generalized plane strain as it moves down at the casting speed. It includes the effects of heat conduction, solidification, nonuniform superheat dissipation due to turbulent fluid flow, mutual dependence of the heat transfer and shrinkage on the size of the interfacial gap, the taper of the mold wall, and the thermal distortion of the mold. The stress model features an elastic-viscoplastic creep constitutive equation that accounts for the different responses of the liquid, semisolid, delta-ferrite, and austenite phases. Functions depending on temperature and composition are employed for properties such as thermal linear expansion. A contact algorithm is used to prevent penetration of the shell into the mold wall due to the internal liquid pressure. An efficient two-step algorithm is used to integrate these highly nonlinear equations. The model is validated with an analytical solution for both temperature and stress in a solidifying slab. It is applied to simulate continuous casting of a 120 mm billet and compares favorably with plant measurements of mold wall temperature, total heat removal, and shell thickness, including thinning of the corner. The model is ready to investigate issues in continuous casting such as mold taper optimization, minimum shell thickness to avoid breakouts, and maximum casting speed to avoid hot-tear crack formation due to submold bulging.     

结晶器内坯壳应力分析方法的优化

在考虑连铸坯壳应力遗传特性的基础上,建立了结晶器内坯壳的二维应力分析模型,利用ANSYS的初应力方法实现了坯壳应力遗传行为分析。分析结果表明,与传统应力模型相比,遗传分析模型坯壳的位移和应力分布规律基本相同,但应力值存在明显差距。拉速对坯壳应力存在显著影响,而浇注温度影响很小;在正常范围内锥度对坯壳热应力的影响较小。     

Heat flow,gap formation and break-outs in the continuous casting of steel slabs

A theoretical investigation of heat flow and gap formation in the mold of a continuous slab caster has been undertaken using a mathematical model, with the ultimate purpose of predicting the casting conditions which can lead to break-outs. The mathematical model that has been developed for this study is capable of treating the heat flow and air gap as coupled phenomena, and can accept operating variables such as slab size, casting speed, mold taper, and thermal conductivity of the mold powder, as input. Four different cases of slab casting have been investigated; and it has been found that hot spots can form on the surface of the slab within a few centimeters of the corners. Depending on their temperature, it is suggested that these hot spots may give rise to the formation of break-outs off the corners of the slab. From an examination of the behavior of the hot spots, the susceptibility of the cases studied to break-outs has been evaluated. The usefulness of the present analysis in qualitatively ascertaining the location and extent of mold wear under different casting conditions has also been examined. A. Grill was formerly affiliated.