大型铸锭的宏观偏析及其数值模拟

宏观偏析是金属凝固过程中产生的不可避免的缺陷,且难以通过热处理消除,会导致金属制品不同部位的组织和力学性能有差异.因凝固时间长且熔体流动复杂,大型铸锭的宏观偏析尤为严重.A型偏析的形成主要与夹杂物上浮有关,而V型偏析的形成机制较为复杂,普遍认为形成于铸锭凝固的后期.连铸过程中采用脉冲磁致振荡技术可大大减轻大型铸锭的宏观...     

电磁离心凝固过程中宏观偏析的数值模拟

基于连续模型建立了非惯性坐标系下电磁离心凝固过程流动、传热、传质耦合数学模型．依此模型对Al-5％Cu合金进行了模拟计算．结果表明，电磁离心凝固过程中，电磁力使熔体的平均径向运动速度下降．熔体流动状态的改变使凝固合金外层的逆偏析减轻，凝固过程中两相区的负偏析也减轻．与普通离心铸造相比，电磁离心凝固可减轻铸件宏观偏析．模拟结果与实测铸件成分分布基本吻合，表明本数学模型较好地描述了电磁离心凝固过程．     

铸造钢锭宏观偏析的数值模拟

铸钢凝固过程的溶质再分配是产生宏观偏析的根本原因.利用数值模拟技术,对一个采用垂直定向凝固工艺的钢锭进行了铸造过程模拟分析,考虑了材料参数和边界条件的非线性特征,以及凝固过程中液态金属的自然对流和溶质扩散,预测了钢锭各部位的凝固时间和硫元素宏观通道偏析的位置和偏析程度,模拟结果与相关文献的实验结果基本一致.模拟结果表明,为保证钢锭质量,应从优化钢锭结构和铸造工艺两方面入手,达到减轻宏观偏析、提高钢锭利用率的目的.     

Numerical Simulation of Macro-Segregation in Steel Ingot During Solidification

A mathematical model coupling the momentum, energy and species conservation equations was proposed to calculate the macro-segregation of Fe-C alloy ingot during solidification. The corresponding simulation software which concurrently solves the macroscopic mass, momentum, energy and species conservation equations has been developed by applying the SIMPLE algorithm. The thermo-solutal convection in a NH4 Cl-H2O ingot is verified and the result shows good agreement with that reported. Then macro-segregation in a steel ingot is simulated by using the developed program. The steel ingot is in a rectangular mold with a riser. The fluid flow is mainly induced by the temperature field and the solid fraction. The macro-segregation pattern is mainly affected by the thermo-induced convection in the mushy zone. The negative segregation forms along the walls of the casting. The positive segregation forms at the top center of the casting into the riser. The species concentration reaches the peak in the center of the ingot where solidification ends lastly.     

钢锭凝固过程温度场数值模拟

本研究采用大型商业软件MSC.Marc建立了38t钢锭凝固传热数学模型,模型中的钢热物性参数是通过钢凝固过程微观偏析模型预测钢锭凝固过程相的变化规律,并根据钢锭凝固过程钢热物性参数与相组成之间的关系式来确定.随后采用红外测温试验验证了钢锭凝固传热数学模型,并模拟了钢锭凝固过程温度场变化规律以及不同浇注温度和冒口保温条件对钢锭凝固过程的影响.结果表明:钢锭凝固过程由钢锭底部向冒口逐渐凝固,随着钢锭冒口发热剂的加入,钢锭凝固末期,最后凝固区域逐渐从无发热剂情况时位于钢锭本体向冒口区域移动.38t钢锭4125V2钢可采用向浇注后冒口加入200 mm厚发热剂增强钢锭凝固末期钢液补缩能力,脱模时间为浇注后12.5 h.     

大型钢锭凝固数值模拟与试验研究

利用Procast软件包对6t钢锭的凝固过程进行了计算机模拟,并预测了钢锭的缩孔疏松分布,计算结果发现原有工艺中钢锭的缩孔深度大,轴线疏松严重.将模拟结果与试验结果进行对比,两者吻合良好.在此基础上,研究了绝热板和发热剂对钢锭的缩孔疏松分布的影响,优化了绝热板工艺.模拟与试验结果表明,优化后的绝热板加发热剂工艺可显著改善钢锭冒口的保温效果,减小缩孔深度,提高钢锭的质量和利用率.     

大钢锭凝固过程的数值模拟研究

运用大型商业软件MARC的有限元分析法,对85 t S34MnV大型钢锭凝固过程的温度场分布进行了数值模拟计算分析,基于模拟结果进行了工业试验.模拟结果表明,钢锭的凝固趋势在轴向上由钢锭底部向钢锭顶部逐步推进,径向上由四周向中心慢慢延伸.通过对不同浇注温度下的钢锭凝固过程进行数值模拟,得出适当提高钢锭的浇注温度可以延长凝固时间,这有利于夹杂物的上浮.工业试验结果表明,提高钢锭模初始温度50℃后,冒口夹杂物总量与钢锭底部夹杂物总量的比值提高了约0.63％,验证了模拟结果.     

中空侧壁保温定向凝固过程温度场数值模拟

为了优化宽厚板钢锭的生产工艺,以铸造模拟软件ProCAST为平台进行不同中空间距侧壁保温下钢锭温度场数值模拟,研究中空间距对45 t大型钢锭定向凝固过程的影响。模拟结果表明,中空侧壁对钢锭定向凝固具有明显的保温作用,抑制了侧壁传热;当中空厚度为4 mm时保温效果最好,延长了全凝时间,从而提高了宽厚板钢锭的质量。     

铸造凝固过程宏观偏析数值模拟研究

宏观偏析普遍存在于铸造合金凝固过程中,严重影响了材料的使用性能。本文利用宏观偏析数学模型,分别对53 t钢锭和500 t铸件宏观偏析进行数值模拟研究。模型考虑了凝固收缩与等轴晶沉降,模拟结果和实验结果吻合较好。     

铸锭凝固过程温度场的数值模拟

为改善钢锭头部保温性能,利用有限元分析软件ANSYS对模铸低合金钢凝固过程的温度场进行了数值模拟。重点讨论了绝热板热导率、发热板生热率对钢锭头部保温性能的影响。结果表明,绝热板热导率符合保温材料的性能指标;将发热板生热率调整为不低于5.185×107 W/m3时能满足钢锭头部保温要求。     

锻造用钢锭凝固过程温度场数值模拟

采用三维瞬态传热有限元方法,对13 t锻造钢锭和钢锭模在凝固过程中的温度场分布进行了数值计算及分析,探讨了钢锭内部凝固速度变化和钢锭模在凝固过程中的温度分布规律。分析结果表明,钢锭本体距离底部60%-70%的部位纵向凝固速度受横向凝固速度的影响而大大加速;凝固开始阶段,钢锭模内壁温升速度远大于模外壁,随后外壁温升速度迅速增大,随着钢锭凝固的进行,壁内外温差逐渐减小。本模拟可为优化钢锭模设计、提高钢锭质量提供依据。     

连铸过程溶质元素宏观偏析的数值模拟

采用商业软件CALCOSOFT模拟了实际连铸冷却条件下铸坯内部的温度场、流场和溶质场的分布。为了对模拟结果进行验证,将实际铸坯进行了刨屑化学成分检测。结果表明：模拟的宏观偏析结果与实际铸坯中检测的情况极为相似。凝固初期自然对流可能引起较大的内部紊流,将凝固前沿溶质带到中心液相起到了稀释作用;在凝固末期,糊状区显著阻碍了液相的流动,自然对流非常微弱,不能将枝晶间的浓化液相带到中心,大大减小了溶质元素向中心聚集的程度。     

铸钢锭凝固过程数值模拟和缩孔缩松预测

用有限元法对22t钢锭凝固过程进行了模拟,计算中采用了Galerkin方法和八节点等参数单元,同时考虑钢锭和锭模界面上初期紧密接触和后期气隙形成过程中界面热阻的变化。建立的模型具有通用性,能够处理各种不同类型的边界条件和变热物性参数,用等效凝固收缩量法预测钢锭冒口部位缩孔的位置和大小,用经适当修正后的G/(?)参数(G-温度梯度,R-冷却速度)预测钢锭内部缩松。计算温度与实测温度基本吻合。     

锻造用钢锭凝固过程热应力场数值模拟

采用三维瞬态传热有限元方法,对13t锻造钢锭在凝固过程中的温度场和热应力场分布进行了数值计算及分析,探讨了钢锭在凝固过程中的应力分布规律.分析结果表明,在钢锭凝固初期,钢锭模内部承受压应力,外部承受托应力.由于凝固收缩,钢锭在凝固初期外表面受拉应力的作用.随着凝固的进行,锭模的热应力值不断下降.凝固结束时,钢锭呈表面受压心部受拉的应力分布状态.在凝固过程中,钢锭在反向圆弧处的收缩量最小,小倒角处的收缩量最大.本模拟可为优化钢锭模设计、提高钢锭质量提供依据.     

合金凝固过程再辉现象的数值模拟

本文采用二元合金的等温相场模型,在假定温度在计算区域空间上保持一致的情况下耦合计算热平衡方程,以Al4.5%Cu合金为例模拟了在不同冷却速率下二元合金凝固过程的枝晶生长过程及其再辉现象.结果表明:利用相场模型可以逼真地模拟二元合金过冷熔体中的枝晶生长过程,与试验得到的枝晶形貌吻合较好;凝固潜热和冷却速率显著影响枝晶的生长行为,再现其凝固过程的再辉现象,模拟的结果与经典枝晶生长理论相吻合.     

Numerical Simulation of Macrosegregation Caused by Thermal–Solutal Convection and Solidification Shrinkage Using ALE Model

Solidifi cation shrinkage has been recognized as an important factor for macrosegregation formation. An arbitrary Lagrangian–Eulerian(ALE) model is constructed to predict the macrosegregation caused by thermal–solutal convection and solidi-fi cation shrinkage. A novel mesh update algorithm is developed to account for the domain change induced by solidifi cation shrinkage. The velocity–pressure coupling between the non-homogenous mass conservation equation and momentum equation is addressed by a modifi ed pressure correction method. The governing equations are solved by the streamline-upwind/Petrov–Galerkin-stabilized fi nite element algorithm. The application of the model to the Pb-19.2 wt%Sn alloy solidifi cation problem is considered. The inverse segregation is successfully predicted, and reasonable agreement with the literature results is obtained. Thus, the ALE model is established to be a highly effective tool for predicting the macrosegregation caused by solidifi cation shrinkage and thermal–solutal convection. Finally, the effect of solidifi cation shrinkage is analyzed. The results demonstrate that solidifi cation shrinkage delays the advance of the solidifi cation front and intensifi es the segregation.     

数值模拟技术在大型铸钢件生产中的应用

大型铸钢件在实际生产中易产生缩孔缩松、应力变形等缺陷。本文采用清华大学机械工程系开发的FDM／FEM集成分析系统，对马钢双板轧机机架及5000t油压机横梁凝固过程中的温度场、应力场进行了模拟分析，并根据模拟结果对工艺进行了改进。按照制定的工艺进行实际生产，均一次浇注成功。     

Direct Numerical Simulation of Solid Deformation During Dendritic Solidification

Deformation of the semisolid mush during solidification is a common phenomenon in metal casting and can lead to defects such as hot tears, macrosegregation, and porosity. The morphology of the solidifying mush, including the shape of the dendrites and the distribution of grain boundaries, plays a key role in determining its mechanical behavior. In the current study, a polycrystalline phase-field model is combined with a material point method stress analysis to numerically simulate the fully coupled dendritic solidification and elasto-viscoplastic deformation behavior of a pure substance in two dimensions. It is shown that solid compressive and shear deformations result in variations in the crystallographic orientation angle within a single dendrite that, in turn, affect the subsequent solidification behavior. Shearing of a dendritic structure occurs primarily in relatively narrow bands near or inside the grain boundaries or the thin junctions between different dendrite arms. The deformations can cause the formation of low-angle tilt grain boundaries inside of individual dendrite arms. In addition, grain boundaries form when different arms of a deformed single dendrite impinge. During compression of a high-solid-fraction dendritic structure, the deformations are limited to a relatively thin layer along the compressing boundary. The compression causes consolidation of this layer into a fully solid structure that consists of numerous subgrains.     

数值凝固模拟在大型铸钢件生产中的应用

利用华铸 CAE/ Inte CAST软件对 JGL - 6 80六辊矫直机下机架进行了数值凝固模拟 ,在此基础上对其铸造工艺进行了优化。生产结果表明 ,采用改进工艺方案生产浇注出的下机架完全符合图纸和产品质量要求     

基于均衡凝固理论的锌锭模铸造工艺数值模拟

基于铸件均衡凝固理论,拟定锌锭模铸件的浇注方案及浇注系统的设计计算;然后利用Pro/E和Procast软件,模拟锌锭模铸件的浇注工艺过程.对比结果表明,两者基本吻合.通过模拟可以预知铸件可能产生的铸造缺陷,优化铸造工艺.