锻造用钢锭凝固过程温度场数值模拟及其应用

在分析锻造用钢锭凝固过程特点的基础上,建立起钢锭铸造凝固的二维非稳态温度场计算数学模型,并编制程序。计算结果反映了钢锭铸造凝固过程中温度场分布。利用该程序,可以对钢液在相似结构钢锭模中的凝固温度场进行预测和评价,也可以通过对比来优化钢锭模设计。     

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.     

大型钢锭凝固过程三维数值模拟

开发了大型钢锭凝固过程三维模拟程序。利用本程序对53 t钢锭的凝固过程进行了模拟,预测的钢锭和锭模中典型测试点的冷却曲线、钢锭完全凝固时间及冒口一次缩孔形状等与商用有限元软件ProCAST的计算结果吻合良好。     

大钢锭定向凝固技术研究

本文简述了定向凝固技术的基本原理,介绍了定向凝固钢锭的主要参数H/D和WB/WI的计算原则。通过解剖实验和计算机模拟定性定量地对定向凝固过程的温度分布和凝固速度变化以及影响偏析形成与分布的因素进行了讨论,阐明了定向凝固钢锭工艺参数对实现自然精炼的作用。     

钢锭模表面温度与内部质量对应关系研究

利用红外热像仪和红外测温仪测定了钢锭凝固过程中铸模外表面的温度分布,再通过模拟实验对测温结果进行修正。着重对钢锭表面纵向各代表位置点温度随时间变化的趋势及规律进行了分析,探讨了其与钢锭凝固过程的关系,对可能导致的铸锭缺陷进行了预测。通过数值模拟及生产情况的验证,证明了利用红外测温对钢锭表面测温进行内部质量判定的可行性,可为钢锭凝固模拟与质量控制提供参考。     

钢锭凝固过程中温度场和流场的数值模拟研究

运用商业软件Procast对25 t钢锭凝固过程的流场和温度场进行了数值模拟。钢锭凝固过程的温度分布云图和冷却曲线显示了钢锭凝固过程的一般规律,为预测缩孔、缩松情况提供了参考依据。分析冷却速率曲线和钢液流动情况可知,考虑钢液流动对传热的影响十分重要。     

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。     

第三类边界条件下大型圆柱体钢锭加热速度计算

针对大型钢锭在第三类边界条件下的加热过程进行分析,利用加热时温度沿钢锭横截面的分布变化和由温度梯度导致的钢锭瞬时热应力计算方法,建立了加热过程中钢锭径向、横向和切向的瞬时应力模型。在瞬时应力模型的基础上,根据钢锭在某一温度下的屈服强度和加热炉温度值,提出了控制钢锭加热速度的计算式。用此计算式计算加热工艺参数,可以有效控制钢锭在加热过程的温升速度,避免钢锭在加热过程中产生裂纹,该计算方法已在某特殊钢锻造厂得到实际应用,生产实践证明该方法可行。     

无冒口钢锭凝固过程温度场数值模拟及应用

本文介绍了以数值模拟为工具开发的用于无冒口钢锭凝固过程温度场计算及缩孔、疏松预测的应用软件 ,利用实际生产的无冒口钢锭及所制锻件的质量情况证明了软件的可靠性 ,分析了部分工艺参数对无冒口钢锭内部质量的影响 ,提出了最佳工艺方案。     

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.     

钢锭模帽部结构的优化设计

本文利用数值模拟方法设计钢锭模帽部结构,改变了传统的钢锭模帽部结构设计方法,大大提高了钢锭模帽部结构设计的可靠性和科学性。文中提出了无二次缩孔、最小帽容比的钢锭模帽部结构优化准则,并为短计算机运算时间,建立了一种简易优化方法。通过对鞍钢Fx7.1t钢锭帽部测温实验验证了软件的可靠性。采用计算机提供的设计方案对鞍钢Jc10.66t钢锭模帽部结构进行优化设计,钢锭成坯率提高0.5%。     

数值模拟在大钢锭制造中的应用

针对现有600 t级钢锭模结构,通过理论分析建立了适合低压转子用大钢锭凝固过程中传热及宏观偏析的数学模型。采用有限元数值模拟方法,利用Procast商业软件及自编专用程序分析了钢锭模的冷却条件、高径比、锥度对凝固过程温度分布、缩孔疏松及宏观偏析的影响规律。模拟结果及生产实践表明:现有600t级钢锭模结构比较合理,且数值模拟计算能够为生产提供理论依据与指导。     

A Numerical Study of the Effect of Multiple Pouring on Macrosegregation in a 438-Ton Steel Ingot

In present paper, a ladle–tundish–mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring(MP) process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring(SP) and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.     

Numerical simulation of central shrinkage crack formation in a 234-t steel ingot

Central shrinkage crack is a common defect encountered in steel ingot casting. It is necessary to limit the degree of crack in case of further propagation in forging. A 234-t steel ingot was dissected to check the internal quality, and a central shrinkage crack band of 1,400 mm in height and 120 mm in width, was found at a distance of 450 mm under the riser bottom line. Then, thermo-mechanical simulation using an elasto-viscoplastic finite-element model was conducted to analyze the stress-strain evolution during ingot solidification. A new criterion considering mush mechanical property in the brittle temperature range as well as shrinkage porosity was used to identify the shrinkage crack potential, where the degree of shrinkage porosity is regarded as a probability factor using a modified sigmoid function. Different casting processes, such as pouring speed, mould preheating and riser insulation, were optimized with the simulation model. The results show that fast pouring, proper mould preheating and good riser insulation can alleviate shrinkage crack potential in the ingot center.     

大型钢锭表面夹杂物分布模拟研究

采用基于热焓-多孔介质法、湍流模型、动量和质量守恒方程建立了36 t大型钢锭锭模内钢液流动、传热和凝固的数学模型。采用Lagrange方法通过跟踪单个夹杂物在钢液中的运动,探明表面夹杂物在大型钢锭中的规律性分布,讨论了不同冒口保温条件对夹杂物的去除效果。结果表明,凝固早期,钢液流动强烈,夹杂物容易被先凝固的固相区域捕捉。随着凝固过程的进行,钢液流动减弱,夹杂物以上浮运动为主。加强冒口处保温可大大提高夹杂物的去除率。     

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.     

大型空心钢锭锻造工艺探讨

大型压力容器筒体锻造过程中,使用空心钢锭相比于实心钢锭具有偏析少、材料利用率高、周期短等优点。通过物理模拟和数值模拟相结合的方法,研究了空心钢锭锻造工艺中压下率、拔长V型砧夹角等工艺参数对变形的影响规律和作用效果,以期为大型空心钢锭锻造工艺的制定提供实验依据和理论基础。     

电渣重熔体系内磁场的数学模拟

基于Ｍａｘｗｅｌｌ方程组及有关的电磁场理论，提出了更切合实际情况的电渣重熔体系内磁场的数学模型，并应用于结晶器直径２００ｍｍ的实验室重熔装置．对直径７６ｍｍ低碳低合金钢电极的重熔过程（３０００Ａ（有效值），ＣａＦ２＋３０ｍａｓｓ％Ａｌ２Ｏ３＋２０ｍａｓｓ％ＣａＯ渣系），结果表明，磁场强度的幅模在电极内沿端部锥体形成方向不断增大，至接近锥顶处达最大值，约为２．６×１０４Ａ／ｍ，此后在渣池、锭子熔池、液固两相区和固态锭子内沿轴向向下逐渐减小；沿半径方向，在电极和渣池内呈现一峰值，在液、固金属区内则单调增大至边界条件限定值．对在直径１４０ｍｍ的结晶器中以直径８０ｍｍ的电极和ＣａＦ２＋ＣａＯ＋Ａｌ２Ｏ３＋ＭｇＯ渣系生产高速钢（Ｍ２）锭的过程，以该模型估计的重熔体系渣池和金属熔池内磁场强度（幅模）的大小和分布与实测结果较相吻合．该模型可作为研究电渣重熔体系内熔体流动，传热和传质过程的基础．     

A Coupled Cellular Automaton–Finite-Element Mathematical Model for the Multiscale Phenomena of Electroslag Remelting H13 Die Steel Ingot

A coupled cellular automaton–finite-element mathematical model has been developed to investigate the multiscale phenomena of the electroslag remelting (ESR) H13 steel ingot. The heat transfer equation is solved to obtain the temperature distribution and liquid metal pool profile by a coarser finite-element (FE) mesh. Then, a regular network of square cells with a much finer scale is drawn for the simulation of microstructure with the cellular automaton (CA) technique. The continuous nucleation, which is based on the Gaussian distribution, is implemented to describe the heterogeneous nucleation. The growth kinetics of the dendritic tip is taken into account by the Kure–Giovanola–Trivedi model. At each time step, the temperature at the CA cell locations is interpolated from the temperature at four adjacent FE elements. The solute transfer is calculated using the FE method. Moreover, the evolution of the multiscale phenomena with growing of the ingot is considered by the varying boundary conditions. A reasonable agreement is demonstrated between the calculation and experiment. The results indicate that the shallow U-shaped metal pool would change to the deep V-shaped metal pool with the growing of the ingot. The vertical columnar grains appear at the bottom of the ingot, and an inverse V-shaped grain structure can be observed at the upper part of the ingot. It can be inferred that improving the undercooling can refine the microstructure and motivate the growing of the columnar grain during the ESR process.