电渣重熔精炼过程数值模拟研究进展

电渣重熔技术在高品质特殊钢的生产中占据重要地位.由于电渣重熔过程的复杂性以及现场测量条件的限制,数值模拟已成为解析其过程现象和机制的必要手段.主要综述了电渣重熔过程数值模拟的研究进展,包括电磁场、流场、传热、凝固、宏观偏析、精炼反应和夹杂物去除等,还涉及到了导电结晶器、旋转电极、加压电渣重熔、电渣接续制备双合金和电渣重...     

电磁搅拌对电渣重熔钢锭温度场的影响

建立了电磁搅拌条件下电渣重熔钢锭凝固过程数学模型。利用Visual Basic编程模拟分析了旋转电磁搅拌下15Mn钢的电渣重熔凝固过程,结果表明:未施加磁场时,模拟结果与实验结果较吻合;施加磁场时,电磁搅拌加强了钢液内部传热,熔池变平坦,有利于消除电渣锭宏观偏析和缩孔等缺陷,同时有利于晶核发展成等轴晶组织。     

Modeling of Electromagnetic Field and Liquid Metal Pool Shape in an Electroslag Remelting Process with Two Series-Connected Electrodes

A three-dimensional finite-element model has been developed to understand the electromagnetic field and liquid metal pool shape in an electroslag remelting (ESR) process with two series-connected electrodes. The magnetic vector potential is introduced into the Maxwell’s equations, and the nodal-based method is used to solve a three-dimensional harmonic electromagnetic field. The heat transfer of the solidifying processes of ingot is modeled by a source-based enthalpy method, and the Joule heating is included in an inner source. The results show the main part of the current flows through the slag cap and a little enters into ingot in a two-series-connected electrode ESR system. As the interaction of self-induced and mutual-induced of two electrodes occurs, the skin effect is significantly suppressed by the neighbor effect. A symmetrical pattern of magnetic flux density in a two-series-connected electrode ESR system is displayed. The magnetic flux density between two electrodes is reinforced and reduced at the outside of two electrodes. The maximum Joule heat power density is located at the interface of slag and electrodes, and it decreases with an increase of the electrode immersion depth. The averaged Joule heat power density increases when slag cap thickness is reduced. With the increase of ingot height, the liquid metal pool shape changes from arc shaped to “V” shaped. When the ingot height is more than the diameter in the ESR processes, the liquid metal pool shape is constant.     

电流对电渣重熔过程多场耦合行为和凝固参数影响的数值模拟

利用了FLUENT软件建立了电渣重熔(ESR)过程二维轴对称瞬态模型.使用有限体积法求解耦合的电磁场、动量和能量守恒方程,铸锭的凝固过程由焓-多孔介质模型处理,系统地研究了电流对电渣重熔GH984G凝固过程多场耦合行为和凝固参数的影响规律.模拟结果表明:电流由2.3kA增大为2.5kA,体系中电流密度、磁感应强度、洛伦...     

电极填充比对电渣重熔过程影响的数值模拟

利用有限元分析软件ANSYS求得稳定电渣重熔过程电极、渣池和钢锭系统电磁场和焦耳热场分布,并通过计算流体力学软件FLUENT模拟分析了耦合电磁场和焦耳热场的三维电渣重熔过程电极填充比0.3~0.7对电渣重熔系统温度场、速度场和电磁场的影响。结果表明,随着电极填充比的增加,速度最大值和湍动能最大值逐渐增加,但变化速率随填充比增加而下降;填充比0.3和0.5之间的最大湍动能差值约为填充比0.5和0.7之间湍动能的2倍;温度最大值随填充比不是单调变化的。     

Mathematical Model for Electroslag Remelting Process

 A mathematical model, including electromagnetic field equation, fluid flow equation, and temperature field equation, was established for the simulation of the electroslag remelting process. The distribution of temperature field was obtained by solving this model. The relationship between the local solidification time and the interdendritic spacing during the ingot solidification process was established, which has been regarded as a criterion for the evaluation of the quality of crystallization. For a crucible of 950 mm in diameter, the local solidification time is more than 1 h at the center of the ingot with the longest interdendritic spacing, whereas it is the shortest at the edge of the ingot according to the calculated results. The model can be used to understand the ESR process and to predict the ingot quality.     

电渣重熔空心钢锭技术的开发

 首先总结和评价了大型筒体的制造方法,以及不同方法生产空心钢锭的优缺点,重点分析了传统电渣重熔法生产空心钢锭存在的主要问题。在此基础上,与乌克兰Elmet-Roll公司合作开发了基于双电源、T型导电结晶器和电极交换的电渣重熔空心钢锭的新技术。成功地试制了多个钢种（35CrMo、P91、TP347和Mn18Cr18N等）和不同规格（[?]900/[?]500 mm、[?]900/[?]200 mm、[?]650/[?]450 mm,最长锭尺寸为6 000 mm）的电渣空心钢锭。工业试验表明,生产的空心锭表面质量和内部质量优异,结晶组织致密,洁净度高,是生产高端厚壁管和筒体锻件的理想材料。     

60 t电渣炉结晶器冷却水流速计算-设计优化和重熔不锈钢的应用

采用传热学理论对大型电渣炉结晶器冷却强度的影响因素进行了分析,计算得出直径1 800 mm结晶器的最佳水流速为1.2 m/s,并提出了套层厚度为10 mm的高速水套型结晶器优化设计方案,经电压77.5 V,电流19 kA,熔速31. 6 kg/min,水流1. 2 m/s,重熔60 t 0. 030C-17.16Cr-11.80Ni-2.55Mo-0.072N奥氏体不锈钢电渣锭的生产结果表明,电渣锭成型良好,表面光洁,渣皮分布均匀,改善了电渣锭成型质量。     

Magnetohydronamic and thermal behavior of electroslag remelting slags

The paper is based on the development and use of a mathematical model that simulates the electroslag remelting (ESR) operation. The model assumes axisymmetrical geometry and steady state. Maxwell equations are first solved to determine the electromagnetic forces and Joule heating. Next, coupled fluid flow and heat transfer equations are written for the two liquids (slag and liquid metal). Thek-ε model is used to represent turbulence. The system of coupled partial differential equations is then solved, using a control volume method. Using the operating parameters as inputs, the model calculates the current density, velocity, and temperature throughout the fluids. This paper is concerned with fluid flow and heat transfer in the slag phase. After being validated by comparing its results with experimental observation, the model is used to evaluate the influence of operating variables, such as the fill ratio, and the thermophysical properties of the slag.     

Assessment of Oxygen Control and Its Effect on Inclusion Characteristics during Electroslag Remelting of Die Steel

Deoxidation during electroslag remelting of S136 die steel was experimentally studied. The characteristics of inclusions in the electrode and ESR ingots were determined by image analyzer and SEM‐EDS. The results show that the oxygen content can be reduced from 89 ppm in the electrode to the lowest (12 ppm) in the ingot only when protective Ar gas remelting in combination with specially designed slag deoxidation treatment were employed simultaneously. The proportion of the oxygen combined as oxide inclusions increases with decreasing the total oxygen content in ESR ingot. The original inclusions in the electrode are mainly large (Mn,Cr)S and the large inclusions in the form of Al₂O₃ core surrounded by an outer sulfide layer, besides a few pure Al₂O₃ inclusions. After ESR process, while only pure Al₂O₃ inclusions with the size of about 1 µm were observed in ESR ingots. The large inclusions in the electrode were removed during ESR process. With higher oxygen content in the ingot, the contents of inclusions and large inclusions would be relatively higher. The results from industrial experiments have confirmed the availability of the present oxygen control technique. The mechanisms of oxygen behavior and control as well as inclusion evolution during ESR process were proposed based on experimental results along with thermodynamic analysis.     

大型钢锭电渣重熔工艺数学模型的建立及模拟计算

 基于传热学基本理论,建立了80 t级三相电渣炉大型钢锭电渣重熔过程数学模型,并通过工业生产75t TP316LN奥氏体不锈钢钢锭验证模型,研究了大型电渣钢锭温度场分布情况及二次晶间距的变化情况。结果表明：渣池中心部位温度达1800℃,自上而下沿着传热方向中心线温度逐渐降低;金属熔池最深处达1500mm,大约等于钢锭直径的0.8倍;金属熔池上方具有50mm圆柱段以保证渣皮薄而均匀;二次枝晶间距大小由钢锭外侧边缘向中心部位呈递增趋势,模拟结果与实际生产情况吻合。     

Review of mathematical models of fluid flow,heat transfer,and mass transfer in electroslag remelting process

Abstract

The electroslag remelting (ESR) process has been used effectively to produce large ingots of high quality based on the controlled solidification and chemical refining that can be achieved. Despite the widespread application of industrial facilities, there are still issues that prevent an effective control of the process. This is particularly critical considering the large ingots produced industrially which makes the traditional trial and error approach prohibitively expensive. Thus, mathematical models of the process are a good alternative as a process control tool. To predict the relationship between operating parameters such as power input and type, fill ratio, depth of electrode immersion, and slag chemistry and the casting rate, microstructural features, and ingot chemical composition, it is then necessary to develop mathematical models based on differential equations describing the fluid flow, heat transfer, and mass transfer phenomena that take place during the process. In the present paper, mathematical models of the transport phenomena occurring during ESR are reviewed. Although the models have evolved to a point where several features of the process can be predicted and the dominant transport mechanisms have been elucidated, more effort is required before the models can be applied to define actual operating conditions.     

Heat transfer and fluid flow phenomena in electroslag refining

A mathematical formulation has been developed to represent the electromagnetic force field, fluid flow and heat transfer in ESR units. In the formulation, allowance has been made for both electromagnetically driven flows and natural convection; furthermore, in considering heat transfer the effect of the moving droplets has been taken into account. The computed results have shown that the electromagnetic force field appears to be the more important driving force for fluid motion, although natural convection does affect the circulation pattern. The movement of the liquid droplets through the slag plays an important role in transporting thermal energy from the slag to the molten metal pool, although the droplets are unlikely to contribute appreciably to slag-metal mass transfer The for-formulation presented here enables the prediction of thermal and fluid flow phenomena in ESR units and may be used to calculate the electrode melting rates from first principles. While a detailed comparison has not yet been made between the predictions based on the model and actual plant scale measurements, it is thought that the theoretical predictions are consistent with the plant-scale data that are available.     

大型冷轧辊的电渣重熔工艺研究

电渣重熔(ESR)钢能显著改善冷轧辊质量,提高轧辊使用性能。通过对电渣重熔工艺的系统研究,在国产10t大型电渣重熔炉上开发了以递减功率模型为核心的钢锭结晶质量控制,渣皮厚度控制和防止增氢等先进工艺技术。采用该技术的重熔电耗为1 400(kW·h)/t,所生产的产品质量稳定,各项性能指标达到比国家标准更为严格的企业内控标准,得到用户好评。     

USS122G钢锭真空电弧重熔工艺的数值模拟

 超高强度不锈钢以其超高强度和良好的韧性以及优异的耐腐蚀性能而广泛地应用在航空、航天等领域。真空自耗重熔(VAR)作为生产超高强度不锈钢铸锭的主要生产技术,具有去除钢中有害杂质、改善钢中元素偏析的功能。为了研究新型Cr-Co-Ni-Mo合金体系超高强度不锈钢USS122G的真空电弧重熔过程,通过工艺仿真优化软件(Melf-Flow-VAR),对VAR过程的宏观传热、传质和流动现象进行模拟,建立USS122G合金VAR过程的二维轴对称数学模型,预测了不同冷却速度下的温度场和熔池形貌,并着重分析了特定熔速下的温度场、流场的演变,有无氦气冷却的元素宏观偏析情况,最后以模拟工艺制备了USS122G合金660 mm铸锭进行验证。结果表明,熔速增加,熔池深度加深,熔池形貌由低熔速扁平状圆弧状高熔速深“U”变化,熔炼速率为4.5 kg/min的熔池形貌具有较窄的糊状区,在此熔速下,熔池形貌呈现圆弧状,且真空自耗炉的输入功率较低,流场模拟结果显示流体的流动方向沿边部向下,中部向上,在铸锭右侧呈现顺时针运动规律;模拟熔池在达到稳态后深度为132 mm,此时模拟熔池深度与实测结果基本一致;在熔炼过程中Cr和C元素均发生正向偏析,采用氦气冷却的铸锭中元素偏析程度较小,在距钢锭1/2R处到边部Cr和C元素分布规律与模拟结果吻合较好。本项研究成果为钢的工业化稳定生产提供了可靠的数据支撑。     

Macro- and Microstructure Evolution of 5CrNiMo Steel Ingots during Electroslag Remelting Process

A comprehensive mathematical model was established and used to simulate the macro and microstructure evolution during the production process of 5CrNiMo steel ingot by electroslag remelting （ESR） method. Along the ingot height, the macrostructure distribution characteristics changed from vertical, fine columnar grains to tilted, coarse columnar grains, and this transformation process occurred at the very beginning of ESR. In the cross section of the ingot, there were three grain morphology regions and two grain type transition regions from the outside to the center of the ingot. These regions were the fine columnar grain region, columnar competitive growth transition re gion, coarse columnar grain region, columnar to equiaxed grain transition （CET） region, and coarse equiaxed grain region. The influence of the remelting rate on the macrostructure and mlcrostructure was investigated using a series of experiments and simulations. The results showed that a low remelting rate could produce a small grain growth angle （GGA） ; the average secondary dendrite arm spacing （SDAS） firstly decreased and then increased as the remelting rate increased. An excessively high or low remelting rate can increase the GGA and average SDAS in ingots. Thus, the remelting rate should be controlled within a suitable range to reduce composition microsegregation and microshrinkage in the ingot to produce an ESR ingot with satisfactory hot forging performance.     

电渣冶金技术的最新发展趋势

简要回顾了电渣重熔工业生产50年的发展历史,重点对近年来电渣冶金新技术进行了介绍和评价,包括快速电渣重熔,双极串联电渣连铸技术,特厚板坯电渣重熔,大型电渣重熔钢锭凝固偏析控制,可控气氛电渣炉和电渣液态浇铸技术。在新的发展阶段,电渣冶金技术向高效、节能、环保和满足更高质量方向发展。     

电渣重熔板锭过程中温度场的动态模拟

根据钢的电渣重熔过程的特点,建立了板锭电渣重熔的非稳态模型,以模拟在不同重熔速度下板锭重熔过程的温度场和分析影响金属熔池深度的因素。模拟结果表明:横截面尺寸400 mm ×2000 mm,20 t板锭重熔过程中,当重熔速度3～5 mm/min时,重熔速度越大,熔池深度越深;当重熔锭的高度达到铸锭厚度的2倍左右时,系统处于准稳定状态,熔池深度不再变化。     

Heat transfer and fluid flow phenomena in electroslag refining

A mathematical formulation has been developed to represent the electromagnetic force field, fluid flow and heat transfer in ESR units. In the formulation, allowance has been made for both electromagnetically driven flows and natural convection; furthermore, in considering heat transfer, the effect of the moving droplets has been taken into account. The computed results have shown that the electromagnetic force field appears to be the more important driving force for fluid motion, although natural convection does affect the circulation pattern. The movement of the liquid droplets through the slag plays an import-ant role in transporting thermal energy from the slag to the molten metal pool, although the droplets are unlikely to contribute appreciably to slag-metal mass transfer. The for-formulation presented here enables the prediction of thermal and fluid flow phenomena in ESR units and may be used to calculate the electrode melting rates from first principles. While a detailed comparison has not yet been made between the predictions based on the model and actual plant scale measurements, it is thought that the theoretical predictions are consistent with the plant-scale data that are available. Presently on leave from Institute of Chemical Engineering and Technology, Punjab University, Lahore-1, Pakistan.     

Directional solidification of aluminum-nickel eutectic alloys using electroslag remelting

Attempts were made to produce directionally solidified, specifically grain aligned Al-6 wt pct Ni eutectic alloy using a laboratory scale ESR unit. For this purpose sand cast alloy electrodes were electroslag remelted under different mold conditions. The grain structure of the ingots obtained from these meltings showed that insulated silica molds gave the best vertical alignment of grains along the length of the ingot. The NiAl₃ fibers within the grains tended to fan out and there was only a preferred alignment of fibers along the growth direction under the conditions of our experiments. The ESR parameters most suitable for vertical alignment of eutectic grains have been identified. In some electroslag remelting trials ingots were grown on a seed ingot. This resulted in a fewer vertical grains compared to the case when no seed ingot was used. The sand cast specimen of the eutectic exhibited a maximum tensile strength of around 88.2 MN/m² (9.0 kg/mm²) whereas conventional ESR using water cooled mold gave strength value of 98.0 MN/m² (10 kg/mm²). The directionally solidified ESR material showed longitudinal tensile strength as high as 213.7 MN/m² (21.8 kg/mm²) which could be further increased to 220.6 MN/m² (22.5 kg/mm²) by using the seed ingot. The average growth rate was varied between 5 to 25 mm/min during electroslag remelting in this study. The flow stresses, tangent modulus and ultimate tensile strength of directionally solidified eutectic increased with increasing growth rates. Formerly Research Fellow, Indian Institute of Science, Bangalore 560012 is now