工艺参数对电渣重熔空心钢锭凝固过程影响的数值模拟

凝固过程的控制对于保证和提高钢锭的质量十分重要,电渣重熔空心钢锭过程的凝固控制主要是对电渣重熔过程中金属熔池形状和深度进行控制,尤其以熔池深度作为凝固控制的主要参数.本文基于ANSYS和CFX软件对电渣重熔空心钢锭的凝固过程进行数值模拟研究,通过改变渣池深度、电极插入深度、电极布置方式来比较不同工艺参数对电渣重熔空心钢锭金属熔池形状的影响.模拟结果表明,在相同输入功率下,随着渣池深度的增加,金属熔池逐渐变浅;随电极插入深度的加深,金属熔池逐渐变深;十电极布置方式比八电极布置的金属熔池深,但渣/金界面的温度变化相对较小.     

基于数值模拟的镍基高温合金电渣重熔工艺优化

利用MeltFlow软件对镍基高温合金电渣重熔过程进行数值模拟计算,探究了电渣重熔过程中温度场、流场、熔池形貌及微观组织的分布特点,通过工业试验验证模拟的准确性,定量分析熔速对熔炼过程的影响规律,提出了一种改善铸锭凝固质量的工艺优化方法.结果 表明,渣池内的温度相对较高且分布均匀,熔池形貌近似"V"型.铸锭一次枝晶间距...     

纯钛VAR熔池形貌和凝固组织模拟及其工业验证

运用ANSYS和μMat Ic软件分析了980 mm纯钛锭VAR过程中熔池形貌以及凝固组织的变化规律。模拟计算结果表明:起弧阶段的熔池很小,呈浅U型;随后熔池形貌由U型逐渐变为V型;当坩埚内热量输入与输出达到平衡时,熔炼进入稳定阶段,熔池深度和宽度不再变化;补缩过程中,熔池不断缩小直至消失。凝固组织的变化规律为:与坩埚壁接触的钛液快速冷却形成细晶组织;随着熔炼的进行,以枝晶形状生长的部分细晶粒最终形成具有一定择优取向的柱状晶;铸锭中心区域和液固临界区域,晶粒直接在金属液内形核并长大,形成的等轴晶粒阻碍了柱状晶的生长,发生柱状晶-等轴转变。通过解剖工业铸锭验证,熔池形貌和凝固组织与数值模型的计算结果相吻合。     

利用元胞自动机法模拟电渣重熔钢锭定向凝固组织

本文应用元胞自动机法发展电渣重熔钢锭组织结构的计算模型,建立基于高斯分布的连续形核模型和生长模型;在节点上采用元胞自动机法(CA)对钢液凝固进行形核和生长计算.结果表明:电渣重熔钢锭凝固组织结构主要由柱状晶构成,在底部有一个垂直的柱状晶带,两边有一个延伸的倒Ⅴ形柱状晶带.本文还考查了电极熔速、渣池温度等工艺参数对温度场...     

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。     

抽锭电渣重熔过程的流场和温度场的分布规律

建立抽锭电渣重熔过程多物理场三维数值模型,采用商业软件ANSYS对抽锭电渣重熔体系的流场和温度场进行了模拟计算。比较分析了不同电极浸入深度和不同渣池深度下抽锭电渣重熔过程的流场、温度场和金属熔池结构。通过实验测定抽出结晶器时的钢锭表面温度,验证了模拟结果的准确性。研究结果表明,抽锭电渣重熔过程的渣池内有2对漩涡生成,一对大的漩涡逆时针转动,另外一对小的漩涡顺时针转动;熔渣的速度随着电极浸入深度的增加而增大,随着渣池深度的增加而减小;渣池内有2个高温区,渣池内的温度高于金属熔池的温度;抽锭电渣重熔体系(电极、渣池和钢锭)的温度随着电极浸入深度的增加而上升,随着渣池深度的增加而下降。     

电渣重熔板锭的温度场计算

建立了电渣重熔板锭过程的非稳态模型,计算了板锭重熔过程中的温度场,得到不同熔速、不同重熔时刻的熔池深度;分析了影响熔池深度的主要因素及板锭的凝固规律,计算表明:熔速是影响熔池深度的最大因素,当铸锭到达一定高度时,系统处于准稳定状态,熔池深度不再变化.同时铸锭底部的冷却条件对熔池深度影响不大.     

导电结晶器电渣重熔中非金属夹杂物的去除

导电结晶器电渣重熔渣池局部发热密度最高值在电极角部和结晶器壁附近,电极端部下方仍存在"高温区",对非金属夹杂物去除提供热力学与动力学条件。电渣重熔过程中非金属夹杂物的去除主要发生在自耗电极端头熔滴形成阶段以及熔滴穿过熔渣层阶段。综合自耗电极端部熔化至熔滴形成过程阶段、熔滴滴落并穿过渣池至金属熔池阶段和金属熔池至铸锭凝固非金属夹杂物的上浮阶段的去除率,导电结晶器电渣重熔去除非金属夹杂物的能力不低于传统电渣重熔。     

旋转电极电渣重熔过程熔滴滴落及熔池形状的模拟

建立了瞬态三维耦合数学模型以探索旋转电极对电渣重熔过程中电磁场、流场、温度场和熔池形状的影响。通过求解麦克斯韦方程组得到电磁场的相关信息,利用VOF方法描述金属熔滴的运动,采用焓-多孔介质模型计算凝固过程。当电极旋转,金属熔滴在离心力作用下,从电极边缘抛出,增加了金属熔滴在渣池中停留的时间与沿途路径,有利于提高电渣重熔工艺的精炼效率。模拟结果表明,随着电极旋转,熔滴数量增多,尺寸变小,渣池内的温度分布变得均匀,当电极的转速由0 r/min提高至20和50 r/min,熔池深度由81 mm降至78和61 mm,熔池形状逐渐变得浅平,有利于提高电渣重熔铸锭的质量。     

Ti2AlNb合金锭真空自耗过程宏观偏析的数值模拟

Ti₂AlNb合金锭的真空电弧重熔 (VAR) 是一种超高温且不透明冶金过程,很难对这一过程中的熔体流动行为和宏观偏析的形成过程进行试验研究。发展了基于欧拉多相流的电磁场、温度场、流场、溶质场的多场强耦合数学模型,研究了真空自耗过程中的多物理场相互作用机制,对Ti₂AlNb合金锭中成分偏析形成过程及分布规律进行了预测。模拟结果表明,电磁力主要分布于熔池表面,自感电磁力推动金属液由中心向下流动而加深熔池;搅拌电磁力的离心效应则大幅提升熔池的温度场均匀度,促使熔池内金属液中的溶质混合均匀。尽管铸锭外围和中心分别形成了大范围的正、负偏析区,但区域内的成分较为均匀。在搅拌和沉降的作用下,金属熔池中的等轴晶极大地缩短了铸锭中的柱状晶区。该模型的模拟结果在熔池深度与宏观偏析分布方面与试验结果吻合良好,可进一步应用于预测和研究工业级大型铸锭中的成分偏析。     

电渣重熔连续定向凝固René88DT镍基合金锭工艺参数的计算

René88DT镍基合金(%:0.02～0.05C、15.5～16.5Cr、3.8～4.2Mo、≤0.20Ta、12.5～13.5Co、0.6～1.0Nb、0.025～0.050Zr、3.5～3.9Ti、2.0～2.4Al、0.006～0.015B、3.8～4.2W、0.005～0.010Ce)母合金棒由200 kg真空感应炉熔炼,并按照凝固组织显微结构要求,通过控制铸锭凝固的二次枝晶间距和金属熔池形状及深度来确定重熔时熔化的速度,再通过热平衡计算得到相关的熔炼参数,由500 kg气氛保护抽锭式电渣重熔炉按连续定向凝固工艺熔炼出Φ160 mm×220 mm René88DT合金锭结果表明,计算重熔总时间与实际时间的误差仅为4.5%,熔池浅平,凝固组织均匀细小,获得了全〈100〉方向的柱状晶组织,二次枝晶间距为60～80μm。     

Microstructure homogeneity of high speed steel M2 ingot by electroslag remelting

The homogeneity of the microstructure in M2 high speed steel ingot with a diameter of 400mm was studied by means of electroslag remelting process combined with numerical simulation. The microstructure differences between the center and the edge of the ingot were compared. The effects of local solidification time on eutectic carbides were discussed. The result shows that the size of the eutectic colonies varies from 100??m to 400??m near the center of the ingot, and lamellar eutectic carbides can reach a maximum thickness of tens of microns, and a length of more than 100??m. The maximum local solidification time is about 1300s at the center of ingot by calculation. Close to the edge of the ingot, the columnar crystals become small, and the size of eutectic colonies is among 50-200??m, and eutectic carbide lamellae are about 10??m in width, and tens of microns in length. The local solidification time at the edge of ingot is as short as 365s. When solidification of the ingot becomes quasi- steady state during electroslag remelting, the metal pool is pot- bottom- like. The pool depth is about 178mm by experiment, and the calculated pool depth is in accordance with that of experiment.     

The Cellular Automata Model of Electroslag Remelting Ingot Structure

Electroslag remelting (ESR) is an advanced process for the production of high quality steels. The microstructure of remelted steel which affect the mechanical properties and the performance of the ingot was determined by the technological parameters. A two-dimensional axisymmetric geometry which was established in this paper was divided into macro-grid finite element in order to compute temperature field; then the grid was divided into more detailed and uniform cells, and at last the continuous nucleation model based on the Gaussian distribution and KGT growth model was established for nucleation and growth calculations using cellular automaton method (CA) on the solidification of molten steel. The results show that: a vertical columnar grain zone and a inverted V-shaped columnar crystal zone appeared in the ESR ingot. In addition, the temperature field with different electrode melting rate and slag pool temperature parameters and the microstructure with different average nucleation under cooling and maximum grain density were studied in this paper. The simulation results agree well with the experimental results, so it is proved that the model and calculation method is reliable. To produce ideal solidified ingot and achieve the purpose of optimizing the production process, the production process was adjusted according to the simulation results.     

Electromagnetic stirring with alternating current during electroslag remelting

An alternating current (AC)-operated electromagnetic stirring (EMS) device, using line frequency, was designed and built to operate on a laboratory electroslag remelting (ESR) furnace for 150-mm-diameter ingots. Laboratory-scale experiments were conducted employing both 4340 alloy steel and INCONEL 718 alloy as electrode material. The initiation of stirring is accompanied by a thin strip of segregated material and favors the formation of spot segregation. Changes produced in the fluid flow conditions in the liquid pool ahead of the solidification front result in a transition from a highly directional columnar to an unoriented, branched structure. Except for small pockets of segregated liquid, the flow of molten metal does not penetrate into the mushy zone. Both electrode material and molten metal pool shape play an important role on the extent of promoting an equiaxed structure.     

Distribution law of flow field and temperature field in electroslag remelting withdrawal process

A three- dimensional mathematical model was developed to describe the interaction of multiple physical fields during the electroslag remelting withdrawal (ESRW) process. Flow fields and temperature fields of the ESRW system were simulated by commercial software ANSYS. The flow fields, temperature fields and the shapes of the molten pool during the ESRW process with different electrode immersed depths and slag heights were analyzed and compared. The temperature of ingot surface was measured, and the accuracy of simulation results was verified. The results show that there are two pairs of vortexes in slag bath during the ESRW process. A pair of large vortexes turns counterclockwise, and another pair of small vortexes rotates clockwise. The speed of slag increases with the increasing of immersion depths of the electrode, and decreases with the increasing of slag heights. There are two high temperature zones in the slag bath, and the temperature in the slag bath is higher than that in the metal bath. The temperature of ESRW system (electrode, slag bath and ingot) becomes higher with the increasing of immersion depths of the electrode, whereas becomes lower with increasing of slag heights.     

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.     

Effects of relative motion between consumable electrodes and mould on solidification structure of electroslag ingots during electroslag remelting process

Abstract

Steel solidification process control, especially in the solidification process of high alloy steel, and improvement of the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the advantage of the ingot solidification structure, the effects of relative motion between the consumable electrodes and the mould (namely, mould rotation) on chemical element distribution were observed in this study, as well as the compact density changes in electroslag ingots. Experiment results show that applying relative motion between the mould and the consumable electrodes in ESR results in a more uniform chemical element distribution in the electroslag ingots. Compared with the electroslag ingot of conventional ESR, maximum segregation of carbon could decrease from 3·19 to 1·146, and statistical segregation decreased from 0·2636 to 0·0608. Maximum segregation of chromium could decrease from 1·316 to 1·253, and statistical segregation decreased from 0·2753 to 0·1201. The compact density for the stationary mould increased from 0·7693 to a compact density of 0·9501 for the rotating mould. The improvement in the solidification structure of the electroslag ingot can be attributed to mould motion, which led to the generation of a shallow pool and the improvement of the solidification structure. But the excessive rotation rate is harmful to solidification structure instead due to the molten metal pool motion caused by violent slag pool motion.     

Study on Factors Affecting the Structure of High SpeedSteel Ingot Produced by ESR

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结晶器旋转数值模拟及对高速钢电渣锭碳化物的影响

为了改善M2高速钢中的碳化物分布,通过数值模拟详细分析了结晶器旋转对M2高速钢电渣重熔过程温度场、金属熔池形状的影响,并进一步通过实验室双极串联结晶器旋转电渣炉研究了旋转速率对M2高速钢电渣重熔过程的影响。采用扫描电镜观察并分析了结晶器旋转对电渣锭中碳化物形貌、分布的影响;采用小样电解萃取实验,分析了结晶器旋转速率对碳化物组成的影响。结果发现,随着结晶器旋转速率的增加,渣池的高温区从芯部向边部迁移,温度分布更加均匀;金属熔池的深度变浅,两相区的宽度收窄,从而导致局部凝固时间降低、二次枝晶间距减小。与此相对应,随着结晶器旋转速率的增加,M2电渣锭的渣皮更薄、更加均匀,结晶器对电渣锭的冷却强度更大,碳化物网格开始破碎、变薄,碳化物由片状改变为细小的棒状。X射线衍射分析表明,不论结晶器是否旋转,碳化物的类型始终不变,由M₂C、MC和M₆C组成,但是随旋转速率增加M₂C含量增加,MC和M₆C含量降低。碳化物组织得以改善的主要原因在于,结晶器旋转导致金属熔池深度降低、两相区宽度收窄,改善了凝固条件,减轻了元素偏析。