旋转电极电渣重熔过程熔滴滴落及熔池形状的模拟

摘要：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0r/min提高至20和50r/min,熔池深度由81mm降至78和61mm,熔池形状逐渐变得浅平,有利于提高电渣重熔铸锭的质量。     

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。     

电极更换对电渣重熔过程传热和熔渣凝固的影响

建立了电渣重熔轴对称瞬态耦合模型，研究了电极更换对电渣重熔过程中电磁场、流场、温度场、热平衡和电极端部熔渣凝固行为的影响。结合旋转矢量法和谐波法对电磁场求解，采用动态网格技术描述铸锭生长，建立渣池与电极间的瞬态导热模型，准确预测电极熔化速率。结果表明，原电极脱离后，0～100 s,渣池表面热损失最多增加了2.1倍，热平衡改变，渣池温度从1 933.3 K降低到1 720.3 K,熔池轮廓向内缩紧，且外侧变化更明显。在新电极加热阶段，电极端部形成一层固态渣壳，热源恢复，渣池温度从1 720.3 K增加到1 901.2 K,渣壳由外侧向内熔化。结合响应面分析法，重熔电流、电极预热温度均与固态渣熔化时间呈正相关，原电极脱离时间呈负相关，其中重熔电流影响最为明显。     

多电极电渣重熔系统电磁场和焦耳热场研究

多电极电渣重熔系统比单电极系统具有感抗小、电耗低、熔化率高等特点,目前广泛应用于生产大型钢锭.掌握多电极电渣重熔系统中电磁场的分布情况对于提高钢锭质量和节省电能都很重要.本文以多电极电渣重熔工艺中电极、渣池和钢锭为研究对象,建立了能够考虑集肤效应的三维谐波电磁场数学模型,采用Maxwell方程、Lorentz定律和Joule定律分析了渣、钢锭和电极的磁场、电磁力、电流密度和焦耳热功率密度分布.结果表明:电流的最大值出现在电极内侧,与渣池的交界面处;由于电极的自感和互感的相互作用,两对电极内侧的磁感应强度增大,外侧的磁感应强度减小;焦耳热的最大值出现在渣中,电极底部内侧与渣的交界处.参数研究还发现:当源电流增大时,在电极内靠近壁面处的电流呈线性增大;当频率大于等于35 Hz时,在电极内部电流密度趋向线性分布;当电极侵入深度增大或渣层的厚度减小时,渣池中焦耳热的最大值增大.     

电渣重熔过程渣池流场数值模拟

采用商业软件ANSYS和FLUENT建立了电渣重熔过程渣池流场数学模型,分析了电渣重熔过程电磁力和热浮力共同作用下渣池流动行为,以及典型电渣重熔工艺参数(电极形貌、插入深度、填充比和电流强度)对电渣重熔过程渣池内流场的影响规律.结果表明:电磁力有利于渣池内产生逆时针涡流,浮力有利于渣池产生顺时针涡流.电极端部形貌对渣池流动影响较大,当电渣重熔电流均为5 000 A,频率为50 Hz时,平头电极所在渣池内同时存在逆时针涡流和顺时针涡流,锥形电极所在渣池内只存在逆时针涡流.电极填充比和电流都对渣池内流动行为影响较大,减小电极填充比和增大电流强度都会使渣池内逆时针涡流增加.     

电渣重熔9CrMoCoB钢过程电极表面氧化行为及脱氧制度

非保护气氛电渣重熔9CrMoCoB钢过程中，电极表面氧化生成的氧化铁皮进入渣池，导致渣池氧势升高，造成金属熔池中易氧化元素发生严重烧损。为降低渣池氧势以提高易氧化元素收得率，冶炼过程中需向钢中加入适量脱氧剂。首先利用热重分析仪研究了不同温度下9CrMoCoB钢高温氧化行为，建立相应氧化动力学；其次对试样氧化皮进行XRD和SEM-EDS分析；最后基于上述实验和非保护气氛电渣重熔过程中电极表面温度分布，提出较优脱氧制度。结果表明，低温(500～700℃)9CrMoCoB钢氧化增重量可忽略；中温(900～1000℃)氧化增重由快速氧化期的直线规律阶段和扩散控制的抛物线规律阶段两段组成；高温(1100～1200℃)氧化增重呈抛物线规律。不同温度下，9CrMoCoB钢高温氧化速率k=exp(44.1317-40163.707/46⁽(h+0.33))+723.15)；氧化皮呈复层结构，外层为铁的氧化物和内层为铁铬复合氧化物相；冶炼过程中，9CrMoCoB电极(直径75mm)每5min带入渣池FeO为9.02g，为完全还原带入的FeO，加入纯Si为1.75g，可避免易氧化元素...     

电渣重熔过程渣/金界面行为的模拟

建立了电渣重熔体系下三维数学模型,以电渣重熔渣池、钢液为研究对象,利用Fluent商业软件,基于VOF多相流模型,对电渣重熔系统渣金两相流场进行模拟计算.计算结果表明:熔炼初期,金属电极采用薄膜熔化,从两端开始熔化并以小液滴的形式掉落,随着熔炼的进行,电极中部也开始产生小熔滴,最终在中心处形成一个大熔滴掉落,此后进入稳定熔炼期.对比不同电极端部形状,电极端部为圆头时比电极端部为平头时熔滴更容易在电极中心汇聚,渣金界面波动更大;对比不同电极插入深度,插入位置浅,熔滴通过渣层时间长,渣金界面波动更大;对比不同熔速,熔速为0.15 kg/s时,熔滴产生后,一滴一滴不连续掉落,这样熔滴可以与渣充分反应;加大熔速至0.20 kg/s时,可见熔滴成股流下,大熔速下,熔滴进入金属熔池时速度较大,渣金界面波动更大.     

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。     

T型结晶器抽锭电渣重熔高速钢90 mm方锭新工艺

 晶界处碳化物严重影响高速工模具钢的红硬性和耐磨性能,电渣重熔工艺能够有效地改善钢锭中碳化物尺寸及分布。传统电渣重熔生产较小钢锭的截面尺寸约为[?]200 mm,减小钢锭截面尺寸和增大冷却速率将会进一步减轻碳化物的偏析程度,但将降低生产效率、提高生产成本。采用双极串联、T型结晶器、抽锭电渣重熔新工艺生产90 mm方锭,并与相同熔化速度传统电渣重熔生产[?]200 mm钢锭进行对比试验。对钢锭成分、低倍、夹杂物、显微组织进行检验分析结果表明,90 mm方钢锭中碳化物尺寸和分布明显优于[?]200 mm钢锭,碳化物在后序锻造或轧制过程中更容易被破碎。新工艺电耗也低于传统电渣重熔工艺。     

振动电极电渣重熔过程中流场、温度和熔池形状的参数化研究

文章探究了电极直径变化时电渣重熔系统温度场、速度场、液滴和熔池形状的变化规律。结果表明:随着电极直径的增大,渣池中的高温区开始由振动电极的正下方向电极两侧转移,高温区的范围逐渐扩大,渣池温度整体升高,渣池温度变得均匀。当渣厚为140mm时,随着电极直径由100mm增加到140mm时,水平振动下,渣池内最高温度增加了36K,渣池内平均温度增加了52K;无振动下,渣池内最高温度增加了39K,渣池内平均温度增加了54K;竖直振动下,渣池内最高温度增加了22K,渣池内平均温度增加了49K。另外,熔池形状变浅,糊状区变薄,熔池整体下移。     

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.     

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.     

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.     

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。      

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。     

Observations of melt rate as a function of arc power,CO pressure,and electrode gap during vacuum consumable arc remelting of Inconel 718

Statistically designed experiments were conducted at two different production melt shops to evaluate the influence of arc power, CO pressure, and electrode gap on melt rate. Approximately 11,000 kg of Inconel 718 alloy 0.4 m diameter electrodes were vacuum consumable arc remelted into 0.5 m diameter ingots. Analysis of the experimental results revealed that melting efficiency (melting rate/kW) was maximized when CO pressure and electrode gap were held at low levels. Under these conditions, the heat distribution (created by the vacuum arc) on the electrode tip and the molten pool exhibited macro uniformity. Increased CO pressure and/or electrode gap depressed the melt rate, and at 13.3 Pa (100 microns) and a 0.050 m electrode gap, this depression exceeds 46 pct. Increasing these parameters also changed the arc behavior to that of a constricted arc with a highly localized heat input. It is hypothesized that the change from the usual diffuse arc to this constricted arc results in intense Lorentz pumping in a localized region of the molten pool atop the ingot causing fluid flow transients. These transients could, in turn, create solidification defects.     

Numerical investigation on the fluid flow and heat transfer in electroslag remelting furnace with triple-electrode

Electroslag remelting (ESR) furnace with triple-electrode is always used to produce large ingots and the process complexity makes the application not widely spread. Thus, a transient three-dimensional coupled model in industrial scale has been developed to investigate the coupled magneto-hydrodynamics two-phase flow and heat transfer in system. Different from the previous studies with multi-electrode, the current work reveals the triple-electrode ESR with the formation of metal droplets and the solidification of liquid metal. Compared with single-electrode system with the same fill ratio, the heat source in the slag pool with triple-electrode is much more dispersive, and the U-shape metal pool in the ESR furnace with triple-electrode is much shallower and flatter than the V-shaped one in the single-electrode system. A shorter distance from each electrode to the center of system brings a higher heat efficiency, as well as a deeper and narrower metal pool.     

Numerical Study on the Effect of Low-Frequency Power Supply on Desulfurization in the Electroslag Remelting Process

In the electroslag remelting (ESR) process, low-frequency power supply can significantly reduce power consumption and achieve three-phase balance of power supply. Therefore, a transient coupling model of fluid flow, heat transfer, and component transport in the ESR process, which is coupled to the electromagnetic field calculated using Maxwell 3D software, is established to study the influence of low-frequency power supply on desulfurization. When a 50 Hz power supply is used, a skin effect is observed in the metal, and the direction of the Lorentz force at the slag/metal interface changes. However, this effect becomes less pronounced with decreasing current frequency. Sulfur is mainly transferred at the electrode tip, and the desulfurization rate is approximately 50%. Electrochemical reactions mainly occur at the electrode tip/slag interface and the metal pool/slag interface. The removal rate of sulfur using direct current (DC) power supply is less than that using an alternating current power supply. The DC reverse polarity power supply leads to higher desulfurization rate than DC straight polarity, which is 74% and 31%, respectively. The sulfur removal rate increases from 81.37% to 84.59% as the frequency decreases from 50 to 2 Hz because of the longer electrochemical reaction time at this lower frequency.     

AOD炉渣熔化温度的实验研究

利用炉渣半球点测定法,测定了宝钢不锈钢分公司炼钢厂AOD炉（120 t）氧化期渣和终渣的熔化温度,研究了AOD炉渣熔点的影响因素。结果表明,对于AOD氧化期渣,碱度和氧化镁对炉渣熔点影响不大;渣中w(TFe)在97%～20%之间变化时,增加渣中全铁可使炉渣熔点明显升高;渣中w(Cr2O3)从225%增加到30%,可使炉渣熔点升高140 ℃。对于AOD终点脱硫渣,当R＝14～18时,炉渣熔点随碱度的增大而显著升高;脱硫渣R＝18时,w(CaF2)加入12%～13%则炉渣熔点显著降低;AOD还原渣R＝16时,w(CaF2)加入95%～10.5%可显著降低炉渣熔点。