电渣重熔中的脱氧热力学

 为了研究电渣重熔的脱氧制度,基于熔渣的离子分子共存理论,以模具钢和脱氧剂铝为研究对象,根据渣 金反应中各组元的质量守恒定律和热力学平衡定律,构建了电渣重熔中的脱氧热力学模型。模型结合试验得到了钢中各个合金元素的热力学平衡质量分数随脱氧剂铝添加量的变化关系,并依据模具钢的合金成分要求对脱氧剂铝的添加量进行了分析。结果表明,钢中硅、铝、锰和渣中氧化铝的平衡质量分数随着脱氧剂铝的增加呈升高的趋势,而渣中氧化硅、氧化铁、氧化锰呈降低趋势;考虑到模具钢中各个合金元素的成分要求,脱氧剂铝的添加量不宜超过1.7 kg/t(钢)。     

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.     

气体保护电渣重熔过程中电渣锭的洁净化控制

进一步提高电渣重熔过程钢的洁净度是提高最终钢材综合机械性能的关键环节之一.本文探讨了洁净钢电渣重熔过程的几个重要方面.降低钢中总氧和硫含量,减少钢中非金属夹杂物是洁净钢生产的重要任务.本文还介绍和讨论了电渣冶炼洁净钢过程中氧、硫和夹杂物控制的相关理论及最新研究结果.     

渐变式电压、电流电渣重熔工艺分析

为了研究渐变式电压、电流电渣重熔工艺对铸锭组织性能的影响,以45号钢为试验原料,采用低倍腐蚀、光学显微镜(OM)、扫描电子显微镜(SEM)、拉伸力学试验等手段,对比了传统电渣工艺与参数渐变工艺对铸锭凝固组织及性能的差异。结果发现,重熔阶段先逐步降低过程电压,待电压降到一定值后,再逐步降低电流,直至结束熔炼,可以减小铸锭柱状晶组织与铸锭轴线的夹角,使铸锭组织倾向于定向凝固,提高铸锭轴线方向的抗拉强度。此外,通过该工艺获得的凝固组织中铁素体量降低,珠光体中层片结构得到明显细化。     

电渣重熔过程电源频率对电渣锭洁净度的影响

电渣重熔采用低频供电可以提高功率因数、降低电耗,并实现电力系统的三相平衡。然而,其对电渣锭冶金质量特别是洁净度的影响还缺乏足够的数据支撑。为了研究电源频率特别是低频操作对电渣重熔锭洁净度的影响,采用实验室小型低频电渣重熔炉,以304奥氏体不锈钢、GCr15轴承钢为研究对象,详细分析了不同的电源频率对电渣锭化学成分、气体含量、夹杂物分布的影响规律。研究结果发现,与工频电渣重熔相比,不论是不锈钢还是轴承钢,当采用低频电源(2、1、0.4、0.1 Hz)电渣重熔后(在其他工艺参数如渣系、渣量、电流、电压、气氛等完全相同的情况下),电渣锭中的氧质量分数(0.010%～0.013%)大幅增加,对氮含量影响很小。电渣锭中的铝含量明显增加,而其他化学成分变化很小。与此相对应,低频电渣重熔锭的夹杂物数量也明显增加,且增加的夹杂物主要以氧化铝为主,但是夹杂物主要以小于10μm的细小夹杂为主,大颗粒夹杂物略有增加,但是数量较少。氧含量增加的主要原因是低频电源的直流倾向增大,使重熔渣池中的氧化铝发生了电解(30%Al₂O₃+70%CaF₂渣系...     

The thermal conductivity of slags used in electroslag remelting

Measurements of thermal diffusivities of solid ESR slags from the system CaF₂ + Al₂O₃ + CaO for temperatures between 200 and 1200°C using laser flash method. Thermal conductivities derived from these data. In the polycrystalline specimens used in this study the radiation conduction is shown to be negligible, heat transfer occurs predominantly by phonon conduction. An appreciable contribution to the thermal conductivity arises from gaseous conduction across pores and microcracks in the specimen. Thermal conductivity decreases with decreasing CaF₂ content.     

Numerical simulation of inclusion movement in electroslag remelting process

A comprehensive three- dimensional mathematical model, which adopted the Euler- Lagrange approach, was developed to study the motion of inclusions in electroslag remelting (ESR) process. The gravity, buoyancy, drag, added mass, lift and electromagnetic pressure forces were taken into account for the solution of inclusion trajectories. Due to the great difference between the conductivity of non- metallic inclusion and molten metal, the non- metallic inclusion would be drove to migrate to the mold wall by the electromagnetic pressure force. The movement behavior and removal rate of inclusions with different diameters were investigated in detail while the current ranged from 1200A to 1800A. The results show that more than 90% inclusions are captured by the top surface of the slag pool and the slag/mold wall. Only a small part of the inclusions are still suspended in the slag, and less than 4% inclusions would pass through slag/metal interface and enter into the metal pool. The removal rate of inclusions with larger diameter is higher than that of smaller diameter in the remelting process. With the increase of the current intensity, the removal rates of the inclusions with all diameters increase.     

不同工艺参数下电渣重熔过程的数值模拟

为研究工艺参数对电渣重熔过程的影响,建立了能够考虑电磁现象并耦合动量和热量传输的三维瞬态数学模型,运用商业软件Fluent进行了模拟研究,计算值与测量值吻合较好。模拟结果表明:在极间距相同的2种工况下,监测点的电流密度值基本相同,说明当渣池深度变化时,可以通过调节电极浸入深度,以符合设定的操作制度。电势降主要发生在渣池区域,渣金界面处的电压仅为0.1V;焦耳热最大值出现在电极端角与渣池接触区域,最小值出现在渣金界面;电磁力最大值出现在电极边角附近,随着纵向深度增加,轴向分量越来越小。极间距为20mm时,电极端角与渣池接触区域的速度和温度均出现最大值,金属熔池深度也最大,其大小分别为0.045m/s,2 250K,41.5mm。     

电渣重熔过程中金属凝固的控制方法

分析了表征凝固质量的各种参数及凝固过程参数对凝固质量的影响.讨论了电极熔化速度与凝固质量之间的关系,及如何计算合理的熔化速度.通过数学模拟计算凝固过程的温度场,进而计算二次枝晶间距是获得合理凝固组织的有效手段.     

S08A自耗电极及电渣重熔工艺试制

本文论述了优化电炉配料、选用优质石灰、精选萤石、电炉出钢换渣工艺;电渣重熔采用四元渣系,选用提纯萤石,重熔过程全程氩气保护铝粒脱氧等工艺措施,生产出低碳、低硅、低氮及残余、五害元素符合要求的自耗电极及电渣锭,经轧制成材检验低倍组织及非金属夹杂物符合技术协议要求。     

国外电渣重熔概况及我国电渣重熔的发展方向

对国外电渣重熔现状进行了概述,并对我国电渣重熔的发展方向提出设想.     

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     

镍基高温合金中硫的危害及电渣重熔脱硫实验研究

镍基高温合金中硫极易在合金晶界和表面处偏聚,导致合金的高温持久寿命和使用稳定性下降.为进一步降低镍基高温合金中的硫含量,分别采用3种电渣重熔工艺对GH4169进行脱硫实验研究.结果表明,大气下重熔的脱硫效果明显,硫含量(质量分数)由18×10-6降低到6×10-6,渣中的硫含量无变化;氩气氛保护重熔不能提高脱硫效果,初始硫含量降至7×10-6逐渐增至9×10-6,渣中硫含量增加明显;氩气氛保护重熔过程中,向渣中加金属钙能够改善脱硫效果,合金中硫含量随钙含量的增加而减少,最低降至3×10-6,合金中实测的w[Ca]-w[S]关系与热力学计算结果基本一致.     

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。铸锭一次枝晶间距从中心到边缘沿径向逐渐减小,而二次枝晶间距没有明显差别。对比试验数据,数值模拟结果误差较小,可以准确预测镍基高温合金电渣重熔过程中的熔池形貌和枝晶间距。随着熔化速率的减小,金属熔池深度降低,ESR铸锭二次枝晶间距逐渐减小,且宏观偏析程度得到改善,黑斑产生概率逐渐降低。控制熔化速率由0.47 kg/min降低至0.45 kg/min,有利于获得凝固质量较好的镍基高温合金电渣重熔铸锭。     

The thermal characteristics of the electroslag process

The heat balance of a laboratory electroslag furnace working in quasisteady state is considered in detail. Results are presented for all possible melting mode combinations of direct and alternating (60Hz) current, with live and insulated molds, in air or argon atmospheres. The material studied is AISI 4340 steel, using a slag of CaF₂ + 25 wt pct A1₂O₃. The temperature and potential fields of the slag are determined, together with heat fluxes in the furnace. Heat balances are given for each subregion of the process, showing good agreement where results are available which permit cross checks of the balance. Suggested explanations are given for the differing behavior of the various melting modes based on variations in effective slag resistivity due to electrochemical reactions, and on variations in current path. The most important factors in determining the ingot heat balance are shown to be the electrode immersion, the slag volume’s dimensions, and the depth of the cylindrical liquid metal head on the ingot. Formerly Graduate Student, Department of Metallurgy, University of British Columbia,.     

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.     

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.     

刀剪材料9Cr14Mo电渣锭尾夹杂物的分析

研究了刀剪材料9Cr14Mo电渣锭尾夹杂物类型、尺寸及含量.结果表明:电渣前及电渣后锭尾的夹杂物主要是含钛的复合夹杂物,电渣后锭尾有内生夹杂物的形成,导致复合夹杂物中Si、Mn、Cr含量升高,电渣后锭尾夹杂物含量升高,且夹杂物尺寸变大.电渣前钢中夹杂物含量为0.633 mg/kg,电渣后锭尾夹杂物含量为4.38 mg/...