Novelty in the ESR process of making large hollow ingots

The development of the formation of hollow ingots is briefly reviewed. The reasonability of application of large electroslag remelting hollow ingots, including the replacement of the forged and rolled metal of shells and rings by the low-deformed or even as-cast ESR metal, is shown. Data are presented on ESR of commercial hollow ingots produced by the remelting of short consumable electrodes exchanged in remelting.     

真空电渣重熔炉发展前景的探讨

真空电渣重熔炉是在真空电弧重熔炉和气体保护电渣炉的基础上发展起来的一种冶炼高性能合金的特殊真空重熔冶金装备。真空电渣重熔炉冶炼的钢种和合金有优质合金钢,高温合金,精密合金,耐蚀合金,铝、钛、银等合金。介绍了真空电渣重熔炉的工作原理,冶金特点,比较了真空电弧重熔、普通电渣重熔和真空电渣重熔的钢材的冶炼成本、冶金质量和性能,并讨论了真空电渣重熔炉的应用前景。     

High Nitrogen Austenitic Stainless Steels Manufactured by Nitrogen Gas Alloying and Adding Nitrided Ferroalloys

 A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe Cr Mn Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 069% in 18Cr18Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 081%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 μm. After homogenization of the hot rolled plate at 1 150 ℃×1 h followed by water quenching, the microstructure consisted of homogeneous austenite.     

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...     

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。     

现代电渣重熔先进技术特征与演进

 电渣重熔是制备高端特殊钢和合金的关键冶炼工艺,在铸锭质量和成材率方面优势明显。随着中国装备制造业的快速发展,对所用钢及合金的质量和性能要求不断提高,而传统电渣重熔技术面临电耗高、产品质量稳定性差等问题。现代电渣冶金技术的发展核心在于浅平熔池形状的稳定控制和杂质元素的高效去除,目标是更高洁净度、更高凝固质量和更高生产效率。为了让国内冶金工作者了解目前电渣重熔技术的最新发展动态,助力中国电渣冶金技术的开发和应用,综述了近年来国内外相继涌现的先进技术与理论,分析了国内外在相关技术的应用特征和演进方向。中国在电渣炉设备制造、气体保护电渣重熔技术、同轴供电技术和结晶器导电技术方面基本与国际先进水平同步,但尚未形成完善可靠的渣系配置理论、精炼过程的热力学及动力学理论,较国外仍有差距,这已成为限制电渣产品质量提升的主要因素之一。低频电源技术、真空电渣重熔技术和旋转电极电渣重熔技术具有极高的工业化应用前景,需要进一步明确其对工艺过程和产品质量的影响规律。摆动控制已成为国际先进电渣企业的主流控制技术,却是中国电渣炉设备制造的短板,借助在线检测和模拟仿真技术的恒熔池形状控制技术是中国电渣冶金控制技术的发展方向。     

Possibility of producing multilayer ingots by electroslag remelting

A new method is proposed for the production of multilayer ingots by electroslag remelting of a composite electrode consisting of different steel grades. This method differs from the well-known technology in electrode rotation, which makes it possible to substantially decrease the transition zone length. A scheme is suggested to produce a thick bimetal plate.     

Electroslag remelting of the metal wastes of nickel alloys

The electroslag remelting (ESR) of the metal wastes of nickel alloys is studied. It is shown that the chemical composition, physicomechanical properties, and service properties of the formed castings meet the requirements of the specifications for these alloys. ESR workpieces are used as a charge for remelting in a vacuum induction furnace according to a standard technology.     

Control of Hydrogen During ESR Process

Experimental and numerical studies were carried out for the behavior of hydrogen in a three-phase electroslag furnace using double electrode series technique during electroslag remelting (ESR) process. The effect of water vapor content of furnace gas on the hydrogen content of ingots was studied through the “gas-slag-metal” osmosis experiment. Based on the experimental results, a mathematical model was set up for the behavior of hydrogen pick-up during ESR process. Then the flow of furnace gas during ESR process was studied through a commercial code FLUENT, and the relationship between the water vapor content of furnace gas and argon gas flux in practical production was derived. Finally, the desired reasonable argon gas flow for controlling the hydrogen content of ingots below 2×10^?6 in practice was obtained.     

电渣炉智能控制系统的开发与应用

递减功率熔炼控制被认为是保证电渣炉钢锭质量的有效的控制方法。根据电渣工艺优化的要求，开发了基于递减功率熔炼控制为核心的电渣炉智能控制系统。该系统具备连续有载调压和电极插入位置精确控制的功能。系统在近20台工业电渣炉上得到应用，实际运行结果表明系统可靠性高、运行稳定、人机界面好、易于操作和维修，能达到预期的各项工艺操作控制要求，特别是在保证钢锭结晶质量、降低电耗和加快生产节奏方面效果明显。     

Effect of Slag on Inclusions During Electroslag Remelting Process of Die Steel

Many factors influence the non-metallic inclusions in electroslag steel including furnace atmosphere and inclusions’ content in the consumable electrode, slag amount and its composition, power input, melting rate, filling ratio, and so on. Fluoride containing slag, which influences the non-metallic inclusions to a great extent, has been widely used for the electroslag remelting process. The current paper focuses on the effect of fluoride containing slag on the inclusions in electroslag ingots based on the interaction of the slag-metal interface and electroslag remelting process. In this work, die steel of CR-5A and several slags have been employed for investigating the effect of slag on inclusions in an electrical resistance furnace under argon atmosphere in order to eliminate the effect of ambient oxygen. Specimens were taken at different times for analyzing the content, dimensions, and type of non-metallic inclusions. Results of quantitative metallographic analysis indicate that a multi-component slag has better capacity for controlling the amount of inclusions; especially protective gas atmosphere has also been adopted. The findings of inclusions in electroslag steel by SEM–EDS analysis reveal that most non-metallic inclusions in electroslag steel are MgO-Al₂O₃ inclusions for multi-component slags, but it is Al₂O₃ inclusions when remelting using conventional 70 wt pct CaF₂-30 wt pct Al₂O₃ slag. The maximal inclusions’ size using multi-component slags is less than that using conventional binary slag. Small filling ratio as well as protective gas atmosphere is favorable for controlling the non-metallic inclusions in electroslag steel. All the results obtained will be compared to the original state inclusions in steel, which contribute to choice of slag for electroslag remelting.     

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。     

Effect of TiCN-Ti modifiers on the chemical composition of nickel alloys

The effect of nitrogen-containing modifiers on the variations in the chemical composition of nickel alloys during electroslag refining and vacuum induction remelting has been discussed.     

电渣连铸技术的开发

在结合电渣重熔和连铸技术优点的基础上。东北大学钢铁冶金研究所采用双极串联、交换电极及在线切割等技术，在国内首次成功地开发了电渣连铸（ESCC）技术；解决了电渣重熔钢锭直径小于300mm时熔速很慢、冶炼费用很高的难题。通过对重熔方坯质量的低倍、高倍、夹杂物检验等分析表明，该技术生产的方坯表面质量和内部质量良好，具有广泛应用前景和经济价值。     

700℃超超临界锅炉材料617B合金铸态组织及均匀化工艺

利用光学显微镜、扫描电镜和能谱分析对采用真空感应熔炼和保护气氛电渣重熔双联工艺生产的617B合金电渣锭进行组织分析、析出相和元素偏析情况研究.依据残余偏析指数模型通过Dictra热力学软件计算提出七种不同的均匀化制度,并结合均匀化后的组织分析和热模拟压缩试验,确定了617B合金的最终均匀化制度.结果表明:经双联工艺生产的617B合金电渣锭中存在枝晶和元素偏析,其中Mo和Ti是主要的偏析元素;电渣锭组织的晶内存在较多的块状碳化物,表现为多种碳化物共生生长.经过1210℃保温48h均匀化处理后,枝晶和元素偏析基本消除,晶内的块状碳化物部分溶解,且均匀化后的合金表现出良好的塑性.      

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.     

Effect of Noncontact Ultrasonic Technology on Solidification Quality of Electroslag Steel

A new electroslag furnace with ultrasonic vibration introduced through water-cooled base plate was designed and the effects of ultrasonic power on the distribution of elements,compactness and carbides in the electroslag remelting(ESR)ingots was investigated.The results showed that the distribution of elements on the entire excitation section changed with the change of ultrasonic power under experimental conditions.The statistical segregation of elements was minimum when the ultrasonic power was 500 W,whereas excessively high or excessively low power was not conducive to the uniform distribution of elements.Meanwhile,the compactness of ESR ingots gradually increased with the increase in ultrasonic power and distribution of compactness was the most uniform when ultrasonic power reached 500 W.Further increase in the ultrasonic power was not conducive to the improvement of compactness.The distribution characteristic of carbides was similar to the distribution of elements and compactness.The results indicated that the ultrasonic vibration introduced through water-cooled base plate was advantageous in improving solidification quality.However,this method needed reasonable ultrasonic power.Moreover,the effects of ultrasonic power varied for different elements.     

电渣重熔技术在中国的应用和发展

中国电渣冶金起步于１９５８年,至今,全国所有特殊钢厂都建立了电渣重熔车间,拥有工业电渣炉８６台,年生产能力１０万ｔ,产品包括估质合金 与超级合金２４３个牌号。     

Modeling of flow and temperature distribution in electroslag remelting withdrawal process for fabricating large-scale slab ingots

Currently, the market demands for large-scale and high-quality slab ingots are increasing significantly.A novel electroslag remelting withdrawal (ESRW) process with two series-connected electrodes and a T-shaped mould was developed to produce large-scale and high-quality slab ingots.It is very difficult to ob-tain large slab ingots with good surface quality and high width-to-thickness ratio.And it is not efficient for improving the quality of slab ingots by using trial-and-error-based approaches because the ESRW mecha-nisms are very complex.Thus, a three-dimensional mathematical model was developed to determine the relationship between process parameters and physical phenomena during the ESRW process.The relation-ship between the temperature field of the ESRW process and the surface quality of slab ingots was estab-lished.A good agreement between the simulated and measured temperature fields of slab ingots was ob-tained.The results indicate that the maximum values of current density, electromagnetic force and Joule heat all occur at the electrode-slag interface between the two electrodes.It can be found that the flow is turbulent and the temperature distribution is uniform in the slag pool with the influences of buoyancy and electromagnetic force.The wrinkles in the narrow faces of slab ingots are caused by the relatively lower in-put power.Increasing the electrode width and reducing the curvature can significantly improve the surface quality of slab ingots.     

Physicochemical comparison of electroslag remelting with consumable electrode and electroslag refining with liquid metal

The paper is devoted to comparison of electroslag remelting (ESR) with consumable electrode and electroslag refining with liquid metal (ESR LM) processes. The possibility of rearrangement of the heat contributions coming from the consumable electrode and current supplying mould (non-consumable electrode, CSM) makes the core of the ESR process organisation in the CSM. The usage of liquid metal instead of consumable electrodes allows to reduce liquid bath temperature and volume in order to provide low segregation ingot. The formal assessment of physico-chemical conditions and experimental measurements of desulphurisation have shown the same level of refining ability of both processes. Replacing the classic ESR by the ESR LM is a prospective way to produce high-quality ingots from sophisticated and hard-to-deform materials, whereas manufacturing of the consumable electrodes is technically problematic and costly.