Study on the melting characteristics of steel scrap in molten steel

Steel scrap is of great benefit for environmental protection. In converter steelmaking, bottom carbon injection was applied to enhance the scrap ratio and in EAF steelmaking, submerged carbon powder injection was used to accelerate the smelting of scrap. In these two cases, carbon powder is directly injected into molten metal to improve the scrap melting with effective carburization capacity and intense stirring effect. In this study, the induction furnace experiments were carried out to study the melting characteristics of steel scrap with different carbon contents and bottom-blowing gas flow rates. The results show that larger carbon content and faster fluid flow can promote scrap melting because the carburizing reaction can be accelerated by larger carbon concentration gradient and the heat transfer can be enhanced by larger stirring intensity. Finally, the convective mass transfer coefficient and heat transfer coefficient between steel bar and molten metal were also calculated.     

钢液中废钢熔化行为的热模拟试验

废钢熔化过程是控制转炉炼钢过程温度轨迹和废钢比以及电弧炉炼钢能耗和生产率的限制因素.为研究废钢在钢液中的熔化机理,考虑了废钢熔化过程中的传热传质过程,并基于废钢熔化理论分析模型,在实验室中进行了废钢熔化的热模拟试验.研究结果表明,当钢棒浸泡在熔池中较短时间时,钢棒外层形成凝固层.由于激冷效应,在凝固层与钢棒之间形成气隙...     

Kinetics of steel melting in carbon-steel alloys

For the melting of scrap metal in baths with a high carbon content, in which the melting temperature lies below the bath temperature, a model is being developed which is based on the coupling of mass and heat transfer. It will be shown that the mass transport determines the melting rate only for very low bath temperatures. Furthermore, it will be discussed how the melting efficiency is influenced by the supplied energy flow and mass transfer in the bath.     

铁碳熔池中废钢熔化行为的研究进展

在钢铁冶金过程中,逐步减少铁矿石比例、增加废钢比例,实现钢铁循环,已成为世界钢铁行业追求的目标.废钢的熔化行为是控制转炉炼钢过程温度轨迹和废钢比以及电弧炉炼钢能耗和产能的关键因素;同时,铁水包中废钢的熔化行为可能影响铁水预处理工艺的顺利进行.研究废钢的熔化行为对提高废钢在转炉、电弧炉和铁水包等设备中的利用率以及对保证钢...     

Transient heat transfer during initial stages of steel scrap melting

The rates of dissolution of solid pure iron in carbon saturated liquid iron were investigated under nonisothermal conditions. Solid cylindrical specimens were preheated to various temperatures below the liquid bath temperature prior to immersion. The effects of heat transfer were evaluated, including freezing of a carbon-rich iron crust on the specimen which subsequently remelts. An analytical model for the process is derived and the numerical solution is compared with experimental results.     

中国现代电弧炉炼钢废钢快速熔化技术进展

在钢铁行业结构转型关键时期,提高电弧炉短流程工艺比例是降低钢铁行业温室气体排放、脱碳化的有效措施。为了推动短流程炼钢工艺发展,近年来电弧炼钢在废钢快速熔化方面取得明显进展。在回顾前人对废钢熔化速率研究的基础上,全面概述了废钢熔化机理以及影响因素,并结合近年来国内电弧炉炼钢在装备、工艺以及技术上就废钢快速熔化方面取得的进展,探讨了制约电弧炉废钢快速熔化的限制性环节,为废钢快速熔化在电弧炉炼钢装备、工艺、技术方面未来发展提供可行方向。     

废钢熔化的热模试验

 为了解废钢的熔化速度和熔化机理,在250 kg感应炉中进行了热模拟试验。测量熔化速度采用直径为[?20～?50 mm]的Q235圆钢,熔池温度为1 300、1 400和1 600 ℃。根据试棒直径不同确定在熔池中浸泡时间。根据钢棒浸泡前后的质量和尺寸差别,计算出熔池为1 300、1 400和1 600 ℃时,其质量熔化速度分别为1.8～4.0、3.5～6.5和12.6 g/s;径向熔化速度为0.012～0.026、0.035～0.045和0.060 mm/s。熔池液体与试棒之间的对流换热系数在1 400 ℃时为32 931 W/（m2·℃）,1 600 ℃时为32 884 W/（m2·℃）。在温度为1 300 ℃时,碳在液体与试棒之间的对流传质系数为6.3×10－5 m/s,温度为1 400 ℃时为6.4×10－5 m/s。热模拟试验所测得的钢棒熔化速度、液-固相之间的对流换热系数、碳的对流传质系数都与国外冶金工作者的试验结果相近,可以作为炼钢生产中计算废钢熔化的基础数据。     

Aluminium scrap melting under different liquid aluminium flow conditions: part-I: single phase flow

The melting characteristics of aluminium (Al) scrap were studied in a pilot-scale revolving liquid metal tank (RLMT) which sits in a resistance furnace. Commercially pure Al of about 39?kg was melted in the RLMT. Experiments were carried out in a stagnant and in a revolving Al bath at different liquid metal temperatures and speeds. Cylindrical Al 6061 alloy samples were used in this experimental work. Their melting time inside the Al bath was recorded with a specially designed electrical circuit. Upon immersion of a cold cylindrical sample into liquid Al, a shell solidifies around the specimen and subsequently melts back. The time during which the shell exists around the cylinder is called shell period. The free melting period commences when the shell period ends. The thermal contact resistance (TCR) at the Al shell/cylinder interface affects how long the shell lasts. A methodology was developed to estimate this TCR. The convective heat flux from the Al bath to the cylindrical specimen influences the shell and free melting periods, and is a function of liquid Al temperature and speed. The Part I of this research work presents a baseline of Al melting measurements under single phase flow conditions, that will be compared against two phase flow conditions in Part II of this research.

On a étudié les caractéristiques de fusion de rebut d’aluminium (Al) à l’échelle pilote dans une citerne rotative de métal liquide (RLMT), située dans un four à résistance. On a fait fondre dans la RLMT environ 39?kg d’Al commercialement pur. On a effectué les expériences dans un bain stagnant ou dans un bain rotatif d’Al à diverses températures et à diverses vitesses du métal liquide. Dans ce travail expérimental, on a utilisé des échantillons cylindriques d’alliage d’Al 6061. On a enregistré leur temps de fusion dans le bain d’Al au moyen d’un circuit électrique spécialement conçu. Au moment de l’immersion d’un échantillon cylindrique froid dans l’Al liquide, une coquille se solidifie autour de l’échantillon et subséquemment, fond à son tour. La période durant laquelle la coquille existe autour du cylindre s'appelle la période de coquille. La période de fonte libre commence quand la période de coquille se termine. La résistance du contact thermique à l’interface coquille et cylindre d’Al affecte la durée de vie de la coquille. On a développé une méthodologie pour estimer cette résistance du contact thermique. Le flux de chaleur par convection du bain d’Al à l’échantillon cylindrique influence les périodes de coquille et de fonte libre, et il est une fonction de la température et de la vitesse de l’Al liquide. La première partie de ce travail de recherche présente une ligne de base des mesures de fusion de l’Al sous des conditions d’écoulement monophasé, qui sera comparée à des conditions d’écoulement biphasé dans la deuxième partie.     

Aluminium scrap melting under different liquid aluminium flow conditions: part-II: two phase flow

This experimental research work deals with aluminium (Al) alloy melting in an Al bath. In this liquid metal, nitrogen gas was introduced at specific locations and at different gas flow rates. The samples employed, along with their position in the liquid Al, and the procedure for melting detection, were identical with the ones utilised in Part I. The introduction of gas into liquid Al has different effects on the melting time of the immersed Al 6061 alloy cylinder. For the range of gas flow rates examined, the addition of gas into a stagnant Al bath (i.e. natural convection conditions) produces insignificant changes in melting time. However, when the liquid Al is moving (i.e. forced convection conditions), the gas addition leads to a sizeable reduction in melting time. The melting time reduction ratio is introduced as a way to compare the melting under single and two phase flow liquid Al conditions. It is found that this ratio is affected by the nozzle position and also by the gas flow rate. The concept of an equivalent single phase velocity is also introduced, and defines the single phase velocity of liquid Al which results in the same melting time of the cylinder as under two phase flow conditions. It is found that the equivalent single phase velocity is influenced by both the gas flow rate and the nozzle position. The parameter which most likely contributes to the acceleration of the melting rate in two phase flow is the turbulence intensity, which is expected to increase due to the nitrogen gas injection.     

2005年我国废钢铁市场的运行状况

中国是世界第一钢铁大国,钢铁产业还将持续快速发展.中国也是一个废钢消费大国,同时也是一个废钢进口大国.每年要从世界各国进口大量的废钢,弥补资源的不足.2005年受国际铁矿石市场涨价71.5%的影响,中国废钢铁市场经过潮起潮落之后,日趋平稳.2006年我国废钢铁市场将继续处于资源偏紧,高价位运行的态势.在"十一五"期间,认真落实我国<钢铁产业发展政策>,加快我国废钢铁供需机制的改革,建立新型的废钢加工配送机制,加快调整产业结构,提高废钢加工处理技术水平,实施精料入炉;构建采购联盟,建立海外稳定的废钢资源供应基地;树立循环经济、环境保护的理念,科学健康地发展废钢回收利用产业,是中国废钢铁产业发展的方向和改革的主旋律.     

基于线性耗散热力学的废钢熔化行为研究

摘要：为揭示废钢熔化过程中的传热传质机制,采用线性耗散热力学理论,研究了钢液与废钢之间的传热,碳的扩散传质以及两者之间的耦合作用关系。结合移动边界层理论模型,得到了钢液温度为1773K、钢液碳质量分数为1.0%、废钢半径为0.03m、废钢的初始温度为300K时界面处碳的质量守恒方程,即基于线性耗散热力学理论的废钢熔化模型,并通过前人的实验结果验证了模型的准确性。研究建立的基于线性耗散热力学的废钢熔化模型可以预测废钢熔化过程中界面处碳含量、碳的活度和界面温度随时间的变化规律,为实际工业生产提供理论指导。     

Kinetics of aluminum oxidation during argon injection into liquid steel

Specification of the argon stirring process. Investigations of the aluminum oxidation kinetics in steel melts for deep drawing steel qualities. Experimental results on the influence of iron oxide, P₂O₅ and MnO concentration in the ladle slag. Exposition of a reaction model under the assumption of an instantaneous and irreversible reaction between dissolved oxygen and aluminum. Discussion about the use of the results for an improved process control during rinsing treatment.     

2005年中国进口废钢形势分析

在过去的2004年当中,中国的钢产量又上了一个台阶,在巨大增幅的背后,是国内钢材市场的跌宕起伏,作为炼钢的主要原料之一的废钢的价格,同样经历了惊心动魄的走势.同时,在如何利用好国际废钢资源的问题上,中国的炼钢企业经过2004年的洗礼,变得愈加理性.下面,在回顾2004年国内企业废钢利用状况的基础上我对2005年中国进口废钢形势作一下预测.     

Steel scrap melting behavior based on linear dissipative thermodynamics

In order to reveal the mechanism of heat and mass transfer in the melting process of steel scrap, linear dissipative thermodynamics was applied to investigate the heat transfer between liquid steel and steel scrap, and the diffusion and mass transfer of carbon and the coupling relationship between them. Combined with the moving boundary layer theory model, the mass conservation equation of carbon at the interface was obtained when the liquid steel temperature is 1773K, the carbon mass fraction of liquid steel is 1.0 mass%, the scrap radius is 0.03m and the initial temperature of scrap is 300K, that is, the scrap melting model based on the theory of linear heat dissipation mechanics. The accuracy of the model is verified by previous experimental results. The scrap melting model based on linear heat dissipation mechanics established can predict the changes of carbon content, carbon activity and interface temperature with time in the scrap melting process, and provide theoretical guidance for practical industrial production.     

Dezincification of galvanized steel scrap by electrolyzing

To remove and retrieve Zn from galvanized scrap by electrolyzing with caustic solution is experimentally confirmed to be a reasonable approach and the galvanized scrap can be completely purified. The concentrations of NaOH and ZnO, and the temperature of electrolyte are important factors to influence the critical current density of passivation of Zn layer. The electrolyzing parameters such as the applied current density, temperature of electrolyte, and the concentrations of NaOH and ZnO are optimized by experiments.     

Supplying steel scrap for electric steelmaking in Russia

This article reports on the steel-scrap balance in Russia and analyzes the demand for this resource from the steelmaking industry, as well as the potential sources of steel scrap. It is shown that the continuing growth of electric steelmaking in Russia will soon be challenged by shortages of steel scrap in the market and the need to more thoroughly process the scrap that will be available. Calculations show that when it is necessary to charge additional steel scrap into an arc furnace twice after the cold charge, the unit consumption of electric power is increased by 8.7 kWh/ton cast semifinished product and the heat is lengthened by 3 min. __________ Translated from Metallurg, No. 6, pp. 46–50, June, 2006.     

中国废钢铁的应用现状及发展趋势

 介绍分析了中国废钢铁资源和钢铁工业废钢铁消耗现状,行业管理、产业改革发展、规范建设的历程,废钢铁的循环利用对发展绿色钢铁和节能减排的重要意义,国家对废钢铁产业发展的扶助和支持,近年来国际、国内经济环境对废钢铁产业发展的影响,行业发展遇到的主要问题,“十三五”时期面临的机遇和挑战,废钢铁产业“十三五”发展思路和目标。     

Kinetics of contact melting in iron-carbon systems

The process of contact melting in iron-carbon systems was investigated using a dilatometric method. Specimens of iron, and diamond or graphite of various structures were studied at different temperatures and pressures. The thickness of the layer of eutectic melt formed and removed from the interface of contact was measured. The experimental data were analyzed and the process mechanism discussed.