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.     

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.     

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.     

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.     

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/...     

Mathematical modelling of electroslag remelting P91 hollow ingots process with multi-electrodes

Abstract

Electroslag remelting (ESR) hollow ingot process with T-shape current supplying mould is a new metallurgical technology. A mathematical model was developed to describe the interaction of multiple physical fields of this process for studying the process technology. Maxwell, Navier-Stokes and heat transfer equations have been adopted in the model to analyse the electromagnetic field, magnetic driven fluid flow, buoyancy driven flow and heat transfer using finite element software ANSYS. Moreover, the model has been verified through the metal pool depth measurements, which were obtained during remelting of 10 electrodes into Φ900/500 mm hollow ingots of P91 steel, with a slag composition of 50–60 wt-% CaF₂, 10–20 wt-% CaO, 20–30 wt-% Al₂O₃, ≤8 wt-% SiO₂. There was a good agreement between the calculated results and the measured results. The calculated results show that the distribution of current density, magnetic induction intensity, electromagnetic force, Joule heating, fluid flow and temperature are symmetric but not uniform due to the multi-electrode arrangement in two symmetric groups. Simulation of the ESR hollow ingot process will help to understand the new technology process and optimise operating parameters.     

Effect of electrode change on solidification of slag and metal pool profile in electroslag remelting process

A two-dimensional axisymmetric model is established to study the effect of electrode change on the solidification of slag and metal pool profile during electros...     

Some electrical characteristics of a DC electroslag unit

The various current paths possible in an electroslag unit are proposed and compared with operational results measured on a dc unit. The current found to pass through the mold walls under “mold-isolated” circuitry is small (less than 0.05 × the operating current). The metallurgical consequences of the possible operating modes are outlined and demonstrated.     

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.     

电渣重熔过程模拟软件Meltflow - ESR理论基础简介及其应用

介绍了电渣重熔过程模拟软件MeltFlow - ESR的理论基础及其应用,并与其他数值模拟进行了比较.分析结果表明:该软件理论基础完整,模拟结果与实验结果吻合良好,能够预测不同工艺条件下缺陷的产生及程度,能够设计和优化现有的工艺并改进钢锭质量.