Physicochemical comparison of electroslag remelting with consumable electrode and electroslag refining with liquid metal (original) (raw)
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Contribution of the Mould Current to the Ingot Surface Quality in the Electroslag Remelting Process
Krane/Proceedings, 2013
Thickness, uniformity and mechanical properties of slag skin are main factors controlling the surface quality of the electroslag remelting (ESR) ingot. Thin and homogeneous slag skin is a key to obtain a nice ingot surface quality. It is classically believed that surface quality is mainly influenced by the slag temperature at the vicinity of the mould. In the present paper considers the effect of the Joule heating on the slag skin energy balance. The slag skin between ingot and mould is expected to have a significantly different electrical resistivity than the bulk slag, complicating the electrical boundary conditions at the ingot/mould interface. The amount of electric current crossing the skin towards the mould depends on the electric slag skin conductivity. It is shown that the magnitude of Joule heating generated within the skin can control its thickness. Thus, it is suggested that the known sensibility of the ingot quality on the melt rate, the electrode immersion depth, fill ratio and the resistivity of the slag can be reduced to its dependence on the electric current path and intensity.
A Comprehensive Model of the Electroslag Remelting Process: Description and Validation
Metallurgical and Materials Transactions B, 2009
Electroslag remelting (ESR) is widely used for the production of high-value-added alloys such as special steels or nickel-based superalloys. Because of high trial costs and the complexity of the mechanisms involved, trial-and-error-based approaches are not well suited for fundamental studies or for optimization of the process. Consequently, a transient-state numerical model has been developed that accounts for electromagnetic phenomena and coupled heat and momentum transfers in an axisymmetrical geometry. The model simulates the continuous growth of the electroslag-remelted ingot through a mesh-splitting method. In addition, solidification of the metal is modeled by an enthalpy-based technique. A turbulence model is implemented to compute the motion of liquid phases (slag and metal), while the mushy zone is described as a porous medium the permeability of which varies with the liquid fraction, thus enabling accurate calculation of solid/liquid interaction. The coupled partial differential equations (PDEs) are solved using a finite-volume technique. The computed results are compared to the experimental observation of an industrial remelted ingot; the melt pool depth and shape, in particular, are investigated, in order to validate the model. These results provide valuable information about the process performance and the influence of the operating parameters. In this way, we present an example of a model used as a support in analyzing the influence of the electrode fill ratio.
Mass Transfer in Electroslag Processes with Consumable Electrode and Liquid Metal
Uspehi Fiziki Metallov
Experimental and numerical comparisons of mass transfer processes during the electroslag remelting with consumable electrode (ESR) and electroslag refining with liquid metal (ESR LM) showed their identical refining capacity, despite the smaller both the slag–metal contact surface (twice) and metal overheat (by 70–95 K) in the latter case. As revealed, due to effect of metal movement inside the liquid metal drop, it moves in liquid slag faster than a solid particle of the same diameter. Under comparable conditions, it is experimentally confirmed that desulphurization at the ESR takes place mainly on the contact surface between the slag and metal baths, but not in the liquid metal film at the tip of a consumable electrode.
Evaluation of the Electroslag Remelting Process in Medical Grade of 316LC Stainless Steel
2009
This study is focused on the effects of electroslag remelting by prefused slag (CaO, Al 2 O 3 , and CaF 2) on macrostructure and reduction of inclusions in the medical grade of 316LC (316LVM) stainless steel. Analysis of the obtained results indicated that for production of a uniform ingot structure during electroslag remelting, shape and depth of the molten pool should be carefully controlled. High melting rates led to deeper pool depth and interior radial solidification characteristics, while decrease in the melting rates caused more reduction of nonmetallic inclusions. Large shrinkage cavities formed during the conventional casting process in the primary ingots were found to be the cause of the fluctuation in the melting rate, pool depth and extension of equiaxed crystals zone.
Review on Modeling and Simulation of Electroslag Remelting
steel research international, 2017
The Electroslag Remelting (ESR) is an advanced technology for the production of high quality materials, for example, hot work tool steels or nickel base alloys. In the past years, several models are developed aiming to predict the way in which the operational parameters affect the structure and chemical composition of the final ESR ingot. Proper modeling of this process depends on the ability of the model to predict the Multiphysics resulting from the complex coupling between many physical phenomena. This review includes the main findings starting from the 1970's, with a special focus on the results obtained in the period of 1999-2017. The difficulties related to the poorly known physical properties of ESR slags are discussed. Then, the main achievements in the field of electromagnetism, fluid flow, heat transfer, and solidification are also summarized. The review finishes by presenting the special topics representing the actual scientific frontiers, such as the physics of mold current, the importance of multiphase phenomena, and the difficulties in predicting the electrode melting rate.
Thermal State of the Electrode During the Electroslag Remelting Process
2011
This paper presents a numerical investigation on the thermal state of a melting electrode and its influence on the shape of the electrode tip. The first part of this work computes the heat necessary to melt an electrode with a flat tip shape. It is shown that to keep a constant meltrate, heat supplied to the electrode must be continuously changed. The results for different electrode descend velocities, corresponding to different meltrates, are presented. The second part uses a full ESR model to simulate the melting process. It is found that the thermal state of the electrode exerts a great influence on the shape of the electrode tip.
Krane/Proceedings, 2013
This paper presents a comprehensive computational model for the prediction of the transient Electroslag Remelting (ESR) process for cylindrical ingots based on axisymmetric two-dimensional analysis. The model analyzes the behavior of the slag and growing ingot during the entire ESR process involving a hot-slag start with an initial transient, near-steady melting, hot-topping and subsequent solidification of the slag and ingot after melting ends. The results of model application for an illustrative ESR process for Alloy 718 and its validation using results from an industrial trial are presented. They demonstrate the comprehensive capabilities of the model in predicting the behavior of the ingot and slag during the entire process and properties of the final ingot produced. Such analysis can benefit the optimization of existing process schedules and design of new processes for different alloys and different ingot sizes.
Process and Refining Characteristics of ESR using MgO containing Slag Systems
2015
The influence of selected process parameters such as slag composition, melt rate or pressure on metal-slag interactions, inclusion characteristics and process behaviour during electroslag remelting (ESR) are currently under investigation at IME, RWTH Aachen University. It is common knowledge that one of the main refining functions of ESR is the removal of non-metallic inclusions (NMI) to increase mechanical properties of the remelted material. On the other hand, metal-slag interactions can lead to continuous changes of alloying (e.g. Al, Si, Mn) and detrimental elements (O, S) with increasing ingot length and weight. This paper focuses on the influence of MgO addition to a common ESR slag system and the consequences regarding behaviour of process parameters such as electrical resistance, current density and power input as well as the modification of NMI characteristics, distribution of dissolved impurities and changes of alloying elements due to metal-slag interactions. In order to investigate the described correlations electrodes (110 mm diameter) of low alloyed steel (21CrMoV5-7) were remelted in a closed 400 kW-lab scale ESR furnace applying 1 bar protective argon atmosphere. Based on a widely used ESR slag composition consisting of approx. 60 wt.-% CaF 2 , 19 wt.-% CaO, 19 wt.-% Al 2 O 3 and 2 wt.-% MgO, pure magnesia was added in order to adjust the MgO content to 5, 10 and 15 wt.-% respectively. After remelting, the ingots as well as the electrode tips, which were immersed in the slag, were subjected to various chemical and structural characterisation methods. The concentration of basic and alloying elements over the ingot height and radius was determined by using optical emission spectroscopy. Interstitially dissolved elements were characterized by applying combustion and inert gas fusion methods. The amount, size, area and composition of non-metallic inclusions were investigated by metallographic methods as well as using SEM-EDX.
MODELLING OF METALLURGICAL PROCESSES IN ELECTROSLAG TECHNOLOGIES
Mathematical models of metallurgical processes have been developed for processes of electroslag welding (ESW), electroslag remelting (ESR), electroslag hardfacing (ESH) and centrifugal electroslag casting (CESC). The models allow to predict chemical composition of metal along and in transversal sections of an ingot, a weld and a surfacing layer, and in thickness of a casting. Using of the models reduces expenses during selection of optimum process conditions and materials which providing weld metal or ingot metal with required composition. One of the most important parameters of the mathematical models is a mass-transfer coefficient. A physical modelling method of study of mass-transfer between molten metal and slag in electroslag technologies (EST) was developed. Influence of electrode melting rate and casting velocity on mass-transfer coefficients was studied.