TECHNOLOGY AND QUALITY OF THE CONSUMABLE ELECTRODES, RECEIVED BY SEMI-CONTINUOUS CASTING, FOR VACUUM-ARC REMELTING

Abstract

The process of vacuum arc melt down is greatly dependent on the quality of the electrodes used. Electrodes of highly alloyed steels are negatively affected by the great amount of films, inversions, subcortical bladders and others; they are being cleansed and sanded down, this leads to substantial waste of expensive metals. For this purpose in the process of casting of highly alloyed steels a great deal of importance is put upon the creation of a method, which could be used for the purpose of protecting the metal from secondary oxidization. The increase in quality of semi-continuous cast electrodes and the removal of previously mentioned defects can be achieved with the use of slag mixtures, which posses thermo-insulating properties and can be partially melted down by the heat which is produced by the liquid metal, that fills the catalyzer. The goal of this project was to research the influence of thermal-insulating slag-producing mixtures on the quality of semi-continuous cast electrodes in the process of vacuum arc melt down in comparison to the ones that were casted under the exothermic mixtures, their effect on the process of melting and the quality of vacuum arc melt down ingots. In this project there were researched such topics as the componential, chemical composition, the physical properties of the thermo insulating mixture and the physical-chemical properties of the melt of said mixture. We researched the quality of the surface of the electrodes, the macrostructure, the chemical uniformity, density, content and the dispersal of non-metallic and gas-like additions on the transverse templates after the main cutting of 600mm, the stability of flow of the vacuum melt down, the quality of the vacuum arc melt down ingots and the rolled sheets made from the arc welded ingots. The geometry of the electrodes, casted under the thermal insulating mixture, is in order with the requirements: the degree of distortion of the profile, in comparison with the one achieved with the use of exothermic mixture, was reduced in half. The macrostructure of the electrodes is dense, without any visual defects. The losses of the metal in the process of sanding during the preparation for the vacuum arc melting were reduced by 2 times in comparison with the casting under exothermic mixture. The depth of the shrinkage cavity is reduced approximately by 12%, the form of the cavity takes the form of a “cup”. The amount of non-metallic and gas-like additions is being significantly reduced. The amount of electrodes that are being recast without issues (the creation of slag, ionization, ionization with slag), during the transition from exothermal to thermal insulating on average is reduced by 3–3,5 times. The purity of metal of vacuum arc melt down electrodes, that are casted under thermo insulating mixture, is in accordance with the requirements; the mechanical properties of rolled vacuum arc ingots exceed the norms of technical conditions.