RU2148089C1 - Electroslag refining flux - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: invention relates to electrometallurgy and, more specifically, to electroslag refining of metals that can be used for working tool steel. Proposed flux contains part of components, in particular, calcium, aluminum, and silicon oxides, and to some extent magnesium oxide incorporated therein in the form of regenerated blast furnace slag formed by desulfurization of blast furnace slag in emulsion- and flow-drop-mode processes. Components are used in the following proportions, wt.%: regenerated blast furnace slag, 75-80; magnesium oxide, 15-20; and calcium fluoride, 4-5; slag is composed, wt.%: silicon oxide, 40-45; calcium oxide, 40-42; aluminum oxide, 10-12; magnesium oxide, 8-9; and sulfur, <0.2. Introduction of regenerated blast furnace slag makes it possible to abolish high-priced technologies for separately preparing each slag component involved. In addition, necessity of expenses on ensuring transportation and storage conditions for separately prepared flux components is avoided. Reduced level of calcium fluoride to its limits ensuring normal proceeding of electroslag refining process, in particular, ensuring required fluidity of slag and conductance of fusion, also contributes to reduced cost price of flux and, additionally, leads to reduced emission of fluoric compounds into atmosphere. EFFECT: enhanced process efficiency. 1 tbl

Description

 The invention relates to a special electrometallurgy, namely, electroslag remelting of metals, which can be used for processing tool steels.

 Electroslag remelting was most widely used for the purpose of deep desulfurization, refining of metal from non-metallic inclusions and obtaining a dense cast structure. To achieve these goals, a number of fluxes based on calcium fluoride systems with thermodynamically strong oxides of calcium, aluminum and magnesium have been developed. These fluxes are characterized by high refining ability and possess a complex of physical and physicochemical properties that ensure a stable remelting regime (see the book "Electrometallurgy of Steel and Ferroalloys" edited by D.Ya. Povolotsky. Ed.2, revised and additional - M .: Metallurgy, 1984. - 568 p.).

However, to obtain such fluxes, a deficient fluorspar is required - a calcium fluoride mineral, as in the well-known flux for electroslag remelting, the components of which are taken in the following ratio, wt.%:
calcium oxide - 10-15
magnesium oxide - 10-15
aluminum oxide - 12-20
silicon oxide - 2-7
calcium fluoride - the rest
With such a content of calcium fluoride in the flux with increased refining ability during the remelting process, fluorine compounds are released from the slag melt into the atmosphere that adversely affect the human body and wildlife (see AS USSR N 258332, class C 22 B 9/10 , C 21 C 5/56, C 21 C 5/52).

Known flux for electroslag remelting, the components of which are taken in the following ratio, wt.%:
calcium fluoride - 30-50
calcium oxide - 12-18
aluminum oxide - 12-18
magnesium oxide - 3-7
silicon oxide - 5-9
titanium oxide - 3-7
chromium oxide - 3-5
borax - 6-12
A flux of this composition has the same drawbacks as the aforementioned one, although it has a high refining ability (see AS USSR N1765191, class C 21 C 5/54).

Currently, cost-effective and efficient methods for producing steel with a low content of sulfur, phosphorus, oxygen and hydrogen have been developed. In this regard, there is no need to refine the metal from impurities during electroslag remelting, and the primary task of remelting is to obtain a favorable structure while maintaining a low hydrogen content and increasing the technical and economic readings of the process. The use of fluxes of low basicity allows to solve the tasks. Deficiency of fluorspar CaF ₂ (calcium fluoride) sharply poses the task of developing fluxes with the lowest possible content of calcium fluoride.

Known welding flux AN - 60, containing components in the following ratio, wt.%:
silicon oxide - 42.5-46.5
calcium oxide - 3-10
manganese oxide - 36-41
calcium fluoride - 5-8
aluminum oxide - up to 5
magnesium oxide - 0.5-3.0
The high content of silicon oxide with a low content of oxide and calcium fluoride, as well as magnesium oxide provides low hydrogen permeability of the flux. The flux possesses a satisfactory complex of physical and physicochemical properties that meets the requirements of the electroslag remelting process, but its high content of thermodynamically unstable oxide manganese gives it a high oxidizing ability, which makes it impossible to use it for remelting alloy steel (see GOST 9087-81. fused welding. Technical conditions).

 In the production of welding fluxes, calcium oxide, aluminum oxide, magnetite powder and fluorspar are used as components (see the book "Theory and Technology of Ferroalloys Production" / Gasik MI, Lakishev NP, Emlin B.I. - M.: Metallurgy, 1988 .-- 784 p.).

The closest in technical essence to the proposed flux is a flux containing components in the following ratio, wt.%:
silicon oxide - 35-40
calcium oxide - 26-38
magnesium oxide - 12-20
aluminum oxide - 4-8
calcium fluoride - 5-20
This flux at the temperature of electroslag remelting has a satisfactory complex of physical and physico-chemical properties, provides a fairly stable electric mode of remelting and allows melt alloy steel without a significant change in its composition. The disadvantage of welding flux is the relatively high content of calcium fluoride in it, as well as the increased hydrogen permeability of its melt (see A.S. USSR N 91422, class B 23 K 35/36).

 Oxide for the production of fluxes of electroslag remelting is obtained by calcining limestone in shaft or rotary kilns, and only freshly calcined lime is used. Its high cost is determined not only by the cost of firing, but also by the costs associated with the creation of special conditions for its transportation and storage.

 The high cost of aluminum oxide is due to the expensive scheme for its production, which includes the production of agglomerate from bauxite, which is then smelted in an ore reduction furnace to produce electrocorundum and crush aluminum oxide powder.

 Magnesium oxide is the product of firing in rotary kilns of the scarce mineral magnesite. The high cost of magnesite powder is also due to the complex and energy-intensive production scheme and the need to create special storage and transportation measures.

 The objective of the invention is to reduce the cost of flux while reducing the consumption of fluorspar (calcium fluoride).

The essence of the invention lies in the fact that in the known flux for electroslag remelting containing calcium oxide, alumina, silicon oxide, calcium fluoride and magnesium oxide, some components, namely calcium oxide, silicon oxide, aluminum oxide and partially magnesium oxide are introduced into in the form of regenerated blast furnace slag obtained by desulfurization of blast furnace slag in emulsion (converter) and jet-droplet modes, and the components are taken in the following ratio, wt.%:
regenerated blast furnace slag - 75-80
magnesium oxide - 15-20
calcium fluoride - 4-5
In this case, the slag contains in its composition, wt.%:
silicon oxide - 40-45
calcium oxide - 40-42
aluminum oxide - 10-12
magnesium oxide - 8-9
sulfur - less than 0.2
Introduction to the flux composition of the regenerated blast furnace slag in the range of 75 - 80% will ensure that it contains the required content of the following components, wt.%:
calcium oxide - 30-36
aluminum oxide - 6-10
silicon oxide - 30-38
magnesium oxide - up to 30
Calcium oxide in the flux should be in the range of 30 - 36%. If the flux of calcium oxide is less than 30%, then the viscosity increases and the conductivity of the melt decreases. When the content of calcium oxide in the flux is more than 36%, the basicity of the slag increases and its hydrogen permeability increases.

 Silicon oxide in the flux should be in the range of 30 - 38%. This ensures low hydrogen permeability of the slag melt, high productivity of the process and reduced power consumption. When the content of silicon oxide is less than 30%, the ohmic resistance of the flux is significantly reduced and the technical and economic performance of the process is deteriorated. In addition, due to an increase in basicity, the hydrogen permeability of the flux increases due to the growth of free (not complexed) oxygen ions. When the content of silicon oxide is above 38%, the flux viscosity sharply increases and the electrical conductivity is significantly reduced, which complicates the process of electroslag remelting.

 Magnesium oxide in the flux should be in the range of 22 - 27%. When the content of magnesium oxide is less than 22%, the ingot surface deteriorates, corrugations and pinches appear. When the content of magnesium oxide is more than 27%, the melting point of the flux sharply increases, which complicates the process of electroslag remelting. It goes in an unstable mode, which leads to the formation of coarse surface defects of the ingot.

 Alumina in the flux should be in the range of 6 - 10%. If the aluminum oxide in the flux contains less or more of the specified limits, then a close to eutectic relationship between the main components of the flux of the system of oxides of silicon, calcium, aluminum, magnesium will be violated, and the melting temperature will increase significantly.

 Calcium fluoride in the flux should be in the range of 4-5%. The presence in the proposed flux of calcium fluoride of less than 4% does not provide the necessary slag fluidity. When the content of calcium fluoride is more than 5%, the productivity of the process decreases due to an increase in the electrical conductivity of the melt. In addition, calcium fluoride is an expensive and scarce material. An increase in its content leads to an increase in the cost of flux.

 In the initial state, the flux of the proposed composition can be made in the form of a mixture of granular (crushed) regenerated blast furnace slag, powders of calcined magnesite used to repair bathtubs of steelmaking units, and fluorspar.

 Thus, the proposed composition of the flux for electroslag remelting allows us to solve the problem of reducing its cost by eliminating components that require expensive technologies for their preparation, as well as the use of expensive components in minimal quantities.

 The table shows the results of testing the compositions of the proposed flux, which were obtained during experimental melting at the A-550 ESW unit with a fixed mold with a diameter of 100 mm.

 The initial components of the flux were weighed, and then melted in a flux-smelting furnace or directly in the mold of the electroslag remelting unit.

 Remelted electrodes with a diameter of 60 mm from steel 45X. Remelting at a current of 680 - 720 A and a voltage of 30-40 V. Ingots weighing 30 kg were smelted. During remelting, the technological parameters of the process and the energy consumption were controlled. The surface quality of the ingots was evaluated visually. The viscosity of the melts was determined in special experiments using a vibrational viscometer, electrical conductivity - according to the voltmeter - ammeter scheme. The determination results are shown in the table in accordance with the options for the quantitative compositions of the proposed flux and the composition of the prototype.

 Options 1 and 5 correspond to the transcendental contents of the regenerated blast furnace slag, options 2 and 4 correspond to boundary ones, and option 3 corresponds to the average content.

 Options 6 and 10 correspond to the transcendental content of magnesium oxide, options 7 and 9 to the boundary, option 8 to the average content.

 Options 11 and 14 correspond to the transcendental content of calcium fluoride, options 12 and 13 - boundary.

 Options 15 and 16 correspond to various flux compositions of the prototype.

 The results indicate that when the content of the regenerated blast furnace slag in the flux is less than 75%, the electroslag remelting process is unstable at a low speed and high energy consumption, and when the content of the regenerated blast furnace slag in the flux is more than 80%, the process indicators deteriorate due to a decrease in the electrical conductivity and increase the viscosity of liquid slag. When the content of magnesium oxide is less than 15%, the process proceeds in an unstable mode due to the relatively low flux conductivity. An increase in the content of magnesium oxide to 21% leads to a deterioration in the performance of the process - the remelting rate decreases, the energy consumption increases due to an increase in the melting point of the slag. When the fluorine content of calcium fluoride is less than 4%, the surface quality of the ingot deteriorates due to the high viscosity of the ingot, and when the content of calcium fluoride is more than 5%, the remelting rate decreases.

 When using flux for remelting according to the prototype of option 15, the process proceeds in an unstable mode with obtaining an ingot with a poor surface, and when remelting under the flux according to the prototype of option 16, the remelting proceeds quite steadily, a satisfactory surface of the ingot is obtained, however, the process is characterized by a low remelting rate and high energy consumption .

 Efficiency (low cost) of the proposed flux compared with widely used fluxes is achieved by using cheap regenerated blast furnace slag instead of calcium, aluminum and silicon oxides, low calcium fluoride content and reducing energy consumption during electroslag remelting.

 The invention practically does not require implementation costs.

Claims (1)

Flux for electroslag remelting containing calcium oxide, alumina, silicon oxide, calcium fluoride and magnesium oxide, characterized in that calcium oxide, alumina, silicon oxide and partially magnesium oxide are introduced in the form of regenerated blast furnace slag obtained by desulphurization of blast furnace slag in emulsion and jet-drop modes, and the components are taken in the following ratio, wt.%:
Regenerated blast furnace slag - 75 - 80
Magnesium Oxide - 15 - 20
Calcium Fluoride - 4 - 5
while the slag contains in its composition, wt.%:
Silica - 40 - 45
Calcium oxide - 40 - 42
Alumina - 10 - 12
Magnesium Oxide - 8 - 9
Sulfur - Less than 0.2

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