RU2395589C2 - Procedure for melting iron-carbon alloys in induction furnaces - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to ferrous metallurgy, particularly to melting iron-carbon alloys in induction furnaces. The procedure consists in charging metal part of the charge, in melting and in alloying melt with silicon and carbon containing materials. Alloying is carried out with a complex mixture containing silicon and carbon at ratio C_Σ: Si=(25÷90):(0.5÷65), where Si is contents of silicon in the complex mixture, and C_Σ - is summary contents of carbon in the complex mixture. Also silicon is present in the composition of the mixture as silicon carbide metallurgical and/or its slimes, while carbon is present as heat treated carbon containing materials of electrode production and/or graphite.

EFFECT: facilitating melting iron-carbon alloys with preliminary specified properties and grade contents of silicon and carbon in melt; ensuring flexible corrections of its chemical composition at various stages of melting; reduced chill in iron and increased graphitising property.

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Description

The invention relates to ferrous metallurgy, namely to foundry, and can be used in the production of iron-carbon alloys for various functional purposes. A carburetor for carburizing synthetic cast iron is known from the patent literature (Ah. USSR No. 1018976, C21C 1/10, bull. No. 19, 1983), which suggests using dehydrated “tails” from coal “foam” flotation as synthetic carbonizer. The specified invention can only increase the carbon content in the melt.

Also known is a deoxidizer for cast iron (AS USSR No. 697568, C21C 1/08, bull. No. 42, 1979), which consists of a mixture of silicon carbide or its sludge and lime, and also additionally contains shungite in the following ratio of components , the weight.%:

Silicon carbide or its sludge 15-20 Lime 5-10 Shungite rest

This mixture can only increase the degree of reduction of iron and increase the concentration of carbon and silicon in cast iron.

The closest in technical essence to the achieved effect is the briquette used in the production of cast iron (options) (Pat. RF. 2247155 C21C 1/10, Bull. No. 6, 2005). According to the first embodiment, the briquette includes a silicon-containing material, a carbon-containing material and a binder, while it contains metallurgical silicon carbide as a silicon-containing material, contains a carbon-silicon mixture as a carbon-containing material, and cement as a binder in the following ratio of components, wt.%:

Silicon Carbide Metallurgical 59-62 Silicon Carbon Blend 21-25 Cement 13-20

According to the second embodiment, the briquette includes a silicon-containing material, a carbon-containing material and a binder, while it contains metallurgical silicon carbide as a silicon-containing material, contains a carbon-silicon mixture as a carbon-containing material, and cement as a binder in the following ratio of components, wt.%:

Silicon Carbide Metallurgical 44-48 Silicon Carbon Blend 36-39 Cement 13-20

According to the third option, the briquette includes a silicon-containing material, a carbon-containing material and a binder, while it contains metallurgical silicon carbide as a silicon-containing material, contains a carbon-silicon mixture as a carbon-containing material, and cement as a binder in the following ratio of components, wt.%:

Silicon Carbide Metallurgical 18-21 Silicon Carbon Blend 62-66 Cement 13-20

According to the fourth embodiment, the briquette includes a silicon-containing material, a carbon-containing material and a binder, while it contains metallurgical silicon carbide as a silicon-containing material, contains a carbon-silicon mixture as a carbon-containing material, and cement as a binder in the following ratio of components, wt. %:

Silicon Carbide Metallurgical 1-5 Silicon Carbon Blend 79-82 Cement 13-20

The compositions of the above briquettes can qualitatively improve the composition of the briquette by replacing ferrosilicon with silicon carbide metallurgical at certain quantitative ratios of all components, the compositions can be used in the production of iron-carbon alloys based on synthetic melt.

The use of the above briquettes involves the use of them when filling in the composition of the mixture, which increases the requirements for stability of the chemical composition of the charge materials. As a result, subsequent refinement of the melt in silicon and carbon is necessary. Moreover, the technical solution for this patent does not take into account the initial and predetermined concentrations of silicon and carbon in the melt, which is very important in the smelting of iron-carbon alloys.

The technical task of this invention is to obtain iron-carbon melts for various functional purposes with predetermined properties and branded silicon and carbon content in the melt with the possibility of flexible adjustment of the chemical composition at different periods of smelting, as well as slag deoxidation and reduction of bleached in cast irons and increase their graphitizing ability.

The problem is solved due to the fact that in the method of smelting iron-carbon alloys in induction furnaces, including filling the metal part of the charge, melting and alloying the melt with silicon and carbon-containing materials, characterized in that the alloying is carried out with a complex mixture containing silicon and carbon, with a ratio of _Σ : Si = (25 ÷ 90) :( 0.5 ÷ 65), where Si is the silicon content in the complex mixture; C _Σ is the total carbon content in the complex mixture, while silicon is contained in the mixture in the form of metallurgical silicon carbide and / or its sludge, and carbon is in the form of heat-treated carbon-containing materials of electrode production and / or graphite.

If it is necessary to adjust the content of carbon and silicon during the refinement period, the above dependencies are also correct, providing the necessary content of silicon and carbon in accordance with regulatory and technical documents. The use of a complex mixture in the smelting of iron-carbon alloys of various functional purposes in an amount determined by an empirical dependence makes it possible to vary the content of silicon and carbon over a wide range based on their initial concentration in the melt and the oxidation of furnace slag. The use of silicon carbide as a silicon-containing and carbon-containing material allows complex alloying of a carbon-iron melt with silicon and carbon. The interaction of silicon carbide with liquid iron occurs by the reaction:

SiC _TB + Fe = [Si] _Fe + [C] _Fe

With the assimilation of silicon and carbon by the metal, the reduction of iron oxides contained in the slag and formed during the melting of the mixture by the reaction occurs simultaneously:

SiC _TB +2 (FeO) = (SiO ₂ ) +2 [Fe]

Depending on the FeO content in the slag (metal oxidation), the coefficient K is taken into account in the calculation expression, taking into account the slag oxidation (K = 1 ÷ 2);

coefficient K takes into account the consumption of SiC for iron reduction with the transition of reaction products to slag.

The value of the empirical coefficient K, characterizing the physicochemical laws of alloying and deoxidation of iron-carbon melts, within 1 ÷ 2 is regulated by the initial content of FeO in the slag and a given concentration of silicon and carbon in the melt.

In this case, silicon is introduced into the mixture in the form of metallurgical silicon carbide and / or its sludge.

As a silicon-containing material using substandard fraction of ferrosilicon.

As the carbon-containing material, heat-treated carbon-containing electrode materials are used.

Metallic silicon carbide and / or sludge, as well as heat-treated electrode materials and / or graphite, are used as the carbon-containing material.

Carbon-containing materials according to TU 1914-01827208846-99 and / or TU 1914-00194042-026-01, and / or TU 48-4805-130-99, and / or GOST 5279, and / or GOST 5420, as well as silicon carbide, are products of chemical-thermal reactions of pure components, therefore they do not contain harmful impurities (sulfur, phosphorus, non-ferrous metals), which negatively affect the quality of cast irons.

Metallurgical silicon carbide is a finely crystalline material fraction 0-20 mm, containing SiC 75-92%, SiO ₂ 5-20%. The active ingredient is SiC (70% Si, 30% C), which is both a source of silicon and carbon. Silicon carbide is an inert material (does not melt), is stable up to a temperature of 2610 ° C, when interacting with an iron melt, the Si - C bond breaks and these components dissolve directly in the metal. Compared with ferrosilicon, less silicon fumes, the combined action of Si and C as graphitizing elements positively affects the metal structure.

Upon receipt of a commercial product (grain and powders) of abrasive silicon carbide, the primary piece is crushed with further sieving on screens in fractions. At all stages of processing, dust collection is carried out by bag filters. The product precipitating filters (sludge) in the sleeves is a finely dispersed material with particle sizes less than 0.05 mm and contains SiC 70-90%. Metallurgical silicon carbide is the product of a chemical-thermal reaction for the reduction of silica sand with carbon petroleum coke:

SiO ₂ + C = SiC + 2CO

The implementation process in self-propelled furnaces of resistance according to the Acheson method. In contrast to abrasive silicon carbide (a-SiC), metallurgical is represented by a structural modification of p-SiC (the formation of which consumes less energy).

Silicon carbide contains fewer non-metallic inclusions and impurities of non-ferrous metals than ferrosilicon, a lower gas content and contributes to the release of elemental carbon, forming graphitization centers in the liquid melt that reduce bleaching.

Material heat-treated carbon-containing electrode production is a secondary product of chemical-thermal reactions containing SiC and carbon at a ratio of C bond .: With free. = (1 ÷ 5) :( 7 ÷ 30), which ensures saturation of the melt with carbon particles, which are also active centers of graphitization. The material heat-treated carbon-containing electrode production is anthracite burnt at high temperatures and is a secondary material of electrode production. As a result of heating, the crystal lattice is ordered, which makes it more inert to the oxidizing atmosphere and more active to glandular melts. The carbon content is at least 80%, silicon carbide 3-15%, sulfur no more than 0.5%, fraction 0-13 mm. Compared to coke, it is a cheaper and less sulfurous material, and is also well absorbed by metal melt.

The introduction of metallurgical silicon carbide into the melt together with the material heat-treated carbon-containing electrode production and / or graphite ensures the sufficiency of the carburization process, the silicon concentration in the melt and the graphitizing ability increase, the slag oxidation and the tendency to bleach are reduced.

The amount of complex mixture introduced is calculated according to empirical dependencies, based on the physicochemical laws of alloying iron-carbon melts in induction furnaces, the chemical composition of the melt for the finishing period, and the requirement of GOST for the finished material, while a complex mixture containing silicon and carbon is introduced into the melt at a ratio of C _Σ : Si = (25 ÷ 90) :( 0.5 ÷ 65)

The inventive mixture allows alloying cast iron for various functional purposes with silicon and carbon both during filling and during finishing, strictly observing the Si / C ratio. The ratio of components in the mixture varies based on specific production conditions and the content of Si and C in the finished metal of a given brand.

The range of silicon content in the inventive mixture in the range of 0.5-65% is due to the physicochemical laws of alloying iron-carbon melts with silicon and carbon. At lower values, there will be an increase in the oxidation of slag (FeO> 10%), which, in turn, leads to increased waste of alloying components. At high values, the required chemical composition will not be provided.

The range of total carbon content of 25-90% provides a high and stable carbonizing ability of the mixture. When the total carbon content in the mixture is less than 25%, its carburizing ability is reduced. When the total carbon content is more than 90%, the shape, size and distribution of graphite inclusions deteriorate, which reduces the quality of castings.

The analysis of scientific, technical and patent literature shows the absence of coincidence of the distinguishing features of the proposed method in comparison with the known technical solutions in this field. The following are examples of the invention, not excluding other options within the claims.

Concrete example

Cast iron was melted in an induction furnace LP3-57 with acid lining. As the mixture was used scrap steel 1A, 2A (GOST 2787-88), trim transformer steel (examples 2, 5 and 6), pig iron PL1, PL2 (GOST 805-95). After melting the metal charge, a sample was taken for express chemical analysis, then the calculated amount of the mixture was introduced. Cast iron in the furnace was overheated to 1450 ° C and held for 10 minutes, then adjusted to the required chemical composition with additives of ferroalloys and the necessary alloying elements.

After slag removal, standard technical samples ⌀30 mm were poured to study the mechanical properties of cast iron and determine the chemical composition of the metal.

The studies were carried out on various grades of cast irons with varying both the chemical composition of the initial melt and the component composition of the given mixture. The amount of specified material was determined on the basis of the expression as claimed in the claims. The results of pilot tests of the technology of application of the mixture, which is claimed, are presented in the table.

The results of pilot tests of the claimed technology Options Examples one 2 3 four 5 6 Test marks of cast iron Midrange 20 Midrange 20 MF 18-36 Midrange 15 RF-450-5 SCH 21-40 The carbon content of C ₀ , wt.% 0.1 3.4 1.7 2.6 2.95 3.4 The carbon content of C ₁ , wt.% 3,5 3,5 3,7 3.6 3.75 3.6 The silicon content of Si ₀ , wt.% 0.1 2.0 0.8 0.2 1,5 1.4 The silicon content of Si ₁ , wt.% 2.1 2.1 1.8 2.2 2.0 1,6 The content of SiC in the mixture, wt.% 1,0 1,0 90 90 0.5 95 The total carbon content in the mixture, With _Σ , wt.% 90 90 25 25 95 twenty The initial content of FeO in the slag, wt.% 10.0 5,0 8.0 9.0 7.5 7.5 The value of the coefficient K 1.3 1.15 1.4 1,5 0.9 2.1 The amount of the given mixture, m, kg / t 49.4 1.27 112 60 7.56 21 The final content of FeO in the slag, wt.% 2.5 2.1 ¹ ' ⁷ 1.3 7.0 0.5 The value bleached, mm 0,0 0,0 0,0 0,0 3.0 1.8 Assimilation of carbon,% 92.4 89.1 88.3 87.9 95.6 64,2 The absorption of silicon,% 93.2 96.8 98.2 99.1 94.4 99.5

where the legend in the table,

K - coefficient taking into account the oxidation of slag (K = 1-2);

With ₀ - the carbon content in the metal by melting (calculated by metal charge), in%;

Si ₀ - the silicon content in the metal by melting (calculated by metal charge), in%;

C ₁ - a given carbon content in the metal (at the outlet before discharge from the furnace), in%;

Si ₁ - the specified silicon content in the metal (at the outlet before discharge from the furnace), in%;

C _with - carbon content in the carbon-containing material used in the manufacture of the complex mixture, in%

Si _c is the silicon content in the silicon-containing material used in the manufacture of the complex mixture, in%

С _Σ is the total carbon content in the complex mixture, in%;

the final content of FeO in the slag, wt.%;

value bleached, mm;

carbon assimilation,%;

assimilation of silicon,%

The experiments performed show that deviations of the parameters from the required values lead to a deterioration of the technical and economic indicators of the process. So, in the fifth example, increased bleaching and high oxidation of slag are observed. In the sixth example, the obtained metal does not correspond to a given chemical composition with a low degree of carbon assimilation. In optimal examples 1-4, bleach is completely eliminated in the metal obtained, the oxidation of slag is within acceptable limits with a high degree of carbon assimilation.

From the above examples it is seen that in this method the required state standard specification is provided for this type of alloy, the content of carbon and silicon. Using the dependencies declared in this decision, any composition of the mixture can be selected based on specific production conditions. If it is necessary to adjust the content of carbon and silicon during the refinement period, the above dependencies are also correct, providing the necessary content of silicon and carbon in accordance with regulatory and technical documents. The use of a complex mixture in the smelting of iron-carbon alloys of various functional purposes in an amount determined by the stated dependence allows you to vary in a wide range the content of silicon and carbon based on their initial concentration in the melt and the oxidation of slag (furnace). The use of silicon carbide as a silicon-containing and carbon-containing material allows complex alloying of a carbon-iron melt with silicon and carbon. These examples confirm the technical applicability of the claimed method.

Claims (1)

A method of smelting iron-carbon alloys in induction furnaces, including filling the metal part of the charge, melting and alloying the melt with silicon and carbon-containing materials, characterized in that the alloying is carried out with a complex mixture containing silicon and carbon, with the ratio C _Σ : Si = (25 ÷ 90) : (0.5 ÷ 65), where Si is the silicon content in the complex mixture; C _Σ is the total carbon content in the complex mixture, while silicon is contained in the mixture in the form of metallurgical silicon carbide and / or its sludge, and carbon is in the form of heat-treated carbon-containing materials of electrode production and / or graphite.