RU2343204C1 - Charge for steel melting - Google Patents

Abstract

FIELD: metallurgy; chemistry.

SUBSTANCE: charge contains iron-carbon alloy: 2.5-4.8% C; 0.05-1.20% Si; 0.05-0.70% Mn; 0.01-0.16% V; less than 0.15% P; less than 0.030% S; less than 0.15% Cr; less than 0.10% Cu; less than 0.10% Ni; less than 0.05% Al; less than 0.008% As; less than 0.15% Ti, and oxide material: 3.0-98.0% FeO; 0.5-15.0% SiO₂; 0.1-8.5% Al₂O₃; 0.15-12.5% CaO; 0.15-3.8% MgO; 0.1-6.5% MnO; 0.01-0.12% S; 0.03-0.18% P₂O₅. Charge contains components in a following ratio, wt %: iron-carbon metal 70-99.9; oxide material 0.1-30. Charge is manufactured by method of casting in the form of ingot, weight 5-50 kg, with envelope made of iron-carbon alloy and oxide material of fractions 0.01-10 mm in 1-3 layers in central part of ingot. Ratio of ferric oxide concentration in oxide material to carbon content in iron-carbon alloy is 1:(1-2.5). Ratio of oxide material density to iron-carbon alloy density - 1:(2.2-7.8).

EFFECT: reduction of melting duration, decreasing of melted steel cost price, improving of melted steel.

Description

The invention relates to ferrous metallurgy, and specifically to the composition of the mixture for steelmaking.

Known iron-carbon alloy - pig iron used in steelmaking [1], containing 0.5-0.9% Si, not more than 1.5% Mn, not more than 0.05% S, not more than 0.30% R.

Significant disadvantages of this material are:

- a high concentration of silicon, leading to an increase in the multiplicity of slag, an increase in the consumption of lime and electricity for the formation of furnace slag;

- a high concentration of carbon, increasing the duration of the smelting in connection with the removal of a significant excess, for a certain grade of steel, its content;

- high concentrations of sulfur and phosphorus, which impede the smelting of high-quality steel grades, while increasing the duration of the smelting, consumption of charge materials and energy costs for redistribution;

- the possibility, when using solid cast iron with a solid oxidizing agent, of fusing individual pieces together, followed by overheating of the melt during the unmelted ore part of the charge and emissions from the furnace as a result of the violent exothermic reaction of carbon oxidation.

There is also known a method of steelmaking in an electric arc furnace, including the filling of scrap metal and lime, the melting of scrap metal, pouring molten iron, oxidizing carbon with gaseous oxygen, dephosphorization, the subsequent release of steel into the ladle, the additive in the ladle during the production of slag-forming mixture, characterized in that instead of liquid cast iron is used in an amount of 30-60% of the weight of the filling intermediate product containing 2.0-3.5% C, less than 0.01% Si, less than 0.015% P, less than 0.025% S, which is poured at a temperature of 1280-1400 ° C from above to the furnace after scrap metal penetration at an energy consumption of 180-300 kWh / t of scrap metal, the temperature in the furnace during carbon oxidation is maintained no more than 1700 ° C, the steel and slag in the furnace are not deoxidized, the discharge is carried out with cut-off furnace slag leaving 10-15% of the total liquid mass metal in the furnace, a slag-forming mixture consisting of lime and fluorspar in a ratio of (0.8-1.2) :( 0.2-0.5) with a flow rate of 10-17 kg / t of steel and necessary ferroalloys [2].

Significant disadvantages of this method of steelmaking are:

- a significant duration of the smelting associated with the need to oxidize impurities in cast iron (carbon, silicon, phosphorus) due to the oxidation of carbon only by gaseous oxygen, without the use of a solid oxidizer;

- the inability to transport molten iron over long distances;

- the need to regulate the pouring conditions of molten iron, in connection with possible emissions from the furnace.

Also known is a composite material for metallurgical redistribution [3], containing a conglomerate with characteristic geometric dimensions and formed from a mixture capable of endo-exothermic reactions containing a metal-containing additive, carbon-containing, slag-forming and iron-containing oxidized materials, in which, as a metal-containing additive, in a charge mixture contains iron-carbon alloy or iron-carbon alloy and cast iron and / or metal scrap, iron-containing oxidized material contains iron oxides in an amount of 20-100% of its mass, while the ratio of the total outer surface of the iron-containing oxidized material to the mass of the iron-carbon alloy is 5-500 m ² / t, and the ratio of the total amount of oxidized charge elements to the amount of oxygen in iron oxides is 0 , 3-3.6 in the following ratio of components, wt.%:

Iron Oxidized Material 5-35 Slag-forming material 0.2-30 Carbon material 0,1-10 Carbon alloy or iron-carbon alloy and cast iron and / or metal scrap Rest

Significant disadvantages of this material when used are:

- a large amount of slag formed from oxide-containing material, in connection with which increases the duration of the smelting and production costs associated with an increase in the amount of slag in the furnace;

- low mechanical strength of the composite material due to the location of a large amount of oxide material in the central part;

- a high melting time due to the fact that the oxides in the material are not distributed over the volume of the material, but are located in the central part, which leads to additional time for the diffusion of active oxygen from the oxide-containing alloy to the carbon of the iron-carbon alloy;

- the introduction of a carbon-containing material into the composition of the composite material leads to an increase in the melting time of the material and an increase in the heat costs associated with the dissolution of solid carbon in the iron-carbon melt, while the iron-carbon alloy already contains reactive carbon that can enter into an exothermic reaction with oxygen from the oxidized material.

Also known [4] is a charge briquette for the production of high-quality steel, containing metallic iron, iron oxides, carbon and waste rock, characterized in that it contains these components in the following ratio, wt.%:

Metal iron 63-75 Iron oxides 18-29 Carbon 5-7 Waste rock Rest,

the ratio of carbon to oxygen of iron oxides is greater than or equal to 0.8.

Significant disadvantages of this briquette are:

- high costs associated with the manufacture of this briquette as a result of which the cost of the resulting steel increases;

- reduced strength of these briquettes, leading to the formation of a large amount of fines during transportation of briquettes, as a result of which the technical and economic indicators of smelting are worsened;

- a high melting time due to the fact that the oxides in the material are not distributed over the volume of the material, but are located in the central part, which leads to additional time for diffusion of the active oxygen of the oxide-containing alloy to the carbon of the iron-carbon alloy;

- the selected ratio of carbon to oxygen of iron oxides leads to undesirable carburization of the steel melted from the material.

Also known is selected as a prototype [5] the mixture for steelmaking in electric arc furnace, containing iron-carbon alloy, characterized in that the alloy contains, wt.%;

Carbon 2.0-4.0 Manganese 0.05-0.30 Silicon less than 0.01 Chromium less than 0.15 Copper less than 0.10 Nickel less than 0.10 Sulfur less than 0,030 Phosphorus less than 0,030 Arsenic less than 0,008 Titanium less than 0.15 Aluminum less than 0.04 Iron rest

Significant disadvantages of this charge for steelmaking in electric arc furnaces are:

- high costs associated with the manufacture and preparation of the mixture for melting (including smelting, deoxidation and casting of the mixture);

- significant melting time associated with the fusion of individual pieces of the mixture with each other with the formation of refractory cast iron-steel conglomerate;

- a decrease in the rate of melting and homogenization of steel associated with the development of the decarburization reaction during melting of this charge only in the gaseous oxygen supply area in the external melting horizons, while the development of decarburization reaction in the internal horizons (volumes) does not occur, and therefore the sulfur concentration increases, phosphorus and non-metallic inclusions in steel, which significantly reduces the quality indicators of steel.

The desired technical results of the invention are: reducing the duration of the smelting, reducing the cost of smelting steel by reducing the cost of preparing the charge, improving the quality of the smelted steel.

For this purpose, a charge for steelmaking is proposed, containing an iron-carbon alloy and an oxide material, in which an alloy with a content of 2.5-4.8% C, 0.05-1.20% Si, 0.05- is used as an iron-carbon alloy. 0.70% Mn, 0.01-0.16% V, less than 0.15% P, less than 0.030% S, less than 0.15% Cr, less than 0.10% Cu, less than 0.10% Ni, less 0.05% Al, less than 0.008% As, less than 0.15% Ti, and the material with the content of: 3.0-98.0% FeO, 0.5-15.0% SiO ₂ , 0 is used as the oxide material , 1-8.5% Al ₂ O ₃ , 0.15-12.5% CaO, 0.15-3.8% MgO, 0.1-6.5% MnO, 0.01-0.12% S, 0.03-0.18% P ₂ O ₅ ; moreover, the components are contained in the following ratio, wt.%:

carbon alloy 70-99.9 oxide material 0.1-30

the mixture is made by casting in the form of ingots weighing 5-50 kg, and the shell contains only iron-carbon alloy, and the oxide material of the fraction of 0.01-10 mm is placed in 1-3 layers in the central part of the ingot, while the ratio of the concentration of iron oxides in the oxide material to the carbon content in the iron-carbon alloy is maintained equal to 1: (1-2.5) and the ratio of the density of the oxide material to the density of the iron-carbon alloy is maintained equal to 1: (2.2-7.8).

The claimed limits are selected experimentally.

Iron-carbon alloy is the main component of the charge for steelmaking, and in the manufacture of a charge with a content of less than 70% of the iron-carbon alloy, the mechanical strength of the ingot decreases markedly, and with an increase of more than 99.9% there is no effect of active mixing of the metal during melting due to the reaction of the carbon of the alloy with oxides oxide material.

The carbon concentration in the iron-carbon alloy was chosen on the basis that it is impossible to conduct an active oxidation period with a carbon content of less than 2.5%, and with an increase in carbon content of more than 4.8%, the melting time increases due to the oxidation of the "excess" carbon concentration.

With an increase in silicon content of more than 1.20% to neutralize SiO ₂ formed during oxidation, a significant amount of lime is necessary, in connection with which significant heat losses are observed and the consumption of electricity and electrodes is increased, while the silicon content is reduced to less than 0.05%, the charge exotherm is reduced, associated with the chemical heat of the inventive charge.

The manganese content is selected based on the following assumptions: when the manganese content is less than 0.05%, a significant amount of manganese-containing ferroalloys must be introduced to bring the steel to the levels required by State standards; on the contrary, with an increase in the concentration of manganese in the claimed material more than 0.70%, additional measures are necessary to oxidize the excess manganese content, which increases the duration of smelting.

Exceeding the declared concentrations of phosphorus and sulfur in the iron-carbon alloy leads to an increase in the duration of smelting due to more intense dephosphorization and desulfurization of steel, which, in turn, increases the consumption of electricity and electrodes.

The concentration of chromium, nickel, copper and arsenic was selected on the basis of obtaining the required concentrations of these elements (taking into account the use of scrap metal) in high-grade steel grades with a regulated concentration of impurities.

The content of vanadium, titanium and aluminum is selected based on the exclusion of non-metallic inclusions of titanium and aluminum oxides in the finished steel, which sharply reduces the mechanical properties of high-quality steels.

The oxide material, due to the presence of the oxygen component, contributes to the early onset of oxidation of impurities of the iron-carbon alloy, moreover, when the amount is less than 0.1%, it is not possible to efficiently mix and homogenize the iron-carbon alloy, and with an increase of more than 30%, the mechanical strength decreases and the technical and economic performance of the melting is reduced due to with an increase in the ratio of slag.

The content of iron oxides in the oxide material was chosen based on the fact that when the content of iron oxides is less than 3%, the effect of the oxidation period is almost completely absent, and with an increase in the concentration of iron oxides over 98%, the method of preparing oxide material requires additional costs and an increase in the cost of production.

The content of oxides of silicon, aluminum, calcium, magnesium and manganese is selected on the basis of obtaining the required concentrations of these oxides to optimize the slag regime.

Exceeding the declared concentrations of phosphorus and sulfur in the oxide material leads to a decrease in the quality indicators of steel being smelted, and also leads to an increase in the duration of smelting due to more intense dephosphorization and desulfurization of steel, which, in turn, increases the consumption of electricity and electrodes.

The mass of manufactured ingots is selected from the fact that, with a mass of less than 5 kg, the strength of the ingot for its overload and transportation is not ensured, and with an increase in mass of more than 50 kg, the bulk density of the mixture decreases and the need arises to work with additional basements, in addition, in some cases it is necessary to use various lifting mechanisms for additive in the furnace.

The fraction of the added oxide material was selected on the basis that with a fraction of less than 0.01 mm, certain costs for additional grinding are required, and with a fraction of more than 10 mm, the surface of interaction of the ore material with carbon of the iron-carbon alloy decreases, resulting in a longer melting time.

The number of layers of oxide material in the ingots more than three reduces the strength of the ingots and leads to breakage of ingots during transportation.

The ratio of the concentration of iron oxides in the oxide material to the carbon content in the iron-carbon alloy is maintained equal to 1: (1-2.5) based on the charge of the smelting: for the complete oxidation of carbon by the oxide material in the ingot, the ratio is 1: 1, if necessary, carbonization of steel from the inventive charge maintain a ratio of 1: 2.5.

The ratio of the density of the oxide material to the density of the iron-carbon alloy is maintained equal to 1: (2.2-7.8) based on ensuring the strength and reactivity of the carbon oxidation reaction of the inventive charge with oxygen of the oxide material.

The inventive charge for steelmaking was obtained by pouring oxide materials with iron-carbon melt according to a special technology. Further, the resulting mixture was used in steelmaking in 100-ton electric arc furnaces with a transformer with a capacity of 95 MVA, both in a mixture with a metal charge and at 100% furnace load of the inventive charge. When smelting by the present method on 176 smelting steel grades NE76F, E76F, Art. 80-90, 50-70G reduced melting time compared to using pig unprepared cast iron, depending on the steel grade, by 6-9 minutes. In the production of steel intended for the production of NE76F and E76F railroad rails, the content of chromium and nickel is reduced by 0.02%, copper to 0.03%, and the contamination of steel by non-metallic inclusions is reduced (the average length of the line of oxides does not exceed 0.3 mm). The cost of smelted steel was reduced by 0.9-8.8 rubles / kg of steel.

Information sources

1. GOST 805-95 "Converted cast iron. Technical conditions. "

2. RF patent No. 2258084, IPC ⁷ C21C 5/52, 7/06.

3. RF patent No. 2231558, cl. С21С 5/28, С22В 1/00, 1/24, В22D 3/00.

4. RF patent No. 2150514, cl. C21C 5/52, C22B 1/24.

5. Application No. 2005115632/02 (017896), IPC C21C 5/52, C22C 37/00.

Claims (1)

A mixture for steelmaking containing an iron-carbon alloy and an oxide material, characterized in that it as an iron-carbon alloy contains: 2.5-4.8% C; 0.05-1.20% Si; 0.05-0.70% Mn; 0.01-0.16% V; less than 0.15% P; less than 0.030% S; less than 0.15% Cr; less than 0.10% Cu; less than 0.10% Ni; less than 0.05% Al; less than 0.008% As; less than 0.15% Ti, and as the oxide material contains: 3.0-98.0% FeO; 0.5-15.0% SiO ₂ ; 0.1-8.5% Al ₂ O ₃ ; 0.15-12.5% CaO; 0.15-3.8% MgO; 0.1-6.5% MnO; 0.01-0.12% S; 0.03-0.18% P ₂ O ₅ ; moreover, the mixture contains components in the following ratio, wt.%: iron-carbon alloy 70-99.9; the oxide material is 0.1-30, in the form of ingots weighing 5-50 kg, with a shell of an iron-carbon alloy and an oxide material of a fraction of 0.01-10 mm in 1-3 layers in the central part of the ingot, while the ratio of the concentration of iron oxides in the oxide the material to the carbon content in the iron-carbon alloy is 1: (1-2.5), and the ratio of the density of the oxide material to the density of the iron-carbon alloy is 1: (2.2-7.8).