RU2770657C1 - Method for steel melting from scrap in electric arc furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy and can be used in the production of steel in arc steel-smelting electric furnaces. The method includes loading scrap metal onto the hearth of a furnace, melting it, carburizing the melt by blowing a mixture of powdered lime and carbonaceous material into the melt in a gas jet, oxidation and reduction periods. A powdered mixture of brucite and a carbon-containing material with a fraction of 0.1-3 mm is blown into the melt in a stream of nitrogen in the ratio (31-35):(65-69) respectively and with a mixture flow rate of 4.0-16.0 kg/t of the mass of the melt.

EFFECT: invention makes it possible to reduce melting time by 0.3-0.8 min and power consumption by 10-15 kW⋅h/t, reduce electrode consumption by 0.02-0.11 kg/t and increase furnace lining durability up to 1360 heats.

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Description

The invention relates to the field of metallurgy, more specifically to the production of steel in electric arc steel-smelting furnaces, and can be used in the production of steel using scrap.

Known steel flux containing, wt. %: 0.1-2.0 calcium oxide; 25.0-50.0 silicon oxide; 5.0-20.0 iron oxide; 0.5-10.0 aluminum oxide; 0.5-20.0 loss on ignition; magnesium oxide the rest. At the same time, the ratio of the contents of magnesium oxide to silicon oxide is 0.4-1.8, and the ratio of the contents of the sum of calcium and iron oxides to the content of silicon oxide is 0.1-1.0 (RU 2623168 IPC C21C 5/36, C21C 5/ 54 published 06/27/2017).

Significant disadvantages of the known flux are:

- the used fractional and chemical compositions do not allow to quickly melt and form a highly efficient liquid steel-smelting slag, which, on the one hand, has protective properties in relation to the lining, on the other hand, a high degree of foaming of the resulting furnace slag;

- the chemical composition used predetermines the high melting point of the flux, which increases the melting time.

Also known high-temperature magnesia flux for a steel furnace, which contains, wt. %: MgO not less than 70.00; From 4.00-12.00; SiO ₂ up to 3.00; Al ₂ O ₃ up to 5.00; Fe ₂ O ₃ up to 2.00; Cr ₂ O ₃ 3.00-8.00; CaO is the rest, while fused waste of refractory materials is used as oxide components (RU No.

Significant disadvantages of this flux are:

- high power consumption for melting due to the use of refractory materials, in particular Cr ₂ O ₃ ,

- increased duration of melting due to the use of a large fraction of the material and the high melting point of the flux used.

A known method of steelmaking in an electric arc furnace, including filling the metal charge and slag-forming materials, heating and melting them, carrying out oxidative refining by purging the bath with oxygen with foaming of the slag, supplying magnesian material, discharging the melt with leaving part of the metal and slag in the furnace, at which brucite is used as a magnesia material, with a content of magnesium oxide to losses on ignition of 1.5-3.5, which is supplied after the release of part of the slag of the period of oxidative refining of the metal and / or at the end of melting before the metal is poured into the ladle (RU No. 2645170 MPK C21C 5/52, F27B 3/08 published 02/16/2018).

Significant disadvantages of this method are:

- high duration of melting due to the introduction of brucite not in the form of a powder when blown during the melting, but in portions at certain melting intervals;

- low degree of efficiency of slag foaming due to the absence of carbon-containing material in the composition of the mixture;

- increased consumption of electrodes due to inefficient arc cover during slag foaming in the furnace;

- high power consumption due to the addition of coarse slag-forming materials.

It is also known, chosen as a prototype, a method of smelting steel from scrap metal in an electric arc furnace, including loading scrap metal onto the hearth of the furnace, melting it, carburizing the melt by blowing powdered carbon-containing material into it in a gas jet, supplying lime, oxidation and reduction periods, characterized in that that a powdered mixture of lime and carbon-containing material is blown into the melt in a gas stream at a ratio of 1:1 and with a mixture flow rate equal to 0.4-3.0% by weight of the melt, while the carburization rate of the melt is maintained within 0.2- 0.6% carbon in 1 minute, and the powder mixture is blown into the melt until the required carbon content is obtained in it before the start of the oxidation period (RU No. 2107738 IPC S21S 5/52, publ.

Significant disadvantages of this method are:

- low resistance of the furnace walls due to the absence of magnesium oxide in the composition;

- high duration of melting due to the low degree of efficiency of slag foaming;

- increased consumption of electrodes due to inefficient arc cover during slag foaming in the furnace;

- high power consumption due to the addition of coarse slag-forming materials.

The technical problem solved by the claimed invention is to ensure high resistance of the lining of the walls of the electric arc furnace, as well as to improve the technical and economic performance in steelmaking, in particular: to reduce the consumption of electrodes, electricity and the duration of melting.

To solve the existing technical problem, a powdered mixture of brucite and carbonaceous material is blown into the melt in a gas jet.

The technical results obtained as a result of using the invention are:

- in increasing the resistance of the furnace lining due to the formation of a skull, as a result of the introduction of brucite into the mixture;

- in reducing the duration of melting due to the intensification of the processes of slag foaming;

- in reducing the consumption of electrodes due to good foaming of the slag;

- in reducing the consumption of electricity by reducing the duration of melting and intensifying the processes of melting the charge.

For this, a method is proposed for smelting steel from scrap metal in an electric arc furnace, including loading scrap metal onto the furnace bottom, melting it, carburizing the melt by blowing a powdered mixture of lime and carbon-containing material into the melt in a gas jet, oxidation and reduction periods, in which the melt in a nitrogen jet a powdered mixture of brucite and a carbon-containing material is blown in with a fraction of 0.1-3 mm in the ratio (31-35):(65-69) respectively and with a mixture flow rate of 4.0-16.0 kg/t from the mass of the melt.

The claimed limits are selected empirically, based on the results obtained, in particular the formation of a skull on the lining of the furnace and the associated resistance of the walls; the efficiency of the slag foaming process and obtaining high technical and economic indicators - the consumption of electrodes, electricity and the duration of melting.

The use of brucite powder and carbon-containing material over 3 mm slows down the process of dissolution of the injected mixture, which affects the degree of efficiency of slag foaming, with a decrease of less than 0.1 mm, a fine fraction of brucite escapes through gas cleaning and inefficient use of the material.

The content of brucite is selected on the basis of providing the required content of magnesium oxide in the slag, which ensures the presence of a skull on the furnace lining. At the same time, at a consumption of brucite less than 31%, the formation of a scull was insignificant, and an increase in consumption of more than 35% led to an increase in the viscosity of the slag and, as a result, an increase in the melting temperature of the mixture, which affected the increase in the consumption of electricity and electrodes.

At less than 65% carbonaceous material consumption, inefficient arc cover was observed, which led to increased wear of the furnace lining and high consumption of electricity and electrodes. An increase in this material to more than 69% led to a sharp foaming of the slag and, in some cases, emissions from the furnace.

The experiments were carried out using screenings of brucite according to TU 1517-001-89444155-2015 with a chemical composition, wt %: MgO 52-55%, CaO 5-7%, SiO ₂ 5-7% with a weight change index upon ignition of not more than 35, 0%.

As a carbon-containing material, anthracite was used according to TT TPB-03-2021 with a chemical composition, wt. %: carbon 85-90%, with the release of volatile substances 5-7%, sulfur content 0.3-0.4%.

Experimental melts were carried out on EAF 100N10 during the smelting of steel grade E76KhF.

Smelting was carried out according to the following scheme. The filling consisted of 100-120 tons of scrap metal, 5-35 tons of hard iron and 2-45 tons of lime. Carbon oxidation was carried out in a furnace to a concentration of 0.05-0.20% by purging with oxygen, while the temperature in the furnace varied within 1630-1710°C.

In the process of melting, after working out (140-250) kWh/t of charging, brucite powder and carbon-containing material were injected in a nitrogen jet at a pressure of 1-1.5 atm with a consumption of 400-1600 kg per melt, which corresponds to 4.0-16.0 kg/t from the mass of the melt.

On experimental melts, a powder mixture of brucite and anthracite fraction 0.1-Zmm was used in the following chemical composition: C 55-58%; MgO 15-20%; with an ash content of 31-35%; S 0.35-0.40%.

The use of the proposed method of steel production in comparison with the prototype allows:

- reduce the melting time by 0.3-0.8 min;

- reduce the consumption of electrodes by 0.02-0.11 kg/t;

- reduce electricity consumption by 10-15 kWh/t;

- increase the durability of the furnace lining up to 1360 heats.

Claims (1)

A method for smelting steel from scrap metal in an electric arc furnace, including loading scrap metal onto the hearth of the furnace, melting it, carburizing the melt by blowing a powdered mixture of lime and carbon-containing material into the melt in a gas jet, oxidation and reduction periods, characterized in that a powdered mixture of brucite and a carbon-containing material with a fraction of 0.1-3 mm in the ratio (31-35):(65-69) respectively and with a mixture flow rate of 4.0-16.0 kg/t by weight of the melt.