RU2818526C1 - Low-silicon steel production method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to production of calcium-modified low-silicon steel grades. Steel melting is carried out by duplex process from vanadium cast iron containing 4.2–5.2% of carbon, 0.015–0.20% of silicon, 0.30–0.60% of vanadium, to obtain at the first stage a semi-finished metal with a carbon content of 2.5–3.5%. Then metal-semi-finished product is treated at desulphurisation plant till sulfur content is 0.001–0.0025%, and at the second stage it is blown with oxygen in converter till carbon content is 0.02–0.15%. Calcined silica-containing additive and manganese-containing materials are used. During out-of-furnace treatment steel is deoxidized to active oxygen content of not more than 3.5 ppm and sulfur content of not more than 0.010%, after which steel is vacuum treated, modified with calcium-containing wire with subsequent cleaning blowing with argon.

EFFECT: invention provides reduced formation of non-metallic inclusions in steel in the form of deoxidation products, reduced shutdowns of continuous casting machine without tightening of refractories of metal wiring, which allows increasing seriality of metal casting at continuous casting machine.

1 cl, 1 ex, 1 tbl

Description

The invention relates to the field of ferrous metallurgy, in particular to steelmaking, and can be used in the production of low-silicon (low-silicon) steel grades modified with calcium, with the possibility of casting in batches on a continuous casting machine.

There is a known method for the production of low-silicon steel [1] (patent RU No. 265340, MPK S21S 7/00, published on October 27, 2012), which includes out-of-furnace processing of the metal on a ladle-furnace unit; after the melt arrives at the specified unit, the cover slag is removed from a steel-pouring ladle, add new slag by adding lime and fluorspar in the proportion (4...5):1 with a total consumption of materials of 7...12 kg/t, deoxidize the steel with primary aluminum to obtain an acid-soluble aluminum content of at least 0.080%, heat metal to a temperature of at least 1620°C. After that, fluidized lime is injected in an amount of 2.8...4.2 kg/t.

The disadvantages of this method are:

- carrying out an additional operation (removing the covering slag from the steel-pouring ladle);

- use of expensive materials (primary aluminum, fluidized lime) for deoxidation and desulfurization;

- the issue of stable continuous casting of low-silicon steel is not resolved.

There is a known method for the production of low-silicon steel [2] (patent No. 2166550, MPK S21S 7/064, publ. 05/10/2001, Bulletin No. 13), including metal smelting, cutting off slag from the metal at the beginning and end of its release from the steel-smelting unit, complex processing of the metal when released into a ladle with the main lining by adding aluminum, a slag-forming mixture, deoxidizers, alloying materials, purging the metal in the ladle after its release with an inert gas, while calcium-containing deoxidizers are additionally introduced into the metal, for which an aluminum-calcium alloy is added during the release of the metal , containing, wt. %: calcium 15-35, aluminum 65-85, and after completion of metal production with a content of 0.02-0.05 wt.% aluminum, flux-cored wire is added with a filler from a mixture containing, wt.%: granulated calcium 60- 80, aluminum powder 40-20, while the amount of calcium introduced during and after metal production is maintained within the range of 0.2-0.4 and 0.3-0.6 kg per ton of steel, respectively.

The disadvantages of this method are:

- no guarantee of obtaining low-silicon steel with a regulated silicon content of no more than 0.03% (the method ensures that the finished steel contains a silicon content of no more than 0.055).

The closest technical solution adopted for the prototype is a method for producing low-silicon steel [3] (patent RU No. 2353667, MPK S21S 7/10, published on April 27, 2009), including smelting metal in a steel-smelting unit, cutting off the slag from the metal at the end of production it from the steel-smelting unit into the ladle, the addition of slag-forming and alloying materials, deoxidation and purging of the metal in the ladle with inert gas, while metal with a carbon content of more than 0.03% is smelted, vacuum processing of the metal is carried out in the ladle, slag-forming materials are added, the oxygen content in metal, then the metal and slag are deoxidized with calcium- and aluminum-containing materials, while calcium carbide ( _CaC2 ) is used as the calcium-containing material, which is fed into the ladle with a flow rate according to the dependence m = 0.21(a _{o_start} -a _{o_end} ) ⁿ kg/t , where a _{o_init} is the oxygen content in the metal after vacuum treatment, ^ppm ; and _{o_kon} - the required oxygen content in the metal up to 15 million ^-1 ; n - empirical coefficient in the range of 0.3-0.5; 0.21-empirical coefficient, kg/t⋅million ^-1 , and the supply of aluminum-containing material is carried out in an amount based on the recalculation of the material for the content of pure aluminum within the ratio CaC ₂ /Al _pure = 1-7, and then the chemical composition is adjusted become.

The disadvantages of this method are:

- the need for significant overheating of the metal before it is drained from the steelmaking unit and vacuum treatment,

- there is no guarantee of casting metal in batches on a continuous casting machine (CCM).

The technical result of the invention is: reducing the formation of non-metallic inclusions in steel in the form of deoxidation products; reduction of continuous caster shutdowns without overgrowing of the refractory channels of the metal wiring, increase in the serial casting of metal at the continuous caster.

The specified technical result is ensured due to the fact that in the method of producing low-silicon steel, cast iron is devanadized and a metal product is obtained, a metal intermediate is desulfurized, steel is smelted in an oxygen converter, after-furnace processing in a ladle furnace installation, vacuum treatment in a circulation degasser, modification steel with calcium with its regulated consumption and cleaning purification of steel, followed by casting on a continuous caster, according to the invention,Steel smelting is carried out by a two-stage duplex process from vanadium cast iron containing 4.2-5.2% carbon, 0.015-0.20% silicon, 0.30-0.60% vanadium and other impurities, producing metal in the first stage - intermediate product with a carbon content of 2.5-3.5%, minimal contents of vanadium and silicon, after which the metal intermediate product is processed in a desulfurization unit to a sulfur content of 0.001-0.0025% and at the second stage the metal intermediate product is purged with oxygen in a converter until it contains carbon 0.02-0.15%, depending on the regulated brand carbon content; In addition, to form slag, they additionally use a calcined silica-containing additive in an amount of 500-1200 kg/pl and manganese-containing materials in an amount of 100-700 kg/pl, while during the release of the melt from the steel-pouring ladle and in the process of out-of-furnace processing of the melt, the steel is deoxidized to an active oxygen content of no more than 3.5 ppm and a sulfur content in steel of no more than 0.010%, after which the steel is vacuum treated for at least 7 minutes at a residual pressure of less than 3 mbar, and after completion of the vacuum treatment the steel is modified with calcium-containing flux-cored wire at the rate introduction of calcium in an amount of 25 to 100 kg per melt, followed by cleaning purging with inert gas argon without exposing the metal surface for at least 5 minutes.

Desulfurization of the semi-product metal intended for smelting low-silicon steel to a sulfur content of no more than 0.0025% ensures a low sulfur content after deoxidation of the steel of no more than 0.010%.

Reducing the consumption of silicon additives to less than 500 kg/pl. and manganese-containing materials less than 100 kg/pl. in the process of steel smelting in a converter, it complicates the process of forming liquid-moving homogeneous slag and reduces the dephosphorization of steel. Increase in consumption more than 1200 kg/pl. for silicon additive and 700 kg/pl. for manganese-containing materials it leads to excessive fluid mobility of the slag and increased loss of iron.

The active oxygen content of no more than 3.5 ppm and the sulfur content of no more than 0.010%, obtained before deoxidation of steel, reduce the likelihood of the formation of complex oxysulfide inclusions, which can form during further processing of steel with calcium and lead to overgrowing of refractory channels of metal wiring.

The duration of vacuum treatment of steel is at least 7 minutes. is sufficient to reduce the dissolved oxygen content in steel and obtain the required calcium content in steel when introducing calcium-containing wire. When reducing the duration of vacuum treatment to less than 7 minutes. incomplete removal of oxygen occurs, which leads to increased loss of calcium and the formation of complex oxides CaOxAl2O3, which impair the pourability of steel.

Reducing the consumption of calcium-containing wire based on the introduction of calcium to less than 25 kg/pl. does not allow carrying out the final process of modifying aluminous inclusions, increasing the wire consumption based on the introduction of calcium by more than 100 kg/pl. leads to the interaction of calcium with sulfur with the subsequent formation of complex oxysulfides, which also worsen the bottling process.

The essence of the proposed method is as follows.

Example. The proposed method for producing low-silicon steel was carried out using the duplex process from vanadium cast iron.

Vanadium cast iron with the chemical composition wt.%: carbon 4.2-5.2, silicon 0.015-0.20, vanadium 0.30-0.60 and other impurities at the first stage of the process was blown with oxygen in a 160 t oxygen converter to obtain metal - an intermediate product with a carbon content of 2.5-3.5% and minimal contents of vanadium and silicon.

After which the semi-product metal was poured into a pouring ladle, which was transferred to a desulfurization unit to remove sulfur to 0.001-0.025%, depending on the regulated grade sulfur content. When pouring the metal product into the ladle, to reduce the degree of magnesium consumption during desulfurization, deoxidizing agents were added in the following amounts: pig aluminum 10-40 kg/pl, calcium carbide 10-40 kg/pl.

Granulated magnesium or mixtures based on it and finely dispersed fluidized lime were used as desulfurizers in the desulfurization plant. The consumption of desulfurates depends on the initial sulfur content in the semi-product metal in the amount of: granulated magnesium (or a mixture based on it - 50-200 kg/pl, fine fluidized lime - 200-600 kg/pl.

After processing, the slag from the ladle is carefully removed by a slag downloading machine using a mechanical scraper. Slag downloading time is at least 7 minutes.

Steel was smelted from the product metal in another converter without the use of scrap metal. The semi-product metal was purged in the converter with oxygen in the amount of 400-500 m ³ /min until the carbon content in the metal reached 0.02-0.15%, depending on the regulated grade of carbon content.

Next, slag-forming materials were added to the converter: lime in an amount of 2500-4500 kg/pl, silicon-containing additives in an amount of 500-1200 kg/pl and manganese-containing additives in an amount of 100-700 kg/pl.

After the end of the purging, a metal sample was taken from the converter. When the results of the chemical analysis were obtained, the metal from the converter was poured into a steel-pouring ladle.

Before draining the melt (or before it began), a fireproof plug was installed in the converter steel outlet - a slag stopper to reduce the ingress of over-oxidized converter slag into the ladle. At the beginning of the drain, in the period from 0 to 5 seconds, calcium carbide or a mixture based on it was added in an amount of 50-200 kg/pl, while when the ladle was filled with metal by 25-60%, ferroalloys were added in the amount required for a specific grade of steel and pigs aluminum in the amount of 50-150 kg/p. During the draining of metal from the converter, a solid slag-forming mixture (SSM) was added to the ladle in an amount of 350-1000 kg/pl. Lime and thinners (fluorspar, alumina-containing materials, etc.) were used as TSS in a ratio of lime and thinner of 3:1.

After the metal was drained, a metal sample was taken from the steel-pouring ladle. When receiving the results of the chemical analysis of the metal, the metal was purged with an inert gas argon for 2-5 minutes. After which the steel-pouring ladle with metal was transferred to the out-of-furnace steel processing department.

During the period of out-of-furnace metal processing, highly basic homogeneous slag with a FeO content of no more than 1.5% was created in the ladle furnace installation, and aluminum-containing materials were introduced to obtain an active oxygen content in the metal of no more than 3.5 ppm. If necessary, additional heating of the metal was carried out and the chemical composition was adjusted according to the content of elements regulated for a specific steel grade.

After obtaining an active oxygen content in the metal of no more than 3.5 ppm and sulfur of no more than 0.010%, it was transferred to a circulation degassing unit.

The melt was evacuated in a vacuum installation for at least 7 minutes under the condition of a residual pressure of less than 3 mbar. After the end of the evacuation, calcium-containing flux-cored wire was introduced at the rate of introducing calcium in an amount of 25-100 kg per melt.

Then the melt was purged with inert gas argon without exposing the melt for at least 5 minutes.

The use of the proposed method before evacuation ensures an increase in the number of heats cast in a series through one tundish by 1-4 heats, which leads to a decrease in the required number of tundishes for casting, savings in lining refractories and metal wiring products, reduction in costs for preparing tundishes for casting, reduction loss of metal with scrap and trimmings.

The proposed technology was tested in converter shop No. 1 of EVRAZ Nizhny Tagil Iron and Steel Works JSC. Table 1 presents the results of using the developed technology.

Table 1 Options Examples 1 2 3 4 5 6 Consumption of silicon-containing additive at the second stage of the duplex process, kg/pl. 903 902 108 900 1001 803 Consumption of manganese-containing additive at the second stage of the duplex process, kg/pl 290 - 34 333 500 351 Oxygen content after deoxidation during extra-furnace metal processing, ppm 2.0 3 3 2.4 2.9 2.2 Duration of evacuation at a residual pressure of 3 mbar, min Not carried out Not carried out Not carried out 7 7 7 Consumption of pure calcium from flux-cored wire at the end of evacuation, kg/pl - - - 25.4 25.5 27.2 Sulfur content after steel deoxidation, % 0.010 0.0079 0.013 0.009 0.008 0.008 Result It's drawn out
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steel ladle It's drawn out
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steel ladle Without comments Without comments Without comments

Analysis of patents and scientific and technical information did not reveal the use of new essential features used in the proposed solution. Therefore, the proposed invention meets the “inventive step” criterion.

Information sources:

[1] patent RU No. 265340 “Method for the production of low-silicon steel”, MPK S21S 7/00, publ. 10/27/2012;

[2] patent No. 2166550 “Method for the production of low-silicon steel”, MPK S21S 7/064, publ. 05/10/2001, bulletin. No. 13;

[3] patent RU No. 2353667 “Method for the production of low-silicon steel”, MPK S21S 7/10, publ. 04/27/2009.

Claims (1)

A method for producing low-silicon steel, including devanadation of cast iron and production of a metal product, desulfurization of a metal intermediate, smelting steel in an oxygen converter, after-furnace processing in a ladle furnace installation, vacuum treatment in a circulation degasser, modifying steel with calcium with its regulated consumption and purifying purging of steel followed by casting on a continuous caster, characterized in that steel is produced by a two-stage duplex process from vanadium cast iron containing 4.2-5.2% carbon, 0.015-0.20% silicon, 0.30-0.60% vanadium and impurities, producing at the first stage a metal intermediate with a carbon content of 2.5-3.5%, after which the metal intermediate is processed in a desulfurization unit to a sulfur content of 0.001-0.0025% and at the second stage the metal intermediate is purged with oxygen in converter to a carbon content of 0.02-0.15%, depending on the regulated brand carbon content, in addition, to form slag, a calcined silica-containing additive in the amount of 500-1200 kg/pl and manganese-containing materials in the amount of 100-700 kg/pl are additionally used, at the same time, during release from the steel-pouring ladle and during the out-of-furnace processing of the melt, the steel is deoxidized to an active oxygen content of no more than 3.5 ppm and a sulfur content in the steel of no more than 0.010%, after which the steel is vacuum treated for a duration of at least 7 minutes at residual pressure less than 3 mbar, and after completion of vacuum treatment, the steel is modified with calcium-containing flux-cored wire based on the introduction of calcium in an amount of 25 to 100 kg per melt, followed by cleaning purging with an inert gas argon without exposing the metal surface for at least 5 minutes.