RU2515403C1 - Method of steel casting in arc steel furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed process comprises the feed of scrap, iron, iron-magnesium concentrate, slag-forming material and carbon-bearing material into the furnace. It includes charge furnacing, producing cover slag and steel tapping into teeming ladle. Note here that iron-magnesium scrap is fed as pellets sized to 20-80 mm over said metal scrap. Note here that 1-75% of iron-magnesium concentrate is introduced in metal burden charging to scrap before furnacing period. Remainder 25-99% of said concentrate is added not earlier that 0.1 and not later than 0.9 of total furnacing period. Note here that said concentrate is introduced in amount sufficient for reaching the relationship between magnesium oxide content in slag and furnace lining in the limits of 0.05-0.16. Note also that slag basicity is kept equal to 1.7-4.5. Besides, at making the cover slag carbon-bearing material is blows into slag in amount of 0.1-100 kg per slag ton to foam the slag and to reduce iron from its oxides.

EFFECT: better assimilation of iron-bearing material, higher hardness of furnace lining.

Description

The invention relates to the field of metallurgy, in particular to the production of steel in electric arc furnaces (EAF).

There are various methods for the production of steel with high purity in terms of harmful non-oxidizable impurities.

A known method for the production of steel, including the production of partially reduced iron-containing oxidized material, its subsequent supply to the charge of an electric arc furnace, the supply of flux and a reducing agent, the melting of the mixture, the final reduction of the material and the refining of the melt, the production and casting of steel, characterized in that the partially reduced iron-containing oxidized material receive in the form of a conglomerate of oxidized iron-containing material and an iron-carbon alloy with a total degree of initial metal tion of 50-95%, with an electric arc furnace, fed in an amount of 5-100% of the iron-containing part of the charge. The material is fed into steelmaking units in the form of ingots (RU 2092572 of 09.26.1994).

The disadvantages include the need to use cast iron for the production of partially reduced iron-containing oxidized material, which makes its production more expensive.

Another disadvantage is the input form of the partially reduced iron-containing oxidized material - ingots, i.e. large lumpy material, the melting and dissolution of which is slower compared to pelletized materials in the form of pellets or briquettes.

A known method of production (smelting) of steel, which consists in obtaining iron-magnesium concentrate in the form of briquettes from iron-containing material based on siderite metallization products and introducing it together with lime, sand and carburizer into a charge of a laboratory induction or industrial small-tonnage electric arc furnace (Development of a technology for the metallization of metallized siderite ore to obtain a concentrate for smelting electric steel. Melamud S.G. et al. / Steel, No. 6, 2011).

The disadvantages of the method include the following. There are no indications of the size of briquettes used in pilot melting of small-tonnage aggregates, which makes it impossible to transfer this technology to industrial aggregates, since lumpy material requires a long heating time and its use slows the melting period, and small material is carried out of the furnace with exhaust gases and as a result is lost. In addition, steel smelting of laboratory and semi-industrial melts is carried out on low-base slags, which is impossible in real steelmaking in furnaces with basic magnesia lining both for dephosphorization and desulfurization processes and for reducing the aggressive effect of slag on chipboard lining.

In laboratory conditions, the lining collapsed, which indicates the imperfection of the technology, potentially capable of increasing the durability of the lining of a metallurgical unit due to the saturation of steelmaking slag with magnesium oxide.

The technical result of the invention is to increase the absorption of iron-containing material and increase the resistance of the refractory lining of particleboard.

The specified technical result is achieved by the fact that in the method for producing steel in an electric arc furnace, comprising supplying scrap metal, cast iron, iron-magnesium concentrate, slag-forming material, carbon-containing material to the furnace, melting the charge and discharging the steel-pouring ladle according to the invention, iron-magnesium concentrate is introduced in the form of briquettes with dimensions of 20-80 mm over scrap metal, with 1-75% of iron-magnesium concentrate being introduced into the charge of scrap metal for scrap before the start of the pl phenomenon, and the remaining 25-99% iron-magnesium concentrate introduced no earlier than 0.1 total duration of the melting and within 0.9 melting period duration period; iron-magnesium concentrate is introduced in an amount that ensures the achievement of a ratio between the content of magnesium oxide in the slag and the lining in the range of 0.05-0.16; while the basicity of the slag is provided at the level of 1.7-4.5 units; during the formation of the coating slag, carbon-containing material is injected into the slag in an amount of 0.1-100 kg / t of slag, which ensures the reduction of iron from oxides and foaming of the slag.

The iron-magnesium concentrate used in the present invention is a metallized raw material recovered from siderite ore with a high content of magnesium oxide, up to 15%. Siderite ore with a high MgO content is heated in the presence of a reducing agent, and iron-magnesium concentrate is isolated for subsequent briquetting. Iron-magnesium concentrate is characterized by a high dissolution rate in slag melts of the main composition and resistance during transportation and storage.

Experience shows that when the size of briquettes or pieces of iron-magnesium concentrate is less than 20 mm during the melting process, the material is carried out mechanically with exhaust gases, which leads to loss of part of the metal charge and a decrease in the yield. When the size of the pieces is more than 80 mm, the processes of iron melting and assimilation are limited by the thermal conductivity of the material, as a result, the iron oxides contained in the indicated iron-magnesium concentrate pass into the slag phase at a rate lower than the optimum, which increases the loss of iron with slag and reduces the yield.

When iron-magnesium concentrate is introduced into the filling under the scrap, it is sintered into metal-oxide conglomerates, characterized by a low dissolution rate due to difficult heat transfer.

The introduction of more than 75% of the indicated iron-magnesium concentrate into the scrap charge earlier than 0.1 of the duration of the melting period leads to stagnation of the processes of dissolution and assimilation of iron and magnesium oxides due to lack of heat in the initial melting period. Entering 25-99% of the indicated iron-magnesium concentrate later than 0.9 of the duration of the melting period leads to incomplete melting of the metal part at the beginning of the oxidation period and low efficiency of the use of the magnesian component due to the late participation in the formation of slag.

The range of values of the ratio of the content of magnesium oxide in the slag and lining in the range of 0.05-0.16 provides a sufficient viscosity of the slag, and also helps to create a protective layer (skull) on the surface of the refractories. When the consumption of iron-magnesium concentrate in the total amount ensuring the achievement of a ratio between the content of magnesium oxide in the slag and the lining <0.05, there is a high gradient of the chemical potential between the lining and the slag, which leads to a quick transition of magnesium oxide from the lining to the slag, t .e. physico-chemical wear of the lining. When the consumption of iron-magnesium concentrate in the total amount ensuring the achievement of a ratio between the content of magnesium oxide in the slag and the lining> 0.16, the chemical potential gradient between the lining and the slag is small and practically no wear occurs, but the viscosity of the ladle slag is too high for refining processes to occur and foaming slag.

When the slag basicity is below 1.7 units, the processes of dephosphorization and desulfurization do not proceed in full, which reduces the quality of the final intermediate by harmful impurities, and there is also a high wear of the lining.

Slag basicity of more than 4.5 units leads to an increased viscosity of the slag melt, which complicates the course of refining processes and leads to entanglement of the metal kings and oxides from the iron-magnesium concentrate, and ultimately leads to a decrease in the yield. The calculation of basicity is performed on the basis of a known expression that takes into account the content of magnesium oxide: $$B=\frac{\left(\%CaO\right)+\left(\%MgO\right)}{\left(\%SiO2\right)}$$

The injection of carbon-containing material allows you to flexibly control the recovery of iron from slag, including from oxides from iron-magnesium concentrate, and increases the yield. When carbon-containing material is injected less than 0.1 kg / t of slag, the probability of interaction of carbon particles with molecules of iron oxides decreases and the reduction of iron from the slag is ineffective. At a flow rate of more than 100 kg / t of slag, the effect of carbonization of steel occurs due to the presence in the system of a super-equilibrium amount of carbon.

The inventive method was implemented in the smelting of steel in DSP-100. Smelting was carried out according to the following scheme. Scrap metal and cast iron were loaded into the furnace; lime was fed into the charge as a slag-forming material. Iron-magnesium concentrate in the form of briquettes with sizes of 20-80 mm was planted in the furnace over scrap metal before the start of the melting period in the amount of 3 tons, the remaining 7 tons of this material was introduced 10 minutes after the start of melting. This ensured the ratio between the content of magnesium oxide in the slag and the lining in the range of 0.05-0.16 and the basicity of the slag at the level of 1.7-4.5 units. During the formation of the coating slag, coke was blown in an amount of 60 kg / t of slag, which ensures the reduction of iron from oxides and foaming of the slag. Steel was produced with cut-off furnace slag. By melting the metal charge and before the release of the smelting, samples of metal and slag were taken.

As a result, the share of scrap in the filling was reduced to 95 tons (90%). An increase in the absorption of iron-magnesium concentrate is achieved through the use of iron-magnesium concentrate with an optimized fractional composition, as a result of which the processes of heat transfer, melting and mass transfer proceed at an optimal speed. According to the results of the furnace campaign, the lining resistance increased by 1-2%.

Claims (1)

A method of producing steel in an electric arc furnace, comprising supplying scrap metal, cast iron, iron-magnesium concentrate, slag-forming material, carbon-containing material to the furnace, melting the charge, forming slag and releasing it into a steel-pouring ladle, characterized in that the iron-magnesium concentrate is introduced in the form briquettes with dimensions of 20-80 mm over scrap metal, with 1-75% of iron-magnesium concentrate being introduced into the metal charge for scrap before the melting period, and the remaining 25-99% iron-magnesium about the concentrate is introduced not earlier than 0.1 and not later than 0.9 of the total duration of the melting period, and the iron-magnesium concentrate is introduced in an amount that ensures that the ratio between the content of magnesium oxide in the slag and the lining of the furnace is within 0.05-0.16, while the basicity of the slag is provided at the level of 1.7-4.5 units, and during the formation of the coating slag, carbon-containing material is injected into the slag in an amount of 0.1-100 kg / t of slag for foaming the slag and reducing iron from its oxides.