RU2269577C1 - Steel producing method in electric arc steel melting furnace - Google Patents

Abstract

FIELD: ferrous metallurgy, namely processes for producing steels in electric arc steel melting furnace.

SUBSTANCE: method comprises steps of charging metal scrap into electric arc steel melting furnace and pouring cast iron; melting metal charge and oxidizing carbon by means of gaseous oxygen; dephosphorizing steel by adding iron ore or agglomerate and lime; in order to add lime, adding mixture containing ferruginous lime-magnesia flux and lime at relation of flux to lime (0.15 -0.50):1 in quantity 2.5 -4.0% of melt mass till achieving concentration of MgO equal to (8 - 15)%, CaO equal to (35 - 55)% in slag. In order to provide concentration of FeO no less than 15%, gaseous oxygen is blown. Slag is drawn off through lip of working window and steel is poured to ladle. At pouring steel furnace slag is removed. Lime in quantity 1.7 - 2.5% of mass of melt steel, necessary killing and alloying components are added to ladle.

EFFECT: improved strength of lining, increased degree of dephosphorization, lowered consumption of ferroalloys.

Description

The invention relates to ferrous metallurgy, in particular to methods for producing steel in electric arc furnaces.

Known as a prototype is a method of producing steel in electric arc furnaces, including filling in a scrap metal furnace, pouring molten iron, melting a metal charge, dephosphorizing steel by adding portions of iron ore and sinter in a mixture with lime, deoxidizing steel and slag in a furnace, releasing steel in a ladle under furnace slag, an additive in the ladle of a desulfurizing mixture consisting of lime, fluorspar aluminum powder, characterized in that sinter or iron ore is introduced into the filling composition in an amount of 30-60 kg / t of steel, after melting the metal charge at an energy consumption of 220-320 kW · h / t of scrap metal, molten iron is poured into the furnace at a temperature of at least 1200 ° C with a pouring speed of 6-12 t / min, gaseous oxygen is oxidized at a flow rate of 1500- 3000 nm ³ / h, the ratio of iron ore or sinter to be adhered to the mixture with lime is maintained respectively (1-2) :( 2.5-3.5) at a flow rate of 70-110 kg / t of steel, and then slag is lowered through the threshold the working window, and the ratio of lime, fluoride millet and aluminum powder in the desulphurizing seeded in the bucket B respectively support (1.1-1.5) :( 0.3-0.5) :( 0.05-0.1) mixture at a flow rate of 14-18 kg / t steel [1].

Significant disadvantages of this method of producing steel are:

- high wear of the lining due to the reduced concentration of magnesium oxides in the primary slag and saturation of the slag with magnesium oxides from the refractory masonry of the furnace;

- a significant phosphorus content in the steel due to the deoxidation of furnace slag in the furnace and significant rephosphorization in the furnace and when melting into the ladle;

- a high concentration of oxygen in steel due to the ingress of oxidized furnace slag from the furnace into the ladle;

- increased "burnout" of deoxidizers and alloys in connection with the introduction of ferroalloys into the furnace and contact with oxidized slag.

There is also known a method of steelmaking in a converter, which includes introducing scrap metal into the converter, casting iron, blowing metal with oxygen, an additive of lime, and as a slag-forming material of iron-calcined magnesia flux [2].

Significant disadvantages of the invention are:

1. The amount of MgO introduced with iron-calcareous lime flux leads to the production of MgO in slag of more than 15%, which affects the formation of thick magnesian slag with low reactivity, which reduces the degree of dephosphorization of steel and increases the contamination of steel with non-metallic inclusions, in addition, the metal mirror is exposed, as a result of which the steel is saturated with nitrogen, oxygen and hydrogen. All of the above parameters reduce the level of mechanical properties of steel.

2. When using the inventive slag system in an electric arc furnace due to the low foaming ability, shielding of the arcs by slag is reduced, which due to intense radiation leads to burnout of water-cooled panels and erosion of the furnace lining.

The desired technical results of the invention are: an increase in the resistance of the furnace lining, an increase in the degree of dephosphorization of steel, and a decrease in the consumption of ferroalloys.

To this end, a method is proposed for producing steel in an electric arc furnace, including filling scrap metal in a furnace, casting iron, melting a metal charge, oxidizing carbon with gaseous oxygen, dephosphating steel by adding portions of iron ore or sinter and lime, downloading slag through a threshold of the working window, and releasing steel into ladle and additive of lime, deoxidants and alloying, characterized in that the lime during melting is introduced into the composition of the mixture containing lime-magnesian iron flux and lime when the ratio of flux to lime (0.15-0.50): 1 in an amount of 2.5-4.0% by weight of the heat to achieve a concentration in the slag MgO = 8-15%, CaO = 35-55%, while purge with gaseous oxygen to obtain an FeO concentration of at least 15%, when steel is released into the ladle, furnace slag is cut off, and lime is planted in the ladle in an amount of 1.7-2.5% by weight of molten steel.

The claimed limits are selected based on the following assumptions experimentally. The ratio of the mixture containing calc-magnesian iron flux and lime, respectively (0.15 0.50): 1, provides an MgO concentration in the slag of 8-15%.

The amount of slag 2.5-4.0% by weight of the smelting is selected based on the refining ability of the slag. With a decrease in the amount of slag less than 2.5%, the required degree of steel dephosphorization is not achieved, and with an increase of more than 4.0%, additional losses of electricity are required to heat the slag and increase operating costs.

At a concentration of less than 35% CaO, it is impossible to provide the required level of dephosphorization, and with an increase in CaO> 55%, dense, low-reaction slags are formed, the phosphide capacity of the slag is not fully used and the unreasonable costs of lime, as well as heat loss for melting the slag, increase.

With a decrease in the FeO concentration of less than 15%, the dephosphorization of steel slows down and the melting time increases.

In connection with the cutoff of furnace slag, lime is planted in the bucket, the amount of lime is selected based on the refining and heat-insulating ability of ladle slag. When lime is added to the ladle in an amount of less than 1.7% of the mass of molten steel, heat losses through slag are large, and when the amount of lime is more than 2.5%, a significant amount of heat is required for melting.

The inventive method of producing steel was implemented in the smelting of steel in electric arc furnaces DSP-100I7 with a transformer 95MVA. Smelting was carried out according to the following scheme. The filling consisted of scrap metal and molten iron. A mixture consisting of calc-magnesian iron flux and lime in an amount of 2500-4000 kg per heat was sown in the furnace during the melting period at a ratio of (0.15-0.50): 1. At the same time, the concentration of MgO = 8-15%, CaO = 35-55% and FeO≥15% was ensured. In the experiments we used calc-magnesian flux containing FeO _total = 5.0-9.0; CaO _total ≥51.0; MgO≥28,0%, SiO ₂ ≤5,0%, S≤0,06%, P≤0,06% , less than 3.0% PPP. The size of the pieces is 13-60 mm. Flux melting point 1300-1380 ° C.

After reaching the required temperature, as well as the concentrations of carbon and phosphorus in the steel, the latter was discharged from the furnace with slag cut-off. In the bucket during the release, lime in the amount of 1700-2500 kg was planted, as well as the necessary deoxidizers and alloys. The inventive method allowed to increase the resistance of the lining by 6-8%, increase the degree of dysphosphorization of steel by an average of 3.7%; to reduce the consumption of ferroalloys: silicon-containing by 15-18%, manganese-containing by 1.5%, vanadium-containing by 1.5-3%, chromium-containing by 3-4%.

List of sources

1. Pat. RF №2197535, IPC ⁷ С 21 С 5/52, 7/06.

2. Pat. RF №2164952, IPC ⁷ С 21 С 5/28.

Claims (1)

A method of producing steel in an electric arc furnace, including filling a scrap metal furnace, casting iron, melting a metal charge, oxidizing carbon with gaseous oxygen, dephosphorizing steel by adding iron ore or sinter and lime, downloading slag through a threshold of the working window, releasing steel into a ladle and adding lime , deoxidizing and alloying, characterized in that the lime during melting is introduced as part of a mixture containing calc-magnesian iron flux and lime, with a ratio of flux to lime sti (0.15-0.50): 1 in an amount of 2.5-4.0% by weight of the heat to achieve a concentration in the slag MgO = 8-15%, CaO 35-55%, while purging with gaseous oxygen for obtaining a FeO concentration of at least 15%, when steel is released into the ladle, furnace slag is cut off, and lime is planted in the ladle in an amount of 1.7-2.5% by weight of molten steel.