RU2399681C1 - Procedure for rail steel melting - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: procedure consists in charging furnace with metal charge corresponding to metal scrap and liquid iron, in melting, in oxidation, in melting steel in batches, in tapping melt leaving slag and part of metal in furnace, in adding solid slag forming mixture, deoxidisers and alloying elements into ladle during tapping and in finishing steel at aggregate ladle-furnace. Metal scrap at amount of 15-35 % of charge weight, composite semi-finished product at amount of 10-40 % and lime at amount of 2.8-4.2 % of charge weight are charged upon melt tapping on slag and on part of metal left in the furnace. Liquid iron with contents of silicon not more, than 0.45 % and phosphorus not over 0.09 % at amount of 25-75 % of charge weight is poured upon metal scrap melting at specific consumption of electric power 130-380 kWTh/t of summary weight of metal scrap and semi-finished composite product. Oxidation is performed with gaseous oxygen at consumption 80-120 m3/h per ton of metal charge. Lime is added into furnace by portions of 50-200 kg at amount 0.4-1.2% per weight of metal charge upon liquid iron supply; carbon containing dust is blasted at consumption 35-120 kg/min. ^ EFFECT: upgraded quality of steel, reduced duration of melting, and reduced consumption of lime, electric power and ferroalloys.

Description

The invention relates to ferrous metallurgy, in particular to methods for smelting rail steel in electric furnaces.

A known method of smelting rail steel selected as a prototype is known, which includes feeding scrap metal and molten iron into a electric arc furnace as a metal charge, melting, oxidizing period, steel smelting in batches, smelting with leaving slag and part of the metal in the furnace, an additive in the ladle during production solid slag-forming mixture, deoxidizing agents and alloying alloys, in which the slag and part of the metal remaining in the furnace after melting is released before pouring molten iron in an amount of 25-70% by weight of the filling and metal 30-75% of the filling weight is filled with silicon-containing materials at the rate of 0.325-1.625 kg of silicon per ton of metal residue in the furnace or aluminum-containing materials at the rate of 0.425-2.16 kg of aluminum per ton of metal residue in the furnace, oxidation is carried out with gaseous oxygen at a rate of 80 -120 m ³ / h per tonne of metal charge to a carbon content of 0.10-0.70% and a temperature of not more than 1700 ° С, before slag discharge, the metal in the furnace is not deoxidized, manganese-containing alloys are planted in the ladle upon release, based on the introduction of manganese on 0.60-0.75% and lime at the rate of 3-12 kg / t liquid steel, further refinement of the steel according to temperature and chemical composition is carried out on the ladle-furnace unit [1].

Significant disadvantages of this method of smelting rail steel are:

- increased consumption of ferroalloys due to the need for deoxidation of steel and slag in the furnace,

- high energy and lime costs associated with increased melting time,

- a high phosphorus content in steel and a decrease in connection with this the quality characteristics of steel.

A charge for steelmaking is also known, containing an iron-carbon alloy and an oxide material, in which an alloy with the content of 2.5-4.8% C, 0.05-1.20% Si, 0.05-0 is used as an iron-carbon alloy , 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 is used a material with a content of: 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 components are contained in the following ratio, wt.%:

carbon alloy 70-99.9 oxide material 0.1-30;

the charge 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) [2].

Significant disadvantages of this mixture for steelmaking are:

- high energy consumption during the melting of the charge due to the need for melting in comparison with the use of liquid iron in electric melting;

- increased consumption of lime during melting in connection with high concentrations of silicon and phosphorus in the mixture;

- a decrease in the quality indicators of steel due to the high phosphorus content in the charge.

There is also known a method of smelting rail steel, including filling scrap metal, cast iron and lime in an electric arc furnace, melting a metal charge, oxidizing carbon with gaseous oxygen, dephosphorizing by adding iron ore and lime, downloading oxidizing slag through a working window threshold, deoxidizing steel and slag in a furnace, subsequent production of steel under the furnace slag in the ladle, an additive in the ladle during the production of a mixture consisting of lime, fluorspar, silicocalcium and ferrovanadium, characterized in that iron ore is additionally planted in an amount of 4-5% of the weight of the filling, lime is fed in the amount of 4-8% of the weight of the filling, the iron is planted in the form of molten iron, which is poured from above into the furnace after scrap metal is melted at an energy consumption of 220-320 kW · h / t of scrap metal in an amount of 30-35% of the weight of the filling at a speed of 6-12 t / min, while gaseous oxygen is supplied with a flow rate of 15-30 nm ³ / t of steel, and the temperature in the furnace during carbon oxidation is maintained no more than 1680 ° C, iron ore and lime for dephosphorization are added at a rate of 70-120 to / t of steel in the ratio, respectively, (1-2) :( 2.5-3.5) followed by the discharge of oxidizing slag, and the flow rate of the mixture that is seated in the ladle during the production of steel is maintained within 18-27 kg / t of steel at the ratio of lime, fluorspar, silicocalcium and ferrovanadium (1-1.50) :( 0.30-0.40) :( 0.50-0.65) :( 0.07-0.15), respectively [ 3].

Significant disadvantages of this method of smelting rail steel are:

- low consumption of molten iron,

- a significant duration of smelting due to the need for deoxidation of steel and slag in the furnace;

- high energy costs associated with increased melting time;

- high "waste" of ferroalloys and alloys due to the increased oxidation of furnace slag and the addition of a significant amount of ferroalloys to the furnace;

- low degree of dephosphorization with a significant consumption of lime.

The desired technical results of the invention are:

- improving the quality of steel;

- reducing the duration of the heat;

- reduction of consumption of lime, electricity and ferroalloys.

To this end, a method is proposed for smelting rail steel, which includes supplying scrap metal and molten iron to the electric arc furnace as a metal charge, melting, oxidizing period, steel smelting in batches, smelting with leaving slag and part of the metal in the furnace, an additive in the ladle during the production of solid slag-forming mixture, deoxidizers and alloying, steel refinement on the ladle-furnace unit, in which the slag and part of the metal remaining in the furnace after the smelting is dumped with scrap metal in an amount of 15-35% by weight of the filling composite product in the amount of 10-40% by weight of the filling and lime in the amount of 2.8-4.2% by weight of the filling, pouring liquid cast iron with a silicon content of not more than 0.45% and phosphorus not more than 0.09% in the amount of 25 -75% of the weight of the filling is carried out after the scrap is melted at a specific electric power consumption of 130-380 kW · h / t of the total mass of scrap and semi-finished composite, oxidation is carried out with gaseous oxygen at a rate of 80-120 m ³ / h per tonne of metal charge, lime is added to the furnace after pouring liquid iron, produce in portions of 50-200 g in an amount of 0.4-1.2% by weight of metallic charge injecting carbonaceous dust is carried out with an intensity of 35-120 kg / min. The claimed limits are selected experimentally.

The amount of molten iron in the amount of 25-75% by weight of the filling is selected based on obtaining the required carbon concentration in the steel; when using molten iron less than 25% of the filling weight, it is not possible to obtain the concentrations of residual elements (chromium, nickel and copper) required for rail steel and the resulting carbon concentration during melting will not allow enhanced degassing of steel and the removal of non-metallic inclusions with increased oxygen consumption, and when using molten iron in an amount of more than 75% by weight of the filling increased concentration of carbon at melt leads to an increase in the duration of melting due to the necessity of oxidation of carbon "surplus" steel. Moreover, to ensure successful dephosphorization, cast iron should contain no more than 0.45% silicon and up to 0.09% phosphorus.

The amount of scrap metal and semi-finished composite is associated with molten iron. When using scrap metal in an amount of less than 15% of the weight of the filling and the semi-finished composite material of less than 10% of the weight of the filling, the carbon concentration in the melt increases, and therefore the melting time increases due to the limitation of the rate of carbon burnout, with the amount of these materials more than 35% and 40% is possible to obtain high concentrations of residual metals.

The consumption of lime was chosen based on the fact that with an additive in an amount of less than 2.8% by weight of the filling, it is not possible to obtain the required degree of dephosphorization, and with an additive of more than 4.2% by weight of the filling, an increased consumption of lime leads to an increase in energy consumption and an increase in the melting time .

Pouring molten iron is carried out after the melting of scrap metal and semi-finished composite with a specific energy consumption of 130-380 kW · h / t the total mass of scrap and semi-finished composite. With a specific energy consumption of less than 130 kW · h / t of scrap metal, the metal is quenched when pouring molten iron, and at a consumption of more than 380 kW · h / t, when pouring, sharp boiling and emissions from the furnace are observed.

The oxygen flow rate is selected based on the following conditions: when the oxygen flow rate is less than 80 m / h per ton of metal charge, the melting time increases, and when the oxygen flow rate is more than 120 m ³ / h per ton of metal charge, the carbon oxidation rate is much lower than the oxygen diffusion rate, and therefore decreases coefficient of oxygen utilization.

The lime additive in portions of 50-200 kg in an amount of 0.4-1.2% of the mass of the metal charge was selected on the basis that the lime additive of more than 200 kg leads to local cooling of slag in the additive zone and the ineffective use of lime during dephosphorization, and a portion less than 50 kg is ineffective. With a decrease in the amount of lime of less than 0.4% by weight of the metal charge, it is not possible to obtain the required degree of dephosphorization and to meet the requirements of standards for the phosphorus content in steel. With an amount of more than 1.4% by weight of the metal charge, the unproductive consumption of lime, electricity, and the duration of the smelting increase.

Carbon-containing dust blowing is selected based on the following conditions. With a decrease in the amount of dust less than 35 kg / min, it is impossible to conduct good foaming of furnace slag, and with an increase of more than 120 kg / min, dust is used inefficiently.

The inventive method of smelting rail steel was implemented in the smelting of rail steel grades E76F, steel in electric arc furnace type DSP 100N10. After releasing the smelting to the remainder of the metal and slag into the furnace, scrap metal was loaded in an amount of 15-35 tons, a semi-finished composite in an amount of 10-40 tons and lime in an amount of 2.8-4.2 tons. Semi-finished product containing alloy as an iron-carbon material with a content of: 3-4% C, 0.1-0.50% Si, 0.1-0.50% Mn, 0.07-0.11% P, and in as the oxide material, pellets containing: 50-70% Fe, 2-10% SiO ₂ , 1-8% Al ₂ O ₃ , 0.5-10% CaO, in the form of ingots weighing 10-20 kg, made by casting iron in the blast furnace shop. Melting was carried out, and at a specific consumption of 130-380 kWh / t of the total mass of scrap metal and semi-finished composite, liquid iron was poured into the furnace from the top of the iron ladle in an amount of 25-75 tons.

The work was carried out without subsequent dumping of scrap metal into the furnace. Carbon oxidation was carried out by purging the steel in the furnace with gaseous oxygen through a system of gas-oxygen burners with a flow rate of 80-120 m ³ per ton of metal charge. During the melting period and the oxidation period, an additive was added to the furnace through a lime bore hole in portions of 50-200 kg in an amount of 400-1200 kg. For foaming the slag, carbon-containing powder was injected with an intensity of 35-120 kg / min.

When steel was released, silicomanganese and lime were planted in the bucket. Further refinement of steel grades NE76F and E76F in temperature and chemical composition was carried out on a ladle-furnace type unit and processing on a chamber-type vacuum. Steel was cast on 4-strand continuous casting machines with a mold section of 300 × 330 mm. Then, continuously cast billets were heated in a walking beam furnace and rolled onto P65 rails.

With experimental steelmaking according to the claimed method, the melting time is reduced from 55-59 min to 53-56 min, electricity from 276-295 kW · h / t to 259-289 kW · h / t, the burning of ferroalloys (manganese-containing 1.8 %, silicon-containing by 2.1%), the consumption of lime was reduced from 58-59 kg / t to 51-56 kg / t.

Information sources

1. RF patent №2328534, cl. C21C 5/52, 7/07.

2. Application No. 2007110459, class C21C 5/00.

3. RF patent No. 2197536, cl. C21C 5/52, 7/06.

Claims (1)

A method of smelting rail steel, including supplying scrap metal and molten iron to a electric arc furnace as a metal charge, melting, oxidizing period, steel smelting in batches, smelting with leaving slag and part of the metal in the furnace, an additive to the ladle during the smelting of a solid slag-forming mixture, deoxidizers and alloying, steel refinement on the ladle-furnace unit, characterized in that 15-35% of the filling mass is fed to the slag and part of the metal remaining in the furnace after the smelting is released, semi-finished composite ikat in the amount of 10-40% by weight of the filling and lime in the amount of 2.8-4.2% by weight of the filling, the supply of molten iron with a silicon content of not more than 0.45% and phosphorus not more than 0.09% in the amount of 25 -75% of the weight of the filling is carried out after the scrap is melted at a specific energy consumption of 130-380 kW · h / t of the total mass of scrap and semi-finished composite, while the oxidation is carried out with gaseous oxygen with a flow rate of 80-120 m ³ / h per ton of charge, after feeding liquid iron produce lime additive in the oven in portions of 50-200 kg in the amount of 0.4-1.2% of the mass of the metal charge and blow carbon-containing dust with an intensity of 35-120 kg / min.