RU2394917C1 - Procedure for rail steel melting - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: procedure consists in charging arc electric furnace with metal charge corresponding to metal scrap and liquid iron, in melting, in oxidation, in melting steel in series, 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. Upon melt tapping metal scrap at amount 25-70% of charge weight and lime at amount of 1.5-3.0% of charge weight are charged onto part of metal and slag left in the furnace. When metal scrap has been melted with specific consumption of electric power 125-300 kWt-h/per t of metal scrap, there is cast liquid iron with contents of silicon not over 0.45% and phosphorus not over 0.09% at amount of 30-75% of weight of charge together with ladle slag of FeO contents below 3.0 % and ratio CaO/SiO2 2.0-4.4 at amount 0.5-6.0% of charge weight. Oxidation is performed with gaseous oxygen at consumption 50-140 m3/h per ton of metal charge. Lime is added into furnace by portions of 50-200 kg at amount 0.3-1.0% per weight of metal charge upon liquid iron casting; carbon containing dust is blasted at consumption 40-80 kg/min. ^ EFFECT: upgraded quality of steel, reduced consumption of lime and electric power.

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, characterized in that 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 silicon-containing materials at a rate of 0.325-1.625 kg of silicon per ton of metal residue in a furnace or aluminum-containing materials at a rate of 0.425-2.16 kg of aluminum per ton of metal residue in a furnace are planted and scrap metal 30-75% by weight of the filling, oxidation is carried out with gaseous oxygen at a rate 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 ° C, before slag is released, the slag and metal in the furnace are not deoxidized, manganese-containing alloys are planted in the ladle at the rate of introduction of manganese by 0.60-0.75% and lime from the calculation 3-12 kg / t-molten steel become further fine-tuning of temperature and chemical composition is performed at the ladle furnace [1].

Significant disadvantages of this method of smelting rail steel are:

- 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.

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 planted at a rate of 70-120 kg / 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 a ratio of lime, fluorspar, silicocalcium and ferrovanadium (1-1.50) :( 0.30-0.40) :( 0.50-0.65) :( 0.07-0.15), respectively [2] .

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,

- 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 consumption of lime and electricity.

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 25-70% of the weight of the filling is dumped with slag and a part of the metal remaining in the furnace after smelting, and lime in the amount of 1.5-3.0% 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 30-75% of the weight of the filling together with ladle slag with a content FeO less than 3.0% and a CaO / SiO ₂ ratio of 2.0-4.4, in an amount of 0.5-6.0% by weight of the filling, is carried out after the scrap is melted at a specific power consumption of 125-300 kWh / t of scrap , the oxidation is carried out with gaseous oxygen with a flow rate of 50-140 m ³ / h per tonne of metal charge, the lime additive in the furnace after pouring liquid iron is produced in portions of 50-200 kg in an amount of 0.3-1.0% by weight of the metal charge and the blowing of carbon-containing dust is carried out with an intensity of 40-80 kg / min.

The claimed limits are selected experimentally.

The amount of scrap metal is associated with molten iron. When using scrap metal in an amount of less than 25% by weight of the filling, the concentration of carbon in the melt increases, and therefore the melting time increases due to the limitation of the rate of carbon burnout, with an amount of more than 70% it 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 1.5% by weight of the filling, it is not possible to obtain the required degree of dephosphorization, and with an additive of more than 3.0% by weight of the filling, an increased consumption of lime leads to an increase in energy consumption and an increase in the duration of smelting.

The amount of molten iron in the amount of 30-75% by weight of the filling was selected on the basis of obtaining the necessary carbon concentration in the steel; when using molten iron less than 30% of the filling weight, it was 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 quantity and composition of ladle slag is selected from the following premises. The ratio CaO / SiO ₂ = 2.0-4.4 together with the added lime provides the required dephosphorization. When the ratio of CaO / SiO _{2 is} less than 2.0 and the amount of slag is less than 0.5% of the weight of the filling, it is necessary to increase the consumption of lime that is deposited in the furnace, and when the ratio of CaO / SiO _{2 is} more than 4.4 and the amount of slag is more than 6% of the weight of the filling significantly increases the amount of furnace slag and increase unproductive energy costs. The concentration in the ladle slag FeO less than 3.0% allows the joint addition of ladle slag and molten iron without sharp boiling and emissions of steel-slag emulsion from the furnace when pouring molten iron.

Pouring molten iron is carried out after the melting of scrap metal at a specific energy consumption of 125-300 kW · h / t of scrap metal. With a specific electric energy consumption of less than 125 kW · h / t of scrap metal, metal “freezes” when pouring molten iron, and at a consumption of more than 300 kW · h / t, sharp boiling and emissions from the furnace are observed during casting.

The oxygen flow rate is selected based on the following conditions: when the oxygen flow rate is less than 50 m ³ / h per tonne of metal charge, the melting time increases, and when the oxygen flow rate is more than 140 m ³ / h per tonne of metal charge, the carbon oxidation rate is much lower than the oxygen diffusion rate, and therefore the efficiency of oxygen is reduced.

The lime additive in portions of 50-200 kg in an amount of 0.3-1.0% by weight of the metal charge is selected on the basis that the lime additive in a portion 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 of less than 50 kg is ineffective. With a decrease in the amount of lime of less than 0.3% 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 1.0% by weight of the metal charge, the unproductive consumption of lime, electricity increases, and the duration of the smelting increases.

Carbon-containing dust blowing is selected based on the following conditions. With a decrease in the amount of dust less than 40 kg / min, it is impossible to conduct good foaming of furnace slag, and with an increase of more than 80 kg / min.

The inventive method of smelting rail steel was implemented in the smelting of rail steel grades E76F and NE76F, steel in electric arc furnace type DSP 100I10. The ladle slag remaining after casting was poured into a cast-iron ladle filled with cast iron in the casting span. The amount of pig iron in the ladle was 30-75 tons. After that, the iron bucket was transferred to the furnace span. After releasing the smelting to the remainder of the metal and slag, 25–70 tons of scrap metal and 1.5–3.0 tons of lime were charged into the furnace. Melting was carried out and, at a specific consumption of 125–300 kWh / t scrap metal, liquid was poured cast iron in the amount of 30-75 tons together with ladle slag in the amount of 0.5-6.0 tons to the furnace from the top of the iron ladle.

The work was carried out without subsequent dumping of scrap metal into the furnace. The oxidation of carbon 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 50-140 m ³ per ton of metal charge. During the melting period and the oxidation period, an additive was added to the furnace through the lime aperture in portions of 50-200 kg in an amount of 300-1000 kg. For foaming the slag, a carbon-containing powder was injected with an intensity of 40-80 kg / min.

When steel was released, 800-1000 kg of silicomanganese MnC17 and lime in an amount of 300-1000 kg were planted in the ladle. Further refinement of steel grades NE76F and E76F in temperature and chemical composition was carried out on a ladle-furnace type unit. 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.

When steelmaking according to the claimed method, the consumption of lime is reduced by 6-12 kg, the contamination of steel by non-metallic inclusions is reduced (the index of total pollution by non-metallic inclusions is reduced by 0.18%), the phosphorus content in the finished steel is reduced by 0.003%, the degree of dephosphorization is increased by 10 -12%.

Information sources

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

2. 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 release of solid slag-forming mixture, deoxidizing agents and alloying, steel refinement at the ladle-furnace assembly, characterized in that the slag and part of the metal remaining in the furnace after melting are heaped up with scrap metal in an amount of 25-70% by weight of the filling and lime in 1.5-3.0% 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 30-75% of the filling weight, together with ladle slag with an FeO content of less than 3.0% and a ratio of CaO / SiO ₂ = 2.0-4.4 in an amount of 0.5-6.0% of the weight of the filling is carried out after the scrap is melted at a specific power consumption of 125 · 300 kW · h / t of scrap metal, oxidation is carried out with gaseous oxygen with a flow rate of 50-140 m ³ / h per ton of metal charge, and after pouring liquid iron into the furnace, lime is added in portions of 50-200 k g in an amount of 0.3-1.0% by weight of the metal charge and blowing carbon-containing dust with an intensity of 40-80 kg / min.