RU2269578C1 - Rail steel melting method in electric arc furnace - Google Patents

Abstract

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

SUBSTANCE: method comprises steps of charging scrap metal to furnace; pouring melt cast iron; adding lime; melting metal charge; oxidizing carbon by means of gaseous oxygen; performing dephosphorization due to adding iron ore and lime; adding lime in mixture containing ferruginous lime-magnesia flux and lime at relation of flux to lime (0.15 -0.50):1 in quantity 25 - 40 kg/steel t till achieving concentration of MgO equal to 8 -15%, CaO no less than 35% in slag; blowing off gaseous oxygen for providing concentration of FeO in slag no less than 15%; drawing off slag through lip of working window; discharging steel to ladle at cutting off furnace slag; at discharging steel, adding to ladle mixture of lime and fluorspar in quantity 15 - 20 kg/t and 3 -5 kg/t of steel respectively and silicomanganese in quantity 0.8 - 1.0 kg/t of steel; correcting chemical content of steel in "furnace-ladle" type aggregate.

EFFECT: increased strength of furnace lining, lowered consumption of ferroalloys, improved mechanical properties of steel.

Description

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

A known method of smelting rail steel selected as a prototype is known, 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 oxidative slag through a working window threshold, deoxidizing steel and steel in the furnace, the subsequent release of steel under the furnace slag into the ladle, the additive in the ladle during the production of the mixture consisting of lime, fluorspar, silicocalcium and ferrovanadium, characterized by the fact that iron ore is additionally planted in the 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 a power consumption 220-320 kW · h / t 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 · h / t steel, and the temperature in the furnace at carbon oxidation is supported by no more than 1680 ° C, iron ore and lime for dephosphorization they are pulled at a flow rate of 70-120 kg / t in a ratio, respectively (1-2) :( 2.5-3.5) followed by a run-off of oxidizing slag, and the flow rate of the mixture that is seated in the ladle during steel production is maintained within 18-27 kg / t of steel with a ratio of lime, fluorspar, silicocalcium and ferrovanadium (1 ÷ 1.50) in it: (0.30 ÷ 0.40) :( 0.50 ÷ 0.65) :( 0.07 ÷ 0.15) respectively [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 concentration of phosphorus in steel due to late slag formation in the furnace and rephosphorization due to the deoxidation of furnace slag and the release of steel under furnace slag;

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

- high consumption of ferroalloys in connection with the introduction of the latter into the furnace and contact with oxidized slag;

- increased pollution became non-metallic inclusions of endogenous and exogenous nature and in connection with this low level of mechanical properties.

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-lime-magnesia flux leads to the production of more than 15% MgO in slag, as a result of which thick magnesian slags are formed, which reduce the degree of dephosphorization of steel and contribute to an increase in steel pollution by non-metallic inclusions of an exogenous nature. In addition, thick magnesian slag contributes to the exposure of the metal mirror and the saturation of the steel with gases (nitrogen, oxygen and hydrogen), while the level of mechanical properties of the steel decreases markedly.

2. The use of a slag system for an oxygen converter for an electric arc furnace is claimed to result in a low foaming ability of the slag, which reduces the shielding of the arcs by slag, due to which the intense emission of arcs leads in some cases to burnout of water-cooled panels and erosion of the furnace lining.

The desired technical results of the invention are: increasing the resistance of the furnace lining, reducing the consumption of ferroalloys, increasing the degree of dephosphorization of steel, reducing the level of contamination of steel with non-metallic inclusions and increasing the level of mechanical properties of steel.

To this end, a method is proposed for smelting rail steel in an electric arc furnace, including filling in a scrap metal furnace, pouring molten iron, an additive for lime, melting a metal charge, oxidizing carbon with gaseous oxygen, dephosphorization by adding iron ore and lime, downloading oxidative slag through the threshold of the working window, and releasing steel in the bucket, an additive in the bucket during the production of a mixture of lime, fluorspar and ferroalloys, characterized in that the lime is introduced into the mixture containing lime-magnesia known flux and lime, with a ratio of flux and lime (0.15-0.50): 1 in the amount of 25-40 kg / t of steel until the concentration of MgO = 8-15% and CaO is not less than 35% in the slag, and purge with gaseous oxygen to obtain a concentration of FeO in the slag of at least 15%; when steel is released into the ladle, furnace slag is cut off, lime and fluorspar are added to the ladle in the amount of 15-20 kg / t of steel and 3-5 kg / t of steel, respectively and as ferroalloy, silicomanganese is introduced in an amount of 0.8-1.0 kg / t of steel, and the steel is refined according to the chemical composition of and a ladle-furnace unit.

The claimed limits are selected based on the following premises.

To form the slag required for melting and ensure the concentration of MgO ÷ 8-15% and CaO at least 35%, the ratio of the mixture containing calc-magnesian iron flux and lime should be in the range respectively (0.15 ÷ 0.50): 1.

The amount of the mixture less than 25 kg / t does not provide the required level of dephosphorization, as well as the required "covering" property of the slag from the penetration of gases from the atmosphere of the furnace into steel.

When the amount of the mixture is more than 40 kg / t of steel, the amount of furnace slag increases significantly, which leads to the loss of thermal energy for heating the slag and increase operating costs.

At a FeO concentration of less than 15%, due to the high viscosity of the slag, the degree of dephosphorization decreases and the contamination of steel with non-metallic inclusions of an exogenous nature increases.

The elimination of the deoxidation of steel and slag in the furnace eliminates the reduction of phosphorus from the slag and its transition to steel, and therefore, in combination with the slag cut-off, the total phosphorus level in steel smelted without deoxidation is much lower than with the deoxidation of steel and slag in the furnace.

To form slag in the ladle in order to reduce the contamination of steel by non-metallic inclusions and desulfurization during lime production, lime and fluorspar are put in the ladle. With an additive of less than 15 kg / t of steel and fluorspar in the ladle of less than 3%, the required refining properties of slag cannot be achieved, and with an increase in the additive of lime more than 20 kg / t of steel and fluorspar, heat losses and operating costs increase.

In order to reduce the oxidation of steel and alloy steel with manganese, silicomanganese is added to the lower limit of smelted steel, which is 0.8-1.0 kg / t of steel. In order to reduce the "burnout" of ferroalloys, the alloying of steel in the furnace and in the ladle was transferred to a ladle-furnace unit.

The inventive method of smelting rail steel in an electric arc furnace was implemented in the smelting of rail steel grades NE76F and E76F in electric arc furnace type DSP-100I7 with transformers 95 MVA.

In the experimental melts, a lime-magnesia flux was used, containing, wt.%: FeO _total = 5.0-9.0%; CaO _total >51.0%;MgO>28.0%; SiO ₂ <5.0%; S <0.06%; P <0.06%; PPP - less than 3%. The size of the pieces is 13-60 mm. Flux temperature - 1300-1380 ° С.

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 in a ratio of (0.15-0.50): 1 was seated in the furnace during the melting period. In this case, the concentration of MgO = 8-15%, CaO> 35%, FeO> 15% was ensured. Slag and steel in the furnace were not deoxidized. The release was organized with a furnace slag cut-off, during the release, 1500-2000 kg of lime and 300-500 kg of fluorspar were planted in the ladle, and depending on the concentration of manganese in the steel, 800-1000 kg of silicomanganese MnC17. Further refinement of steel (an additive of ferrovanadium, silicocalcium and other ferroalloys) was carried out on a ladle-furnace unit.

The inventive method allowed to increase the lining resistance by 6-8%, increase the degree of dephosphorization of steel by an average of 3.7%, reduce the consumption of ferroalloys: silicon-containing by 15-18%, manganese-containing by 1.5%, vanadium-containing by 1.5-3, 0%, calcium-containing - 1.5-2.5 times, reduce the length of the line of oxide inclusions by 0.1-0.2 mm; increase the impact strength of rail steel by an average of 0.05 MJ / m ² .

Information sources

1. Pat. RF №2197536, class C 21 C 5/52, 7/06.

2. Pat. RF №2164952, class C 21 C 5/28.

Claims (1)

A method of smelting rail steel in an electric arc furnace, including filling in a scrap metal furnace, pouring molten iron, adding lime, melting a metal charge, oxidizing carbon with gaseous oxygen, dephosphorizing by adding iron ore and lime, downloading oxidative slag through the threshold of the working window, releasing steel into a ladle, an additive in the bucket during the production of a mixture of lime, fluorspar and ferroalloy, characterized in that the lime is introduced into the mixture containing lime-magnesian iron flux and lime, p At a ratio of flux and lime (0.15-0.50): 1 in the amount of 25-40 kg / t of steel until the concentration of MgO = 8-15% and CaO is not less than 35% in the slag, moreover, oxygen gas is purged for obtaining a concentration of FeO in the slag of at least 15%, when steel is released into the ladle, furnace slag is cut off, lime and fluorspar are added to the ladle in the amount of 15-20 kg / t and 3-5 kg / t of steel, respectively, and they are introduced as a ferroalloy silicomanganese in the amount of 0.8-1.0 kg / t of steel and carry out the refinement of steel by chemical composition on the unit type "ladle furnace".