RU2315115C1 - Method of making rail steel - Google Patents

Abstract

FIELD: ferrous metallurgy; melting rail steel in electric arc steel melting furnaces.

SUBSTANCE: proposed method includes delivery of scrap used as metal burden and molten cast iron to electric arc steel melting furnace, melting and oxidizing them; melting period is continued till carbon content in steel is no less than 0.15%. Then, furnace slag and part of metal at tapping are cut off and metal is tapped into ladle. Lime, silico-manganese and coke are added to ladle at the following ratio: (0.4-0.7) : (0.75-1.0) : (0.15-0.30), respectively in the amount of 1.3-2.0% of molten steel mass. Then, blowing with inert gas is carried out at flow rate of gas of 15-25 nm³/h; blowing is continued for 15-30 minutes.

EFFECT: reduced concentration of oxygen in steel and contamination with non-metallic inclusions.

Description

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

A known method of smelting rail steel, which includes feeding scrap metal and molten iron into a electric arc furnace as a metal batch, melting, oxidizing period, deoxidation of aluminum with steel and slag by coke powder, crushed ferrosilicon and granular aluminum, melting into a ladle, adding to the ladle when the production of a solid slag-forming mixture consisting of lime and fluorspar, characterized in that the steel is smelted in batches, and the metal charge of the first smelting in the batch is given a mass of 10-15% more mass of the metal charge of the subsequent melts, and the mass of the metal charge of the last heat in the series is reduced by 10-15%, the oxidation period is carried out to obtain steel with a carbon content of at least 0.60% and a temperature above liquidus of 180-240 ° C; moreover, steel is deoxidized in all melts of the series with aluminum in an amount of 0.07-0.10% of the mass of the metal charge, and slag deoxidation in the furnace with coke powder, crushed ferrosilicon and granular aluminum in the amount, respectively, of 0.09-0.10% of each the mass of the metal charge is carried out on the last heat in the series, when the first and subsequent melts are discharged, furnace slag is cut off, and the last heat is let out with furnace slag, when the melts are released, a solid slag-forming mixture consisting of lime and fluorspar is planted in the ratio (1.0 -1.5): (0.3-0, 5) respectively, in the amount of 3-3.3% of the mass of liquid steel, and the necessary deoxidizers and alloying [1].

Significant disadvantages of this method of smelting rail steel are:

- high oxygen content due to the low deoxidizing ability of the ferroalloys to be seated and the improper order of their addition;

- high consumption of nitrided ferroalloys due to the increased oxygen content in steel,

- a high level of nonmetallic inclusions of the endogenous type due to the increased oxygen content in steel;

- a reduced level of physical and mechanical properties due to the significant concentration of oxygen in the steel and contamination of the steel by nonmetallic inclusions of the endogenous type.

Known, selected as a prototype, a method of smelting rail steel in an electric arc furnace, including filling in a scrap metal furnace, pouring molten iron, adding lime, melting the metal charge, oxidizing carbon with gaseous oxygen, dephosphorizing by adding iron ore and lime, downloading oxidative slag through the threshold of the worker windows, the release of steel into the ladle, the additive into the ladle during the production of a mixture of lime, fluorspar and ferroalloys, in which lime is introduced into the mixture containing lime-magnesia ironized 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% in the slag and CaO at least 35%, moreover, oxygen gas is purged 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 an amount of 15-20 kg / t of steel and 3-5 kg / t, respectively steel, and as a ferroalloy, silicomanganese is introduced in an amount of 0.8-1.0 kg / t of steel, and the steel is refined by chemical left on the machine type "ladle-furnace" [2].

Significant disadvantages of this method of smelting rail steel are:

- high consumption of ferroalloys due to the increased oxygen content in steel;

- a high level of nonmetallic inclusions of the endogenous type due to the increased oxygen content in steel;

- low level of physical and mechanical properties associated with the contamination of steel oxide non-metallic inclusions.

The desired technical results of the invention are: a decrease in the oxygen concentration in steel and contamination with non-metallic inclusions, a decrease in the consumption of nitrided ferroalloys, an increase in the complex of physicomechanical properties of rail steel.

To this end, a method for smelting rail steel is proposed, which includes supplying scrap metal and molten iron to the electric arc furnace as a metal batch, melting the metal batch, oxidizing period, cutting off furnace slag and part of the metal during discharge, melting the ladle, adding to the ladle when releasing solid slag-forming mixture and deoxidizers, processing of smelting on a ladle-furnace unit with an additive of ferroalloys, in which the oxidation period is carried out to obtain steel with a carbon content of at least 0.15%, in the ladle in lime, silicomanganese, and coke are added as solid slag-forming mixture and deoxidizing agents at a ratio of (0.4-0.7) :( 0.75-1.0) :( 0.15-0.30), respectively, in an amount of 1.3 -2.0% by weight of liquid steel, before introducing ferroalloys on a ladle-furnace unit, coke is added to the bucket in an amount of 0.4-0.6% by weight of liquid steel and an inert gas is blown at a flow rate of 15-25 nm ³ / h for 15-30 minutes.

The claimed limits are selected experimentally. The carbon content was chosen based on the fact that with a decrease in carbon concentration of less than 0.15%, the oxygen content in steel increases significantly and long-term processing of steel on a ladle-furnace unit is necessary in order to reduce carbon content and carburization.

In connection with the cut-off of furnace slag, a mixture consisting of lime, silicomanganese and coke is introduced into the ladle when melting is released. The ratio and number of components in the mixture is selected based on the refining and heat-insulating ability of ladle slag. When the ratio in the mixture of lime, silicomanganese and coke is less than 0.4: 0.75: 0.15, respectively, it is not possible to reduce the oxygen content in steel to the required values and to obtain refining slag with a high degree of desulfurization and low oxidation, while the main amount of dissolved oxygen when the mixture is added, it interacts with carbon to form carbon monoxide WITH, as a result of which the steel is not contaminated by non-metallic inclusions (such as MeO), which significantly reduce the physical and mechanical properties of steel. When the ratio of lime, silicomanganese and coke in the mixture is more than 0.7: 0.75: 0.30, respectively, an increase in the concentration of silicon, manganese and carbon is higher than the required values for certain steel grades, in addition, poor slag formation due to prolonged dissolution is observed a lot of lime.

An amount of the mixture less than 1.3% by weight of liquid steel leads to a low refining and heat-insulating ability of ladle slag, with an increase in the amount of the mixture more than 2.0% by weight of liquid steel, the heat losses associated with the formation of slag increase and contamination of the steel with exogenous slag inclusions is possible .

Before the introduction of ferroalloys on a ladle-furnace unit, an additive in the coke ladle in an amount of less than 0.4% by weight of molten steel does not allow to obtain low required oxygen concentrations and high nitrogen concentrations (since coke contains some nitrogen in its composition), and with a coke additive of more than 0.6% by weight of liquid steel, it is possible to obtain a carbon content above the upper limit of its content in the finished steel.

Inert gas purging with a flow rate of less than 15 nm ³ / h for less than 15 minutes does not provide good mixing of the metal and the required removal of oxygen through diffusion of oxygen and the emergence of non-metallic inclusions. Inert gas purging with a flow rate of more than 25 nm ³ / h for more than 30 min contributes to the secondary saturation of the steel with atmospheric oxygen and pollution of the steel by exogenous non-metallic inclusions associated with erosion of the steel ladle lining.

The inventive method of smelting rail steel was implemented in the smelting of rail steel in an electric arc furnace DSP-100N10. Smelting was carried out "in the swamp" according to the following scheme. The filling of the first heat in the series for metal filling was 10-15 tons more than subsequent fillings, and the last in the heat series was 10-15 tons less. The filling consisted of 80-90 tons of scrap metal and 3-8 tons of lime. Pouring of pig iron in an amount of 30-35 tons was carried out from an iron bucket by means of a bridge crane with an open arch after the melting of “wells” and partial upsetting of scrap metal in the furnace. Carbon oxidation was carried out in a furnace to a concentration of at least 0.15% by blowing steel through water-cooled wall tuyeres. The smelting was carried out through a bay window, ensuring that all furnace slag and 10-15 tons of metal were left in the furnace. 100-110 tons of metal were released into the bucket.

Lime 400-700 kg, silicomanganese 750-1000 kg, coke 150-300 kg, respectively, were planted in the bucket. Dry quenching coke was used in experimental melts (in the manufacture of coke oven batteries after a full coking and dispensing period, the coke is quenched using nitrogen) with a high nitrogen content (1.2-1.4% N), in connection with which the steel was additionally saturated with nitrogen and, accordingly, expensive nitrided ferroalloys were saved. Immediately before the introduction of ferroalloys on a ladle-furnace unit, coke was placed in the bucket in an amount of 400-600 kg by weight of molten steel and purged through refractory tuyeres installed in the steel ladder bottom with argon with a flow rate of 15-25 nm ³ / h for 15- 30 minutes. Next, the steel was brought to the ladle-furnace unit in terms of chemical composition and the temperature required for casting and transferred to casting for continuous casting. Rolling and certification of rails was carried out according to the technology existing at the plant. According to the claimed technology, a series of pilot melts (18 pcs.) Of NE76F rail steel was carried out with rolling on a P65 rail profile.

The inventive method provides a decrease in oxygen content up to 20 ppm, a decrease in steel contamination (the length of the line of non-metallic inclusions for steel smelted according to the claimed technology is no more than 1 mm, while the base reaches 2 mm), the consumption of nitrided vanadium-containing ferroalloys is reduced by 0, 1 kg per ton of smelted steel, mechanical tests of rail products show that the yield strength and tensile strength are increased by 5-8 MPa, impact strength at negative temperatures by 0.5 J / cm ² .

Information sources

1. RF patent 2235790 RF, cl. C21C 5/52, 7/076.

2. RF patent 2269578 of the Russian Federation, cl. C21C 5/52.

Claims (1)

A method of smelting rail steel, including supplying scrap metal and molten iron to the electric arc furnace as a metal charge, melting the metal charge, oxidizing period, cutting off furnace slag and part of the metal during discharge, melting the ladle, adding to the ladle when releasing solid slag-forming mixture and deoxidized processing of smelting on a ladle-furnace unit with the addition of ferroalloys into it, characterized in that the oxidation period is carried out to produce steel with a carbon content of at least 0.15%, in the ladle as f solid slag-forming mixture and deoxidants are added lime, silicomanganese, coke with the ratio (0.4-0.7) :( 0.75-1.0) :( 0.15-0.30), respectively, in an amount of 1.3 -2.0% by weight of liquid steel, before introducing ferroalloys on a ladle-furnace unit, coke is added to the bucket in an amount of 0.4-0.6% by weight of liquid steel and an inert gas is blown at a flow rate of 15-25 nm ³ / h for 15-30 minutes