RU2437942C1 - Procedure for production of low carbon steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in melting metal in steel melting installation, in tapping metal into steel teeming ladle, in introduction of reducers and in vacuumising, Metal is melted with refining a bath with oxygen till content of carbon in metal amounts to as high, as 0.03 %. During melt tapping into the steel teeming ladle there is added high carbon ferro-manganese at amount not over 3.0 kg/t. Metal is vacuumised in two stages. At the first stage vacuum in a chamber is set at the level not over 150 mbar, flow rate of argon for mixing - 1000 l/min, while duration of the first stage is 5…8 min. At the second stage vacuum in the chamber is set at the level not over 10 mbar, flow rate of argon for mixing - 1500 l/min at content of {CO} in fumes - not less, than 10 %, and at less content of {CO} - 2000 l/min, and duration of the second stage is 13…16 min. During vacuumising steel is micro-alloyed with niobium, titanium and aluminium not less, than 2 minutes before end of the second stage by adding niobium and titanium containing lump ferro-alloys and aluminium pellets.

EFFECT: production of steel with low content of carbon at reduced material expenditures.

Description

The invention relates to ferrous metallurgy, and specifically to methods for producing low carbon steels using steel vacuum plants, and can be used in steelmaking shops of metallurgical plants.

A known method of smelting niobium-containing steel, including filling a charge containing carbon and manganese, melting, heating the metal in a steelmaking unit and its subsequent oxidative refining with oxygen purging from above, evacuating, introducing a niobium-containing ferroalloy [RF Patent No. 2243268, cl. C21C 7/10].

The disadvantages of this method include the impossibility of obtaining an ultra-low carbon content in steel (not more than 0.002%), as well as obtaining the required niobium content after evacuation using a flux-cored wire, which leads to an increase in the carbon content in the metal.

The closest analogue is a method of smelting low-carbon titanium-containing steel, including the release of the melt, the introduction of deoxidizers and titanium-containing ferroalloys, evacuation, characterized in that the titanium-containing ferroalloys are introduced into the metal after evacuation in the form of a titanium-containing flux-cored wire [RF Patent No. 2243269, cl. C21C 7/10].

Significant disadvantages of this method are the impossibility of obtaining an ultra-low carbon content in steel (not more than 0.002%), as well as obtaining the required titanium content after evacuation using flux-cored wire, which leads to an increase in the carbon content in the metal.

The problem solved by the invention is to obtain steel with a carbon content of not more than 0.0020% and reduce material costs when obtaining the required content of niobium, titanium and aluminum in steel.

To do this, in the proposed method for the production of low-carbon steel, including the smelting of metal in a steel-smelting unit, the release of smelting into a steel-pouring ladle, the introduction of deoxidizers, evacuation, in contrast to the closest analogue, the smelting of the metal is carried out with refining of the bath with oxygen until the carbon content in the metal is not more than 0.03 %, during the production of smelting, high-carbon ferromanganese in an amount of not more than 3.0 kg / t is added to the steel pouring ladle, the metal is evacuated in two stages: at the first stage do not set a vacuum in the vacuum chamber of not more than 150 mbar and an argon flow rate for stirring of 1000 l / min, the duration of the first stage of evacuation being 5 ... 8 min, at the second stage set a vacuum in the vacuum chamber of not more than 10 mbar and argon flow rate for mixing 1500 l / min with a content of {CO} in the exhaust gases of at least 10% with a lower content of {CO} - 2000 l / min, and the duration of the second stage of evacuation is 13 ... 16 min; in addition, microalloying of steel with niobium, titanium, and aluminum is carried out in the process of evacuation at least 2 minutes before the end of the second stage by the addition of niobium - and titanium-containing lumpy ferroalloys and aluminum shot.

The essence of the invention consists in increasing the degree of carbon removal from steel by applying a rational technology of metal deoxidation at the outlet from the steelmaking unit, evacuating the steel and obtaining the required content of titanium, niobium and aluminum directly in the process of evacuation by introducing lumpy ferroalloys and aluminum fraction.

The declared limits are selected experimentally. The residual carbon content in the intermediate and the amount of carbon ferromanganese added to it provide a residual oxygen content in the metal (at least 650 ppm) sufficient to remove carbon during vacuum. With an increase in the carbon content of more than 0.03% in the intermediate product and an increase in the consumption of carbon ferromanganese more than 3 kg / t at the release of metal from the steelmaking unit, the oxidation of the metal will be less, which will not allow maximum removal of carbon during evacuation.

At the first stage of evacuation, with an increase in vacuum in the vacuum chamber of more than 150 mbar, a decrease in argon consumption of less than 1000 l / min and a reduction in the time of evacuation of less than 5 minutes, the required carbon content at the end of the first stage (not more than 0.020%) will not be achieved.

At the second stage, with an increase in vacuum in the vacuum chamber of more than 10 mbar, a decrease in argon consumption of less than 1500 l / min and a decrease in evacuation time of less than 13 minutes, the required carbon content at the end of evacuation will not be achieved (not more than 0.0020%). An increase in the evacuation time at the first and second stages of more than 8 and 16 minutes, respectively, is impractical due to excessive wear of the lining of the vacuum chamber. With an increase in the first and second stages of argon consumption of more than 1000 l / min and 1500 l / min, the intensity of the bubbling process increases sharply, and there is a risk of metal spills and overgrowth of the exhaust pipe. With a decrease in {CO} content in the exhaust gases of less than 10%, at the second stage it is necessary to increase the argon flow rate to 2000 l / min to achieve the required carbon content at the end of evacuation (not more than 0.0020%). The recoil time of lumpy ferroalloys and aluminum fractions is chosen in order to reduce their waste and reduce material costs.

The claimed method of out-of-furnace steel processing was implemented in an oxygen-converter shop for the production of more than 50 IF-steel melts in a steel evacuation unit.

Metal smelting was carried out in 370-ton oxygen converters. Metal processing was carried out at the installation of degassing steel No. 2.

The oxidation of metal upon arrival at UVS No. 2 was 650 ... 750 ppm. The carbon content in the metal after evacuation was 0.0015 ... 0.0020%. At the first stage, the vacuum in the vacuum chamber was no more than 120 mbar, the evacuation time was 5 ... 8 min, and the argon flow rate was 1000 l / min. At the second stage, the vacuum in the vacuum chamber was no more than 10 mbar, the evacuation time was 13 ... 16 min, and the argon flow rate was 1500 l / min until the {CO} content in the exhaust gases was more than 10%. With a decrease in the {CO} content in the exhaust gases of less than 10%, the argon flow rate increased to 2000 l / min. 1 ... 2 min before the end of the evacuation, the niobium and titanium-containing lumpy ferroalloys and aluminum fraction were refluxed. The content of niobium, titanium and aluminum in the finished steel was 0.040 ... 0.050%, 0.025 ... 0.045% and 0.025 ... 0.045%, respectively.

The proposed method for the production of steel is guaranteed to produce steel with a carbon content of not more than 0.0020% and reduce material costs for obtaining the required content of niobium, titanium and aluminum in steel.

Claims (1)

Method for the production of low-carbon steel, including smelting metal in a steel-smelting unit, releasing smelting into a steel pouring ladle, introducing deoxidizers, evacuating, characterized in that the smelting of the metal is carried out with the refining of the bath with oxygen until the carbon content in the metal is not more than 0.03%, during production melting in a steel ladle add high-carbon ferromanganese in an amount of not more than 3.0 kg / t, the evacuation of the metal is carried out in two stages, and at the first stage set the vacuum the vacuum chamber is not more than 150 mbar, the argon flow rate for stirring 1000 l / min and the duration of the first stage of evacuation is 5 ... 8 min, the second stage sets the vacuum in the vacuum chamber no more than 10 mbar, the argon flow rate for stirring 1500 l / min at the content of {CO} in the exhaust gases is not less than 10%, and with a lower content of {CO} - 2000 l / min, and the duration of the second stage of evacuation is 13 ... 16 minutes, while microalloying of steel with niobium, titanium and aluminum is not carried out less than 2 minutes before the end of the second stage the additive niobium- and titanium-containing lumpy ferroalloys and aluminum fractions.