RU2016088C1 - Method of out-of-furnace treatment of steel - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: method comprises steps of melting semifinished product in a steel melting plant; discharging it to a ladle; introducing alloying and nitride forming elements; blowing the melt by nitrogen; introducing 70-85% of nitride-forming elements, necessary for deoxidizing and alloying, to the ladle upon discharging process, and introducing the remaining part of the nitride forming elements upon blowing process, when the ladle had been filled after lowering a content of ferrous oxide in the slag up to 1-3 %; then blowing the metal over 5-8 minutes. EFFECT: enhanced quality of treated steel. 1 cl

Description

 The invention relates to ferrous metallurgy, in particular to methods for out-of-furnace steel processing.

 A known method of production of steel, including the smelting of the intermediate in the steelmaking unit, the release of the ladle, the introduction of deoxidizers and ferroalloys, metal processing on a batch vacuum [1].

 The disadvantage of this method is a significant increase in the cost of steel due to the increased consumption of refractories and the cost of evacuation.

 There is a method of out-of-furnace steel processing, including blowing silico-calcium into aluminum deoxidized steel [2].

 The disadvantage of this method is the high cost of steel due to the use of sophisticated equipment and a powdered desulfurizer.

 Closest to the claimed method according to the technical essence is a method of out-of-furnace treatment of steel, comprising introducing 30-50% of the nitride-forming necessary for deoxidation and alloying into the ladle during metal production with nitrogen purging and introducing the rest of the nitride-forming after filling the bucket and ending the purge [3] .

 The disadvantage of this method is that the introduction of part of the nitride-forming into the ladle through the slag immediately after the end of the release and purging, on the one hand, increases the nitride-forming fumes due to interaction with oxidizing slag, and on the other hand, due to the lack of metal purging, after the last parts of nitride-forming does not allow to remove large nitrides formed from steel, which leads to increased contamination of the upper layers of the metal in the ladle with non-metallic inclusions and a decrease in plastic properties.

 The purpose of the invention is to increase the technological ductility of steel.

 The goal is achieved by the fact that according to the method of out-of-furnace treatment of steel, including smelting of the intermediate in the steelmaking unit, discharge into the ladle, introduction of alloying and nitride-forming elements, purging of the melt with nitrogen, according to the invention, 70-85% of the nitride-forming elements necessary for deoxidation and alloying are introduced into the ladle during the manufacturing process and the rest is introduced after filling the bucket during the purging process after reducing the content of iron oxide in the slag to 2-3%, after which the metal is blown for 5-8 minutes.

 The invention consists in the following.

 The nitrogen content in the metal in the furnace before release is of the order of 0.007-0.011% and the introduction of most of the nitride-forming in the ladle during the smelting release allows this nitrogen to be bound into nitrides. Intensive mixing of the metal in the ladle during the release process contributes to the emergence of a part of the nitrides and their absorption by the slag.

 Subsequent purging of the metal in the ladle with nitrogen, on the one hand, contributes to the further removal of nitrides from the metal and, on the other hand, allows to reduce the content of iron oxide in the slag, which leads to a higher degree of assimilation of chemical nitride-forming elements into the ladle and to the production of steel most of these elements in the form of a solid solution, and this, ultimately, helps to increase the level of mechanical properties of the metal.

 The metal purge after entering the last portion of nitride-forming allows you to ensure a uniform distribution of these chemical elements throughout the volume of the bucket and thereby achieve improved mechanical properties of the entire metal volume.

 Entering less than 70% of nitride-forming into the ladle during the release process does not allow nitrogen to be completely contained in the metal in nitrides to be completely nitrided; introducing into the ladle more than 85% exceeds the amount of nitride-forming for the formation of nitrides and is therefore impractical.

 The introduction of a second portion of nitride-forming with an iron oxide content in the slag of more than 3% leads to increased fumes of nitride-forming, reducing the mechanical properties of the metal. A decrease in the content of iron oxide of less than 1% is impractical, since, firstly, this leads to an increase in the duration of out-of-furnace treatment, additional heat loss, and, secondly, does not significantly increase the degree of assimilation of nitride-forming. The metal purge after introducing a second portion of nitride-forming less than 5 min does not allow to achieve a uniform distribution of chemical elements throughout the bucket, which leads to a decrease in the mechanical properties of the metal cast at the beginning of casting.

 A purge of more than 8 minutes leads to significant heat losses, as a result of which the conditions for metal casting worsen, part of which is transferred to a reduced grade due to the use of oxygen during casting.

 The method is as follows.

Smelting of steel 25KHGNMT is carried out in 100-ton arc furnaces; Liquid intermediate is produced in a ladle. During the production process, ferroalloys and 70-85% of the nitride-forming materials necessary for deoxidation and alloying are introduced into the ladle, which are aluminum and 30% ferrotitanium. At the end of the release, the metal in the bucket is purged with nitrogen through an immersion lance with a nitrogen flow rate of 40-70 m˙ nm ³ / h. After 3 minutes of purging, while reducing iron oxide in the slag to 2.0%, the rest of the nitride-forming ones are planted in the ladle and the metal is blown for 6 minutes. Finished metal is poured into 8.2-ton ingots.

 After rolling the ingots on the pipe billet, mechanical tests of metal samples are carried out. The test results are shown in the table.

 The proposed technology allows to increase the mechanical properties of the metal by 10-23% and to exclude unsatisfactory values obtained when testing metal samples.

Claims (1)

 METHOD OF EXTRACTIONAL STEEL TREATMENT OF STEEL, including smelting of an intermediate product in a steelmaking unit, discharge into a ladle, introduction of alloying and nitride-forming elements, purging of the melt with nitrogen, characterized in that 70 - 85% of the nitride-forming elements necessary for deoxidation and alloying are introduced into the ladle during the manufacturing process, and the rest part is introduced after filling the bucket during the purging process after reducing the content of iron oxide in the slag to 1 to 3%, after which the metal is blown for 5 to 8 minutes.

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