RU2440421C1 - Out-of-furnace steel treatment method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves introduction to steel-pouring ladle of lime in quantity of 600…700-[S]₁ kg/t and pear spar in quantity of 150…180·[S]₁ kg/t as calcium-containing materials and primary aluminium ingots in quantity of 100…120·[S]₁ kg/t during metal tapping from steel-making unit. At metal supply to the furnace-ladle plant the metal in quantity of 300…350·[S]₂ kg/t and pear spar in quantity of 120…150·[S]₂ kg/t is added to the metal as calcium-containing materials, and aluminium rods in quantity of 60…80·[S]₂ kg/t are added to the metal as aluminium. At the end of out-of-furnace treatment there added are calcium-containing materials in the form of powder wire with ferrocalcium filler in quantity of 400…500·[S]₃ kg/t, where [S]₁ - sulphur content at the end of melting process in steel-making unit, [S]₂ - sulphur content when the metal is supplied to furnace-ladle unit, [S]₃ - sulphur content after extraction of the second portion of slag-forming materials.

EFFECT: use of invention provides the increase in desulphurisation degree, removal of non-metallic inclusions and globularisation of the rest inclusions in the metal.

Description

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

A known method of out-of-furnace treatment of high-carbon steel, comprising introducing aluminum and silicocalcium into the melt [RF Patent No. 2102498, cl. C21C 7/00].

A significant disadvantage of this method of out-of-furnace steel processing is the insufficient degree of desulfurization of steel and the modification of non-metallic inclusions. This is explained as follows. It is known that the speed of the desulfurization process is proportional to the size of the slag-metal interface surface. The mixing of the metal with argon slag allows, to a certain extent, to increase the interfacial surface area and thus intensify the process of the transition of impurities to slag. However, to carry out deep desulfurization, it is necessary to purge for a sufficiently long time, which is not always possible by casting technology, and the metal is significantly cooled: to 4 ... 5 ° C / min, which at a purge time of 10 minutes is 40 ... 50 ° C. In addition, even with prolonged purging, the desired desulfurization effect is not achieved with high oxygen activity.

As a prototype, a method of out-of-furnace steel processing was selected, including guidance of highly basic slag, deoxidation of steel with aluminum, purging of the metal melt with argon, and introducing calcium-containing materials into the metal in the form of flux-cored wire [RF Patent No. 2145640, cl. C21C 7/00].

Significant disadvantages of this method of out-of-furnace steel processing are:

- the presence of free dissolved oxygen in the metal before treatment with calcium-containing materials;

- obtaining at the end of the out-of-furnace treatment the content of calcium and aluminum in the metal, contributing to the formation of solid non-metallic inclusions that worsen the technological parameters of steel casting.

The desired technical result of the invention is an increase in the degree of desulfurization, removal of non-metallic inclusions and globularization of the inclusions remaining in the metal.

For this purpose, a method of out-of-furnace steel processing is proposed, including the release of metal from the steelmaking unit into the steel-pouring ladle, the metal supply to the ladle furnace, the deoxidation of steel by aluminum and the introduction of calcium-containing materials, in which according to the invention, when the metal is released from the steel-making unit into the steel-pouring ladle as calcium-containing of materials, lime is introduced in an amount of 600 ... 700 · [S] ₁ kg / t and fluorspar in an amount of 150 ... 180 · [S] ₁ kg / t, and as aluminum - pig primary aluminum in an amount of 1 00 ... 120 · [S] ₁ kg / t, metal is fed to the ladle furnace and lime is added in the amount of 300 ... 350 · [S] ₂ kg / t and fluorspar in the amount of 120 ... 150 · [S as calcium-containing materials ] ₂ kg / t, and as aluminum - aluminum wire rod in the amount of 60 ... 80 · [S] ₂ kg / t, at the end of the treatment, calcium-containing materials are introduced in the form of a flux-cored wire with ferrocalcium filler in the amount of 400 ... 500 · [S] ₃ kg / t

where [S] ₁ is the sulfur content at the end of the smelting in the steelmaking unit, [S] ₂ is the sulfur content upon arrival at the ladle furnace, and [S] ₃ is the sulfur content after the second portion of slag-forming materials is returned.

The essence of the invention consists in improving the method of out-of-furnace steel processing by creating rational conditions for reducing the activity of oxygen in the metal and at the same time increasing the activity of coating slag, as well as obtaining the maximum contact surface of the metal with calcium-containing materials.

The declared limits are selected experimentally. The consumption of calcium-containing materials and aluminum during the release of metal from the steelmaking unit was selected based on the condition of receipt, upon arrival at the ladle furnace, of the content of iron oxide in the slag of not more than 3% and the sulfur content of the metal not more than 0.010% ([S] ₂ ). The consumption of calcium-containing materials and aluminum after supplying the metal to the ladle furnace is selected based on the calculation of the iron oxide content in the slag of not more than 1% and the sulfur content of the metal not more than 0.005% ([S] ₃ ). The flux-cored wire consumption with a ferrocalcium filler at the end of the after-furnace treatment was selected with the aim of obtaining a final content of iron oxide in the slag of not more than 0.5% and a sulfur content in the metal of not more than 0.003%. Reducing the cost of slag-forming materials at any stage will lead to a decrease in the refining ability of slag and a decrease in the degree of metal desulfurization. An increase in the consumption of slag-forming materials will lead to an increase in material costs for steel production, and, consequently, to an increase in the cost of metal.

The claimed method of out-of-furnace steel processing was implemented in an oxygen-converter shop in the production of pipe steel grade K60.

Metal smelting was carried out in 370 tons of oxygen converters. As scrap metal, the edging of cold rolling shops in the amount of 80 ... 90 tons was used. Cast iron was previously subjected to granular magnesium desulfurization. Cast iron consumption amounted to 310 ... 320 tons. At the end of steelmaking in the converter, the sulfur content was 0.010 ... 0.015%, and the metal temperature was 1640 ... 1680 ° C. During the release of metal from the converter into the steel pouring ladle, 3200 ... 3600 kg of lime, 800 ... 900 kg of fluorspar and 500 ... 600 kg of pig aluminum were given. Upon arrival at the ladle furnace, the sulfur content in the metal was 0.008 ... 0.010%, and the metal temperature was 1600 ... 1620 ° C. After conducting an averaging purge with argon for 6 ... 8 min with a flow rate of 1000 ... 1200 l / min, 800 ... 1000 kg of lime, 300 ... 500 kg of fluorspar and 150 ... 200 kg of aluminum wire rod were planted. Next, heating and vigorous stirring of the metal with argon was carried out at a flow rate of 800 ... 1000 l / min for 8 ... 10 minutes. After this, the flux-cored wire was fed with a ferrocalcium filler in an amount of 600 ... 800 kg. At the end of out-of-furnace treatment, the content of iron oxide in the slag was 0.1 ... 0.3%, and the sulfur content in the metal was 0.0015 ... 0.0028%.

The proposed method of out-of-furnace steel processing has guaranteed to obtain a sulfur content in the metal of not more than 0.003%.

Claims (1)

A method of out-of-furnace steel processing, including the release of metal from a steel-smelting unit into a steel-pouring ladle, deoxidation of steel with aluminum and the introduction of calcium-containing materials, characterized in that when the metal is exhausted from the steel-smelting unit into a steel-pouring ladle, lime in the amount of 600 ... 700 · [S ] ₁ kg / t and fluorspar in the amount of 150 ... 180 · [S] ₁ kg / t, and as aluminum - pig primary aluminum in the amount of 100 ... 120 · [S] ₁ kg / t, metal is fed to the furnace-installation bucket and injected as to ltsiysoderzhaschih materials lime in an amount of 300 ... 350 · [S] ₂ kg / t and fluorspar in an amount of 120 ... 150 · [S] ₂ kg / t, and as aluminum - aluminum rod in an amount of 60 ... 80 · [S] ₂ kg / t, at the end of the treatment, calcium-containing materials are introduced in the form of a flux-cored wire with a ferrocalcium filler in the amount of 400 ... 500 · [S] ₃ kg / t, where [S] ₁ is the sulfur content at the end of the smelting in the steelmaking unit, [S] ₂ - sulfur content upon arrival at the ladle furnace; [S] ₃ - sulfur content after the second portion of slag-forming materials is returned.