EP2039785A1 - Ladle steel deoxidation method - Google Patents

Abstract

The invention relates to producing a high-quality low-carbon steel. The inventive ladle steel deoxidation method consists in introducing granulated or lump desoxidant, the density of which is less than the density of a melt in a ladle, in to a said melt. Said desoxidant is introduced during the melt pouring off a production unit into the ladle by means of a concentrated high-rate flow, the impulse of which allows the desoxidant to penetrate directly inside the melt. The desoxidant is introduced into the melt stream with the aid of a shotblast machine. The desoxidant is embodied in the form of a granulated or lump aluminium of a size ranging from 0,5 to 12,0 mm. The use of the invention makes it possible to reduce the desoxidant loss by two times, to increase the recovery thereof and to improve the metal quality.

Description

• The present invention relates to black metallurgy, in particular to technologies for producing high quality low-carbon steel.
• A common and especially important process used in the production of high quality steels is the process of deoxidation or excess oxygen removal from a melt prepared for ladling.
• A high or inadequate oxygen content of a solid metal predetermines continuation of the residual carbon oxidation processes accompanied by gaseous carbon oxide until the ingot crystallization is over. Further, a finished product shows gas porosity which affects its quality and density.
• Deposition is a deoxidation method most widely used in steel-making. This method consists in oxygen transfer from a solution, where it is present as ferrous oxide, into non-metallic compounds with elements that show more affinity to oxygen than that of iron and less than that of ferrous oxide and are soluble in metal. Thus formed oxidation products escape from metal to slag in a solid or liquid state.
• In practices of special steels production depositing deoxidation is carried out in a ladle or directly at an out-of-furnace treatment plant. Sometimes silicon, manganese, magnesium, barium, calcium, complex alloys, are used, apart of aluminum, as deoxidizing agents and modifiers in steel-making.
• The most common method for adding aluminum is feeding it in a ladle in the form of lumps or commensurable bars. When a deoxidizer material is added by using this method, the adoption degree of its useful element by a melt is at an extremely low level (e.g., 5-20% for aluminum) and is highly unstable. The very addition method has a significant manual labor content.
• For the purpose of reducing deoxidizer loss various methods for adding lump or granulated oxidizers into a ladle are used.
• A method of ladle steel deoxidation including addition of a granulated or lump deoxidizer, which density is less than that of a melt, into the said melt during its pouring off a production unit into a ladle has been taken as the prototype. (Yu.F. Vyatkin, V.A. Vikhrevchuk, V.F. Polyakov et al. "A resource-saving technology of deoxidizing steel with aluminum in a ladle", "Chermetinformatsya Journal, No. 6, 1990, p.53-55).
• But the known method has the following disadvantages: a broken deoxidizer is introduced onto a melt surface or a metal stream surface during pouring off, due to which its major part is burned down with air oxygen and may not dissolve in a metal. This results in loss of the deoxidizer and obtaining of a metal of inferior quality.
• The objective of the invention is to provide a deoxidation method enabling to improve metal quality and reduce deoxidizer loss.
• The anticipated technical effect is a reduced deoxidizer loss, improved stability of its acceptance, higher metal quality.
• The stated technical effect may be achieved due to that in the known method of ladle steel deoxidation, including addition of a granulated or lump deoxidizer, which density is lower than the density of a melt in a ladle, a deoxidizer is introduced, according to the invention, into a melt stream by means of a concentrated high-velocity flow the momentum of which ensures penetration of said deoxidizer directly into the melt.
• Other embodiments of the inventive deoxidation method are possible, which provide the following:
• a deoxidizer is introduced into a melt stream, which is poured off a production unit into a ladle, with the use of a shotblast machine;
• granulated or lump aluminum is used as the deoxidizer, granules or lumps having a size of 0.5 to 12 mm, which may be introduced into a melt stream poured off a production unit into a ladle by a shotblast machine;
• a place of introducing an aluminum flow into said stream is selected depending on its fractional composition, wherein the less are granules, the closer is the flow introduction place to the melt surface in a ladle being filled.
• In order to introduce granules directly inside a melt with a required flow rate, such granules or lumps should be fed at a velocity ensuring, for a given granule, the condition of equilibrium between the high-velocity dynamic pressure and the static pressure inside the metal. $${\omega }^2{\rho }_1/2=l\cdot {\rho }_2\cdot g$$

  

  where:
• ω - velocity of chemical agent flow;
• ρ₁ and ρ₂ - density of chemical agent flow and density of liquid steel flow, respectively;
• g - acceleration of gravity;
• l - depth of chemical agent penetration into a melt.
• The calculations show that in order to ensure conditions for penetration of granulated aluminum having a size of 0.5-12 mm directly into a stream poured off a steel making unit into a ladle, said deoxidizer should be fed with a momentum (impulse of force) from 40 to 318.6 N (where N stands for Newton equal to .102 kgf).
• The above data does not cover all possible values of the flow momentum and are defined for aluminum only. A shotblast machine is a device enabling to achieve penetration of a deoxidizer into a melt, both into a stream and under the metal surface in a ladle. Such machines are usually provided with metering devices and enable to feed a deoxidizer by batches from 50 to 200 kg.
• Another feature of this invention is the fact that a place for introducing aluminum into a metal stream is determined on the basis of its fractional composition, the less is the granule size, the closer to the melt surface in a ladle being filled is the place of introduction. Granules having a size less than 0.5 mm are melted at the time of contact with a metal stream, which leads to significant oxidation of a deoxidizer by air oxygen. When feeding a deoxidizer having a size above 12 mm, certain problems in the operation of a shotblast machine arise that hamper the deoxidizer penetration into a melt and contribute to the deoxidizer combustion in the air. When a melt flows from the outlet edge or the trunk edge metal breaks up and entraps, while moving, air oxygen, which leads to its burn-off loss. Power of stream mixing is so high that, if a small-size deoxidizer is fed to the trunk edge, it would not practically enter into a ladle, and, consequently, when a chemical agent is fed into a stream, a place of introducing the chemical agent is to be determined at which deoxidizer loss would be minimal.
Example 1
• The inventive method was implemented for making Steel 20 in an arc furnace. The metal was deoxidized with manganese and silicon. When pouring the metal into a ladle, aluminum pellets having a size of 6 mm were introduced by 100-kg batches with the use of a shotblast machine with the productivity of 400 kg/minute. The air pressure in the route was 5 bars. The transportation route was made of a metal pipe ensuring introduction of an aluminum flow in to a melt stream at a distance app. 1.5 m to 2.0 m.
• The melt temperature at the furnace outlet was 1545°C. Aluminum was introduced with the momentum of 200 N on the basis of 1.5 kg of aluminum per one ton of steel.
• When deoxidizing steel according to the inventive method, its oxygen content was 0.005-0.006% and the aluminum residual content was 0.022%. Steel made according to the prototype method has the oxygen content of 0.007-0.008% and the aluminum residual content 0.017%.
• When realized in practice, this invention enables to reduce loss of a deoxidizer by two times, increase its acceptance and significantly improve quality of metal.

Claims (5)

1. A ladle steel deoxidation method comprising introduction of a granulated or lump deoxidizer into a melt stream during its pouring off a production unit into a ladle, wherein said deoxidizer has a density that is lower than a density of said melt in said ladle, characterized in that a deoxidizer is introduced into a melt stream by a momentum of a concentrated high-velocity flow, which ensures penetration of said deoxidizer directly into said melt.
2. A method according to Claim 1, characterized in that for introducing a deoxidizer into a melt stream poured off a production unit into a ladle a shotblast machine is used.
3. A method according to Claim 1, characterized in that granulated or lump aluminum having granule or lump size from 0.5 mm to 12 mm is used as a deoxidizer.
4. A method according to Claim 3, characterized in that for introducing aluminum into a melt stream poured off a production unit into a ladle a shotblast machine is used.
5. A method according to Claim 4, characterized in that a place of introducing aluminum flow into a stream is selected on the basis of its fractional composition, wherein the less is a granule size, the closer to the melt surface in a ladle being filled is the place of introducing said flow into said stream.