RU2365461C2 - Granulated slag-forming mixture for protecting steel in tundish during continuous casting of steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used to protect metal surface in the tundish of the continuous casting machine. The granulated slag-forming mixture contains (wt %): carbonaceous material - 2 - 10, fluorine-containing material - 5 - 10, silicon oxide-base material - 8 - 15, cement, SAL and CMC are the rest.

EFFECT: reduced wear of the tundish refractory.

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Description

The invention relates to ferrous metallurgy and can be used mainly to protect the metal surface in the tundish of a continuous casting machine for slab billets.

A known mixture for protecting the surface of a metal containing 60-90% graphite, 5-20% fluorspar and 5-20% cement (as USSR AS No. 5434292, B22D 7/00). The disadvantage of this mixture is the high content of graphite, which can lead to an increase in the carbon content in the finished steel, which is not always desirable. This mixture is expensive due to the high content of amorphous graphite in it. In addition, due to the high content of fluorine-containing material (fluorspar) in the mixture, the lining resistance of the tundish is reduced.

A known mixture used for continuous casting containing amorphous graphite 5-12%, fluorspar 20-30%, Portland cement and blast furnace slag 1-62%, silicate block 5-15% and material based on silicon oxides (5-25% nepheline concentrate) (USSR AS No. 1668018, B22D 11/00). The above mixture is complex in composition (contains 6 ingredients) and expensive because of the silicate block. The nepheline concentrate contained in the mixture contains undesirable aluminum oxides, which reduces the assimilative ability of the slag melt of the mixture with respect to aluminum oxides floating up from the metal.

The closest analogue of the inventive mixture is a mixture for protecting metal in an intermediate ladle during continuous casting, containing 2-10% carbon-containing material, 10-20% fluorine-containing material, 10-25% silicon-based material and the rest (RU No. 2174893, B22D 11 / 111). The disadvantage of this mixture is the high content of fluorine-containing material in the mixture, which leads to wear of the lining of the intermediate bucket in the region of the slag belt and stoppers.

The problem solved by the invention is the selection of the optimal composition of the granular slag-forming mixture, which reduces the wear of the lining of the intermediate bucket.

The problem is solved in that the granular slag-forming mixture for protecting metal in the tundish during continuous casting of steel, including carbon-containing and fluorine-containing materials, a material based on silicon oxides and cement, according to the invention additionally contains sulphite-alcohol bard (SSB) and carboxymethyl cellulose (CMC) , while the ingredients are taken in the following ratio, wt.%:

Carbon material 2-10 Fluoride-containing material 5-10 Silicon Oxide Material 8-15 Cement, PRS and CMC rest.

As a material based on silicon oxides, molding sand is used in accordance with GOST 2138-91.

As fluorine-containing material, fluor-spar flotation concentrates of the FF-85-97 (B) grades are used in accordance with GOST 29219-91.

Amorphous graphite is used as a carbon-containing material in accordance with GOST 5420-74, OST 6-08-7-79, coke dust (fines) - dust of the dry coke quenching unit (dust USTK) according to TU 14-7-115-89.

Cement is used in the form of slag Portland cement grade 300 according to GOST 10178-85.

Powdered technical lignosulfonates (CSP) according to TU 2455-002-00281039-00 and carboxymethyl cellulose (CMC) according to TU 2231-034-79249237-2006 are used as granule formation intensifiers.

The carbon-containing material controls the rate of penetration of the mixture and during the combustion process provides heat, which leads to increased thermal insulation of the melt and the protection of the metal from secondary oxidation.

The content of carbon-containing material in the range of 2-10% promotes uniform penetration of the mixture and, as a result, prevents the slag from thickening and the formation of a hard crust.

When using a mixture with a carbon-containing material content of more than 10%, undesirable carburizing of steels with low limits on the carbon content — low-carbon and especially low-carbon ones — is observed, and it also leads to a choking of the mixture.

When using a mixture with a carbon-containing material content of less than 2%, a deterioration in the conditions of metal surface insulation in the tundish and the formation of a solid slag crust are observed, the dissolution of which requires an increased consumption of the mixture.

When the fluorine-containing material in the mixture is less than 5%, the melting temperature and viscosity of the slag melt of the mixture increase. The assimilative ability of the slag melt decreases. A hard crust is formed - the “roof”, which impedes the technology of casting metal from the tundish.

When the fluorine-containing material contains more than 10% in the mixture, there is no significant improvement in the assimilative ability of the slag melt of the mixture. In this case, the slag melt begins to corrode the lining of the intermediate ladle in the region of the slag belt and stopper, which leads to a decrease in the durability of the intermediate ladle.

When the content of the material based on silicon oxides in the mixture is less than 8%, the basicity of the mixture increases. This leads to the formation of viscous slag and then to thickening of the slag and to the formation of a solid slag crust, which impedes the normal casting of metal from an intermediate ladle.

When the content of this material in the mixture is more than 15%, the basicity in the mixture decreases, which leads to a decrease in the viscosity of the slag melt and, as a result, to increased wear on the lining of the intermediate ladle.

When the contents of the ingredients in the mixture go beyond the specified limits, the maintenance technology for the intermediate bucket is violated (hindered), the thermal insulation of the metal deteriorates and the lining resistance of the intermediate bucket decreases.

The proposed mixture was made in the department of slag-forming mixtures LLC "Shlakservis" OJSC "Magnitogorsk Iron and Steel Works". Slag-forming mixture was prepared as follows. Prepared charge materials from storage hoppers were loaded into a wet grinding mill, where materials were ground with simultaneous mixing. The first in a wet grinding mill (MMP) were loaded suspended powder milled bulk materials (molding sand). After 2-4 hours of co-grinding, a sample is taken to determine the fineness of grinding of materials (i.e., the fraction content is more than 0.063 mm in percent).

With a grinding fineness of 5-15%, the remaining materials were added to the mill (pulverized - fluorspar concentrate, amorphous graphite and cement), then CSP, as well as a solution of CMC glue in an amount of 1.3 m ³ . After co-grinding and mixing all the materials for 1.0-1.5 hours, the finished suspension was poured into a receiving mixer, in which it was constantly mixed to prevent precipitation and separation. Next, the suspension is pumped into a feed mixer for subsequent spraying and obtaining granules in a drying unit. The suspension was dried at a temperature of 190-350 ° C.

The composition and melting point of the inventive mixture are presented in the table. The melting point was determined using a Hesse-Instruments heating high-temperature microscope.

Table Mix No. The content of components, wt.% Melting point, ° С Graphite Fluorspar Sand Cement CMC PRS one 3 7.5 13 76.5 2 0.5 1210 2 fifteen fifteen twenty fifty 2 0.5 1200 3 12 3 5 80 2 0.5 1230

The finished mixture was packaged in paper bags weighing 10-15 kg. The resulting mixture was used in an intermediate ladle of a slab continuous casting machine. The work of the mixture in the tundish and its consumption were evaluated visually.

When using the new mixture No. 1, 9 heats of SAE 1006 steel were cast on one intermediate ladle. There are no comments on the operation of the mixture and slag in the tundish. The average consumption of the mixture was 0.34 kg / t of cast steel. After casting was completed, an inspection bucket was inspected. Wear of the lining of the intermediate bucket in the region of the slag belt was in accordance with the norm.

When using the new mixture No. 2, 6 heats were cast on one intermediate ladle. There are no comments on the operation of the mixture and slag in the tundish. The consumption of the mixture was 0.39 kg / t of cast steel. During use of the mixture, wear of the lining along the slag belt is noted. After the casting was completed, the intermediate ladle was inspected: wear of the intermediate ladle lining in the region of the slag belt was noted, namely, complete wear of the working layer of the lining (100 mm) and wear of the reinforcing layer (15 mm), which led to the withdrawal of the bucket from circulation and setting it to capital repairs.

When using the new mixture No. 3, 4 heats were cast on one intermediate ladle. Further use of the mixture was discontinued due to the formation of viscous slag, which turned into a solid slag crust, which made it difficult for maintenance personnel to service the tundish. The average consumption of the mixture was 0.40 kg / t of cast steel.

Thus, the observation of the mixtures showed the advantage of the inventive mixture No. 1 in comparison with mixtures No. 2 and No. 3 in the wear of the lining of the intermediate bucket and in the work of the mixture in the intermediate bucket.

Claims (1)

A granular slag-forming mixture for protecting metal in an intermediate ladle during continuous casting of steel, including carbon-containing and fluorine-containing materials, a material based on silicon oxides and cement, characterized in that it additionally contains sulphite-alcohol bard (SSB) and carboxymethyl cellulose (CMC), while the ingredients are taken in the following ratio, wt.%:
Carbon material 2-10 Fluoride-containing material 5-10 Silicon Oxide Material 8-15 Cement, PRS and CMC Rest