RU2371280C1 - Slag-forming mixture for continuous pouring of steel - Google Patents

Abstract

FIELD: technological processes, casting.

SUBSTANCE: invention is related to the field of ferrous metallurgy, in particular to continuous pouring of steel. Slag-forming mixture contains (wt %): carbon-containing material (4 - 8), fluorine-containing material (15 - 20), silicate mass (3 - 10), sodium bicarbonate - baking soda (5 - 15), material on the basis of silicon oxides (13 - 18) and cement (the rest). Using sodium bicarbonate in mixture together with material on the basis of silicon oxide makes it possible to improve quality of continuous cast billet surface due to increased assimilating ability of mixture in respect to oxides that float from metal at initial moment of pouring.

EFFECT: improved operation of mixture at continuous pouring of steel,also during technological operations, such as replacement of intermediate bucket or submersible glass.

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Description

The invention relates to ferrous metallurgy and can be used in a mold for continuous casting of low-carbon and carbon steels with a carbon content of up to 0.80%, low alloy and alloy steels, including during technological operations, such as changing an intermediate ladle or a submersible nozzle.

Known slag-forming mixture for continuous casting of steel, including amorphous graphite, fluorspar, datolite concentrate, cryolite and ground mica (phlogopite) (Technological instruction TI 106-ST.KK2-17-86. Preparation of slag-forming mixtures, Lipetsk, 1986 , SCO-9). The cryolite contained in the mixture decomposes at high temperatures with the release of harmful fluorine into the atmosphere. The mica used increases the initial content in the mixture of aluminum oxides, which ultimately reduces the assimilative ability of the mixture melt to aluminates floating from steel.

These disadvantages are especially evident at the initial moment of casting the first heat in the intermediate ladle, when oxides of the refractory lining of the ladle and refractory filling of the channel of the steel pouring nozzle additionally get into the metal. The physicochemical properties of the slag melt of the mixture in the mold deteriorate so much that at the initial moment of casting there are frequent “hangs” of the ingot crust, due to which breaks are possible.

Also known is a slag-forming mixture containing amorphous graphite, a fluorine-containing substance, a datolite concentrate, a material based on silicon oxides and cement (Pat. RF No. 2165823, class 7 B22D 11/00, C21C 5/54, 2001). Due to the absence of a silicate block, this mixture also does not have sufficient capacity with respect to aluminum oxides and other oxides entering the steel at the initial moment of casting, for example, transformer steel, which violates the stability of the casting start technology.

Known slag-forming mixture containing fluorspar 16-24%, silicate block 8-12, materials with silicon oxides 8-12% and boron oxides 12-18% and cement - the rest (Pat. RF №2169633, CL 7 B22D 11 / 00, C21C 5/54, Bull. No. 18, 2001). The mixture has the above disadvantages to a lesser extent. However, due to the relatively high content of fluorspar in the mixture, increased wear of the continuous casting machine is observed - corrosion of equipment parts.

The closest in technical essence and the achieved result is a slag-forming mixture comprising 6-10% of a carbon-containing substance, 5-11% of a fluorine-containing substance, 22-28% of a silicate block, 8-14% of a datolite concentrate and cement - the rest (Pat. RF No. 2261778 Cl. 7 B22D 11/108).

The disadvantage of this mixture is the content of active boron oxide (B ₂ O ₃ ) contained in the datolite concentrate and adversely affecting the surface quality of the continuously cast slab. In addition, when using this mixture during technological operations, such as changing a dipping glass or an intermediate ladle, and pouring a long period of 1 ... 5 minutes at low speeds - less than 0.5 m / min, slag freezes near water-cooled copper walls of the mold and the formation of a slag skull, which must then be removed.

The technical result is an improvement in the operation of the slag-forming mixture during continuous casting of steel, including during technological operations, such as changing an intermediate ladle or an immersion nozzle, and improving the surface quality of the continuously cast billet by increasing the assimilative ability of the slag-forming mixture with respect to oxides floating up from metal at the initial moment of casting.

The specified technical result is achieved by the fact that in the slag-forming mixture for continuous casting of steel containing a block of silicate, carbon-containing material, fluorine-containing material and cement, an additional material based on silicon oxides and sodium bicarbonate is introduced in the following ratio of ingredients, wt.%:

Carbon-containing material - 4-8

Fluorine-containing material - 15-20

Silicate block - 3-10

Sodium Bicarbonate - 5-15

Material based on silicon oxides - 13-18

Cement - the rest

The cryptocrystalline (amorphous) graphite GLS-2 and 3 (GOST 5420-74) is used as a carbon-containing substance in the mixture for the crystallizer.

The fluorine-containing substance is used in the form of fluorspar fluorite concentrate (GOST 29219-91 and 29220-91), a silicate block in accordance with GOST 13079-81, datolite concentrate in accordance with GOST 16108-80, cement (Portland cement or slag Portland cement) according to GOST 10176-76.

A material based on silicon oxides is used in the form of quartz concentrate (GOST 9077-82), quartz or molding sand (GOST 2138-91).

Sodium bicarbonate (baking soda) GOST 2156-76.

The addition of a new material sodium bicarbonate together with a material based on silicon oxide determine the physicochemical properties of the mixture, which lead to a decrease in the cooling rate of the obtained slag melt near the copper walls of the crystallizer due to the release of carbon dioxide from the slag melt, which increases the length of the liquid layer of slag by the height of the mold and, accordingly, increases the assimilative ability of the slag and improves the surface quality of the continuously cast billet.

Analysis of scientific, technical and patent literature shows the lack of coincidence of the distinctive features of the claimed composition of the slag-forming mixture with the signs of known technical solutions. Based on the analysis, we can conclude that the claimed technical solution meets the criteria of "inventive step" and "novelty."

When the content of the carbon-containing material in the mixture is less than 4%, the mirror heat insulation worsens, and when it contains more than 8%, the carburization of the metal occurs, which is undesirable.

When the content of fluorspar concentrate is less than 15%, silicate block less than 3% and sodium bicarbonate less than 5% under the conditions of the beginning of casting or replacement of a submersible glass, the chemical composition of the slag melt of the mixture changes significantly and its melting temperature and viscosity increase sharply. The slag thickens and does not lubricate the walls of the mold. Hanging peel of the ingot occurs.

When the content of fluorspar concentrate is more than 20%, silicate block more than 10% and sodium bicarbonate more than 15%, the melting temperature and viscosity of the slag melt of the mixture sharply decrease, which does not improve its technological properties in the mold, and the consumption of the mixture increases. Deep folds appear on the surface of the slabs, along which transverse cracks form.

The content limits of the material based on silicon oxides are selected taking into account the contents of the remaining ingredients so that the basicity of the mixture is 0.9-1.1.

When the contents of the ingredients in the mixture go beyond the specified limits, the stability of the casting technology is violated and the surface quality of the continuously cast ingot decreases.

An optimal composition mixture contains 6% amorphous graphite, 18% hydrofluoric concentrate, 7% silicate block, 9% sodium bicarbonate, 15% material based on silicon oxides (e.g. foundry sand) and 45% cement. The basicity of the mixture is 1.04.

Specific examples with boundary No. 1 and 2 and average No. 3 (optimal composition mixture) of the contents of the ingredients of the new mixture and the average values of the ingredients of the known mixture No. 4 (prototype. Pat. RF No. 2261778) are presented in table 1.

All mixtures were made in the form of granules with preferred sizes of 0.1-0.5 mm. The moisture content, determined at 105 ° C, did not exceed 0.30%.

Mixtures No. 1-3 were introduced into the molds at the initial moment of casting, and after filling the mold, as needed, the usual mixture for casting carbon steel of type 3 cn was used, for example, slag-forming mixture according to RF patent No. 2261778.

Mixtures 1-3 were tested during casting of carbon steel of grade 3 cn in the first heats in new tundish.

Example No. 1

When testing the mixture No. 1 in the mold, there was a uniform spreading and melting of the slag-forming mixture. On the perimeter of the mold slag skull at a working speed is not detected. The consumption of the mixture was in the range of 0.8 ... 0.83 kg / t of steel. No slag inclusions and cracks were found on the surface of continuous continuous ingots of ingots. There was no "hang" of the ingot crust. During a long change of the tundish (more than 4 min), a weak slag skull on the crystallizer walls was noted

Example No. 2

When testing the mixture No. 2 clumping of the mixture and the formation of welt was not observed. The consumption of the mixture was in the range of 0.85 ... 0.88 kg / t of steel. A small amount of molten slag was found on the pallet. There were no defects on the surface of the ingots. There were no “freezes” of the ingot crust.

Example No. 3

When testing mixture No. 3, there were no comments on the operation of the mixture in the mold and on the surface quality of the head ingots. The consumption of the mixture was 0.85 kg / t of steel. There was no hanging of the ingot crust.

For comparative tests on an industrial scale, mixtures 3 and 4 were used (see table 1 and 2).

Carbon steel was cast on a 2-stream continuous casting machine. For the first and third streams, mixture No. 3 was used, for the second and fourth streams, mixture No. 4 (prototype) was used. The size of the mold 250 × 1730 mm. Comparative tests were carried out at continuous casting starts at 5 heats in a series of carbon steel. On the first stream used a mixture of No. 3, and in the second mixture No. 4 (prototype)

All types of mixtures in the mold worked at operating speed without significant comments. At the casting operating speed, a weak slag skull with a thickness of not more than 1 mm was noted on the mold walls using a mixture of the prototype. During the launch of the continuous casting machine and technological operations, namely the replacement of the submersible nozzle, mixture No. 4 (prototype) formed a thickened slag skull (welt) with a thickness of 2 ... 3 mm along the perimeter of the mold. The experimental mixture did not reveal such shortcomings. After casting, the slabs were cooled to a temperature of 80 ° C and cleaned with oxy-fuel cutters. No surface defects were found on the surface of the slabs of the stream using mixture No. 3, and on the surface of the slabs of the second stream using mixture No. 4, transverse cracks were noted from the side of a narrow face and ribs up to 5 mm deep, which were then cleaned with 2-3 passes of an oxy-fuel torch .

Thus, the use of a slag-forming mixture for continuous casting of steel of the claimed composition allows to improve slag operation during technological operations, such as changing an intermediate ladle or an immersion nozzle, and to achieve the required surface quality of a continuously cast billet by increasing the assimilating ability of the slag-forming mixture with respect to oxides floating up from metal at the initial moment of casting.

table 2
Comparative evaluation of the work of slag-forming mixtures The name of the characteristics of the mixture No. of mixtures No. 1 Number 2 Number 3 Number 4 The average consumption of the mixture 0.81 0.87 0.84 0.75 Mixture Performance A slag skull is marked near the walls of the mold during the replacement of the tundish. At working speed, there is no slag skull. Lack of slag skull. Liquid slag leaking onto the mold pan was noted Leakage of slag and slag skull is not marked A permanent slag skull on the walls of the mold at a working speed was noted. During technological operations during the change of the submersible glass, the slag skull is increased by 2 ... 3 times Continuous Cast Billet Surface Quality There are minor defects in the form of small non-metallic inclusions in the transitional section of the workpiece. There are no defects in the area cast at operating speed. Marked increased folds on the surface of the workpiece No comments Small slag inclusions and cracks on the surface of the workpiece cast at operating speed are noted. On the site, cast during the change of the immersion nozzle, there are large slag inclusions Metal surface treatment Selective surface control of first blanks is required. Spot inspection of slabs cast at working speed due to large creases is required. Not required Spot surface inspection required due to surface cracks

Claims (1)

Slag-forming mixture for continuous casting of steel, containing a silicate block, a carbon-containing material, a fluorine-containing material and cement, characterized in that it additionally contains a material based on silicon oxides and sodium bicarbonate in the following ratio of ingredients, wt.%:
carbon material 4-8 fluorine-containing material 15-20 silicate block 3-10 silicon oxide material 13-18 bicarbonate of soda 5-15 cement rest