RU2311258C2 - Slag-forming mixture for protecting surface of metal in mold at continuous steel casting - Google Patents

Abstract

FIELD: ferrous metallurgy, possibly slag forming mixtures used in intermediate ladles and in molds at continuous casting of steel.

SUBSTANCE: mixture includes, mass %: carbon containing material 6 - 10; fluorine containing material 17 - 23; silicate lumps, 24 -30; material on base of silicon oxides, 2 - 6; cement, the balance.

EFFECT: possibility for enhancing assimilation capability of mixture relative to floating from metal aluminum oxides at increased casting speed, improved quality of ingot surface, stabilized process of continuous steel casting.

2 cl, 3 ex, 1 tbl

Description

The present invention relates to ferrous metallurgy and can be used to protect the surface of the metal in the intermediate ladle and mold during continuous casting of steel.

Known slag-forming mixture, comprising 2-10% of a carbon-containing material, 10-20% of a fluorine-containing material, 10-25% of a material based on silicon oxides and the rest is cement (US Pat. RF No. 2174893, 7B22D 11/111, 2001, bull. 29).

Due to the relatively high melting temperature and viscosity of its slag melt (there are practically no alkali metal oxides), this mixture is of little use for use in a continuous casting mold.

Known slag-forming mixtures, additionally containing alkali metal oxides in the form of a silicate block. As part of a mixture of ed. No. 1668018 (B22D 11/00), in addition to carbon and fluorine-containing ingredients, contains 10-15% silicate block and 5-25% nepheline concentrate. The nepheline concentrate introduces unwanted aluminum oxides, which reduces the assimilative ability of the slag melt relative to the aluminum oxides floating from the metal. The content of silicate block (alkali metal oxides) in this case is insufficient. The mixture according to RF patent No. 2238820 (7В22D 11/108, 11/111, 2004, bull. 30) contains 8-12% of carbon-containing material, 20-24% of fluorine-containing material, 19-23% of silica block, 17-23% datolite concentrate, 3-9% of the material based on silicon oxides and cement - the rest. The datolite concentrate contains boron oxides, which, when casting carbon and medium carbon steel, often cause cracks on the surface of continuously cast ingots.

The closest analogue to the inventive mixture is a slag-forming mixture for continuous casting of steel, comprising 7-12% of carbon-containing material, 18-22% of fluorine-containing material, 12-18% of silicate block, 8-14% of material based on silicon oxides and cement - the rest (patent RF №2165822, 7В22D 11/00, 2001, bull. 12).

The disadvantage of this mixture is the relatively low assimilating ability of its slag melt in the continuous casting mold with respect to aluminum oxides floating out of the metal under conditions of an increased casting speed and a significant (up to 12-15%) of their arrival.

So, with an increase in the casting speed from 0.8 m / min by 10-20% and an increase in the content of aluminum oxides in the slag of the crystallizer from the initial 3-5% to 15-20%, the work of the mixture with slag significantly worsens - the mixture with slag crumbles, a coarse welt is formed around the perimeter of the mold, the viscosity of the slag increases sharply. The thickness of the slag skull between the walls of the mold and the crystallizing crust of the ingot also increases. This leads to the formation of defects on the surface of the ingot (various cracks and slag inclusions) and often to stops the steel casting process.

The technical effect when using the inventive composition of the slag-forming mixture is to increase its assimilative ability (capacity) with respect to aluminum oxides floating out of the metal with an increase in casting speed without compromising the technological properties of the resulting slag melt. This leads to an increase in the surface quality of the continuously cast ingot, the elimination of the causes of “hangs” of the ingot crust and stops of casting of steel.

The specified technical effect is achieved by the fact that the ingredients of the slag-forming mixture, including carbon-containing material, fluorine-containing material, silicate block, material based on silicon oxides and cement, are taken in the following ratio, wt.%:

carbon material 6-10 fluorine-containing material 17-23 silicate block 24-30 silicon oxide material 2-6 cement 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, and the coke dust of the coke dry drying unit (TU 14-7-115-89 )

Fluorine-containing material is used in the form of fluorspar fluorite concentrate (GOST. 29219-91), silicate block - in accordance with GOST 13079-81, cement (Portland cement or slag Portland cement) in accordance with GOST 10178-85.

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

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 this analysis, we can conclude that the claimed technical solution meets the criteria of "inventive step" and "novelty."

If the content of the carbon-containing material in the mixture is less than 6%, the conditions for the warming of the metal mirror worsen, and if it contains more than 10%, there is a risk of significant carburization of the metal, which is undesirable, for example, for low-carbon steels.

When the fluorine-containing material in the mixture is less than 18% and the silicate block is less than 24%, the melting temperature and viscosity of the slag melts of the mixtures sharply increase, their assimilative ability decreases. Large slag inclusions appear on the surface of cast ingots. When the content of fluorine-containing material is more than 22% and the block of silicate is more than 30%, the melting temperature and viscosity of the slag melt of the mixture decrease so much that the traces of the mold swing on the surface of the cast ingots become very deep, such that transverse cracks appear on these traces.

The limits of the content of the material based on silicon oxides in the amount of 2-6% and cement in the amount of 33-51% are selected taking into account the required physicochemical properties of the mixtures and the resulting slags with high assimilating ability and satisfactory lubricating properties in the absence of surface defects on ingots or their minimum quantity and insignificant in size.

The slag-forming mixture of the optimal composition for the mold and the intermediate ladle contains 8% amorphous graphite, 20% fluor-spar concentrate, 27% silicate block, 4% quartz or molding sand concentrate and 41% cement. To reduce the cost of the mixture when used in the trash bucket, coke dust USST in similar quantities is used.

Specific examples with boundary No. 1 and 2 and average No. 3 and 4 (mixture of optimal composition) values of the contents of the ingredients of the new mixture and average No. 5 of the contents of the ingredients of the known mixture (US Pat. RF No. 21585822 - prototype) are presented in table 1.

Table 1 - The composition of the claimed (No. 1-4) and known (No. 5) mixtures. Mixture number The content of ingredients, wt.% Amorphous graphite Dust dust Fluorspar concentrate Silicate block Silicon Oxide Material Cement one 6 - 17 24 2 51 2 10 - 23 thirty 6 31 3 8 - twenty 27 four 41 four - 8 twenty 27 four 41 5 10 - twenty fifteen eleven 44

Mixtures No. 1-4 were tested in the casting of steels with a carbon content of 0.05-0.78%. The casting speed was 0.90-0.95 m / min.

Example 1. When using mixture No. 1 in the mold, a welt was formed with a thickness of not more than 1.5 mm. There was no freezing (sticking) of the ingot crust. No cracks and slag inclusions were found on the surface of the ingots. On the surface of the slag melt in the bucket there are individual amorphous-type slag clots.

Example No. 2. When using mixture No. 2 in the mold, the welt was not formed, but there was a slight leakage of slag on the pallet, which did not affect the atomization of water by nozzles. No defects (cracks and slag inclusions) were found on the surface of the ingots. Slag in the tundish was liquid.

Example 3. When using the mixture No. 3, neither the formation of welt, nor clumping of the mixture with slag, nor the flow of slag on the pallet occurred. Slag in the tundish was fluid-moving. The surface of the ingots was free of defects.

In all experiments with mixtures Nos. 1 and 3, in the cases of using the dust of the CCCT instead of amorphous graphite, the behavior of the slag melt on the metal surface in the intermediate ladle was practically the same.

For comparative industrial tests used the optimal composition of the inventive mixtures No. 3 and 4 and the optimal composition No. 5 of the known mixture (prototype) (see table).

Comparative tests of mixtures were carried out during the casting of low carbon, carbon and low alloy steels. The size of the molds was 250 × 750 ... 1350 mm. The casting speed was 0.85-1.05 m / min, about 511 thousand tons were cast with a mixture of No. 3 and 4, and 490 thousand tons of steel with a mixture of No. 5.

The following results were obtained: the number of hangs of the ingot crust in terms of 1000 heats when using mixture No. 5 was 2.14 pcs., When using new mixtures No. 3 and 4, there were no hangs of the ingot crust.

The number of breaks of the peel of the ingots (emergency situation - stopping the casting of steel) in terms of 1000 heats when using mixture No. 5 was 0.71 pcs .; when using new mixtures No. 3 and 4, ingot peel breakouts were absent, and in the intermediate ladle no slag metal crusts (cakes) were observed.

The surface quality of the ingots when using new mixtures improved: per 1000 linear meters of the surface of the ingots 3 non-metallic inclusions with a depth of up to 2 mm were found, and when using the known mixture No. 5, 12 non-metallic inclusions with a depth of up to 3 mm were found.

Positive results of production tests allow us to recommend a new mixture for implementation in production.

The technical and economic effect of using a new composition of the slag-forming mixture consists in the possibility of increasing the steel casting speed up to 20% (i.e., the possibility of increasing the production of cast steel), the absence of suspension of the ingot crust and its breakthroughs (accidents), and improving the surface quality of continuously cast ingots.

Claims (2)

1. Slag-forming mixture to protect the metal surface in the intermediate ladle and mold during continuous casting of steel, containing carbon-containing and fluorine-containing materials, silicate block, material based on silicon oxides and cement, characterized in that the ingredients of the mixture are taken in the following ratio, wt.%: carbon material 6-10 fluorine-containing material 17-23 silicate block 24-30 silicon oxide material 2-6 cement rest 2. The slag-forming mixture according to claim 1, characterized in that amorphous graphite is used as the carbon-containing material in the crystallizer mixture, and amorphous graphite and coke dust of the dry coke quenching unit are used in the mixture for the bucket.