RU2352434C2 - Slag-forming mixture for metal surface protection in tundish ladle and mold while steel continuous casting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: slag-forming mixture contains (wt %): carbon-bearing material 4-8, fluorine-containing material 10-20, silicate block 25-35, cement - the rest.

EFFECT: surface condition improving of continuously casted ingot and casting speed enhancing.

1 tbl, 4 ex

Description

The alleged 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 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 (RF patent No. 21585822, 7 B22D 11/00, 04/27/2001).

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 by 10-15% and an increase in the content of aluminum oxide in the slag from the initial 3-5% to 15-20%, the work of the mixture with slag deteriorates significantly - the mixture with slag crumbles, a rough welt forms along the perimeter of the mold, viscosity slag rises sharply. The thickness of the slag skull between the walls of the mold and the crystallizing crust of the ingot also increases, which often happens when casting steels with a high aluminum content (for example, dynamo steel). 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.

Also known is a slag-forming mixture containing 15-25% graphite, 15-25% nepheline, 20-35% block of silicate, 2-10% peat flour and the rest is ferroalloy waste slag - RU patent. 2148470 C1, B22D 11/111. 05/10/2000. The mixture is multicomponent (5 ingredients). The content of aluminum oxide in nepheline reaches 30%. Due to the use of 15-25% nepheline, an additional 5-7% aluminum oxides are introduced into the mixture, which impairs its physicochemical properties, namely, its capacity decreases with respect to the aluminum oxides floating up from the metal.

During continuous casting of aluminum-containing steels, the arrival of aluminum oxides in the slag melt of the mixture reaches 10-15% abs. The total content of aluminum oxides in the slag is 15-22%. This reduces the assimilative ability of the slag melt of the mixture with respect to aluminum oxides. This leads to a deterioration in the work of the mixture with slag in the mold. The melting point and melt viscosity increase sharply, the mixture with slag crumbles, a rough welt forms along the perimeter of the crystallizer. Ultimately, this leads to the formation of defects on the surface of the ingot and the deterioration of its macrostructure. It is also possible to terminate the process of continuous casting of steel.

This mixture is used only at low casting speeds (0.1-0.3 m / min.)

The low rate of slag formation and high melting point and viscosity do not allow its use in the mold at high casting speeds (0.6-1.0 m / min).

The closest analogue of the inventive mixture is a mixture containing 2-10% of a carbon-containing material, 10-20% of a fluorine-containing material, 10-25% of a material based on silicon oxides and cement - the rest. As a material based on silicon oxides, molding sands, quartz concentrates are used (patent RU 2174893 C1, B22D 11/111, 10/20/2001).

The disadvantage of this mixture is its low physicochemical properties of the slag melt (melting point and viscosity), due to which coarse welts and slag metal cakes are formed along the perimeter of the mold. This leads to the appearance of coarse surface defects on the surface of continuously cast ingots and even to the termination of the steel casting process.

Therefore, this mixture, by its physicochemical properties, is suitable for use only in the continuous caster.

The technical effect when using the claimed composition of the slag-forming mixture is to improve its physico-chemical properties (lowering the melting temperature from 1160-1200 ° C to 1130-1150 ° C and the viscosity of its slag melt to 0.3 Pa.s) and increasing its assimilative ability (capacitance) in relation to pop-up aluminum oxide from a metal. This allows you to use the new mixture not only in the tundish, but also in the continuous casting mold. That is, the expansion of its functional (technological) capabilities with respect to the known mixture is achieved.

The specified technical effect is achieved in that the slag-forming mixture for continuous casting of steel, including carbon-containing material, fluorine-containing material and cement, additionally contains a silicate block in the following ratio of ingredients, wt.%:

Carbon material 4-8 Fluoride-containing material 10-20 Silicate block 25-35 Cement Rest

As a carbon-containing substance, cryptocrystalline (amorphous) graphite of the GLS-2 and 3 grades (GOST 5420-74) is used.

Fluorine-containing material is used in the form of fluor-spar 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.

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."

When the content of the carbon-containing material in the mixture is less than 4%, the conditions for warming the metal mirror are worsened, and when it contains more than 8%, 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 10% and the silicate block is less than 25%, 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 20% and the block of silicate is more than 35%, the melting temperature and viscosity of the slag melt of the mixture decrease so much that the traces of the crystallizer swing on the surface of the cast ingots become very deep, such that transverse cracks appear on these traces.

The content limits of fluorine-containing material, silicate block and cement are selected taking into account the required physicochemical properties of the mixtures, the basicity of the slag melt in the range of 0.7-1.3 and the resulting slag with high assimilating ability and satisfactory lubricating properties in the absence of surface defects on ingots or their minimum number and insignificant in size.

The slag-forming mixture of the optimal composition for the mold and the tundish contains 6% amorphous graphite, 15% fluor-spar concentrate, 30% cob silicate and 49% cement. To reduce the cost of the mixture when it is used in the scoop bucket, it is possible to use coke dust USST instead of amorphous graphite in similar quantities.

Specific examples with boundary No. 1 and 2 and average No. 3 (mixture of optimal composition) values of the contents of the ingredients of the new mixture and average No. 4 of the contents of the ingredients of the known mixture (RF patent No. 2174893 - prototype) are presented in the table.

The composition of the claimed (No. 1-3) and known (No. 4) mixtures. Mixture number The content of ingredients, wt.% Amorphous graphite Fluorspar concentrate Silicate block Silicon Oxide Material (Quartz Sand) Cement one four 10 25 - 61 2 8 twenty 35 - 37 3 6 fifteen thirty - 49 four 6 fifteen - eighteen 61

New mixtures No. 1-3 were tested during casting of low-carbon and carbon steels. The casting speed for different steels was 0.50-0.90 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 mixture No. 3 in the mold, neither welt formation, nor clumping of the mixture with slag, nor slag flowing onto the pallet occurred. Slag in the tundish was fluid-moving. The surface of the ingots was free of defects.

Example 4. When using mixture No. 4, the slag in the pit was liquid-moving, and a rough welt formed around the perimeter of the mold and solid slag-metal cakes formed on the ingot mirror, which prevented further casting of steel using this mixture.

For industrial testing used the optimal composition of the inventive mixture No. 3.

Industrial testing of mixture No. 3 was carried out during casting of transformer, dynamo and 08Yu OSV and VOSV steels. The size of the molds was 250 × 750 ... 1350 mm. The casting speed for the transformer steel was 0.50-0.60 m / min, and for the remaining steels 0.80-0.90 m / min. About 120 thousand tons of steel were cast with mixture No. 3.

The surface quality of the ingots when using the new mixture increased: non-metallic inclusions with a depth of more than 2 mm were not found. Positive results were achieved due to improved physicochemical properties of the new slag-forming mixture. So, the melting point of the new mixture No. 3 was 1140 ° C, and the melting temperature of the known mixture No. 4 was 1180-1190 ° C. The viscosity of their slag melts at a temperature of 1300 ° C was respectively 0.3 and 1.2 Pa.s. Therefore, the obtained results 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 by 10-15% (that is, 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 (1)

Slag-forming mixture for continuous casting of steel, including carbon-containing material, fluorine-containing material and cement, characterized in that it further comprises a silicate block in the following ratio of ingredients, wt.%:
carbon material 4-8 fluorine-containing material 10-20 silicate block 25-35 cement rest