RU2555277C1 - Slag-forming mixture for continuous steel pouring - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: slag-forming mixture contains in wt %: fluor spar 10.0-25.0, graphite 0.1-6.0, dusty quartz 10.0-24.0, technical soda 1.0-17.0, syenite concentrate 2.0-24.0, coke dust 1.0-6.0, lithium carbonate 1.0-5.0, technical chalkstone 3.0-23.0, magnesium oxide 0.5-5.0, one or several components from group: slag of ferrochrome production 30.0-45.0, silicate lump 4.0-12.0, colemanite 2.0-15.0, microcalcite 18.0 max, cement - rest. Chemical composition of mixture in wt %: free C 0.5-8.0, SiO₂ 21.0-42.0, Al₂O₃ 0.5-12.0, CaO 23.0-52.0, MgO 0.5-10.0, R₂O 1.0-15.0, F 1.0-13.0, Li₂O 3.0 max., B₂O₃ 5.0 max., inevitable admixture - rest. Mixture basicity is 0.85-1.25.

EFFECT: improved steel macrostructure, reduced contamination by non-metal inclusions, reduced quantity of surface defects.

2 cl, 2 tbl

Description

The invention relates to the field of ferrous metallurgy, in particular to the protection of the metal surface in the mold.

The slag-forming mixture (SCO) is used during continuous casting in the UNRS mold to prevent heat loss through the metal mirror, to protect steel from secondary oxidation, to reduce friction between the workpiece and the walls of the mold, and to assimilate floating non-metallic inclusions, which improves the quality of continuously cast billets.

Steel grades are divided into groups: by the content of carbon, silicon, aluminum, manganese and other microalloying additives. In turn, the SCO are divided according to the type of UNRS. In order to obtain an optimal surface quality for continuously cast billets for each group of steel grades and types of UNRS, it is necessary to use a certain type of SCO with specified properties.

Known slag-forming mixture for feeding into the mold installation of a continuous casting of steel, containing, by weight. %: fluorspar concentrate - 12-20, syenite concentrate - 15-25, powdered silica quartz - 8-15, anhydrous sodium carbonate - 4-8, ammonium chloride - 2-8, cryptocrystalline foundry graphite - 3-6, activated carbon - 3-5, mica ground in the form of phlogopite - 1-5, Portland cement - the rest [Patent RU 2410193, IPC B22D 11/04, B22D 11/111, 2011].

The disadvantage of this mixture is its high cost, insufficient ability to assimilate non-metallic inclusions, and the lack of optimal separation for use in casting various groups of steel grades.

Closest to the technical nature of the present invention is a slag-forming mixture for continuous casting of steel, containing, by weight. %: nepheline 15-40, fluorspar 5-30, graphite 1-9, calcium chloride 0.5-9.0, lime 21.45-36.00, pulverized silica 9.00-17.55, carboxylmethyl cellulose 0, 2-3.0, lignosulfonate with a density of 1.2-1.5 g / cm ³ 0.3-3.0 [Patent RU 1459068, IPC B22D 11/00, C21C 5/54, 1996].

The disadvantage of this mixture is its high cost, insufficient ability to assimilate non-metallic inclusions, and the lack of optimal separation for use in casting various groups of steel grades.

The technical result of the invention is to improve the quality of steel as a result of improving its macrostructure, reducing contamination by non-metallic inclusions, reducing the number of surface defects due to improved lubrication and heat removal in the mold, for various groups of steel grades and types of URS.

The specified technical result is achieved in that the slag-forming mixture for continuous casting of steel obtained by mixing fluorspar, graphite, pulverized quartz, according to the invention contains technical soda, syenite concentrate, coke dust, lithium carbonate, technical chalk, magnesium oxide, slag from ferrochrome production, silicate block, colemanite, microcalcite and cement, in the following ratio of components, wt. %:

Fluorspar 10.0-25.0 Graphite 0.1-6.0 Dust Quartz 10.0-24.0 Technical soda 1,0-17,0 Syenite concentrate 2.0-24.0 Coke dust 1.0-6.0 Lithium carbonate 1.0-5.0 Chalk technical 3.0-23.0 Magnesium oxide 0.5-5.0

one or more components from the group:

Slag production ferrochrome 30.0-45.0 Silicate block 4.0-12.0 Colemanite 2.0-15.0 Microcalcite no more than 18.0 Cement rest

while it has the following chemical composition, wt. %:

C free 0.5-8.0 SiO ₂ 21.0-42.0 Al ₂ O ₃ 0.5-12.0 CaO 23.0-52.0 MgO 0.5-10.0 R ₂ O 1.0-15.0 F 1.0-13.0 Li ₂ O no more than 3.0 B ₂ O ₃ no more 5,0 inevitable impurities rest

SCO basicity should be in the range of 0.85-1.25.

The essence of the proposed slag-forming mixture is as follows.

The declared limits of the components are selected experimentally based on the need to obtain a low cost of SCO, as well as requirements for its chemical composition, ensuring optimal physical properties of the mixture (melting onset temperature and viscosity) for various groups of steel grades and type of UHRS.

The carbon concentration is selected based on the need for lubrication in the mold - continuously cast billet zone. A decrease in carbon content below 0.5% leads to increased consumption of the SCO. An increase in the carbon content in the SCO above 8.0% reduces the thickness of the molten layer in the mold, which leads to an increase in the friction of the ingot crust on the mold wall.

The content of calcium and silicon oxides in the SCO is limited by the requirements of its optimal thermal conductivity. The required thermal conductivity of the SCO is ensured with a basicity (CaO / SiO ₂ ratio) in the range of 0.85-1.25 (depending on the groups of steel grades and the type of URS). With a basicity below 0.85, the SCO will have a vitreous structure with increased viscosity, which will exclude the possibility of its use at operating speeds of the UNRS. If the basicity increases above 1.25, the slag will be crystalline, which will reduce the lubricity of the SCO.

The content of aluminum oxide (Al ₂ O ₃ ) was selected experimentally. For better assimilating ability of non-metallic inclusions in the mixture, the content of Al ₂ O ₃ should be at least 0.5% and no more than 12.0%.

The fluorine content in the mixture is selected based on the requirements for obtaining the SCO of a given viscosity. When the fluorine content in the amount of less than 1.0 and more than 13.0%, the viscosity properties of the SCO do not allow efficiently assimilate non-metallic inclusions.

The content of magnesium oxides, alkaline oxides (R ₂ O, K ₂ O, Na ₂ O), as well as lithium and boron oxides, was selected based on the requirements for obtaining a given temperature for the onset of melting of the mixture for each of the steel grades and the type of UHRS.

An increase in the content of magnesium oxides and alkaline oxides above the claimed ranges does not lead to an additional decrease in liquidus temperature. When the content of magnesium oxides and alkaline oxides is lower than the declared ranges, the temperature of the onset of melting of the mixture will be above the optimal range for this type of SCO.

Oxides of lithium and boron are introduced to obtain the required properties of the SCO at a given temperature of its onset of melting. The introduction of lithium and boron oxides in an amount of more than 3.0 and 5.0%, respectively, does not lead to an additional decrease in liquidus temperature.

An example of the use of a slag-forming mixture

The inventive slag-forming mixture was used in the casting of steels of type IF, dynamo, low-silicon, micro-alloyed, carbon steel grades on radial and curved double-strand slab-type continuous casting units with a casting speed of 0.6-1.4 m / min.

The mixture was prepared by mixing fluorspar (not less than 95.0% CaF ₂ ), GLS-3 graphite, pulverized quartz, technical soda (GOST 5100-85 premium), syenite concentrate, coke dust, lithium carbonate, technical chalk, magnesium oxide , one or more components from the group: slag from the production of ferrochrome, silicate block, colemanite, microcalcite (Micromarram Km-160), as well as cement (42.5N) in a mixing plant for 20 minutes at a speed of 800 rpm.

Various SCO formulations were prepared. A number of prepared SCO formulations are shown in Table 1. Compositions 1–13 in compliance with the proposed ratios of components and chemical composition, formulations 14–24 with non-compliance with a number of claimed parameters.

The results of the use of SCO of different compositions are shown in table 2.

From the presented results it is seen that, subject to the proposed ratios of the components and the chemical composition of the SCO (examples 1-13), the surface of continuously cast billets was cleaned less times than when using the SCO, the parameters of which are outside the claimed ranges (examples 14-24).

The SCO was also prepared according to the prototype, using which the surface cleaning of the continuously cast billet was at the level of 4 points.

Thus, the use of the inventive SCO for continuous casting of steel can improve the quality of continuously cast billets, ensuring a decrease in the number of scrapings of surface defects.

Table 1

Claims (2)

1. Slag-forming mixture for continuous casting of steel, obtained by mixing fluorspar, graphite, pulverized quartz, characterized in that it additionally contains technical soda, syenite concentrate, coke dust, lithium carbonate, technical chalk, magnesium oxide, slag from ferrochrome production, silicate block , colemanite, microcalcite and cement, in the following ratio of components, wt. %:
Fluorspar 10.0-25.0 Graphite 0.1-6.0 Dust Quartz 10.0-24.0 Technical soda 1,0-17,0 Syenite concentrate 2.0-24.0 Coke dust 1.0-6.0 Lithium carbonate 1.0-5.0 Chalk technical 3.0-23.0 Magnesium oxide 0.5-5.0
one or more components from the group:
Slag production ferrochrome 30.0-45.0 Silicate block 4.0-12.0 Colemanite 2.0-15.0 Microcalcite no more than 18.0 Cement rest
while it has the following chemical composition, wt. %:
C free 0.5-8.0 SiO ₂ 21.0-42.0 Al ₂ O ₃ 0.5-12.0 CaO 23.0-52.0 MgO 0.5-10.0 R ₂ O 1.0-15.0 F 1.0-13.0 Li ₂ O no more than 3.0 B ₂ O ₃ no more than 5,0 inevitable impurities rest 2. Slag-forming mixture for continuous casting of steel according to claim 1, characterized in that the basicity of the slag-forming mixture corresponds to a range of 0.85-1.25.