RU2419510C1 - Slag forming mixture for pony ladle - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to ferrous metallurgy, particularly to compositions of slag forming mixtures used for heat insulation and protection of bath level in pony ladle from secondary oxidation at continuous steel casting. Slag forming mixture contains, wt %: carbon containing material 7-22, pegmatite fine milled 30-35, fluorspar fluorite concentrate 7-10, cement - the rest. Also, mixture has the following chemical composition, wt %: 5.0-17.0 % C; 33.0- 45.0 % CaO; 28.9-37.0 % SiO₂; 6.5-9.0 % Al₂O₃; ≥3.0 % F; ≥1.0 % Na₂O; ≥0.7 % K₂O at ratio CaO/SiO₂=0.9-1.4.

EFFECT: increased heat-insulating capacity of mixture, reduced surface defects due to stabilisation of temperature-rate mode, reduced contamination with non-metallic inclusions.

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Description

The invention relates to ferrous metallurgy, and in particular to compositions of slag-forming mixtures used for thermal insulation and protection of a metal mirror in an intermediate ladle from secondary oxidation during continuous casting of steel.

Known [1] is selected as a prototype slag-forming mixture for thermal insulation of a metal in an intermediate ladle, containing material based on silicon oxide and a carbon-containing material, characterized in that as the material based on silicon oxide, feldspar is used in the following ratio of ingredients, wt.%:

Carbon material 15-25; Feldspar 75-85.

Significant disadvantages of this mixture when used in the tundish are:

- low heat-insulating properties, as well as the uncontrolled process of carburization of steel, due to the content of amorphous graphite in the mixture;

- low refining properties of the mixture due to the high content of aluminum oxides that make up the feldspar;

- low seriality of the heats taken on one tundish due to the low basicity, leading to increased wear of the slag belt of the tundish.

The technical results of the invention are:

- increase the heat-insulating ability of the mixture;

- reduction of screening for surface defects due to stabilization of temperature and speed conditions;

- reduction of contamination by non-metallic inclusions by increasing the refining ability of the mixture;

- increasing the seriality of swimming trunks taken on one industrial ladle.

To achieve this, a slag-forming mixture for thermal insulation of a metal in an intermediate ladle is proposed containing a material based on silicon oxides and a carbon-containing material, characterized in that finely ground pegmatite, fluorspar fluorite concentrate and cement are used as the material based on silicon oxides in the following ratio of ingredients, wt. %:

Carbon material 7-22; Fine pegmatite 30-35; Fluorspar fluorite concentrate 7-10; Cement rest

and provide the following chemical composition, wt.%:

5.0-17.0% C; 33.0-45.0% CaO; 28.9-37.0% SiO ₂ ; 6.5-9.0% Al ₂ O ₃ ; ≥ 3.0% F; ≥1.0% Na ₂ O; ≥0.7% K ₂ O; the ratio of CaO / SiO ₂ = 0.9-1.4.

The claimed ratio of the components is selected empirically, and with a change in the ratio of components, the fluidity and heat-insulating properties of the slag mixture are reduced.

A decrease in the content of finely ground pegmatite in the mixture below 30% leads to an increase in the melting temperature of the mixture and a decrease in the heat-insulating properties. When the content of finely ground pegmatite in the mixture is more than 35%, an increase in the viscosity of the slag melt is observed, which leads to the formation of a skull around the stoppers of the tundish.

When the content of the carbon-containing material in the mixture is less than 7%, the heat-insulating properties of the mixture decrease, and when the content is more than 22%, an uncontrolled process of carbonization of steel is observed.

When the content of fluoride fluorite concentrate in the mixture is less than 7%, the melting temperature of the mixture rises; increased clumping is observed, which leads to a decrease in the assimilative ability of the slag melt. With a content of more than 10%, an increased consumption of the mixture is observed.

Cement together with other components of the slag mixture provides the optimal physico-chemical characteristics of the slag melt, necessary for the assimilation of non-metallic inclusions and insulation of the metal.

An experimental slag mixture was made by dosing the starting materials by weight using the following starting materials:

1) Carbon-containing material - cryptocrystalline (amorphous) graphite GLS-2, GLS-3 grades (GOST R 52729-2007), with a carbon content of at least 72.0% or coke dust (TU 0763-200-00190437-2004) with a content carbon not less than 80.0%;

2) Fine-ground pegmatite - KPSHTM 0.20-2 (GOST 7030-75) containing 1.0% CaO, 67.5% SiO ₂ , 15.5% Al ₂ O ₃ , 5.0% Na ₂ O, 5 , 0% K ₂ O;

3) Fluorspar fluorite concentrate according to GOST 4421-73, containing 68.21% CaO, 3.0% SiO ₂ , 46.23% F;

4) Cement - Portland cement or slag Portland cement (GOST 10178-85) containing 54.6% CaO, 27.0% SiO ₂ , 7.6% Al ₂ O ₃ , 1.0% K ₂ O.

The preparation of the heat-insulating mixture for the ladle was made by installing a dispenser on the weight frame of the trolley with an electronic weight indicator. Moving the cart with the dispenser under the bunker overpass, it was alternately stopped under one of the four bunkers with the starting materials (graphite (coke dust), finely ground pegmatite, cement, fluorine-containing material). After installing the dispenser under the hopper, the shutter was opened on it and the dispenser was filled. In electronic scales, weight information about each source material was laid.

The filled dispenser was transferred to the mixing plant. To achieve a uniform composition of the mixture, the materials were mixed in a mixing unit for at least 15 minutes.

The ratio of the starting materials per dispenser and the chemical composition of the SCO are presented in table 1.

Table 1 The effect of the chemical composition of the SCO on the temperature of the onset of softening and melting SCO composition SCO Options one 2 3 four 5 6 SCO component composition,% amorphous graphite 7.0 21.8 7.0 7.2 19.3 22.0 fluorspar concentrate 8.0 7.0 7.1 7.3 9.1 10.0 Pegmatite 35.0 31,2 30.1 35 33.1 30,0 cement 50,0 40,0 55.8 39.1 38.5 38 chemical composition of the SCO FROM 5,0 17.0 5,6 7.2 16.6 17.0 CaO 40.8 33.0 45.0 38.9 33,4 38.1 SiO ₂ 34.8 33.3 32.8 37.0 33,4 28.0 Al ₂ O ₃ 8.7 8.5 7.4 9.0 8.1 6.5 F 5,0 3.2 3.0 3.8 4.2 4.6 K ⁺ 3.0 3.0 3,1 2.2 2.1 3,1 Na ⁺ 2.7 2.0 3,1 1.9 2.2 2.7 Basicity 1,2 0.9 1.4 1,1 1,0 1.4

The experiments were carried out on a four-strand bloom caster with a cross-section of a mold of 300 × 340 mm in a trash can with a capacity of 25 tons when casting steel grades st.3-5 cp, E76, E76F.

During casting in the intermediate ladle, a slag-forming mixture in the amount of 120-160 kg was set in a series on the mirror of the first melting metal; when changing the next casting ladle, a slag-forming mixture in the amount of up to 60 kg was planted in the intermediate ladle.

The use of slag mixture during continuous casting of steel made it possible to reduce the temperature gradient of the metal in the intermediate ladle to 5-10 ° C and, as a result, the rejection of metal by surface defects associated with the violation of the temperature-speed regime by 0.5%, to reduce the pollution of non-metallic steel inclusions from 0.150 to 0.079 mm, to increase the seriality of the heats taken for one blast furnace.

Information sources

1. RF patent No. 2311258 B22D 11/111.

Claims (1)

Slag-forming mixture for thermal insulation of metal in an intermediate ladle, containing material based on silicon oxides and a carbon-containing material, characterized in that it contains finely ground pegmatite, fluoric acid fluorite concentrate and cement as a material based on silicon oxides in the following ratio of ingredients, wt.%:
Carbon material 7-22 Fine pegmatite 30-35 Fluorspar fluorite concentrate 7-10 Cement Rest,
and has the following chemical composition, wt.%:
FROM 5.0-17.0 CaO 33.0-45.0 SiO2 28.9-37.0 Al ₂ O ₃ 6.5-9.0 F ≥3.0 Na ₂ O ≥1.0 K ₂ O ≥0.7
with a ratio of CaO / SiO ₂ = 0.9-1.4.