RU2843647C1 - Slag-forming mixture for metal protection in crystallizer during continuous steel casting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: slag-forming mixture for protection of metal in a crystalliser during continuous steel casting contains the following, wt. %: 0.1-3 of technical carbon, 15-25 of fluorspar, 5-8 of quartzite, 3-6 of borax, 9-15 of talc, 8-12 of soda and up to 100 of wollastonite. Addition of wollastonite increases strength of the granules of the mixture. Soda and fluorspar reduce melting temperature and viscosity of slag. Addition of borax and talc facilitates fast recovery of the molten surface of the mixture.

EFFECT: fast recovery of fused mix surface in casting steel with hydrogen content over 6.5 ppm.

1 cl, 1 tbl, 3 ex

Description

The invention relates to the field of metallurgy, in particular to protecting the surface of a metal in a crystallizer.

A slag-forming mixture for continuous casting of steel is known, containing a carbon-containing material, a fluorine-containing material, a material based on silicon oxides, calcium and sodium carbonates and a silicate material in the form of wollastonite and nepheline concentrate, the ingredients are taken in the following ratio, wt.%: carbon-containing material 4-6, fluorine-containing material 9-11, material based on silicon oxides 6-9, sodium carbonate 1-3, calcium carbonate 21-25, silicate material in the form of wollastonite and nepheline concentrate the rest (RU Patent No. 2699484, B22D 11/111, published 09/05/2019 Bulletin No. 25).

The disadvantage of the analogue is the low rate of restoration of the surface of the molten layer of the mixture when pouring steels with a hydrogen content of more than 6.5 ppm.

The technical result is to impart to the mixture the property of quickly restoring the molten surface when pouring steels with a hydrogen content of more than 6.5 ppm.

The specified technical result is achieved by a slag-forming mixture for protecting metal in a crystallizer during continuous casting of steel, containing wollastonite, carbon black, fluorspar, quartzite, anhydrous borax, talc, soda, with the following ratio of components, wt.%:

Carbon black 0.1-3 Fluorspar 15-25 Quartzite 5-8 Bura 3-6 Talc 9-15 Soda 8-12 Wollastonite up to 100

Wollastonite has reinforcing properties due to its needle-like structure and significantly increases the strength of the mixture granules.

Technical carbon (carbon black P-803) (GOST 7885-86) is added to regulate the melting rate of the slag. Located between the solid particles and melt droplets, free carbon creates a kind of inert barrier. Carbon is not wetted by the molten slag, so liquid slag globules cannot agglomerate until the carbon particle is oxidized. In addition, carbon forms a reducing atmosphere (CO) during combustion.

Fluorspar (GOST 29219-2023) CaF ₂ has a strong effect on the viscosity and melting point of slag, reducing them.

Soda (GOST 5110-85 – premium grade, GOST 10689-75 – 1, 2, 3 grade) reduces the melting point, and simultaneously with fluorspar reduces the viscosity. In slag, it is capable of forming strong compounds with Al ₂ O ₃ and SiO ₂ .

Anhydrous borax is used due to its low melting point and ability to dissolve metal oxides. Borax acts as a flux that protects the surface of the melt of non-ferrous and precious metals from oxidation and ensures increased purity of metals. The presence of borax and talc ensures rapid restoration of the molten surface when pouring steels with a hydrogen content of more than 6.5 ppm.

Talc (GOST 21234-75) is a source of MgO flux. This mineral is used as a thickener and lubricant. Increases thermal expansion to resist element burnout.

Quartzite (TU 571726-001-94779610-2014) is a source of _SiO2 as a high-quality flux.

In the process of continuous steel casting, the mixture performs the following main functions:

- isolates liquid metal from air, preventing its oxidation;

- assimilates non-metallic inclusions that float in liquid metal;

- thermally insulates the metal mirror in the crystallizer and protects it from excessive cooling;

- improves the conditions of heat transfer from the continuously cast blank to the water-cooled walls of the crystallizer;

- acts as a lubricant between the moving shell of the ingot and the crystallizer.

The mixture has the following chemical composition, wt. %:

With common ≤4.5; F 8.0-10.0 _{Al2O3 ​} ≤1.5 MgO ≤2.0-5.0 _Na2O + _K2O 5.0-8.0 Fe total ≤2 In ₂ O ₃ 2.0-4.0 CaO 33.5-38.5 _SiO2 34.0-39.0

The preparation of a slag-forming mixture for protecting metal in a crystallizer during continuous casting of Thermoisolit KR/S-01-C steel is carried out in two stages: preparation of a suspension in wet grinding mills (WGM) and drying of the suspension and obtaining granules in a tower spray dryer (TSD).

Before preparing the suspension in the MMP, water in the required amount is poured through measuring containers according to the batching. The prepared batch materials - carbon black 0.1-3 wt. %, fluorspar 15-25 wt. %, quartzite 5-8 wt. %, borax 3-6 wt. %, talc 9-15 wt. %, soda 8-12 wt. % and wollastonite up to 100% are loaded into the MMP, where the materials are ground with simultaneous mixing. Ceramic cylindrical bodies are used as grinding bodies. After joint grinding and mixing of all materials, the finished suspension from the MMP is drained by gravity into the receiving mixers, in which it is constantly stirred to prevent sedimentation and stratification. Next, a sample of the suspension is taken from the receiving mixers to determine the density, which should be within the range of 1.70 - 1.90 g / cm³ and chemical composition (the dried sample of the suspension is sent to the LAC KKC). After obtaining satisfactory results, the suspension from the receiving mixer is pumped to the feed mixer using a slip pump to create a reserve before the high-pressure pump and the BRS.

The granules of the GShOS are obtained in the BRS. The suspension is fed to the BRS by a plunger pump under pressure through a ring-shaped device with nozzles. The suspension is sprayed and granules are formed in counter-current to the heat supplied to the BRS by injection-type burners. The tower spray dryer is heated by a mixture of natural gas and air. The temperature in the working space of the spray dryer is 360-480 °C. The dried granulated mixture should have a moisture content of no more than 0.5%. From the BRS, the mixture enters the cooler, where it is cooled and fed to the storage bin using a belt elevator and packed into valve bags weighing about 10 kg, or into Big Bag type large bags with an insert of no more than 1.0 ton.

To assess the quality of the GSMS, a sample of the granulated mixture weighing about 0.3-0.5 kg is taken from the container and sent to the laboratory of physical and mechanical tests of the USHS section to determine the moisture content and granulometric composition, and to the LAC (CLC) of the KKC of PJSC MMK to determine the chemical composition according to the analytical control scheme approved by the head of the STC of PJSC MMK. If necessary, a sample of the GSMS is transferred to the Federal State Budgetary Educational Institution of Higher Education Nosov Moscow State Technical University to determine the melting point.

The physical properties of the mixture are presented in Table 1.

Table 1. Physical properties

Parameter KRS-01C Form granules Bulk density, g/ ^cm3 ±deviation 0.75±0.15 Melting point, °C ±deviation 1020±30 Viscosity, Pa s at 1300°C±deviation 0.22±0.08 Granulometric composition, %: Residue on sieve 1.0 mm ≤ 5 Residue on sieve 0.2 mm ≥ 65 Residue on sieve 0.063 mm ≤ 25 Passage through sieve 0.063 mm ≤ 5

Example 1

The required amount of water was poured into the MMP through measuring tanks according to the batching. The prepared batch materials wollastonite 31 wt.%, carbon black 3 wt.%, fluorspar 25 wt.%, quartzite 8 wt.%, borax 6 wt.%, talc 15 wt.%, soda 12 wt.% were loaded into the MMP, where the materials were ground with simultaneous mixing. Ceramic cylindrical bodies were used as grinding bodies. After combined grinding and mixing of all materials into a finished suspension, it was poured from the MMP by gravity into the receiving mixers, in which it was constantly mixed to prevent sedimentation and stratification. Then, a sample of the suspension was taken from the receiving mixers to determine the density, which was 1.81 g / cm³.

After obtaining satisfactory results, the suspension from the receiving mixer was pumped into the feed mixer using a slip pump to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS was carried out in the BRS. The suspension was fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules was carried out in counter-current to the heat supplied to the BRS by injection-type burners. The tower spray dryer was heated by a mixture of natural gas and air.

The temperature in the working space of the spray dryer was 360 °C. The dried granulated mixture had a moisture content of 0.5%. From the BRS, the mixture entered the cooler, where it was cooled and, using a belt elevator, the mixture was fed into a storage bin and packaged into valve bags weighing about 10 kg.

Chemical composition of the mixture:

With common 3.7 F 8.7 _{Al2O3 ​} 1,1 MgO 3.9 _Na2O + _K2O 7.2 Fetotal 1.7 In ₂ O ₃ 2.6 CaO 36.2 _SiO2 34.9

Example 2

The required amount of water was poured into the MMP through measuring tanks according to the batching. The prepared batch materials wollastonite 59.9 wt.%, carbon black 0.1 wt.%, fluorspar 15 wt.%, quartzite 5 wt.%, borax 3 wt.%, talc 9 wt.%, soda 8 wt.% were loaded into the MMP, where the materials were ground with simultaneous mixing. Ceramic cylindrical bodies were used as grinding bodies. After combined grinding and mixing of all materials into a finished suspension, it was poured from the MMP by gravity into the receiving mixers, in which it was constantly mixed to prevent sedimentation and stratification. Then, a sample of the suspension was taken from the receiving mixers to determine the density, which was 1.79 g / cm³.

After obtaining satisfactory results, the suspension from the receiving mixer was pumped into the feed mixer using a slip pump to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS was carried out in the BRS. The suspension was fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules was carried out in counter-current to the heat supplied to the BRS by injection-type burners. The tower spray dryer was heated by a mixture of natural gas and air.

The temperature in the working space of the spray dryer was 360 °C. The dried granulated mixture had a moisture content of 0.13%. From the BRS, the mixture entered the cooler, where it was cooled and, using a belt elevator, the mixture was fed into a storage bin and packaged into valve bags weighing about 10 kg.

Chemical composition of the mixture:

With common 3.1 F 8.6 _{Al2O3 ​} 1,2 MgO 2,3 _Na2O + _K2O 5.5 Fetotal 1.3 In ₂ O ₃ 2.4 CaO 37.0 _SiO2 38.6

Example 3.

The required amount of water was poured into the MMP through measuring tanks according to the batching. The prepared batch materials wollastonite 49 wt.%, carbon black 2 wt.%, fluorspar 20 wt.%, quartzite 6 wt.%, borax 4 wt.%, talc 10 wt.%, soda 9 wt.% were loaded into the MMP, where the materials were ground with simultaneous mixing. Ceramic cylindrical bodies were used as grinding bodies. After combined grinding and mixing of all materials into a finished suspension from the MMP, it was drained by gravity into the receiving mixers, in which it was constantly mixed to prevent sedimentation and stratification. Then a sample of the suspension was taken from the receiving mixers to determine the density, which was 1.80 g / cm³. After obtaining satisfactory results, the suspension from the receiving mixer was pumped into the feed mixer using a slip pump to create a reserve before the high-pressure pump and the quick-release mixer.

The production of granules of the GShOS was carried out in the BRS. The suspension was fed into the BRS by a plunger pump under pressure through a device in the form of a ring with nozzles. Spraying of the suspension and formation of granules was carried out in counter-current to the heat supplied to the BRS by injection-type burners. The tower spray dryer was heated by a mixture of natural gas and air.

The temperature in the working space of the spray dryer was 450°C. The dried granulated mixture had a moisture content of 0.12%. From the BRS, the mixture entered the cooler, where it was cooled and, using a belt elevator, the mixture was fed into a storage bin and packaged into valve bags weighing about 10 kg.

Chemical composition of the mixture:

With common 3.2 F 9.1 _{Al2O3 ​} 1,2 MgO 3.5 _Na2O + _K2O 6.4 Fetotal 1,1 In ₂ O ₃ 3.0 CaO 36.0 _SiO2 36.5

The claimed slag-forming mixture Thermoisolit KR/S-01C was used in the PAO MMK CCC for casting ultra-low-carbon steel grades (with a mass fraction of carbon of less than 0.01%), high-carbon steel grades (with a mass fraction of carbon of more than 0.25%) and low-carbon steels with alloying elements. The mixture was also used in the PAO MMK EAFC for casting steels with a hydrogen content of more than 6.5 ppm and high-carbon steel grades.

The mixture is characterized by rapid restoration of the molten surface when pouring steels with a hydrogen content of more than 6.5 ppm.

Claims (2)

A slag-forming mixture for protecting metal in a crystallizer during continuous casting of steel, containing wollastonite, carbon black, fluorspar, quartzite, borax, talc and soda, in the following ratio of components, wt.%: carbon black 0.1-3 fluorspar 15-25 quartzite 5-8 borax 3-6 talc 9-15 soda 8-12 wollastonite up to 100