RU2843650C1 - Slag-forming mixture for metal protection in crystalliser during continuous steel casting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: slag-forming mixture for protection of metal in a crystalliser at continuous steel casting contains the following, wt.%: 22-27 of marble, 3.5-5.5 of graphite, 7-11 of fluorspar, 1-3 of bentonite, 1-4 of bauxite, 4-8 of quartzite, 3.5-6.5 of soda, 12-17 of feldspar and up to 100 of wollastonite. Addition of wollastonite, having reinforcing properties, increases the strength of the granules of the mixture. Soda and fluorspar reduce melting point and viscosity of slag, which helps to prevent formation of scull on walls of crystalliser. Addition of marble increases slag assimilating capacity and promotes stability of casting without slag foaming. Feldspar dissolves oxides on metal surface and covers the surface, thus preventing oxidation. Bentonite has chemical resistance and lubricating properties.

EFFECT: eliminating the scull formation at crystalliser walls at simultaneous reduction of slag viscosity.

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.

The closest to the proposed invention is a slag-forming mixture for continuous casting of steel, 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, mass %: 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 that during operation a crust forms on the walls of the crystallizer, preventing the normal course of the process.

The technical result of the proposed invention consists in eliminating the formation of a scum on the walls of the crystallizer while simultaneously reducing viscosity.

The specified technical result is achieved by a slag-forming mixture for protecting metal in a crystallizer during continuous casting of steel, containing wollastonite, marble, graphite, fluorspar, bentonite, bauxite, quartzite, soda, feldspar in the following ratio of components, mass %:

marble 22-27 graphite 3.5-5.5 fluorspar 7-11 bentonite 1-3 bauxite 1-4 quartzite 4-8 soda 3.5-6.5 feldspar 12-17 wollastonite up to 100

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

Marble (TU 5716-001-99242323) is a source of calcium oxide, which increases the assimilating capacity of slag and binds dissolved aluminates in the liquid steel melt, thereby ensuring a stable casting process without slag foaming and mixing it with the slag.

Graphite (GOST 527229-2007) is added to regulate the melting rate of the slag. Free carbon, located between solid particles and melt droplets, creates a kind of inert barrier. Carbon is not wetted by 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, which helps to eliminate the formation of a skull on the walls of the crystallizer. In slag, it is capable of forming strong compounds with Al ₂ O ₃ and SiO ₂ .

Bentonite (GOST 28177-89) has the property of swelling upon hydration. When freely swelling in the presence of water, a dense gel is formed, preventing further penetration of moisture. It also has chemical resistance and lubricating properties.

Bauxite is a source of aluminum oxide (Al ₂ O ₃ ).

A characteristic distinguishing feature of bauxite is that, unlike clays, it does not form a plastic mass with water. It reduces the melting temperature of the mixture.

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

Feldspar (TU 952814-2016) is introduced as a flux to facilitate the separation of metal from waste rock. It dissolves oxides already present on the metal surface and acts as an oxygen barrier, covering the hot surface, preventing oxidation.

The range of cast steel includes all grades of steel, including pipe steel, with a hydrogen mass fraction of no more than 6.5 ^ppm .

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, mass %:

Total 7.0-9.0

F 4.5-6.5

_{Al2O3 4.0-7.0}

MgO ≤2

_Na2O + _K2O 2.5-5.5

Fe total ≤2

CaO 31.0-36.0

_SiO2 32.5-37.5

The preparation of a slag-forming mixture for protecting metal in a crystallizer during continuous casting of Thermoisolit KR/S-0-BS 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 (marble 22-27 wt. %, graphite 3.5-5.5 wt. %, fluorspar 7-11 wt. %, bentonite 1-3 wt. %, bauxite 1-4 wt. %, quartzite 4-8 wt. %, soda 3.5-6.5 wt. %, feldspar 12-17 wt. % and wollastonite up to 100%) are loaded into the MMP, where the materials are ground and mixed simultaneously. 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 mixed 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 the 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 production of granules of the GShOS is carried out in the BRS. The suspension is 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 is carried out 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 with the help of a belt elevator it is fed to the storage bin and packed in valve bags weighing about 10 kg, or in Big Bag type MKR with an insert of no more than 1.0 ton.

To assess the quality of granulated SS, a sample weighing about 0.3-0.5 kg is taken from the container and sent to the laboratory of physical and mechanical tests of the UShOS 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 mixture 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 KR/S-0-BS Form granules Bulk density, g/ ^cm3 ±deviation 0.80±0.15 Melting point, °C±deg 1150±30 Viscosity, Pa⋅s at 1300°C±deviation 0.48±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 18 wt. %, marble 27 wt. %, graphite 5.5 wt. %, fluorspar 11 wt. %, bentonite 3 wt. %, bauxite 4 wt. %, quartzite 8 wt. %, soda 6.5 wt. %, feldspar 17 wt. %) were loaded into the MMP, where the materials were crushed with simultaneous mixing. Ceramic cylindrical bodies were used as grinding media. 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 stirred to prevent sedimentation and stratification. Then, a sample of the suspension was taken from the receiving mixers to determine the density. The density was 1.81 g/cm ³ .

Chemical composition of the mixture:

Total 8.5

F 6.3

_{Al2O36.7 ​}

MgO 1.4

_Na2O + _K2O 5.3

Fe total 1.8

CaO 35.3

_SiO2 34.7

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

Example 2

The required amount of water was poured into the MMP through measuring tanks according to the batching. The prepared batch materials (wollastonite 46 wt. %, marble 22 wt. %, graphite 3.5 wt. %, fluorspar 7 wt. %, bentonite 1 wt. %, bauxite 1 wt. %, quartzite 4 wt. %, soda 3.5 wt. %, feldspar 12 wt. %) were loaded into the MMP, where the materials were crushed with simultaneous mixing. Ceramic cylindrical bodies were used as grinding media. 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 stirred to prevent sedimentation and stratification. Then, a sample of the suspension was taken from the receiving mixers to determine the density. The density was 1.81 g/cm ³ .

Chemical composition of the mixture:

Total 8.4

F 5.1

_{Al2O36.1 ​}

MgO 1.7

_Na2O + _K2O 4.4

Fe total 1.5

CaO 35.5

_SiO2 37.3

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 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 fed into the BRS by injection-type burners. The temperature in the working space of the spray dryer was 360 °C. The dried granulated mixture had a moisture content of 0.4%. From the BRS, the mixture entered the cooler, where it cooled and was fed into the storage bin using a belt elevator and packaged into valve bags weighing about 10 kg.

Example 3

The required amount of water was poured into the MMP through measuring tanks according to the batching. The prepared batch materials (wollastonite 35 wt. %, marble 24 wt. %, graphite 4 wt. %, fluorspar 8.5 wt. %, bentonite 2 wt. %, bauxite 2 wt. %, quartzite 5.5 wt. %, soda 5 wt. %, feldspar 14 wt. %) were loaded into the MMP, where the materials were crushed with simultaneous mixing. Ceramic cylindrical bodies were used as grinding media. After combined grinding and mixing of all materials, the finished suspension was poured from the MMP by gravity into the receiving mixers, in which it was constantly stirred to prevent sedimentation and stratification. Then, a sample of the suspension was taken from the receiving mixers to determine the density. It was 1.81 g/cm ³ .

Chemical composition of the mixture:

Total 8.2

F 5.8

_{Al2O35.4 ​}

MgO 1.8

_Na2O + _K2O4.2

Fe total 1.7

CaO 35.7

_SiO2 37.2

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 GSHO is carried out in the BRS. The suspension was fed to 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 temperature in the working space of the spray dryer was 360 °C. The dried granulated mixture had a moisture content of 0.09%. From the BRS, the mixture entered the cooler, where it cooled and was fed to the storage bin using a belt elevator and packaged in valve bags weighing about 12 kg.

The claimed slag-forming mixture Thermoisolit KR/S-0-BS was used at the Electric Steel Works of PJSC MMK when casting a range of steels with a hydrogen content of less than 6.5 ppm.

The proposed mixture ensures the stability of the steel casting process, eliminating the formation of a skull on the walls of the crystallizer.

Claims (2)

A slag-forming mixture for protecting metal in a crystallizer during continuous casting of steel, containing wollastonite, marble, graphite, fluorspar, bentonite, bauxite, quartzite, soda, feldspar in the following ratio of components, wt. %: marble 22-27 graphite 3.5-5.5 fluorspar 7-11 bentonite 1-3 bauxite 1-4 quartzite 4-8 soda 3.5-6.5 feldspar 12-17 wollastonite up to 100