SU1814587A3 - Slag forming mixture for protecting metal in crystallizer - Google Patents

Description

The invention relates to metallurgy, and in particular to compositions of slag-forming mixtures used to protect metal in the mold during the continuous casting of steel.

The aim of the invention is to improve the quality of continuous casting by improving the insulating properties of the mixture, reducing its cost by utilizing industrial waste, improving sanitary and hygienic working conditions.

This goal is achieved in that the slag-forming mixture for protecting metal in the mold, containing blast furnace slag, graphite and a fluorine-containing substance, according to the invention, as a fluorine-containing substance, the mixture contains dust from gas purification of aluminum production and additionally contains dust from gas purification from ferrosilicon and lime in the following ratio of components, wt.%:

Blast furnace slag 15-23 Gas cleaning dust aluminum lead 18-22 Gas cleaning dust ferrosilicon 25-30 Gas cleaning dust water lime 26-30 G raffite 3-8, dust gas purification aluminum production Niya has the following composition, wt.%: FROM 25-30

1814587 AZ

A1 ₂ 0h

F Na ₂ O '

SIO ₂

Fe ₂ 03

CaO resinous

12-15

18-22

12-15

0.5-1.0

2.5-3.0

0.7-1.0

10-15, and the dust of gas purification production of ferrosilicon has a composition, wt.%:

SIO ₂ 86-88

A! ₂ 0s 1.8-2.5

SI 1.1-1.45

CaO + MgO 5.0-5.8

Generally 2.5-3.0.

Blast furnace slag is a source of oxides of calcium, aluminum, belt, and magnesium, the introduction of which into the mixture as an alloy, as shown by experiments, accelerates the formation of homogeneous slag. In addition, magnesium oxide contained in blast furnace slag enhances the assimilative properties of the slag melt and ensures the adhesion of the skull with the walls of the mold. The specified effect is achieved when the content of blast furnace slag in the mixture in the range of 15-23%. The introduction of less than 15% of blast furnace slag into the composition of the slag-forming mixture reduces the thickness of the layer of molten slag in the mold and its assimilative ability. When the content of blast furnace slag in the mixture exceeds 23%, the melt melting temperature rises, the viscosity of the slag coating sharply increases, and the quality of cast billets deteriorates.

The dust of gas purification of aluminum production used as a fluorine-containing substance, having both fluorine compounds and sodium compounds, is smooth for the whole mixture, while reducing the melting temperature of the mixture and the viscosity of the resulting slag, and contributes to the rapid formation of homogeneous slag at a lower temperature . In addition, it contains up to 30% carbon and a gummy residue, during the combustion of which heat is generated in the mold, additionally heating the slag mixture, and the released products of combustion and decomposition contribute to the improvement of heat-insulating properties due to its loosening.

Dust is a solid finely divided product of high-temperature offsets of aluminum smelting materials. Low bulk density (0.25 t / m ³ ), small particle size (0.1-20 μm) and the presence of carbon determine its high heat-insulating and protective-lubricating properties. Dust is cheap, in preparation for use it does not require grinding, its use will reduce environmental pollution by waste. When forming a protective coating 5 during the casting process, atmospheric fluorine pollution is virtually eliminated.

When the fluorine-containing substance in the mixture is below 18%, the slag viscosity increases, the thermal conductivity of the mixture increases, the quality of cast billets deteriorates (slag inclusions, rough folding are observed), and the stability of the continuous casting process is violated. If the content of the mixture of 22% fluorine-containing substance is exceeded, the thickness of the slag coating layer is unacceptably reduced, the viscosity of the slag decreases, and the consumption of mixture increases. In this case, there is an increase in fluoride emissions and atmospheric pollution.

Ferrosilicon gas purification dust, which is part of the mixture, provides its heat-shielding properties 25 (thermal conductivity 0.08 W / mK), prevents the formation of oxidized crust on the meniscus and is a source of amorphous silicon dioxide, whose chemical activity is higher than all 30 modifications of silicon oxides, therefore the formation of silicates in the slag mixture occurs until it is completely melted. Having a fraction of 0.1-10 microns, the dust does not require preliminary preparation. 35 A decrease in the dust content of gas purifications from ferrosilicon production below 25% in the composition of the slag mixture leads to an increase in the melting temperature of the mixture and a decrease in the insulating properties. If the dust content of gas purification from ferrosilicon production exceeds 30%, then an increase in slag viscosity is observed, conditions for the formation of a skull are worsened, and the quality of cast billets decreases.

Dust from gas purification of lime production is a source of CaO and, together with other components of the mixture, provides optimal physicochemical characteristics of the slag melt necessary for the assimilation of nonmetallic inclusions, isolation of the metal and preservation of alumina in it during casting with a minimum initial fluorine content. It was experimentally established that this effect is achieved when the content in the mixture of lime dust in the range of 25-30%.

The carbon-containing graphite material in the composition of the mixture is introduced as a regulator of the melting rate. At a graphite content of less than 3%, the mixture consumption sharply increases, and an increase in its content of more than 8% leads to a decrease in the positive properties of the protective coating, carburization of the metal and the formation of cracks on the surface of the workpieces are observed.

A new positive effect of the proposed technical solution consists in the application of a certain combination of fine industrial waste, simplifying the preparation of mixtures and providing the necessary physicochemical properties of the slag melt. The use of these components provides a slag mixture with a low bulk density, high heat-insulating properties and increased flowability. This allows to achieve the purpose of the invention.

For experimental verification of the claimed composition of the slag-forming mixture, five compositions of the slag-forming mixtures were prepared. Mixtures according to options No. 2-4 (see table) correspond to the proposed limits of composition and properties, and mixtures according to options No. 1 and No. 5 go beyond these limits.

PRI me R 1 (option mixture No. 3). The mixture was prepared by mechanical mixing of the components to a homogeneous state, and only granulated blast furnace slag was subjected to grinding and drying. The proposed mixture was tested in the process of continuous casting of billets with a cross section of 300x300 mm and 140x140 mm of steel grades ct.20-ct.45.

The metal came from the tundish into the mold through a direct-flow submerged beaker. The mixture contained: blast furnace slag - 20%, dust from gas purification of aluminum production - 20%, dust from ferrosilicon production - 27%, lime dust - 28%, graphite - 5%, had a density of 0.56 t / m ³ , spreadability - 380 mm. The consumption of the mixture was 0.5 kg / t. The thermal conductivity of the mixture was 0.88 W / mK, the viscosity was 0.8 poise, the melting onset temperature was 1070 ° C, and the thickness of the layer of molten slag in the mold was 2.5 mm.

The dust of gas purifications produced by ferrosilicon was an amorphous silicon dioxide fraction of 0.1-10 microns, the dust of gas purifications produced by aluminum had a fraction of 0.1-20 microns, bulk density 0.25 t / m ³ .

The table shows that the best results were obtained for the mixtures of options No. 2-4. The low melting points of the mixtures and the viscosity of their slag melts, combined with increased spreadability and high heat-insulating properties, provided a high-quality surface of continuously cast billets. In the considered variant of mixture No. 3, there were practically no defects on the surface of the workpieces.

When using a mixture of compositions according to options No. 1 and No. 5 during casting to protect the metal in the mold, the rejection by surface defects increased by 0.01-0.06%.

The proposed mixture during casting formed a uniform coating on the metal mirror, which ensured a stable casting process at a speed of 0.5-1.8 m / min depending on the cross section of the workpiece. Due to the low content of graphite in the mixture (3-8%), no carburization of the metal occurred.

The use of slag-forming mixtures of the claimed invention virtually eliminated the release of fluorine into the atmosphere. Its content in the atmosphere above the crystallizer was 0.01 mg / m ³ , on the steelmaker’s working site this content decreased to 0.004 mg / m ³ , and no fluorine was found in other workplaces.

The economic effect of the use of the proposed mixture consists of its cost due to the disposal of production waste, the exclusion of preliminary preparation of materials, the absence of expensive materials in the composition and the reduction of metal rejection for surface defects.

Claims (3)

Claim 1. Slag-forming mixture for protecting metal in the mold, including blast furnace slag, graphite, fluorine-containing substance, with the exception that in order to improve the quality of continuously cast billets by improving the heat-insulating properties of the mixture, reducing it the cost due to the disposal of industrial waste and improvement of the sanitary and hygienic working conditions, as a fluorine-containing substance it contains dust from gas purification of aluminum production and additionally contains dust: gas purification from ferro production Ilica and lime in the following ratio, wt.%: Blast furnace slag 15.0-23.0 Dust for gas purification of aluminum production 18.0-22.0 'Pal for gas purification of production of ferrosilicon 25.0-30.0 _ Dust for gas purification of lime production 26.0 + 30.0 Graphite 3.0 + 8.0 2. The mixture according to claim 1, characterized in that the dust of gas purification of aluminum production has the following composition, wt.%: 3. The mixture according to claim 1, characterized in that. that dust gas purification production of ferrosilicon has the following composition, wt.%: Alumina 12.0 + 15.0 Fluoride 18.0 + 22.0 Sodium oxide 12.0 + 15.0 Calcium Oxide 0.5 + 1.0 Iron oxide 2.5 + 3.0 Carbon 25.0 + 30.0 Resinous substances 10.0 + 15.0 Silica 86.0 + 88.0 Aluminium oxide 1.8 + 2.5 Silicon 1.1 + 1.45 Alkali and alkali oxides earth metal 5.0 + 5.8 Iron (General) 2 * 5 + 3.0 Indicators Mixture number 1 2 3 4 5 The content of components in the mixture, wt.%: blast furnace slag 5 fifteen 20 23 thirty dust gas purification water aluminum dust gas purification production ferrosi- 25 22 20 ¹⁸ fifteen lice 35 thirty 27 25 20 gas cleaning dust lime production 33 thirty 28 26 22 Density, t / m ³ 0.49 0.53 0.56 0.60 0.65 Spreadability, mm Thermal conductivity, 405 390 380 375 340 W / mk 0,080 0,086 0,088 0,095 0,110 Viscosity, Poise 0.6 0.8 0.8 1.0 1.4 The melting temperature, ° C start 1100 1080 1070 1100 1120 end layer thickness 1170 1190 1190 1200 1240 molten slag in mold, mm 1,0 2.0 2.5 3.0 3.0 Mixture consumption, kg / t 0.8 0.6 0.5 0.6 0.6 Surface rejection defects,% 0,03 0.02 not detected 0.02 0.08