RU2574903C2 - Slag-forming mixture to protect steel in intermediate ladle - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed slag-forming mixture contains in wt %: Portland cement 40-50, material based on silicon oxide 30-38, technical sodium carbonate 10-18, rice shell 4-10.

EFFECT: increased assimilation from steel of the alumina inclusions, reduced erosion of lining of the intermediate ladle and locks, reduced heat losses.

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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 refining of metal in an intermediate ladle during continuous casting of steel.

Known heat-insulating mixture for the protection and thermal insulation of metal in the intermediate and steel pouring ladles [1], containing:

- rice husk - 4-20 wt.%;

- carbon-containing material - 1-20 wt.%;

- ash TPP of coal near Moscow deposits - 7-10 wt.%.

Additionally containing ground quartz in an amount of 5-15 wt.% And having the following chemical composition, wt.%: Al ₂ O ₃ ≥20, CaO≤10, Na ₂ O + K ₂ O≤1, FeO≤6, SiO ₂ - rest. This patent is selected as an analogue.

The disadvantages of this mixture are its insufficient refining properties, as well as the high content of rice husk, which, when the mixture is fed to the metal mirror in the tundish, burns out intensively, which can lead to damage to the rubber hoses of the slide gate hydraulic drive and, as a result, a serious accident.

Closest to the technical nature of the claimed invention is a slag-forming mixture for thermal insulation and refining of metal in an intermediate ladle [2], containing:

Carbon-containing material - 2-10%;

Fluorine-containing material - 10-20%;

Material based on silicon oxides - 10-25%;

Cement is the rest.

The disadvantages of this mixture are insufficient refining properties, increased aggressiveness to the lining, the release of an increased amount of fluorine into the atmosphere during its use, as well as carburization of the metal.

The technical result when using the invention is as follows:

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

- reduced wear of the working layer of the lining of the intermediate bucket;

- reducing the temperature drop of steel in the intermediate ladle by increasing the heat-insulating ability of the mixture;

- lack of carburization of the metal during continuous casting of especially low carbon steels;

- the absence of volatile fluorine compounds harmful to the health of personnel in the air of the working area.

To achieve this, a slag-forming mixture for thermal insulation and refining of a metal in an intermediate ladle is proposed, containing Portland cement, a material based on silicon oxides and rice husk, characterized in that technical soda ash is used as a low-melting additive, and pulverized quartz is used as a material based on silicon oxides. or molding sand in the following ratio of ingredients, wt.%:

Portland cement 40-50 Silicon Oxide Material 30-38 Rice husk 4-10 Soda ash technical 10-18

Moreover, the following chemical composition is provided, wt.%:

Cao SiO ₂ Al ₂ O ₃ MgO Na ₂ O CO ₂ 27.0-32.0 43.0-48.0 ≤5.0 ≤ 4.0 7.0-11.0 5.0-8.0

Portland cement of grades 400 or 500 according to GOST 10178-85 is introduced into the mixture as a base with a stable chemical composition. In addition, cement is a pre-sintered material with chemical homogeneity, which provides, firstly, the ability to use additives to reach any desired chemical composition, and secondly, its presence in the mixture contributes to its more rapid penetration. The lower limit of the content of Portland cement is due to a decrease in its positive effect described above on the properties of the mixture. The upper limit of the content of Portland cement is due to an excessive increase in the basicity of the finished mixture, which increases its melting point.

Calcined technical soda according to GOST 5100-85 is introduced into the mixture to provide the necessary sodium oxide content, which reduces the melting temperature of the mixture, reduces the viscosity and surface tension of the slag melt. This allows you to expand the content in the slag of aluminum oxide, not leading to its thickening and thereby increases the assimilative ability of the slag. The soda content below the lower limit does not allow to achieve the necessary parameters of viscosity and reserve for the absorption of alumina. The soda content above the upper limit leads to excessive dilution of the slag melt and its aggressiveness in relation to stoppers and lining.

Molding sand GOST 2138-91 or ground silica powdery GOST 9077-82 introduces silicon oxide into the slag. It is required to derive the basicity of the mixture in that initial region of the ternary CaO-SiO ₂ -Al ₂ O ₃ diagram, the movement from which towards the increase in alumina does not lead to a sharp increase in the melting temperature and slag viscosity. This allows, with a slight change in the basic properties of the melt, to assimilate from steel up to 25% aluminum oxide by weight of the slag. The lower limit of the content of silicon oxide is due to the fact that, at a lower content, the chemical composition of the mixture is shifted toward single-calcium silicate with a melting point of 1548 ° C, which also leads to an increase in the viscosity of the slag melt. The upper limit of the content of silicon oxide is limited by its eutectic ratio with calcium oxide, beyond which begins the region of tridymite with melting points above 1500 ° C, which also takes the values of melting temperature and viscosity beyond the optimum.

Rice husk is introduced to reduce the bulk density of the granular layer and loosen the sintered layer of the mixture on the metal mirror, which leads to a general decrease in its thermal conductivity. The lower limit of rice husk content is determined by its loosening properties, because with its further decrease, the heat-insulating properties of the mixture are lost. The upper limit of the content of rice husk is due to the fact that when it is exceeded, intense and prolonged burning of the mixture on a metal mirror is observed, which is unsafe for both personnel and equipment on the casting site. In addition, exceeding the upper limit of the content of rice husks can lead to carburization of the metal when casting steels with particularly low carbon.

Table 1 shows some of the compositions of the warming-refining mixture, and in table 2 their full melting temperatures, the capacity with respect to alumina, and the average value of the temperature drop of the metal in the intermediate ladle during casting of one heat.

Table 1 Component \ composition The content of components, wt.% In the mixture one 2 3 four 5 Portland cement 35 40 45 fifty 55 Silicon Oxide Material 42 38 34 thirty 26 Rice husk 3 10 7 four eleven Soda ash technical twenty 12 fourteen 16 8

table 2 Structure one 2 3 four 5 Full melting point, ° C 1322 1318 1324 1350 1434 The growth of Al ₂ O ₃ , abs.% 24 twenty 25 21 16 Wed temperature drop, ° C / melting 10.6 4.6 5.1 7.0 4.3

From the data of table 2 it is seen that compositions 1-4 have acceptable values of the initial temperature of complete melting, which ensure the formation of a sufficient amount of the liquid phase of the slag, which is responsible for the efficiency of the process of assimilation of non-metallic inclusions. Composition 5 has a high initial temperature of complete melting, which complicates the transition of non-metallic inclusions from steel to slag; the increase in the content of aluminum oxide in the slag based on this mixture is only 16 wt.%.

Composition 1 provides good assimilation of non-metallic inclusions by the slag, but due to the low content of rice husk it does not protect the metal mirror well from heat loss: the average drop in steel temperature exceeds 10 ° C during smelting.

Mixtures 2-4 provide good thermal insulation of the metal mirror in the tundish and a high increase in alumina in the slag. The optimal characteristics, as can be seen from the data presented in table 2, has a composition of 3.

Bibliography

1. Patent RU 2308350 C2, B22D 11/111, 10.20.2007.

2. Patent RU 2174893 C2, B22D 11/111, 10.20.2001.

Claims (1)

Slag-forming mixture for protecting steel in the intermediate ladle, containing Portland cement and a material based on silicon oxides, characterized in that it additionally contains soda ash technical and rice husk in the following ratio of components, wt.%:
Portland cement 40-50 Silicon Oxide Material 30-38 Technical soda ash 10-18 Rice husk 4-10