RU2639187C1 - Heat-insulating slag-forming mixture - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: heat-insulating slag-forming mixture contains, wt %: ladle white slag produced by rail electric steel - 45-65 and organic additive - 35-55. Use of a mixture of husks of cereal crops - 50-60 and sawdust of hardwood species - 40-50 as organic additive results in an increase of the thickness of the layer of the heat-insulating mixture and formation of a liquid slag on the surface of the slag-forming material from the slag-forming material with a high heat-insulating capacity.

EFFECT: reduction of rejects associated with temperature changes and solidification of steel in the ladle, reduction of heat losses during casting of steel and increase in the seriality of the cast steel.

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Description

The invention relates to ferrous metallurgy, in particular to compositions of heat-insulating mixtures intended for thermal insulation of metal in the intermediate and steel-pouring ladles.

Known heat-insulating slag-forming mixture for continuous casting of steel [SU 1702696 A1, IPC 6 C21C 5/54, publ. 08/20/1996] the following composition, wt. %:

Amorphous graphite 10-20 Lime 20-30 Dusty waste ferrosilicon production 30-40 Dusty waste aluminum production 20-30

The disadvantages of this mixture when used in the tundish are the uncontrolled process of carburizing steel and low heat-insulating and refining properties due to the content of amorphous graphite in the mixture, as well as low heat-insulating properties of the mixture due to the absence of an organic component.

Known heat-insulating slag-forming mixture (RU 2380194 C2, IPC (2006.01) B22D 11/111, B22 D7 / 10, published January 27, 2010), selected as a prototype, containing slag-forming material, organic additive and coke. As an organic additive, it contains husk of grain crops, and as a slag-forming material, it contains material of the following chemical composition, wt. %:

FROM 5.0-15.0 Cao 25.0-48.0 SiO ₂ 33.0-39.0 Al ₂ O ₃ 7.0-12.0 F ≥3.5 Na ₂ O ≥3.0 K ₂ O ≥0.7

with a basicity of 0.7-2.2, taking into account the content of SiO ₂ and CaO in ladle slag, in the following ratio of components, wt. %:

coke 5-30 cereal husk 10-70 slag-forming material 10-85,

providing the flow rate of the insulating mixture of 1-7 kg / t of liquid steel.

The disadvantages of this mixture are:

- high carbon content, leading to carburization of liquid steel and the inability to cast low carbon steels,

- low heat-insulating properties of the mixture due to the non-optimal ratio between the slag-forming material and the organic additive,

- high heat loss, leading to an increase in the level of marriage associated with temperature differences and hardening of steel in the intermediate and steel pouring ladles with long exposure times.

The objective of the invention is to reduce the level of marriage associated with changes in temperature and solidification of steel in steel casting and intermediate ladles; reduction of heat losses during casting of steel and increase in the seriality of cast steel.

The proposed heat-insulating slag-forming mixture also, as in the prototype, contains slag-forming material and an organic additive.

According to the invention, it contains a slag-forming material and an organic additive in the following ratio of components, wt. %:

Slag-forming material 45-65 Organic supplement 35-55,

moreover, as a slag-forming material, it contains ladle white slag for the production of rail electric steel, and as an organic additive contains a mixture of husk of grain crops and sawdust of deciduous trees at a ratio, wt. %:

Grain husk 50-60 Hardwood sawdust 40-50

The use of ladle white slag for rail electric steel production as a slag-forming material allows to reduce thermal radiation.

The use of a mixture of husks of grain crops and sawdust of deciduous trees as an organic additive leads to an increase in the thickness of the layer of the insulating mixture, and heat is additionally generated during combustion. The combustion product of the organic additive is a slag melt having a porous structure, as a result of which low thermal conductivity is ensured. On the surface of the ladle slag from slag-forming material, liquid slag with a high heat-insulating ability is formed.

As a slag-forming material, white ladle slag of rail electric steel production was used with the following chemical composition: 18.9-21.8% SiO ₂ , 45.8-54.9% CaO, 6.09-7.4% Al ₂ O ₃ , 0.5-1.0% FeO; 7.13-19.2% MgO; 0.53-1.07% MnO.

Warming was carried out in steel pouring and intermediate ladles. The specific consumption of the heat-insulating mixture when protecting the melt mirror in the steel pouring ladle was 0.5-3.0 kg / t of liquid metal, in the intermediate ladle 1.8-6.0 kg / t of liquid metal.

The heat-insulating mixture in the ratio, wt. %: husks of grain crops 50-60 and sawdust of hardwood trees 40-50 provides high thermal insulation when casting a series of heats.

The use of organic additives less than 35 wt. % does not provide the required temperature gradient when casting a series of heats.

When using an organic additive over 55 wt. % there is intense combustion of the mixture with the formation of a torch, which leads to unsafe working conditions and to a decrease in thermal insulation of the surface of the melt.

Various options for the component composition of the heat-insulating slag-forming mixture, as well as the effect of the composition on the level of rejects for surface defects are presented in table 1.

The experiments were carried out using 130-ton steel-pouring ladles and 24-ton intermediate ladles on a four-strand bloom continuous casting machine with a mold section of 300 × 360 mm for casting steel of grades st. 20, 45, 50-60G.

Before supplying metal to a continuous casting machine on a ladle-furnace unit, each steel casting ladle intended for casting was given a heat-insulating mixture of 100-600 kg in a series.

In the process of casting steel into the intermediate ladle, a heat-insulating slag-forming mixture in the amount of 50-200 kg was set in the series in the series; when changing the next casting ladle, a slag-forming mixture in the amount of up to 50 kg was planted in the intermediate ladle.

The technical results of the invention are:

- reducing the level of marriage associated with temperature changes and hardening of steel in steel casting and intermediate ladles;

- reduction of heat loss during casting of steel and an increase in the seriality of cast steel.

The use of a heat-insulating slag-forming mixture during continuous casting of steel made it possible to reduce the rejection of metal due to violation of the temperature-speed regime by 0.08%, and also to reduce the temperature gradient of the metal in the intermediate ladle to 3-5 ° C.

Claims (4)

Heat-insulating slag-forming mixture, including slag-forming material and an organic additive, characterized in that the components are taken in the following ratio, wt. %: Slag-forming material 45-65 Organic supplement 35-55, moreover, as a slag-forming material, it contains ladle white slag for rail electric steel production, and as an organic additive contains a mixture of grain husks and sawdust of deciduous trees in the following ratio of components, wt. %: Grain husk 50-60 Hardwood sawdust 40-50