RU2311987C2 - Slag forming mixture for insulation of metal in intermediate ladle - Google Patents

Abstract

FIELD: metallurgy, namely compositions of heat insulation slag forming mixtures used at continuous steel casting.

SUBSTANCE: slag forming mixture includes ingredients at next relation, mass %:carbon containing material, 15 - 25; feldspar, 75 - 85.

EFFECT: enhanced physical and chemical properties of mixture, improved manufacturing process of steel continuous casting, enhanced quality of continuously cast billets.

2 cl, 2 tbl

Description

The alleged invention relates to ferrous metallurgy, and in particular to compositions of heat-insulating slag-forming mixtures for use in an intermediate ladle during continuous casting of steel.

Known slag-forming mixture for continuous casting of steel containing carbonaceous material, fluorspar, soda ash, feldspar, sand and slag Portland cement (RF Patent No. 2175878, 7 B22D 11/111, 2001). This mixture in the tundish is almost completely melted and does not provide thermal insulation of liquid metal.

Known slag-forming mixture for protecting steel in the intermediate ladle during casting (RF Patent No. 2064363, CL B22D 11/00, 1996). The mixture consists of carbon-containing material, mica and bentonite clay. When the mixture is melted, viscous slag of the SiO ₂ - Al ₂ O _{3 system is formed} . Due to the high initial content of Al ₂ O ₃ (20–25%), the assimilative properties of the slag are worsened in relation to the aluminum oxides continuously floating from the metal. Slag hardens with the formation of a hard crust - the "roof".

Also known is a heat-insulating mixture for continuous casting of steel used in the intermediate ladle of continuous casting machine (RF Patent No. 2175279, CL 7 B22D 11/111). The mixture contains 4-25% of carbon-containing material, 4-90% of rice husk and the rest is silica-containing material (ccm).

The disadvantages of this mixture when used in the trap are the transition of its slag melt from liquid to solid with a basicity of more than 3.0, and with a basicity of less than 0.6, there is a sharp decrease in the assimilative ability of the slag, obviously due to the absence or low content of alkaline oxides in the oxide system land metals.

The closest in technical essence and the achieved result is a heat insulating mixture comprising 10-20% of carbon-containing material (amorphous graphite) and 80-90% of a material based on silicon oxides (perlite) (Aut. St. USSR No. 348288, B22D 7/00, 1970).

This mixture is characterized by high heat-insulating properties. A significant disadvantage of the mixture is the insufficiently high assimilating properties due to the low (5.6–9.0%) content of alkaline-earth metal oxides in it. In perlite, the total content of R ₂ O = 7-10%. A thin liquid slag film formed in the zone of contact of the mixture with liquid metal is rapidly saturated with aluminum oxides emerging from the metal. The film passes from a liquid state to a heterogeneous state and then to a solid state without assimilating new oxides. At the same time, it becomes difficult and impossible to carry out certain technological operations (introducing a thermocouple into liquid steel, changing the protective pipe of a steel-pouring ladle, etc.), that is, the manufacturability of continuous casting is disrupted. The quality of continuously cast billet is reduced.

The technical effect when using the inventive composition of the heat-insulating slag-forming mixture is to improve the physicochemical properties of the mixture (to increase the assimilating ability), to ensure the manufacturability of continuous casting of steel and to improve the quality of continuously cast billets.

The specified technical effect is achieved by the fact that the slag-forming mixture containing a material based on silicon oxides and a carbon-containing material contains feldspar as a material based on silicon oxides in the following ratio of ingredients, wt.%:

- carbon material 15-25 - feldspar 75-85

Amorphous graphite (ash content of 15–20%), dust from the dry coke quenching plant (dust CCP) with a carbon content of more than 97% are used as carbon-containing material.

As a material based on silicon oxides, feldspar is used with the following average chemical composition (wt.%): SiO ₂ = 58.6; Al ₂ O ₃ = 22.8; Na ₂ O = 7.5; K ₂ O = 7.5; CaO = 4.8.

The analysis of scientific, technical and patent literature shows the absence of coincidence of the distinctive features of the claimed composition of the slag-forming mixture with the signs of known technical solutions. Based on this analysis, we can conclude that the claimed technical solution meets the criteria of "inventive step" and "novelty."

The carbon-containing material in the composition of the mixture increases its heat-insulating properties, and during combustion it compensates for a part of the heat loss of the metal.

When the content of the carbon-containing material in the mixture is less than 15%, the conditions for warming the metal surface in the scoop deteriorate and a solid slag crust forms, which impedes certain technological operations, and with its content of more than 25%, significant carburization of the steel is possible beyond the brand carbon content.

Feldspar in the composition of the mixture during its melting forms the lower layer of liquid slag of the SiO ₂ - Al ₂ O ₃ - R ₂ O system, which is a liquid glassy mass that assimilates and retains non-metallic inclusions floating up from the metal. Due to this, the best quality of the metal in terms of contamination with non-metallic inclusions is ensured. The top layer of the mixture remains partially melted due to the presence of a melting regulator - a carbon-containing material, performing a protective heat-insulating function.

When the content of feldspar in the mixture is less than 75% and the carbon-containing material is more than 25%, the amount of slag melt decreases, its melting point and viscosity increase, and the assimilative ability of the melt decreases — a solid slag crust forms on the surface of the melt.

When the content of feldspar in the mixture is more than 85% and the carbon-containing material is less than 15%, the assimilative ability of the melt does not increase. The upper bulk layer of the mixture is almost completely melted and does not perform a heat-insulating function.

When the content of ingredients in the mixture goes beyond the specified limits, the physicochemical properties of the mixture deteriorate, the manufacturability of continuous casting is impaired, and the quality of continuously cast billets decreases.

Comparative tests of the mixtures were carried out in an intermediate ladle with a capacity of 25 tons during continuous casting of carbon, high carbon and low alloy steels. The casting speed was 1.8-2.4 m / min.

To assess the quality of the metal, transverse macro templates were selected from cast high-quality billets with a cross section of 152 × 170 mm, and the quality of the macrostructure was evaluated by the value of point contamination by non-metallic inclusions.

The flow rate of mixtures into the pit per 1 ton of cast steel was also estimated.

Component compositions of the inventive mixture (p.1-3) and known (p.4 - average composition) are shown in table 1.

The melting temperature of the mixtures (hemisphere temperature) was determined in a micro-furnace with a platinum substrate, and the viscosity was determined by the rotating cylinder method.

Table 2 presents the properties of slag-forming mixtures, the characteristics of their slag melts, data on the quality of the metal macrostructure and technological data.

The particle sizes of all mixtures were 0.05-0.1 mm. The mixtures were introduced into the pitcher manually through the holes in its lid - into the holes for the input of thermocouples and into the central hole for the protective submerged steel-pouring pipe. Estimated consumption of mixtures and visually - examined the behavior of the mixture in the bucket.

When using the new mixture No. 1, 22 heats per casting ladle were cast. At the end of the series, a slag crust began to form. The consumption of the mixture was slightly increased and on average it amounted to 0.29 kg / t of cast steel.

The average point inhomogeneity of the metal was 0.88 points.

When using the new mixture No. 3, 24 heats per casting ladle were cast. In the last swimming trunks, separate solid slag sections began to form in the remote places of the tundish from the places where the mixture was introduced. The consumption of the mixture was 0.23 kg / t of cast steel. The average point heterogeneity of the metal was 1.03 points.

When using the new mixture No. 2 (optimal composition) 3 series of heats 25-30 heats per series were cast. There were no comments on the behavior of the mixture and slag in the trap. The average consumption of the mixture was 0.25 kg / t of cast steel. The magnitude of the point heterogeneity averaged 0.83 points.

When using the known mixture No. 4, 14 heats were cast in a series. Already on the seventh heat, a solid thick slag crust began to appear, which prevented the introduction of thermocouples into the metal. An increase in the flow rate of the mixture to 0.55 kg / t (average consumption was 0.42 kg / t) did not prevent the formation of a slag "roof". The use of mixture No. 4 was discontinued. Point heterogeneity of the metal in the last melts averaged 1.82 points.

Thus, the data of comparative tests on the operation of mixtures in the industrial ladle and the results on the quality of the metal (in terms of the point heterogeneity) showed the advantage of the new mixtures.

The economic effect of using a new composition of the slag-forming mixture consists in the possibility of stabilizing the technology of continuous casting of steel and improving the quality of continuously cast billets, as well as in increasing the seriality of cast melts by one tundish.

Table 1
Component mixtures Ingredients Composition, wt.% one 2 3 four Dust dust fifteen - 25 - Amorphous graphite - twenty - fifteen Feldspar 85 80 75 - Perlite - - - 85 table 2
Comparative Test Data Indicators Structure one 2 3 four The melting point of the mixture - 1335 - 1470 The content in the mixture, wt.% carbon 12.5 16.5 20.5 12.7 silica 52.7 48.6 41.9 62.9 calcium oxide 4.3 3.9 3.6 2.1 alumina 20.5 18.9 17.1 9,4 alkaline earth metal oxides 13.5 12.5 11.3 5.2 The basicity of the mixture, CaO / SiO ₂ 0.08 0.08 0.09 0,03 Mixture consumption, kg / t steel 0.29 0.23 0.25 0.42 Point heterogeneity of metal, score 0.88 0.83 1,03 1.82

Claims (2)

1. Slag-forming mixture for thermal insulation of metal in an intermediate ladle, containing material based on silicon oxide and a carbon-containing material, characterized in that feldspar is used as the material based on silicon oxide in the following ratio of ingredients, wt.%: carbon material 15-25 feldspar 75-85 2. Slag-forming mixture according to claim 1, characterized in that amorphous graphite or dust from a dry coke quenching unit is used as the carbon-containing material.