RU2308351C1 - Slag forming mixture for in-mold protection of steel at peritectic conversion during batch continuous casting of steel - Google Patents

Abstract

FIELD: metallurgy, namely steel continuous casting processes.

SUBSTANCE: mixture contains next ingredients, mass%: fluorspar concentrate, 12 - 20; cyenite concentrate, 15 -25; milled dust like quartz, 8 - 15; microcrystalline casting graphite, 6 - 12; anhydrous sodium carbonate, 4 - 8; milled mica - phlogopite, 1 - 5; Portland cement, the balance.

EFFECT: stabilized process of continuous casting, elimination of emergency bursts of steel through ingot skin under mold.

1 tbl, 1 ex

Description

The invention relates to ferrous metallurgy, and more particularly to compositions of slag-forming mixtures used to protect steel with peritectic transformation during continuous continuous casting of slabs.

The closest in technical essence is a slag-forming mixture containing, wt.%:

nepheline - 10-40;

carbon-containing substance - 2-15;

silicate block - 5-30;

fluorspar - 2-10;

cement is the rest.

(See Auth. St. USSR No. 503918, C21C 5/54, 02.25.76). This copyright certificate is accepted as a prototype.

A disadvantage of the known slag-forming mixture is that there are many accidental breakthroughs of the melt through the ingot shell under the molds for casting steel with peritectic transformation, and defects in the form of cracks and slag inclusions are observed on the surface of the slabs. The presence of external defects leads to significant metal losses, which are removed by fire stripping.

It was established that the main reason contributing to emergency breakouts and the formation of cracks on the surface of slabs is the high hydrogen content in steel, more than 6 ppm. The main source of hydrogen growth of cast steel is a silicate block, which contains up to 10% of crystalline moisture. Moreover, the content in the mixture of silicate block increases with decreasing CaF ₂ content in the used fluorspar due to the instability of its amount. The slab damage by cracks also increased with insufficient flowability of the powder mixture. As a result of insufficient flowability, an equal-thickness slag skull is not formed in the mold in the mold, which is responsible for heat dissipation and the formation of tensile stresses in the slab shell, which contribute to cracking.

Another disadvantage of the known slag-forming mixture is the lack of components that contribute to the evolution of gases, causing the movement of the protective coating in the process of its formation. This increases the contamination of the slabs by non-metallic inclusions in the case of casting with a slight overheating above the liquidus temperature of the cast steel.

The technical effect when using the invention is to improve the surface quality of continuously cast slabs and increase the stability of the continuous casting process without emergency breakthroughs.

The technical effect is achieved by the fact that powdered silica, anhydrous sodium carbonate and mica are additionally introduced into the slag-forming mixture containing nepheline concentrate, fluorspar, carbon-containing substance and Portland cement, and syenite concentrate is used as nepheline concentrate, and fluorspar concentrate with fluorspar CaF ₂ content _of more than 90%; cryptocrystalline foundry graphite as a carbon-containing component, and milled-phlogopite mica in the following ratio of components, wt.%:

fluorspar concentrate - 12-20;

syenite concentrate - 15-25;

powdered silica quartz - 8-15;

cryptocrystalline foundry graphite - 6-12;

anhydrous sodium carbonate - 4-8;

ground mica, phlogopite - 1-5;

Portland cement - the rest.

It was established experimentally that for casting continuous slabs of steel with peritectic transformation, hardening without external, longitudinal and mesh cracks, it is necessary to use silicate protective slags with a basicity

In this case, the slag skull provides the smallest heat sink from the hardening shell of the ingot in the mold. The main component of the protective slag-forming mixture is Portland cement according to GOST 10178-85, which includes calcium and silicon oxides in the form of clinker 3СаО · S · О ₂ . Clinker is obtained by sintering a finely divided mixture of limestone and clay with the expenditure of a large amount of heat (about 6000 kJ / kg of clinker) in special furnaces. Therefore, this heat does not need to be expended by the metal mirror in the mold when liquid slag is formed from the slag-forming mixture during the continuous casting of steel.

Syenite concentrate according to TU 5726-04700203938-97 is a source of silicon oxides, aluminum and sodium fused by nature. Its necessary amount is established experimentally to achieve a given slag basicity.

Fluorspar concentrate according to GOST 7618-83 serves as the main source of flux CaF ₂ . It is characterized by a constant content of CaF ₂ (more than 90%). The fluorspar concentrate within the stated limits determines the required melting point of the slag-forming mixture and slag viscosity at 1300 ° C. The content of fluorspar concentrate in the mixture is interconnected with syenite concentrate. The upper limit of syenite concentrate corresponds to the lower limits for the content of fluorspar concentrate.

In this case, the syenite concentrate is inversely related to sodium carbonate (anhydrous soda Na ₂ CO ₃ ) according to GOST 5100-73.

It was experimentally established that in the case when the content of fluorspar concentrate, syenite concentrate and sodium carbonate (anhydrous soda) are outside the stated limits, the correspondence between the rate of melting of the mixture in the mold and the removal of molten slag from it is violated. In this case, the claimed technical effect is not achieved.

Ground mica, phlogopite according to TU 21-25-241-80 in an amount of 1-5%, serves as a powder component, providing the necessary flowability of the entire powder mixture. In this case, the mixture is evenly scattered on the surface of the protective coating in the mold. When its content is less than 1%, the effect is insufficient. If its content is more than 5%, the effect of dispersibility of the mixture increases.

Anhydrous sodium carbonate (soda Na ₂ CO ₃ ) GOST 510073 serves as a source of sodium oxides, which reduce the melting point of the slag-forming mixture. If the content of this component is below 4 wt.%, Its effect on the melting temperature is negligible. When the content of sodium carbonate is above 8%, the desired effect increases slightly.

The analysis of scientific, technical and patent literature shows the lack of coincidence of the distinctive features of the claimed slag-forming mixture with the signs of known technical solutions. Based on this, it was concluded that the claimed technical solution meets the criterion of "inventive step".

Below is an embodiment of the invention that does not exclude other variations within the scope of the claims.

An example of the invention. Pipe steel of grade 10G2FBS was poured by peritectic transformation in a continuous “melting” manner into slabs with a cross section of 200 ÷ 250 × 1200 ÷ 1800 mm with operating speeds of 0.7-1.0 m / min. Swimming trunks from the intermediate ladles were poured into crystallizers, making a reciprocating motion, through refractory glasses with side outlet channels submerged below the slag coating. Slag coating on a metal mirror in the molds was obtained from a slag-forming mixture containing the following components, wt.%:

- fluorspar concentrate - 12-20;

- syenite concentrate - 15-25;

- powdered silica quartz - 8-15;

- cast crystalline graphite - 6-12;

- sodium carbonate anhydrous - 4-8;

- milled ground phlogopite - 1-5;

- portland cement - rest

The specific consumption of the slag mixture is 0.8-1.2 kg / m of steel.

Examples of the use of a slag-forming mixture for casting slabs of low alloy steels with peritectic transformation are given in the table.

In the first and fifth examples, due to non-compliance with the stated ratios of the components in the slag-forming mixture, a sufficiently high effect is not provided.

In the optimal examples, a significant decrease in the number of slabs requiring cleaning the surface by mesh cracks and nonmetallic inclusions, as well as by the number of emergency breakthroughs through the shell of the ingot under the mold, was achieved. As a result, the losses due to fire stripping of continuously cast slabs and the elimination of the consequences of emergency breakthroughs of metal with molten liquid steel parts of the equipment of the secondary cooling zone of continuous casting machines are reduced.

Table Options Examples one Fluorspar concentrate, wt.% eleven 12 fourteen twenty 21 2 Syenite concentrate, wt.% 26 25 eighteen fifteen fourteen 3 Powdered quartz, wt.% 16 fifteen 13 8 7 four Cryptocrystalline foundry graphite, wt.% 5 6 10 12 13 5 Anhydrous sodium carbonate, wt.% 3 four 6 8 9 6 Ground mica-phlogopite, wt.% 0.5 one 2 5 6 7 Portland cement, wt.% 38.5 37 3.6 32 thirty 8 Stripping slabs on mesh cracks,% fifteen four 3 four fifteen 9 Slab protection by non-metallic inclusions,% 22 10 9 10 twenty 10 Breakthroughs of metal under the mold, pcs / year thirty 10 9 10 25

Claims (1)

Slag-forming mixture for protection in a crystallizer of peritectic steel during serial continuous casting of slabs containing nepheline concentrate, fluorspar, carbon-containing substance and Portland cement, characterized in that it additionally contains powdered silica, anhydrous sodium carbonate and mica, and as nepheline concentrate it contains syenite concentrate, as fluorspar - fluorspar concentrate with a CaF ₂ content _of more than 90%, as a carbon-containing substance - cryptocrystalline foundry graphite, phlogopite as mica in the following ratio of components, wt.%: fluorspar concentrate  12-20 syenite concentrate  15-25 powdered quartz  8-15 cryptocrystalline foundry graphite  6-12 sodium carbonate anhydrous  4-8 ground mica - phlogopite  1-5 Portland cement  rest