Continuous casting covering slag for low-carbon high-aluminum steel

Abstract

The invention relates to continuous casting covering slag for low-carbon high-aluminum steel. The continuous casting covering slag comprises the following chemical components in percentage by mass: 56%-66% of MgO + Al2O3, 0.8%-1.2% of MgO / Al2O3, 5%-7% of Ce2O3, 5%-10% of Na2O, 5%-8% of F, 8.5%-15.5% of TiO2, 2.5%-4% of C and the balance of inevitable impurities. In order to solve the problem of slag steel reaction in the continuous casting process, heat transfer and lubrication are guaranteed, and meanwhile the phenomena of subcutaneous slag inclusion, slag entrapment and the like are prevented. The method is especially suitable for slab continuous casting production of low-carbon high-aluminum steel (the Al content is greater than 0.55%).

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, specifically to metallurgical auxiliary materials for continuous casting, and more specifically to a continuous casting mold powder for low-carbon high-aluminum steel in the continuous casting process of low-carbon steel. Background Art

[0002] Continuous casting mold powder is a functional material based on CaO and SiO2, with added fluxes (alkali metal oxides, fluorides, etc.) and skeletal materials (carbon black, graphite, coke, etc.). As the medium for the interaction between the mold and the billet shell, its component ratio is an important factor affecting the quality of the cast billet. The component ratio directly affects the melting characteristics, viscosity, interfacial characteristics, inclusion absorption capacity, etc. of the mold powder, thereby affecting heat transfer and lubrication in the continuous casting process. There are currently two problems in the continuous casting production process of low-carbon high-aluminum steel: 1) During casting, the reaction 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3) will occur, that is, Al in the steel will react with SiO2 in the mold powder to form Al2O3 and enter the slag, resulting in a continuous increase in the melting point and viscosity of the molten slag, and the casting cannot proceed smoothly; 2) Surface defects such as subcutaneous slag inclusions and slag entrainment are prone to occur in the continuous casting of low-carbon steel itself, and the above slag-steel reaction will further reduce the surface tension between the slag and the steel, greatly increasing the probability of slag entrainment, and ultimately resulting in voids and other problems during the rolling process of the product, and the rejection rate increases significantly.

[0003] Regarding the problem of the reduction of the mold powder by aluminum during casting, the solutions at home and abroad mainly include: 1. Increasing the viscosity while ensuring the alkalinity to reduce the reaction kinetics between the slag and the steel; 2. Increasing the SiO2 content in the slag system to control the alkalinity within the normal range after the slag-steel reaction; 3. Increasing the alkalinity to weaken the reaction by reducing the activity of SiO2; 4. Strictly controlling the SiO2 in the mold powder. For example, Japanese Patent JP 2000000646 uses a CaO-Al2O3 system to replace the CaO-SiO2 system mold powder, and uses CaTiO3 instead of cuspidine (3CaO·2SiO2·CaF2), but the melting point of CaTiO3 is as high as 1975 °C, which is not conducive to billet lubrication. Patent No. CN109550913B discloses a low-reactivity mold powder for aluminum-containing ultra-low-carbon steel, using BaO to partially replace CaO to form BaTiO3 crystals, but the Na2O content in this slag system is as high as 12-20%, and Na2O will reduce the surface tension of the liquid slag, thereby reducing the viscosity and is not conducive to preventing slag entrainment. Chinese Patent No. CN102019384 B discloses a high-viscosity continuous casting mold powder for solving surface slag inclusions in low-carbon steel, by adding lithium carbonate, fluorite, soda ash, etc. to increase the viscosity and surface tension. There is a problem of high F content in this patent. In addition, a high Al2O3 content is likely to cause an increase in inclusions in the billet, resulting in problems such as the aggregation of inclusions in the billet skin (0-5 mm). Summary of the Invention

[0004] Aiming at the problems existing in the background technology, the object of the present invention is to provide a continuous casting mold powder for low-carbon high-aluminum steel, solve the problem of slag-steel reaction during continuous casting, ensure heat transfer and lubrication while preventing phenomena such as subcutaneous slag inclusion and slag entrainment. It is especially suitable for the slab continuous casting production of low-carbon high-aluminum steel (Al content > 0.55%).

[0005] In order to achieve the above object, the present invention is realized by adopting the following technical solutions:

[0006] A continuous casting mold powder for low-carbon high-aluminum steel, the mass percentages of its chemical components are: MgO + Al2O3: 56% - 66%, MgO / Al2O3: 0.8 - 1.2, Ce2O3: 5% - 7%, Na2O: 5% - 10%, F: 5% - 8%, TiO2: 8.5% - 15.5%, C: 2.5% - 4%, and the balance is inevitable impurities.

[0007] MgO / TiO2 in the mold powder is 1.8 - 4.2.

[0008] The melting point of the mold powder is 1000 - 1050 °C.

[0009] The viscosity of the mold powder at 1300 °C is 0.35 - 0.65 Pa·S.

[0010] The mold powder is applicable to the continuous casting production of steel grades with C content of 0.05 wt% - 0.25 wt% and Al content > 0.55 wt%.

[0011] The research and development mechanism of a continuous casting mold powder for low-carbon high-aluminum steel of the present invention is as follows:

[0012] During the continuous casting of high-aluminum steel, the conventional (CaO-SiO2) slag system will undergo a slag-steel reaction, i.e., 4[Al] + 3(SiO2) = 3[Si] + 2(Al2O3). Therefore, the idea of this slag system is to replace SiO2 with Al2O3, replace CaO with MgO, add a certain content of TiO2, and strictly control MgO / Al2O3 and MgO / TiO2 to ensure that the slag-steel reaction does not occur while MgTiO3 crystals (melting point 1565°C) can precipitate. It can replace the role of cuspidine (3CaO·2SiO2·CaF2) in the CaO-SiO2 slag system and is much lower than the currently widely recognized CaTiO3 (melting point 1975°C); Ce2O3 can significantly increase the viscosity of the slag system, and a certain MgO / Al2O3 content ratio can enhance the activity of Ce2O3. Considering comprehensively, the content of Ce2O3 in this invention is controlled at 5% - 7%, and MgO / Al2O3 is controlled at 1.8 - 4.2; Na2O is a common flux in the mold powder, which can adjust the melting point and viscosity of the mold powder. However, a high content of Na2O promotes excessive precipitation of crystals in the molten slag. Therefore, considering viscosity and crystallization performance comprehensively, Na2O is controlled at 5% - 10%; Fluoride has a good effect on improving heat transfer and lubrication, but it will pollute the environment and corrode production equipment. Considering comprehensively, F is controlled at 5% - 8%, reducing the content of F to a certain extent; TiO2 forms MgTiO3 crystals with MgO, and its melting point is 1565°C, with a moderate melting point. Excessive TiO2 will make the crystallization ability of the molten slag too strong, resulting in weakened lubrication ability and too strong heat transfer control ability. Considering comprehensively, the content of TiO2 is 8.5% - 15.5%; C is a necessary substance for adjusting the melting rate, which can ensure the thickness of the liquid slag layer. However, a high C content may cause the problem of carbon increase in continuously cast low-carbon steel, and the C content is limited to 2.5% - 4%.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] Based on the slag-steel reaction and slag entrainment problems that are prone to occur during the continuous casting of low-carbon high-aluminum steel. The present invention proposes a MgO-Al2O3 binary mold powder. The viscosity and melting point of the slag system are moderate, and the crystallization temperature is low, preventing slag entrainment while ensuring the lubrication effect; the Si-free design avoids the problem of drastic changes in the physical and chemical properties of the slag system caused by the slag-steel reaction, and the precipitated MgTiO3 crystals ensure the heat transfer of the cast slab. Specific embodiments

[0015] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further illustrates the specific embodiments of the present invention in combination with embodiments. The following embodiments are used to specifically illustrate the content of the present invention. These embodiments are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0016] Table 1 Composition of the mold powder in the embodiment

[0017]

[0018] Examples 1-4 carried out casting tests on medium and thin slab continuous casting machines with a casting section of 170 mm×(800-2000) mm for low-carbon high-aluminum steel grades. The continuous casting pulling speed was controlled at 0.60-1.95 m / min, the average slag consumption was 0.59 kg / t of steel, and the liquid slag layer thickness was 10-12 mm. The test results showed that the mold powder of the present invention had good lubrication and filling properties, moderate slag consumption, no adhesion and small slag bars, effectively solved the problems of slag entrainment and slag inclusion, and avoided the phenomenon of slag-steel reaction. No surface defects were found in the subsequent rolling of the steel grades. The mold powder compositions of Examples 1-4 of the present invention are shown in Table 1. It can be seen from the table that the melting point range of the mold powder is 1000-1050 °C, the viscosity at 1300 °C is 0.35-0.65 Pa, the viscosity and melting point of the slag system are moderate, and the crystallization temperature is low, solving the problems of slag entrainment and slag inclusion; in addition, the MgO-Al2O3 system slag system avoided the slag-steel reaction, ensured the stability of the slag system during continuous casting, and the formed appropriate amount of MgTiO3 crystals could effectively ensure the lubrication and heat transfer of the continuous casting billet.

Claims

1. A continuous casting mold powder for low-carbon high-aluminum steel, characterized in that: The mass percentages of its chemical components are as follows: MgO + Al2O3: 56% - 66%, MgO / Al2O3: 0.8 - 1.2, Ce2O3: 5% - 7%, Na2O: 5% - 10%, F: 5% - 8%, TiO2: 8.5% - 15.5%, C: 2.5% - 4%, and the balance is inevitable impurities.

2. The continuous casting mold powder for low-carbon high-aluminum steel according to claim 1, characterized in that: MgO / TiO2 in the mold powder is 1.8 - 4.

2.

3. The continuous casting powder for low-carbon high-aluminum steel according to claim 1, characterized in that: The melting point of the mold powder is 1000 - 1050 °C.

4. The continuous casting mold powder for low-carbon high-aluminum steel according to claim 1, characterized in that: The viscosity of the mold powder at 1300 °C is 0.35 - 0.65 Pa·S.

5. The continuous casting mold powder for low-carbon high-aluminum steel according to claim 1, characterized in that: The mold powder is applicable to continuous casting production of steel grades with C content of 0.05 wt% - 0.25 wt% and Al content > 0.55 wt%.

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