Continuous casting protective mold with colemanite and its application

Abstract

The application discloses a hard boracite-containing continuous casting protective slag and application thereof, wherein the raw material of the hard boracite-containing continuous casting protective slag comprises hard boracite, and the mass fraction of the hard boracite in the raw material is 1-25%. In the application, the hard boracite is used to replace borax, and the hard boracite can be added in a relatively larger amount in the protective slag, so as to avoid the phenomenon that the addition of too much borax can cause the explosion of the protective slag and the excessive dust to easily cause dust pollution. In addition, the addition of the hard boracite in a large amount can make the content of B2O3 in the protective slag large, the B2O3 can effectively reduce the melting point of the protective slag, refine the protective slag film, reduce the viscosity of the protective slag, and improve the filling flowability and lubricity of the protective slag. Most importantly, the hard boracite can replace part of expensive materials, such as lithium carbonate, under the premise of guaranteeing the performance of the protective slag, so as to reduce the cost of the protective slag.

Description

Technical Field

[0001] This invention relates to the field of protective slag technology, and more specifically, to continuous casting protective slag containing borosilicate and its applications. Background Technology

[0002] Boron-containing raw materials added to continuous casting protective slag are usually borax. However, the crystal water content of borax is too high. In the protective slag granulation tower, it loses water and bursts into powder during the process of changing from aqueous solution to solid particles, resulting in a lot of dust. Therefore, the amount added is limited.

[0003] With the gradual implementation of the "China VI" emission standards, higher requirements are being placed on energy conservation, emission reduction, and lightweight vehicle bodies in the automotive industry. Achieving lightweight vehicles inevitably requires the development of lightweight materials, and integrating high-strength steel, aluminum alloys, and other lightweight materials is the future development direction for automotive materials. The next generation of high-strength steel, possessing ultra-high strength, high formability, and low density, is an important research and development direction for steel companies worldwide.

[0004] Ansteel's successfully produced lightweight duplex steel meets all design requirements, with significantly better elongation than traditional 980MPa grade duplex steel, while also reducing density by 5%. This global debut of lightweight duplex steel signifies Ansteel's leading position in the development of high-strength, lightweight automotive steel.

[0005] However, when the existing continuous casting mold flux is used by Ansteel to produce this type of steel, the mold expert system frequently alarms during the production process, and the longitudinal cracking and transverse depression rate of the continuous casting billet is as high as 60%, which cannot meet the production needs. There is an urgent need to develop a mold flux that can meet the production needs of this type of steel.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a continuous casting protective slag containing borosilicate and its application in the continuous casting of high-strength lightweight duplex steel.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides a continuous casting protective slag containing calcareous borosilicate, wherein the raw material includes calcareous borosilicate, and the mass fraction of calcareous borosilicate in the raw material is 1-25%.

[0010] In an optional embodiment, the mass fraction of calcium borate in the raw material is 8-20%.

[0011] In an optional embodiment, the raw materials of the protective slag, by weight, include 11-16 parts of fluorite, 2-5 parts of imported carbon black, 3-6 parts of earthy graphite, 58-65 parts of wollastonite, 5-9 parts of calcite, 0.5-3 parts of lightly calcined magnesia, 1-4 parts of bauxite, 1-4 parts of lithium carbonate, 8-20 parts of calcite and 1-3 parts of polyvinyl alcohol.

[0012] In an optional embodiment, the protective slag comprises the following chemical components by weight percentage: CaO 35.0–39.0 wt%, SiO2 29.5–33.5 wt%, Al2O3 3–5 wt%, Fe2O3 0.3–1.5 wt%, MgO 1.5–3 wt%, Na2O 0–0.5 wt%, F 5–8.5 wt%, Li2O 0.8–1.5 wt%, B2O3 4–10 wt%, C 3–6 wt%, and unavoidable impurities.

[0013] In an optional embodiment, the protective slag comprises the following chemical components by weight percentage: CaO 36.0–39.0 wt%, SiO2 30.5–33.0 wt%, Al2O3 3–4 wt%, Fe2O3 0.3–0.7 wt%, MgO 1.5–2 wt%, Na2O 0–0.3 wt%, F 5–6.5 wt%, Li2O 1.0–1.5 wt%, B2O3 5–8 wt%, C 3–5 wt%, and unavoidable impurities.

[0014] In an optional implementation, the binary basicity is 1.13-1.18.

[0015] In an optional embodiment, the melting temperature is 1100-1130°C.

[0016] In an optional embodiment, the viscosity at 1300°C is 0.11-0.14 Pa·s.

[0017] In an optional implementation, the crystallization rate is less than 1%.

[0018] Secondly, the present invention provides an application of the continuous casting protective slag containing borosilicate as described in any of the foregoing embodiments in the continuous casting of high-strength lightweight duplex steel.

[0019] The present invention has the following beneficial effects:

[0020] This application uses calcium borate instead of borax. A larger amount of calcium borate can be added to the protective slag, avoiding the cracking and dust pollution caused by excessive borax addition. Furthermore, the higher amount of calcium borate results in a higher B2O3 content in the protective slag. B2O3 effectively lowers the melting point of the protective slag, refines the protective slag film, reduces viscosity, improves filling fluidity and lubrication, and most importantly, can replace some expensive materials, such as lithium carbonate, thereby reducing the cost of the protective slag while maintaining its performance. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The high-strength, lightweight duplex steel mentioned in this application has a tensile speed of 1-1.15 m / min, and its main components are shown in the table below:

[0023] element C Si Mn Al Control range wt% 0.16-0.17 1.2-1.5 1.9-2.1 0.02-0.05

[0024] Based on the above composition, firstly, the silicon content of this steel grade is relatively high, exceeding the range of less than 0.4% for conventional carbon steel. This results in higher thermal resistance of the continuously cast billet shell, leading to a very thin initial billet shell. This is the root cause of frequent alarms in the crystallizer expert system during continuous casting. Secondly, the manganese content in the molten steel is excessively high, exceeding the conventional range of less than 1.6%. This indicates very high billet shell strength. If the liquid slag has poor fluidity, it will result in weak filling capacity of the protective slag in the channel between the billet shell and the copper plate, uneven slag film thickness, and uneven consumption, which is the cause of longitudinal cracks. In addition, if the slag film of the protective slag is poorly lubricated, it will easily lead to increased friction between the billet and the crystallizer, thereby increasing the tendency of the billet to crack transversely.

[0025] The inventors studied the characteristics of steel grades and continuous casting process conditions, and designed the performance indicators and composition of protective slag in a targeted manner.

[0026] This application provides a continuous casting protective slag containing calcareous borate, wherein the raw material includes calcareous borate, and the mass fraction of calcareous borate in the raw material is 1-25%.

[0027] This application uses calcium borate instead of borax. A larger amount of calcium borate can be added to the protective slag, avoiding the cracking and dust pollution caused by excessive borax addition. Furthermore, the higher amount of calcium borate results in a higher B2O3 content in the protective slag. B2O3 effectively lowers the melting point of the protective slag, refines the protective slag film, reduces viscosity, improves filling fluidity and lubrication, and most importantly, can replace some expensive materials, such as lithium carbonate, thereby reducing the cost of the protective slag while maintaining its performance.

[0028] In some alternative embodiments of this application, the mass fraction of calcium borate in the raw material is 8-20%.

[0029] In some optional embodiments of this application, the raw materials of the protective slag, by weight, include 11-16 parts of fluorite, 2-5 parts of imported carbon black, 3-6 parts of earthy graphite, 58-65 parts of wollastonite, 5-9 parts of calcite, 0.5-3 parts of lightly calcined magnesia, 1-4 parts of bauxite, 1-4 parts of lithium carbonate, 8-20 parts of calcite and 1-3 parts of polyvinyl alcohol.

[0030] In the production of high-strength steel, due to the small gap between the billet shell and the copper plate, in order to form a uniform initial billet shell, the most taboo thing is the formation of slag streaks that affect the uniformity of liquid slag flow. Therefore, it is necessary to use composite carbon blending technology to ensure the three-layer structure of the protective slag melting. At the same time, in order to ensure the rapid melting of the protective slag, the carbon blending should not be too high. Imported carbon black with smaller particles must be used to ensure its skeleton function and control the melting speed.

[0031] To ensure the strength of the protective slag particles, an adhesive is required. However, to ensure the lubrication effect, adhesives containing sodium, such as sodium carboxymethyl cellulose and dextrin, cannot be selected. Therefore, this solution specifically selects polyvinyl alcohol as the adhesive.

[0032] In some optional embodiments of this application, the protective slag comprises the following chemical composition by weight percentage: CaO 35.0–39.0 wt%, SiO2 29.5–33.5 wt%, Al2O3 3–5 wt%, Fe2O3 0.3–1.5 wt%, MgO 1.5–3 wt%, Na2O 0–0.5 wt%, F 5–8.5 wt%, Li2O 0.8–1.5 wt%, B2O3 4–10 wt%, C 3–6 wt%, and unavoidable impurities.

[0033] It is important to note that, to ensure good lubrication of the protective slag, the introduction of sodium (Na) should be avoided as much as possible in its composition design. Na, when combined with calcium oxide, easily forms feldspar, which readily crystallizes and negatively impacts lubrication. Therefore, the introduction of Na into the protective slag should be minimized. This embodiment uses a combination of lithium carbonate and calcium borate to reduce the use of other sodium-containing raw materials and thus minimize the introduction of sodium ions into the protective slag.

[0034] In some optional embodiments of this application, the protective slag comprises the following chemical composition by weight percentage: CaO 36.0–39.0 wt%, SiO2 30.5–33.0 wt%, Al2O3 3–4 wt%, Fe2O3 0.3–0.7 wt%, MgO 1.5–2 wt%, Na2O 0–0.3 wt%, F 5–6.5 wt%, Li2O 1.0–1.5 wt%, B2O3 5–8 wt%, C 3–5 wt%, and unavoidable impurities.

[0035] In some alternative embodiments of this application, the binary basicity is 1.13-1.18.

[0036] In this embodiment, the binary basicity was reduced. After the basicity was reduced, fewer crystals precipitated from the slag film were produced, and more glassy material was produced, which could lubricate the billet. At the same time, the reduced basicity facilitated heat transfer to the billet shell, and the initial billet shell formed faster in continuous casting, avoiding alarm problems in the crystallizer expert system. However, considering that this steel grade is prone to longitudinal cracking defects, if the basicity design is too low, the billet is prone to longitudinal cracking defects. If the basicity is too high, the thickness of the solid slag film will increase, which may trigger alarm problems. After laboratory analysis, the most reasonable basicity design is 1.13-1.18.

[0037] In some alternative embodiments of this application, the melting temperature is 1100-1130°C.

[0038] In this embodiment, the melting point was lowered. To improve the rapid melting capacity of the protective slag, increase the consumption of protective slag per ton of steel, and avoid alarms from the crystallizer expert system, a lower melting point needed to be designed. To ensure a lower melting point, lithium oxide and hard borate were added to the protective slag. Conventional measures to lower the melting point include introducing materials such as industrial soda ash, NaF2, and cryolite. However, these materials all contain sodium, which can easily produce high-melting-point substances such as nepheline and calcium aluminum feldspar during the crystallization process after the protective slag melts, thus deteriorating the lubrication effect of the protective slag and triggering alarms from the crystallizer expert system. Lithium oxide effectively lowers the melting point and improves slag film morphology, refining grains. During cooling, the liquid protective slag forms finer, more uniform crystals, enhancing its heat transfer uniformity and preventing alarms and longitudinal cracks during continuous casting. However, lithium carbonate is too expensive; excessive use in the protective slag would lead to excessively high costs and a loss of market competitiveness. Hard borate, a mineral material, differs from borax. Borax has a low melting point but is prone to white sphere formation in the high-temperature environment of the granulation tower. Hard borate offers a high effective boron oxide yield and has a better melting point lowering effect than lithium oxide. Furthermore, hard borate is more cost-effective than borax and lithium carbonate. Therefore, the design combines lithium carbonate and hard borate, controlling the protective slag composition to include 0.8–1.5 wt% Li₂O and 4–10 wt% B₂O₃, ensuring a melting point within the range of 1100–1130℃.

[0039] In some alternative embodiments of this application, the viscosity at 1300°C is 0.11-0.14 Pa·s.

[0040] In this embodiment, the viscosity was reduced. This steel grade has a high-strength continuously cast billet shell with a small gap between the shell and the copper plate. Therefore, the shell experiences significant friction from the copper plate, necessitating improved lubrication of the protective slag. Considering the continuous casting billet pulling speed is only 1-1.15 m / min, and the viscosity cannot be too low (too low a viscosity would lead to rapid slag consumption and unevenness during solid slag film formation, increasing the likelihood of longitudinal and transverse cracks), the viscosity was designed to be 0.11-0.14 Pa·s.

[0041] In some alternative embodiments of this application, the crystallization rate is less than 1%.

[0042] This application also provides an embodiment of the application of the continuous casting protective slag containing borosilicate as described in any of the foregoing embodiments in the continuous casting of high-strength lightweight duplex steel.

[0043] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0044] Example 1:

[0045] A high-strength, lightweight, dual-phase steel continuous casting protective slag comprises: fluorite powder, imported carbon black, earthy graphite powder, wollastonite powder, calcite powder, lightly calcined magnesia powder, bauxite powder, lithium carbonate, hard borate powder, and polyvinyl alcohol, with weight percentages of 13%, 2%, 5%, 55%, 6%, 1%, 3%, 3%, 10%, and 2%, respectively.

[0046] A high-strength, lightweight, dual-phase steel continuous casting protective slag has the following composition and exact content: CaO: 37.2%, SiO2: 31.7%, Al2O3: 3.5%, Fe2O3: 0.6%, MgO: 1.9%, Na2O: 0.0%, F: 5.8%, Li2O: 1.2%, B2O3: 5%, C: 5%, binary basicity (CaO / SiO2 mass percentage) 1.17, melting point: 1110℃, viscosity at 1300℃: 0.12 Pa·s, crystallization rate: 0%.

[0047] The experiment was conducted at Ansteel, first in the last two heats, then in the last half-casting test, and finally in the entire casting test. The moldable slag type was A, the steel grade used was DP980, with a cross-section of 230*1250 mm, and the casting speed was 1.1 m / min. The experiment was conducted in three casting cycles. During the experiment, the A-type continuous casting moldable slag exhibited good spreading and fluidity within the mold, with a total slag layer of 50-70 mm and a liquid slag thickness of 10-13 mm. It effectively isolated the molten steel from the slag layer. The flame on the mold surface was moderate, and the slag consumption was moderate, averaging 0.5-0.55 kg / t, ensuring good lubrication. The slag streaks were small during the experiment, no alarms occurred in the mold, and the surface of the cast billet was smooth and defect-free, achieving the experimental objectives.

[0048] Example 2:

[0049] A high-strength, lightweight, dual-phase steel continuous casting protective slag comprises: fluorite powder, imported carbon black, earthy graphite powder, wollastonite powder, calcite powder, lightly calcined magnesia powder, bauxite powder, lithium carbonate, hard borate powder, and polyvinyl alcohol, with weight percentages of 14%, 2.5%, 3.5%, 52%, 5%, 1.5%, 3%, 2%, 15%, and 1.5%, respectively.

[0050] A high-strength, lightweight, dual-phase steel continuous casting protective slag has the following composition and exact content: CaO: 36.9%, SiO2: 32.1%, Al2O3: 3.5%, Fe2O3: 0.5%, MgO: 1.6%, Na2O: 0.2%, F: 6.2%, Li2O: 0.9%, B2O3: 7.5%, C: 4%, binary basicity (CaO / SiO2 mass percentage) 1.15, melting point: 1125℃, viscosity at 1300℃: 0.11 Pa·s, crystallization rate: 0%.

[0051] The experiment was conducted at a domestic plant. First, tests were performed on the last two heats, then on the final half-casting cycle, and finally on the entire casting cycle. The moldable slag type was B, the steel grade used was DP980, with a cross-section of 230*1300 mm, and the casting speed was 1.1 m / min. The experiment was conducted in three casting cycles. During the experiment, the type B continuous casting moldable slag exhibited good spreading and fluidity within the mold, with a total slag layer of 50-70 mm and a liquid slag thickness of 9-12 mm. It effectively isolated the molten steel from the slag layer. The flame on the mold surface was moderate, and the slag consumption was moderate, averaging 0.55-0.6 kg / t, ensuring good lubrication. The slag streaks were small during the experiment, no alarms occurred in the mold, and the surface of the cast billet was smooth and defect-free, achieving the experimental objectives.

[0052] Comparative Example 1:

[0053] A high-strength, lightweight, dual-phase steel continuous casting protective slag comprises: fluorite powder, imported carbon black, earthy graphite powder, wollastonite powder, soda ash, calcite powder, lightly calcined magnesia powder, bauxite powder, lithium carbonate, hard borate powder, and polyvinyl alcohol, with weight percentages of 14%, 2%, 4%, 51%, 4%, 8%, 1%, 3%, 3%, 8%, and 2%, respectively.

[0054] A high-strength, lightweight, dual-phase steel continuous casting protective slag has the following composition and exact content: CaO: 38.1%, SiO2: 29.3%, Al2O3: 3.5%, Fe2O3: 0.6%, MgO: 1.9%, Na2O: 2.4%, F: 6.2%, Li2O: 1.2%, B2O3: 4%, C: 5%, binary basicity (CaO / SiO2 mass percentage) 1.3, melting point: 1140℃, viscosity at 1300℃: 0.13 Pa·s, crystallization rate: 30%.

[0055] The experiment was conducted at Ansteel, starting with the last four heats. The test used type C moldable slag, and the cast steel was DP980 with a cross-section of 230*1250 mm. The casting speed was 1.0 m / min. During the experiment, type C continuous casting moldable slag exhibited good spreading and fluidity within the crystallizer, with a total slag layer of 50-70 mm and a liquid slag thickness of 8-11 mm. It effectively isolated the molten steel from the slag layer. The flame on the crystallizer surface was moderate, and the slag consumption was moderate, averaging 0.5-0.53 kg / t, ensuring good lubrication. Slag bars formed rapidly during the experiment, resulting in three alarm incidents. Adhesive-type vibration marks appeared on the surface of the cast billet due to the reduced casting speed to 0.1 m / min after the alarms. The experimental results were worse than those of types A and B, mainly because the addition of soda ash increased the amount of feldspar in the liquid slag film, leading to higher basicity and crystallization rate, resulting in faster slag bar production.

[0056] Comparative Example 2:

[0057] A high-strength, lightweight, dual-phase steel continuous casting protective slag comprises: fluorite powder, imported carbon black, earthy graphite powder, wollastonite powder, calcite powder, lightly calcined magnesia powder, bauxite powder, lithium carbonate, hard borate powder, and polyvinyl alcohol, with weight percentages of 15%, 3%, 3%, 42%, 2%, 2%, 3%, 4%, 18%, and 3%, respectively.

[0058] A high-strength, lightweight, dual-phase steel continuous casting protective slag has the following composition and exact content: CaO: 36.1%, SiO2: 33.8%, Al2O3: 3.9%, Fe2O3: 0.7%, MgO: 2.6%, Na2O: 0.0%, F: 6.5%, Li2O: 1.9%, B2O3: 9%, C: 4.5%, binary basicity (CaO / SiO2 mass percentage) 1.07, melting point: 1070℃, viscosity at 1300℃: 0.09 Pa·s, crystallization rate: 0%.

[0059] The experiment was conducted at Ansteel, with the last four heats tested. The moldable slag type was E, the cast steel grade was DP980, with a cross-section of 230*1250 mm, and the casting speed was 1.15 m / min. During the experiment, the E-type continuous casting moldable slag exhibited good spreading and fluidity in the mold, with a total slag layer of 50-70 mm and a liquid slag thickness of 6-8 mm. The liquid slag layer was relatively thin, resulting in a large flame on the mold surface. Slag consumption was moderate, averaging 0.55-0.6 kg / t, which was relatively high. There were few slag streaks during the experiment, and no alarms were triggered in the mold. However, upon inspection of the cast billet, the surface was not smooth, with deep vibration marks and a longitudinal and transverse crack rate as high as 10%. The experimental results were not ideal, mainly due to the excessive addition of Li₂O and B₂O₃, which resulted in a lower melting point and viscosity, and a large liquid slag consumption.

[0060] Comparative Example 3

[0061] The protective slag is designed according to the composition of foreign protective slags. Its components include: fluorite powder, imported carbon black, soda ash, earthy graphite powder, wollastonite powder, calcite powder, lightly calcined magnesia powder, bauxite powder, and sodium carboxymethyl cellulose, with weight percentages of 15%, 2%, 7%, 4%, 53%, 13%, 1%, 3%, and 2%, respectively.

[0062] The composition and exact content of each component are as follows: CaO: 39.5%, SiO2: 28.3%, Al2O3: 4.3%, Fe2O3: 0.6%, MgO: 1.7%, Na2O: 4.5%, F: 6.7%, C: 5%, binary basicity (CaO / SiO2 mass percentage) 1.38, melting point: 1150℃, viscosity at 1300℃: 0.10 Pa·S, crystallization rate: 100%.

[0063] The experiment was conducted at Ansteel, with the last four heats tested. The moldable slag type was E, the cast steel grade was DP980 with a cross-section of 230*1250 mm, and the casting speed was 1.1 m / min. During the experiment, the E-type continuous casting moldable slag exhibited good spreading and fluidity within the crystallizer, with a total slag layer of 50-70 mm and a liquid slag thickness of 12-15 mm. The flame on the crystallizer surface was moderate, and the slag consumption was moderate, averaging 0.38-0.44 kg / t, ensuring good lubrication. However, slag streaks formed rapidly during the experiment, and alarms frequently occurred within the crystallizer. Adhesive-type vibration marks appeared on the surface of the cast billet due to the reduced casting speed to 0.1 m / min caused by the alarms, resulting in poor experimental performance. The main reasons were high basicity, rapid slag streak formation, and the inability of the liquid slag to be consumed through the gap between the crystallizer and the copper plate, leading to a high crystallization rate and poor lubrication.

[0064] Comparative Example 4

[0065] The comparative example design of the continuous casting protective slag includes: fluorite powder, imported carbon black, earthy graphite powder, wollastonite powder, calcite powder, lightly calcined magnesia powder, bauxite powder, lithium carbonate, hard borate powder, and polyvinyl alcohol, with weight percentages of 12%, 3%, 3%, 64.5%, 6%, 3%, 4%, 1.5%, 2%, and 1%, respectively.

[0066] The composition and exact content of each component are as follows: CaO: 36.9%, SiO2: 33.6%, Al2O3: 4.2%, Fe2O3: 0.7%, MgO: 2.1%, Na2O: 0.0%, F: 5.5%, Li2O: 0.5%, B2O3: 2%, C: 4.5%, binary basicity (CaO / SiO2 mass percentage) 1.1, melting point: 1140℃, viscosity at 1300℃: 0.13 Pa·s, crystallization rate: 40%.

[0067] The experiment was conducted at Ansteel, with the last four heats tested. The moldable slag type was F, the cast steel grade was DP980, with a cross-section of 230*1250 mm, and the casting speed was 1.0 m / min. During the experiment, the F-type continuous casting moldable slag exhibited good spreading and fluidity within the mold, with a total slag layer of 50-70 mm and a liquid slag thickness of 12-15 mm. It effectively isolated the molten steel from the pulverized slag layer. The flame on the mold surface was moderate, and the slag consumption was moderate, averaging 0.42-0.50 kg / t. However, the slag streaks were large during the experiment, triggering an alarm in the mold's expert system. The longitudinal alignment rate reached as high as 30%, indicating poor experimental results.

[0068] It can be seen that the continuous casting protective slag for high-strength lightweight duplex steel provided in this application embodiment has better performance in all aspects than the continuous casting protective slag for high-strength lightweight duplex steel in the comparative example, indicating that the continuous casting protective slag for high-strength lightweight duplex steel provided in this application embodiment can effectively ensure the smooth progress of the high-strength lightweight duplex steel casting process and prevent crack defects.

[0069] In summary, the high-strength lightweight duplex steel continuous casting protective slag provided in this application can effectively solve the longitudinal and transverse crack defects that occur in the continuous casting process of high-strength lightweight duplex steel due to the thin initial billet shell, high billet shell strength, and large friction between the billet shell and the copper plate.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hard tachevite-containing continuous casting protection shell characterized by, The raw material includes hard tachevite, and the mass fraction of the hard tachevite in the raw material is 1-25%; the covering slag includes the following chemical components in percentage by weight: CaO 35.0-39.0wt%, SiO2 29.5-33.5wt%, Al2O3 3-5wt%, Fe2O3 0.3-1.5wt%, MgO 1.5-3wt%, Na2O 0-0.5wt%, F 5-8.5wt%, Li2O 0.8-1.5wt%, B2O3 4-10wt%, C 3-6wt% and inevitable impurities; the binary basicity of the covering slag is 1.13-1.18, and the crystallization rate is less than 1%.

2. The hard-boracite-containing continuous casting protection shell according to claim 1, characterized in that, The mass fraction of the hard tachevite in the raw material is 8-20%.

3. The hard-boracite-containing continuous casting protection shell according to claim 1, characterized in that, The raw material of the covering slag includes, in percentage by weight, 11-16 parts of fluorite, 2-5 parts of imported carbon black, 3-6 parts of earthy graphite, 58-65 parts of wollastonite, 5-9 parts of calcite, 0.5-3 parts of light-burned magnesia, 1-4 parts of bauxite, 1-4 parts of lithium carbonate, 8-20 parts of hard tachevite and 1-3 parts of polyvinyl alcohol.

4. The hard-boracite-containing continuous casting protection shell according to claim 1, characterized in that, The covering slag includes the following chemical components in percentage by weight: CaO 36.0-39.0wt%, SiO2 30.5-33.0wt%, Al2O3 3-4wt%, Fe2O3 0.3-0.7wt%, MgO 1.5-2wt%, Na2O 0-0.3wt%, F 5-6.5wt%, Li2O 1.0-1.5wt%, B2O3 5-8wt%, C 3-5wt% and inevitable impurities.

5. The hard-boracite-containing continuous casting protection shell according to claim 1, characterized in that, The melting temperature is 1100-1130℃.

6. The hard-boracite-containing continuous casting protection shell according to claim 1, characterized in that, The viscosity at 1300℃ is 0.11-0.14Pa·s.

7. Application of the hard-tachevite-containing continuous-casting covering slag as claimed in any one of claims 1-6 to high-strength light-weight dual-phase steel continuous casting.