A special covering agent for high manganese steel continuous casting tundish

Abstract

This invention relates to the field of metallurgical materials technology, and provides a special covering agent for the tundish of high manganese steel continuous casting, comprising the following components by weight percentage: MnO: 6-10%; CaO: 30-35%; SiO2: 30-35%; Al2O3: 6-10%; MgO: 5-10%; the balance being unavoidable impurities. This invention, by pre-adding MnO to the covering agent components, utilizes the principle of chemical equilibrium to significantly reduce the reaction driving force of SiO2 in the [Mn] reducing slag in the molten steel. This ensures that the covering agent maintains high stability in composition and physical properties throughout the continuous casting process, ensuring good spreadability and heat preservation performance. It fundamentally solves the problem of functional failure caused by compositional changes in conventional covering agents during the casting of high manganese steel, effectively improving the purity of the molten steel and ensuring the continuity and stability of the high manganese steel continuous casting process.

Description

Technical Field

[0001] This invention relates to the field of metallurgical materials technology, specifically to a special covering agent for the tundish of high manganese steel continuous casting. Background Technology

[0002] High-manganese steel, due to its excellent ultra-low temperature toughness and low coefficient of thermal expansion, is widely used in the manufacture of critical equipment such as LNG storage tanks. In continuous casting production, the tundish covering agent plays a crucial role in heat insulation, preventing secondary oxidation, and absorbing inclusions. However, because high-manganese steel has an extremely high manganese content, when using conventional CaO-Al2O3 or CaO-SiO2-Al2O3 tundish covering agents, the Mn in the molten steel undergoes a redox reaction with the SiO2 in the covering agent. This leads to the continuous consumption of SiO2 in the covering agent, resulting in a significant increase in the MnO content. This causes the covering agent's composition to change from "manganese-free" to "high-manganese," and key physical properties such as basicity and viscosity continuously change during casting, leading to degradation. This causes the covering agent to lose its heat insulation and inclusion absorption functions, severely affecting the stability of the molten steel composition and even causing continuous casting production interruptions. Currently, there is no dedicated covering agent specifically designed for the characteristics of high-manganese steel, and a technical solution to solve the aforementioned covering agent degradation problem is urgently needed. Summary of the Invention

[0003] To address the technical problem of unstable composition and physical properties of existing covering agents due to chemical reactions, the present invention aims to provide a special covering agent for high manganese steel continuous casting tundishes. By pre-adding MnO components, the steel-slag interface reaction is suppressed, thereby stabilizing the performance of the tundish covering agent.

[0004] To achieve the objectives of this invention, the following technical solution is adopted: A special covering agent for high manganese steel continuous casting tundish, characterized in that: the covering agent contains the following components by weight percentage: MnO: 6-10%; CaO: 30-35%; SiO2: 30-35%; Al2O3: 6-10%; MgO: 5-10%; the balance being unavoidable impurities.

[0005] The special covering agent for high manganese steel continuous casting tundish provided by this invention significantly reduces the reaction driving force of SiO2 in the [Mn] reducing slag in molten steel by pre-adding MnO components to the covering agent composition and utilizing the principle of chemical equilibrium. This ensures that the covering agent maintains high stability of composition and physical properties throughout the continuous casting process, ensuring good spreadability and heat preservation performance. It fundamentally solves the problem of functional failure caused by compositional changes in conventional covering agents when casting high manganese steel, effectively improving the purity of molten steel and ensuring the continuity and stability of the high manganese steel continuous casting process.

[0006] The special covering agent for high manganese steel continuous casting tundish of the present invention has the following beneficial effects: Improved quality: Significantly improves the purity of molten steel for ultra-low temperature high manganese steel, stabilizes the composition of molten steel, and reduces the defect rate of cast billets.

[0007] Reduce costs: Reduce continuous casting anomalies, casting stoppages, and billet downgrades caused by coating agent degradation, ensure stable production over long casting cycles, and significantly reduce overall production costs.

[0008] Filling a Gap: As the first dedicated covering agent product in the field of high manganese steel, this covering agent has a reasonable formulation design, readily available raw materials, good industrial application prospects and broad market promotion prospects. It can completely replace existing unsuitable conventional covering agents and promote the efficient and high-quality continuous production of high manganese steel. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0010] Example 1

[0011] This embodiment provides a special covering agent for high manganese steel continuous casting tundish, specifically designed for high manganese steel used in ultra-low temperature applications. Its typical composition (by weight percentage) is: C: 0.35-0.55%, Mn: 22.5-25.5%, Cr: 3.0-5.0%, Cu: 0.3-1.0%, Ni: 0.2-1.20%, Si≤0.80%, P≤0.020%, S≤0.005%, with the balance being Fe.

[0012] The special covering agent for high manganese steel continuous casting tundish in this embodiment contains the following components by weight percentage: MnO: 6-10%; CaO: 30-35%; SiO2: 30-35%; Al2O3: 6-10%; MgO: 5-10%; the balance being unavoidable impurities.

[0013] This embodiment pre-adds 6-10% MnO to the covering agent components (specifically, in this embodiment, MnO can be added in the form of MnCO3 raw material, which decomposes into MnO and CO2 at high temperatures during industrial use of protective slag). This ensures that the MnO in the slag already has a high initial activity before the covering agent is put into use. According to the principle of chemical equilibrium, when the activity of the generated MnO increases, it effectively inhibits the redox reaction between [Mn] in the molten steel and SiO2 in the covering agent, preventing the reaction from proceeding in the direction of MnO formation. This is equivalent to applying a reverse "resistance" at the initial stage of the reaction, significantly reducing the driving force of [Mn] in the molten steel reducing SiO2 in the covering agent, inhibiting the steel-slag interface reaction, and thus maintaining a high degree of stability in the composition and properties of the covering agent during the continuous casting process that lasts for several hours.

[0014] In this embodiment, the basicity (CaO / SiO2 mass ratio) of the covering agent is 0.86–1.17. If the basicity of the covering agent is too low, the activity of SiO2 in the slag will be too high, and even with the pre-added MnO, it will be difficult to completely inhibit the reaction between [Mn] and SiO2. If the basicity is too high, although the activity of SiO2 decreases, the slag structure tends to be compact, and the viscosity increases significantly, resulting in poor spreadability of the covering agent and a decrease in thermal insulation performance. This embodiment achieves the best balance between the thermal insulation and flowability of the covering agent by controlling the basicity within the weakly acidic to neutral range of 0.86–1.17 and working synergistically with a specific MnO content.

[0015] In this embodiment, the viscosity of the covering agent is 0.8 to 1.5 Pa·s at 1350°C, ensuring good spreadability.

[0016] In this embodiment, the melting point of the covering agent is 1200-1300℃ and the melting rate is 2-4 min, ensuring that the covering agent can quickly form a liquid slag layer and effectively isolate the air.

[0017] In this embodiment, unavoidable impurities mainly originate from the raw materials themselves. To ensure the purity of the covering agent and avoid oxygenation of the molten steel, the total amount of unavoidable impurities is ≤3.0%, of which T.Fe ≤1.0%.

[0018] In summary, this embodiment optimizes the design of the covering agent components, pre-adds a specific amount of MnO to the components, and controls the physical performance parameters such as basicity, viscosity, melting point, melting rate, and impurity content of the covering agent. This establishes the physical basis for the normal operation of the covering agent in the tundish, fundamentally solving the problem of covering agent deformation during the continuous casting of high manganese steel. Through synergistic effects, it achieves the comprehensive performance of the covering agent, which is characterized by "good spreadability, strong heat preservation, no slag entrainment, and no oxygenation." The covering agent has stable components and long-lasting function, providing a guarantee for the stable operation of the high manganese steel continuous casting process.

[0019] Example 2

[0020] This embodiment provides a special covering agent for high manganese steel continuous casting tundish, which contains the following components by weight percentage: MnO: 7-9%; CaO: 32-34%; SiO2: 31-34%; Al2O3: 7-9%; MgO: 6-8%; the balance being unavoidable impurities.

[0021] In this embodiment, the alkalinity (CaO / SiO2 mass ratio) of the covering agent is 0.94 to 1.10.

[0022] In this embodiment, the viscosity of the covering agent is 0.8 to 1.5 Pa·s at 1350°C, ensuring good spreadability.

[0023] In this embodiment, the melting point of the covering agent is 1200-1300℃ and the melting rate is 2-4 min, ensuring that the covering agent can quickly form a liquid slag layer and effectively isolate the air.

[0024] In this embodiment, unavoidable impurities mainly originate from the raw materials themselves. To ensure the purity of the covering agent and avoid oxygenation of the molten steel, the total amount of unavoidable impurities is ≤3.0%, of which T.Fe ≤1.0%.

[0025] This embodiment limits the MnO content to the range of 7-9% and controls the alkalinity to the range of 0.94-1.10, which can more accurately match the activity of [Mn] in the molten high-manganese steel. While ensuring effective inhibition of interfacial reactions, it minimizes the potential adverse effects of high-melting-point components on the flowability of the covering agent.

[0026] To verify the effect of the tundish covering agent of the present invention in the continuous casting of high manganese steel, the following comparative tests were conducted under the same working conditions through multiple sets of examples and comparative examples.

[0027] Specifically, the component formulations (wt%) and key physical properties of each embodiment and comparative example are shown in Table 1: Table 1. Composition (wt%) and key properties of each embodiment and comparative example. In Examples A to F, the MnO content of the covering agent was strictly controlled between 6% and 10%, and the basicity was strictly controlled between 0.86 and 1.17. Tests showed that the melting point of the covering agent in the above examples was between 1220 and 1280°C, and the viscosity at 1350°C was between 0.85 and 1.30 Pa·s. This indicates that within the preferred composition and basicity range, the covering agent can form a suitable slag layer thickness, ensuring good spreading performance while avoiding slag entrapment due to excessively low melting point or crust formation due to excessively high melting point, thus providing a solid material basis for the stability of the high-manganese steel continuous casting process.

[0028] Among them, Comparative Example 1 simulated an acidic covering agent (CaO-SiO2-Al2O3 system, MnO: 0%), Comparative Example 2 simulated an alkaline covering agent (CaO-Al2O3 system, low silicon, MnO: 0%), and Comparative Example 3 added 5% MnO, with high alkalinity, to investigate the effect of alkalinity on the effect.

[0029] Comparative tests and results of continuous casting: Test steel: Ultra-low temperature high manganese steel with Mn content of 24.0 wt%.

[0030] Test conditions: 30-ton tundish, molten steel superheated at 25±5℃, casting cycle 60 minutes. The covering agent was added all at once, at a rate of 1.5–2.0 kg / ton of steel, with no additional additions during the casting process.

[0031] Evaluation items: Change rate of the coating agent composition throughout the casting process, increase in total oxygen content (T.[O]) in molten steel, and coating agent coverage and crust formation. Specifically, the metallurgical effects of continuous casting tests in each embodiment and comparative example are compared in Table 2: Table 2 Comparison of metallurgical effects in continuous casting tests of various embodiments and comparative examples As can be seen from Tables 1 and 2, the present invention has significant advantages over the prior art: Addressing the root cause of covering agent denaturation: This invention, through the pre-addition of MnO, controls the changes in MnO, SiO2 content, and basicity of the covering agent during casting to ≤15%, ≤12%, and ≤8%, respectively, achieving high stability in composition and physical properties and completely solving the denaturation problem of conventional covering agents. In contrast, Comparative Example 1 showed a significant increase in MnO content from 0 to approximately 380% at the end of casting, indicating severe denaturation.

[0032] Significantly improves the purity of molten steel: Due to the stable physical properties of the covering agent and its ability to absorb inclusions without decay, the application of this invention can reduce the T.[O] increment of molten steel from the conventional 8-15ppm to ≤3ppm, effectively improving the quality of the billet.

[0033] Ensuring smooth and stable casting: The covering agent of this invention maintains good spreadability and fluidity throughout the entire process, does not form a crust or turn red, is easy to operate, and ensures the continuity and stability of continuous casting production.

[0034] Precise inhibition of chemical reactions: The optimal balanced inhibition effect is achieved by controlling the basicity within a specific weak acid to neutral range of 0.86-1.17, combined with 6-10% MnO. While excessively high basicity (such as in Comparative Example 3) can partially inhibit the reaction, it will severely deteriorate the flowability and heat retention properties of the slag.

[0035] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A special covering agent for high manganese steel continuous casting tundish, characterized by, The covering agent comprises the following components by weight percentage: MnO: 6-10%; CaO: 30-35%; SiO2: 30-35%; Al2O3: 6-10%; MgO: 5-10%; the balance being unavoidable impurities.

2. The high manganese steel tundish specific covering agent according to claim 1, characterized in that, The MnO content is 7-9%.

3. The high manganese steel tundish specific covering agent according to claim 1, characterized in that, The mass ratio of CaO / SiO2 in the covering agent is 0.86 to 1.

17.

4. The special covering agent for high manganese steel continuous casting tundish according to claim 3, characterized in that, The mass ratio of CaO / SiO2 in the covering agent is 0.94 to 1.

10.

5. The special covering agent for high manganese steel continuous casting tundish according to claim 1, characterized in that, The covering agent comprises the following components by weight percentage: CaO: 32-34%; SiO2: 31-34%; Al2O3: 7-9%; MgO: 6-8%.

6. The special covering agent for high manganese steel continuous casting tundish according to claim 1, characterized in that, The covering agent has a viscosity of 0.8–1.5 Pa·s at 1350°C.

7. The special covering agent for high manganese steel continuous casting tundish according to claim 1, characterized in that, The melting point of the covering agent is 1200-1300℃.

8. The special covering agent for high manganese steel continuous casting tundish according to claim 1, characterized in that, The total amount of the unavoidable impurities is ≤3.0%, of which T.Fe ≤1.0%.

9. The special covering agent for high manganese steel continuous casting tundish according to claim 1, characterized in that, The melting rate of the covering agent is 2 to 4 minutes.

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