Crystallizer casting powder and application thereof

Abstract

The invention relates to crystallizer casting powder and application thereof. The crystallizer casting powder is applied to the surface of molten steel in a crystallizer. The casting powder comprises the following chemical components in percentage by mass: 35.08% to 39.08% of CaO, 24.08% to 28.08% of SiO2, 0.31% to 0.51% of Li2O, 6.08% to 8.08% of Na2O, 8.33% to 10.9% of F, 2.36% to 3.36% of Al2O3, 0.55% to 1.15% of MgO, 0 to 0.8% of Fe2O3, 3.45% to 5.45% of solid C and the balance of inevitable impurities, and the sum of the mass of carbonate and the mass of oxysalt in the crystallizer casting powder is less than or equal to 5%. According to the crystallizer casting powder, rapid heat transfer in a crystallizer is facilitated, heat transfer uniformity is guaranteed, effective lubrication is achieved, bonding breakout is reduced, alarming is conducted, and continuous and stable production and the surface quality of a continuous casting blank are both considered.

Description

Technical Field

[0001] This application relates to the field of iron and steel smelting technology, specifically to a mold protective slag and its application. Background Technology

[0002] The mold flux in continuous casting is a crucial functional auxiliary material. During the casting process, it covers the surface of the molten steel inside the mold, serving multiple functions such as heat insulation, preventing secondary oxidation of the molten steel, absorbing floating non-metallic inclusions, lubricating the billet, and controlling heat transfer from the billet to the mold. The stability of the mold flux's performance directly affects the smooth operation of the continuous casting process and the surface and internal quality of the billet.

[0003] Existing conventional or general mold flux formulations are not designed for medium carbon steel molten steel or the continuous casting conditions of medium carbon steel, and therefore cannot maintain the performance stability of medium carbon alloy steel billets.

[0004] Therefore, the development of a mold flux is a crucial technical issue that urgently needs to be addressed in the field of steel materials. Summary of the Invention

[0005] In view of this, the embodiments of this application provide a mold flux and its application, which is conducive to rapid heat transfer in the mold, ensures uniform heat transfer, achieves effective lubrication, avoids sticking and leakage of steel and alarms, and is conducive to balancing continuous and stable production and the surface quality of continuously cast billets.

[0006] In a first aspect, embodiments of this application provide a mold flux, which is applied to the surface of molten steel within a mold. The flux comprises, by mass percentage, the following chemical components: CaO: 35.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.51%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe ... 3: 0~0.8%, C 固 The content of carbonates and oxyacids in the crystallizer protective slag is 3.45%~5.45%, with the balance being unavoidable impurities. The total mass of carbonates and oxyacids in the crystallizer protective slag is ≤5%.

[0007] In this embodiment, by controlling the mass percentage of each chemical component in the mold flux, a mold flux with suitable basicity, melting point, viscosity, crystallization temperature, and transition temperature is obtained. Using this mold flux to cast medium-carbon alloy steel, especially high-hydrogen-content steel, can significantly reduce the incidence of mold sticking alarms and emergency speed reductions, as well as steel leakage during continuous casting. The lower mass of carbonates and oxyacids in the mold flux helps control the uniformity of porosity in the solid and liquid layers adjacent to the billet shell during the hardening process of the medium-carbon alloy steel billet. This is beneficial for heat transfer and controlling the surface quality of the billet, promoting rapid heat transfer within the mold, ensuring uniform heat transfer, achieving effective lubrication, and preventing sticking, steel leakage, and alarms. This approach helps to balance continuous and stable production with the surface quality of the continuously cast billet. Therefore, production efficiency is improved while production costs are reduced.

[0008] In some embodiments, the protective slag comprises, by mass percentage, the following chemical components: CaO: 36.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.49%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe2O3: 0.55%~1.15%, Fe2O3: 0.55%~1.15%. 3: 0~0.8%, C 固 3.45%~5.45%, with the balance being unavoidable impurities.

[0009] In some embodiments, the basicity of the crystallizer protective slag is 1.25~1.45; the melting point of the crystallizer protective slag is 1143~1173℃; and the viscosity of the crystallizer protective slag at 1300℃ is 0.08~0.10 Pa·s.

[0010] In some embodiments, the transition temperature of the crystallizer protective slag is 1000~1050℃.

[0011] In some embodiments, the crystallization temperature of the crystallizer protective slag is 1010~1030℃.

[0012] In some embodiments, the raw materials for the crystallizer protective slag include: pre-melted material, glass powder, manganese carbonate, fluorite, sodium fluoride, cryolite, lithium carbonate, and carbon black.

[0013] Secondly, embodiments of this application provide a method for preparing a medium-carbon alloy steel billet, comprising the following steps: S10: The mold flux of the first aspect is introduced into the surface of the molten steel in the mold; S20: The crystallizer is continuously cast at a casting speed of 1.3~1.5m / min to obtain a medium carbon alloy steel billet. During continuous casting, the cooling rate is 1.1~1.3L / kg, and the deviation of the cooling rate is ≤0.2L / kg.

[0014] In some embodiments, the molten steel comprises, by mass percentage, the following elements: C: 0.08%-0.16%, Si: 0.10%-0.20%, Mn: 0.90%-1.20%, P≤0.015%, S≤0.006%, Al: 0.02%-0.06%, Ti: 0.15%-0.30%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0015] In some embodiments, during continuous casting, a protective slag molten layer, a protective slag sintered layer, and protective slag powder are sequentially arranged on the surface of the molten steel in a direction away from the molten steel. The thickness of the protective slag powder is controlled to be 40-50 mm, and the consumption of the protective slag in the crystallizer is 0.30-0.50 kg / t of molten steel.

[0016] In some embodiments, a solid layer and a liquid layer formed by mold flux are sequentially disposed on the side wall of the mold, the solid layer is located on the side away from the molten steel, the thickness of the solid layer is 1~2mm, and the thickness of the liquid layer is 0.1~0.2mm. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of the liquid surface in the crystallizer provided in Embodiment 1 of this application.

[0019] Figure 2 This is a schematic diagram of the structure of the crystallizer sidewall provided in Embodiment 1 of this application.

[0020] Figure 3 This is a surface appearance view of the medium carbon alloy steel billet provided in Embodiment 1 of this application.

[0021] Figure 4 This is a surface appearance drawing of the medium carbon alloy steel billet provided in Comparative Example 1 of this application.

[0022] Explanation of reference numerals in the attached figures: 10. Crystallizer; 11. Molten steel; 12. Molten protective slag layer; 13. Sintered protective slag layer; 14. Protective slag powder; 15. Solid layer; 16. Liquid layer. Detailed Implementation

[0023] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples. In the accompanying drawings and the following description, at least some well-known structures and techniques are not shown to avoid unnecessarily obscuring the application; and, for clarity, the dimensions of some structures may be exaggerated. Furthermore, the features, structures, or characteristics described below can be combined in any suitable manner in one or more embodiments.

[0024] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0025] Medium carbon steel inherently undergoes δ→γ phase transformation shrinkage during continuous casting, resulting in low initial shell strength and a narrow heat transfer window. Furthermore, when the molten steel in the mold contains a high hydrogen content, the impact of hydrogen on the continuously cast billet is significantly amplified in this type of medium carbon steel, which is prone to peritectic reactions.

[0026] To address the shortcomings of hydrogen evolution during the continuous casting of high-hydrogen steel, which leads to uneven heat transfer in the slag film, lubrication failure, and frequent adhesion alarms due to hydrogen participation at the slag-shell interface, a continuous casting protective slag is provided that can suppress the influence of hydrogen on the properties of the protective slag and improve the stability of the crystallizer interface. This solves the problem that existing protective slags are prone to property drift and induce crystallizer adhesion due to insufficient adaptability to the hydrogen environment in the continuous casting of high-hydrogen peritectic steel.

[0027] In summary, in order to solve the problems of the prior art, this application provides a crystallizer protective slag and its application.

[0028] In a first aspect, embodiments of this application provide a mold flux, which is applied to the surface of molten steel within a mold. The flux comprises, by mass percentage, the following chemical components: CaO: 35.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.51%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe ... 3: 0~0.8%, C 固 The content is 3.45%~5.45%, with the balance being unavoidable impurities. The total mass of carbonates and oxyacids in the crystallizer protective slag is ≤5%, which can be selected as ≤3%, and further selected as 2%.

[0029] In this embodiment, by controlling the mass percentage of each chemical component in the mold flux, a mold flux with suitable basicity, melting point, viscosity, crystallization temperature, and transition temperature is obtained. Using this mold flux to cast medium-carbon alloy steel, especially high-hydrogen-content steel, can significantly reduce the incidence of mold sticking alarms and emergency speed reductions, as well as steel leakage during continuous casting. The lower mass of carbonates and oxyacids in the mold flux helps control the uniformity of porosity in the solid and liquid layers adjacent to the billet shell during the hardening process of the medium-carbon alloy steel billet. This is beneficial for heat transfer and controlling the surface quality of the billet, promoting rapid heat transfer within the mold, ensuring uniform heat transfer, achieving effective lubrication, and preventing sticking, steel leakage, and alarms. This approach helps to balance continuous and stable production with the surface quality of the continuously cast billet. Therefore, production efficiency is improved while production costs are reduced.

[0030] Within the aforementioned range, the content of the mold flux F is beneficial in reducing the precipitation of gunmetal, a precipitate. Precise control of the crystallization behavior and high-temperature properties of the mold flux, through precise regulation of the precipitate phase (gunmetal), optimizes its lubrication performance, heat transfer characteristics, and stability. For medium-carbon steel, which is susceptible to both casting cracks and adhesion, especially in continuous casting processes under harsh conditions such as high hydrogen content, this ensures smooth process operation, improves billet quality, and achieves safe and efficient production.

[0031] F (fluorine) significantly reduces the viscosity and melting point of slag, enabling the mold flux to melt rapidly at the meniscus to form a uniform liquid slag layer. It also provides ample, highly fluid liquid slag to flow between the billet shell and the copper wall, ensuring lubrication. F is typically added in the form of fluorite (CaF2). CaF2 significantly disrupts the stable structure of the silicate network (breaking Si-O-Si bonds) and is a powerful crystallizer, significantly increasing the crystallization temperature and crystallization ratio of the mold flux. The CaF2 content directly affects the transformation behavior of the mold flux from liquid to solid (whether it tends to crystallize or form glass), and is the main lever for controlling the crystallization / glass ratio of the slag film.

[0032] MgO is typically added in the form of dolomite or lightly calcined magnesia balls. MgO can adjust the basicity, viscosity, and melting point of the slag, making its variation curve smoother and improving performance stability. It can also change the type of precipitated crystals. When there is no MgO or low MgO: high-basicity, high-F slag tends to precipitate lanceolate crystals, resulting in more ideal crystallization properties and improved slag film uniformity and stability. Combining both can achieve an ideal state of low melting point but with a smooth viscosity-temperature curve.

[0033] Meanwhile, MgO can suppress the excessive precipitation of gunpowder caused by high F. The combined effect of the two can achieve rapid precipitation of slag film with a better crystal type.

[0034] With the Li2O content within the above range, the combined effect of the basicity of the mold flux stabilizes the physical properties of the flux and ensures uniform heat transfer. By reducing the melting point and viscosity, the consumption of the flux is increased, ensuring the thickness of the liquid slag film in the mold flux channel, achieving effective lubrication, and preventing sticking and leakage of steel.

[0035] Specifically, Li in Li2O + With its small ionic radius and high electric field strength, it can efficiently break the Si-O-Si bonds ([SiO4] tetrahedral bonds) in the silicate network, causing the melt structure to depolymerize. This is consistent with, and even more effective than, the effect of increasing basicity (adding CaO) in "providing free oxygen to break the network." Below the meniscus of the crystallizer, the solid slag film formed by the solidification of the protective slag has a moderate crystallinity, fine grains, and uniform distribution. This homogeneous slag film is a uniform conductor of heat transfer from the billet shell to the copper plate of the crystallizer, avoiding "uniform lateral heat flow" caused by too much (poor heat transfer) or too little (fast heat transfer) crystalline phase in some areas. Uniform heat transfer directly leads to uniform thickness growth of the solidified billet shell in the circumferential direction, greatly reducing the risk of sticking and leakage caused by excessively thin local billet shells, while also reducing the generation of thermal stress cracks. In addition, it can also lower the melting point and viscosity, increase consumption to ensure lubrication, and improve the surface quality of medium carbon steel billets.

[0036] In summary, the molten steel used to form medium-carbon alloy steel billets exhibits both crack sensitivity and adhesion sensitivity under the harsh conditions of high hydrogen content and peritectic reaction. By controlling the composition of the mold slag, crystals mainly composed of "gun crystals" can be formed, but their precipitation morphology and proportion are controlled to be "fine, uniform, and appropriate," and may be supplemented with a small amount of other low-melting-point crystals, forming a composite slag film structure of "uniform fine microcrystals embedded in a glass matrix."

[0037] In some embodiments, the protective slag comprises, by mass percentage, the following chemical components: CaO: 36.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.49%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe2O3: 0.55%~1.15%, Fe2O3: 0.55%~1.15%. 3: 0~0.8%, C 固 3.45%~5.45%, with the balance being unavoidable impurities.

[0038] In some embodiments, the basicity of the crystallizer protective slag is 1.25 to 1.45. Exemplarily, the basicity of the crystallizer protective slag can be 1.25, 1.30, 1.35, 1.40, 1.45, etc.

[0039] Formula for calculating alkalinity R: The basicity R of the protective slag (or furnace slag) is calculated using the mass percentages of calcium oxide and silicon dioxide.

[0040] With alkalinity within the above range, relative to the medium carbon steel formed by the molten steel of this application, the thickness of the precipitated material in the solid slag film in the crystallizer channel can be reduced, thereby achieving rapid heat transfer in the crystallizer; the total thickness of the solid slag film can be reduced, and within a certain range of the crystallizer channel, the solid slag film can be reduced and the liquid slag film can be increased, thereby reducing the friction between the solidified billet shell and the copper plate in the crystallizer.

[0041] In some embodiments, the melting point of the crystallizer protective slag is 1143~1173℃. Optionally, the melting point is 1143, 1144, 1145, 1146, 1147, 1148, 1149, 1150, 1151, 1152, 1153, 1154, 1155, 1156, 1157, 1158, 1159, 1160, 1161, 1162, 1163, 1164, 1165, 1166, 1167, 1168, 1169, 1170, 1171, 1172, 1173℃, etc.

[0042] In some embodiments, the viscosity of the mold flux at 1300°C is 0.08~0.10 Pa·s. The viscosity of the mold flux at 1300°C can be 0.08 Pa·s, 0.085 Pa·s, 0.09 Pa·s, 0.091 Pa·s, 0.095 Pa·s, 0.10 Pa·s, etc. By setting the mold flux to have a suitable melting point and viscosity, the consumption of the mold flux is increased, ensuring the thickness of the liquid slag film in the mold flux channel, achieving effective lubrication, and preventing sticking and leakage of steel.

[0043] Viscosity is a physical indicator representing the mobility of structural micro-elements in molten slag, specifically, the ability of molten slag to flow into the gap between the billet and the mold under certain temperature and shear force. Viscosity primarily depends on the casting speed; therefore, it can be controlled to be 0.1 ≤ η·Vc ≤ 2.0.

[0044] In the formula: η represents the viscosity of the protective slag at 1300℃, in Pa·S; Vc represents the casting speed during continuous casting in the crystallizer, in m / min.

[0045] Crystals appeared near the transition temperature of the protective slag, confirming that crystallization is the main reason for the transition temperature of the protective slag.

[0046] In some embodiments, the transition temperature of the mold flux is 1000~1050℃. Optionally, the transition temperature of the mold flux can be 1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1019, 1020, 1021, 1022, or 1023℃. Temperatures range from 1024 to 1050℃.

[0047] Break temperature of mold flux: refers to the temperature at which the viscosity-temperature curve of the mold flux undergoes a significant change, that is, the temperature at which it changes from Newtonian fluid behavior to higher viscosity. It is usually related to the beginning of crystal precipitation in the mold flux and is the temperature at which the "solidification-like" behavior of the molten slag begins, affecting slag film lubrication and heat transfer.

[0048] In some embodiments, the crystallization temperature of the mold flux is 1010~1030℃. Optionally, the crystallization temperature of the mold flux is 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1019, 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027, 1028, 1029, or 1030℃.

[0049] Crystallization temperature of the mold flux: This is generally defined as the temperature at which crystals begin to precipitate in large quantities when the mold flux cools (measured using DTA / TTT, etc.). It affects the crystallinity of the slag film, and consequently, its heat transfer and lubrication properties. The crystallization temperature directly affects the ratio of the glassy phase to the crystalline phase, thus controlling the heat flow stability between the mold and the billet shell and avoiding inhomogeneity of the billet shell caused by local thermal fluctuations. Especially for crack-sensitive steel grades, adjusting these two temperatures during continuous casting can optimize the balance between lubrication and heat transfer, thereby improving the surface quality of the billet and preventing leaks and cracks.

[0050] In some embodiments, the raw materials for the mold flux include: pre-melted material, glass powder, manganese carbonate, fluorite, sodium fluoride, cryolite, lithium carbonate, and carbon black. The mold flux is obtained by proportioning the above raw materials according to the chemical composition of the mold flux. Carbon black, compared to other carbonaceous materials, can control the melting rate and melt structure of the mold flux due to its excellent skeletal effect, enabling the liquid slag to flow uniformly, rapidly, and appropriately into the gap between the billet shell and the mold, improving billet quality and ensuring a large liquid slag thickness.

[0051] Secondly, embodiments of this application provide a method for preparing a medium-carbon alloy steel billet, comprising the following steps: S10: Provide a mold flux according to the first aspect to be added to the surface of the molten steel in the mold; S20: The crystallizer is continuously cast at a casting speed of 1.3~1.5m / min to obtain a medium carbon alloy steel billet. The cooling rate during the continuous casting process is 1.1~1.3L / kg, and the deviation of the cooling rate is ≤0.2L / kg.

[0052] Optionally, the casting speed can be 1.30 m / min, 1.35 m / min, 1.40 m / min, 1.45 m / min, 1.50 m / min, etc. Optionally, the cooling rate during the continuous casting process can be 1.10, 1.15 L / kg, 1.20 L / kg, 1.25 L / kg, 1.30 L / kg, etc.

[0053] A cooling rate of 1.1~1.3 L / kg can be understood as the amount of cooling water used per kilogram of molten steel during continuous casting or casting in the crystallizer. This cooling process control, while keeping the deviation of the cooling rate within the above range, can match the mold flux in the crystallizer, which is beneficial to the uniformity of cooling and improves the surface quality of the continuously cast billet.

[0054] Medium carbon alloy steel billets can be understood as continuously cast billets formed by continuous casting or pouring.

[0055] In continuous casting, the mold flux does not merely serve a covering or lubricating function. It continuously evolves through the liquid, semi-crystalline, and crystalline phases. Its melting point, viscosity, transition temperature, and crystallization temperature collectively determine the formation mode, thickness, and heat transfer characteristics of the slag film, directly influencing the growth rhythm and stability control of the primary steel shell. The characteristics of the mold flux are also dynamically related to the casting speed and cooling conditions. The residence time of the molten steel in the mold, the solidification rate and heat flux distribution of the primary shell, and the time window for slag film formation and evolution are closely related to the casting stretching and cooling conditions.

[0056] If the melting point and transition temperature of the protective slag are too high, the slag will not have enough time to melt and spread under high casting speed conditions, resulting in lubrication failure.

[0057] If the crystallization temperature and cooling rate are not matched, the slag film crystallization will occur prematurely or delayed, causing abrupt changes in heat transfer and leading to longitudinal cracks or abnormal oscillation marks. Matching the slag film crystallization behavior with the cooling intensity avoids abrupt changes in heat flux density, maintains a continuous and stable liquid slag layer at different drawing speeds, stabilizes the initial shell thickness growth rate, reduces stress concentration, and suppresses longitudinal cracks, abnormal oscillation marks, and the tendency for steel leakage.

[0058] The performance of the protective slag, or the casting speed and cooling rate in the continuous casting process, is based on the dynamic evolution mechanism of slag film formation, crystallization, heat transfer and lubrication in the crystallizer. The synergistic control relationship between the key temperature parameters of the protective slag and the casting speed and cooling rate has been systematically established.

[0059] If the cooling rate during continuous casting is lower than the minimum cooling rate, the billet shell will be thinner and the risk of sticking will increase; if the cooling rate during continuous casting is higher than the maximum cooling rate, the medium carbon steel will have concentrated thermal stress and be prone to longitudinal cracking.

[0060] In some embodiments, the molten steel comprises, by mass percentage, the following elements: C: 0.08%-0.16%, Si: 0.10%-0.20%, Mn: 0.90%-1.20%, P≤0.015%, S≤0.006%, Al: 0.02%-0.06%, Ti: 0.15%-0.30%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0061] In some embodiments, during continuous casting, a protective slag molten layer, a protective slag sintered layer, and protective slag powder are sequentially arranged on the surface of the molten steel in a direction away from the molten steel. The thickness of the protective slag powder is controlled to be 40-50 mm, and the consumption of the protective slag in the crystallizer is 0.30-0.50 kg / t of molten steel.

[0062] The protective slag molten layer and the protective slag sintered layer are both formed by protective slag powder.

[0063] For example, the thickness of the protective slag powder can be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 mm, etc. If the thickness is less than this, the protective slag powder layer formed is unstable and easily exposes the steel; if the thickness is greater than this, melting is delayed and lubrication fails. Therefore, this thickness is an important factor in the stability of molten steel in the crystallizer and the stability of the quality of the continuously cast billet.

[0064] Controlling the thickness of the protective slag powder layer and the consumption of protective slag in the crystallizer is beneficial to the formation of solid and liquid layers on the side wall of the crystallizer, which is conducive to the formation of the cast billet, while taking into account both the quality of the cast billet and production efficiency.

[0065] In some embodiments, a solid layer and a liquid layer formed by protective slag are sequentially disposed on the sidewall of the crystallizer. The solid layer is located on the side away from the molten steel, the thickness of the solid layer is 1~2 mm, and the thickness of the liquid layer is 0.1~0.2 mm.

[0066] Under the aforementioned casting speed and cooling conditions, controlling the thickness of the solid layer and the liquid layer can maintain a stable lubrication state within the crystallizer; ensure uniform heat transfer between the billet shell and the crystallizer wall; and reduce the risk of crystallizer adhesion caused by localized heat transfer anomalies. This is beneficial for the stable production of continuously cast billets and the surface quality of the billets.

[0067] Example The following specific embodiments illustrate this application. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0068] Examples 1-4 The mold flux used for medium carbon steel molten steel comprises the following chemical components by mass percentage: CaO: 35.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.51%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe2O3: 2.36%~1.15%, Fe2O3: 2.36%~1.15%, Fe2O3: 2.36%~1.15%, Fe2O3: 2.36%~1.15%, Fe2O3: 2.36%~1.15%, Fe2O3: 2.36%~1.36 ... 3: 0~0.8%, C 固 The content of carbonates and oxyacids in the crystallizer protective slag is 3.45%~5.45%, with the balance being unavoidable impurities. The total mass of carbonates and oxyacids in the crystallizer protective slag is ≤2%.

[0069] The basicity of the crystallizer protective slag is 1.25~1.45, the melting point of the protective slag is 1143~1173℃, the viscosity at 1300℃ is 0.08~0.10Pa·s, the transition temperature is 1000~1050℃, and the crystallization temperature is 1010~1030℃.

[0070] This application provides a method for preparing a medium-carbon alloy steel billet, comprising the following steps: S10: Provide a mold flux as described above for use on the surface of molten steel in the mold. The molten steel comprises the following chemical components by mass percentage: C: 0.08%-0.16%, Si: 0.10%-0.20%, Mn: 0.90%-1.20%, P≤0.015%, S≤0.006%, Al: 0.02%-0.06%, Ti: 0.15%-0.30%, N≤0.008%, with the balance being Fe and unavoidable impurities. S20: The crystallizer is continuously cast at a casting speed of 1.4 m / s to obtain a medium carbon alloy steel billet. The cooling rate during the continuous casting process is 1.2 L / kg, and the deviation of the cooling rate is within 0.15 L / kg.

[0071] During continuous casting, a solid layer and a liquid layer formed by protective slag are sequentially arranged on the side wall of the crystallizer. The thickness of the solid layer is 1~2mm and the thickness of the liquid layer is 0.1~0.2mm.

[0072] The mold fluxes for Examples 1-4 are shown in Table 1.

[0073] Comparative Examples 1-2 The difference between Comparative Examples 1 and 2 and Example 1 is that the chemical composition of the crystallizer protective slag is different, as shown in Table 1.

[0074] Table 1 Examples 6-7 The difference between Examples 6 and 7 and Example 1 is that the composition of the molten steel is different, as shown in Table 2.

[0075] Table 2 Comparative Examples 3-4 The difference between Comparative Examples 3 and 4 and Example 1 is that the composition of the molten steel is different, as shown in Table 2.

[0076] Examples 8-11 The difference between Examples 8-11 and Example 1 is as follows: In Example 8, the crystallizer was continuously cast at a casting speed of 1.5 m / s to obtain a medium-carbon alloy steel billet. In Example 9, the crystallizer was continuously cast at a casting speed of 1.3 m / s to obtain a medium-carbon alloy steel billet. In Example 10, the cooling rate during continuous casting was 1.17 L / kg, with a deviation of 0.12 L / kg. In Example 11, the cooling rate during continuous casting was 1.18 L / kg, with a deviation of 0.16 L / kg.

[0077] Comparative Examples 5-6 The difference between Comparative Examples 5 and 6 and Example 1 is that in Comparative Example 5, the crystallizer was continuously cast at a casting speed of 1.0 m / s, and the sum of the mass of carbonates and oxyacids in the mold flux used in Comparative Example 5 was 4.5%. In Comparative Example 6, the cooling rate during the continuous casting process was 0.8 L / kg, with a deviation of 0.12 L / kg.

[0078] Test section 1. In the examples and comparative examples, the alarm occurrence rate of the continuous casting process is determined by recording the interruption or stoppage phenomenon in the production process, and the steel leakage rate is calculated by recording the steel leakage phenomenon in the production process.

[0079] The steel leakage rate usually refers to the proportion of heats (or castings) with steel leakage occurring within a statistical period to the total number of casting heats (or castings).

[0080] 2. The surface quality of the medium carbon alloy steel billet is tested by a surface quality testing instrument.

[0081] 3. Original pass rate of medium carbon alloy steel billets: Measured by a surface quality inspector. Within the statistical period, the percentage of billets that directly meet quality standards and are delivered to the next process (such as steel rolling) without any scrapping, re-judgment, or rework, out of the total weight of all continuously cast billets produced in that period. The calculation formula is: .

[0082] The samples in the examples and comparative examples were subjected to performance testing, and the test results are shown in Table 3.

[0083] Table 3 Combining the data in Table 3 and Figures 3-4 As can be seen, compared with the comparative example, the liquid level in the crystallizer in this embodiment is good, the continuous casting production process is stable, and there are no abnormalities such as serious slag bars or sticking steel leakage. The surface and subsurface quality of the produced billet is good, with few surface longitudinal crack defects, and the original qualification rate of the billet is over 99%.

[0084] Figure 1 This is a schematic diagram of the structure of the liquid surface in the crystallizer provided in Embodiment 1 of this application. Figure 2 This is a schematic diagram of the crystallizer sidewall provided in Embodiment 1 of this application. From... Figure 1 and Figure 2 In the crystallizer 10, a protective slag molten layer 12, a protective slag sintered layer 13, and a protective slag powder 14 are sequentially arranged on the surface of the molten steel 11. On the sidewall of the crystallizer 10, a solid layer 15 and a liquid layer 16 are sequentially arranged in a direction away from the sidewall of the crystallizer 10. By controlling the composition of the protective slag in the crystallizer, it is beneficial to form a medium carbon alloy steel billet of good quality.

[0085] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A crystallizer protective slag, characterized in that, The mold flux is applied to the surface of the molten steel within the mold; by mass percentage, the mold flux comprises the following chemical components: CaO: 35.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.51%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe ... 3: 0~0.8%, C 固 The content of carbonates and oxyacids in the crystallizer protective slag is 3.45%~5.45%, with the balance being unavoidable impurities. The total mass of carbonates and oxyacids in the crystallizer protective slag is ≤5%.

2. The crystallizer protective slag according to claim 1, characterized in that, The protective slag, by mass percentage, comprises the following chemical components: CaO: 36.08%~39.08%, SiO2: 24.08%~28.08%, Li2O: 0.31%~0.49%, Na2O: 6.08%~8.08%, F: 8.33%~10.9%, Al2O3: 2.36%~3.36%, MgO: 0.55%~1.15%, Fe2O3: 0.55%~1.15%, Fe2O3: 0.55%~1.15%. 3: 0~0.8%, C 固 3.45%~5.45%, with the balance being unavoidable impurities.

3. The crystallizer protective slag according to claim 1, characterized in that, The basicity of the crystallizer protective slag is 1.25~1.45; the melting point of the crystallizer protective slag is 1143~1173℃; and the viscosity of the crystallizer protective slag at 1300℃ is 0.08~0.10 Pa·s.

4. The crystallizer protective slag according to claim 1 or 2, characterized in that, The transition temperature of the protective slag in the crystallizer is 1000~1050℃.

5. The crystallizer protective slag according to claim 1 or 2, characterized in that, The crystallization temperature of the protective slag in the crystallizer is 1010~1030℃.

6. The crystallizer protective slag according to claim 1 or 2, characterized in that, The raw materials for the crystallizer protective slag include: pre-melted material, glass powder, manganese carbonate, fluorite, sodium fluoride, cryolite, lithium carbonate, and carbon black.

7. A method for preparing a medium-carbon alloy steel billet, characterized in that, Includes the following steps: S10: The mold protective slag according to any one of claims 1 to 6 is introduced onto the surface of the molten steel in the mold; S20: The crystallizer is continuously cast at a casting speed of 1.3~1.5m / min to obtain a medium carbon alloy steel billet. The cooling rate of the continuous casting is 1.1~1.3L / kg, and the deviation of the cooling rate is ≤0.2L / kg.

8. The preparation method according to claim 7, characterized in that, The molten steel comprises the following elements by mass percentage: C: 0.08%-0.16%, Si: 0.10%-0.20%, Mn: 0.90%-1.20%, P≤0.015%, S≤0.006%, Al: 0.02%-0.06%, Ti: 0.15%-0.30%, N≤0.008%, with the balance being Fe and unavoidable impurities.

9. The preparation method according to claim 7 or 8, characterized in that, In the continuous casting process, a protective slag molten layer, a protective slag sintered layer, and protective slag powder are sequentially set on the surface of the molten steel in a direction away from the direction of the molten steel. The thickness of the protective slag powder is controlled to be 40~50mm, and the consumption of the protective slag in the crystallizer is 0.30~0.50kg / t of molten steel.

10. The preparation method according to claim 7 or 8, characterized in that, The sidewall of the crystallizer is provided with a solid layer and a liquid layer formed by the crystallizer protective slag. The solid layer is located on the side away from the molten steel. The thickness of the solid layer is 1~2mm and the thickness of the liquid layer is 0.1~0.2mm.

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