Mold flux for casting high-hydrogen-content medium-carbon steel molten steel and use thereof

Abstract

The application provides a crystallizer protection slag for casting high-hydrogen-content medium-carbon steel liquid steel and application thereof, wherein the chemical composition of the crystallizer protection slag has the following mass percentages: SiO2: 25-32%, CaO: 29-36%, Al2O3: 1-4%, MgO: 3-6%, Na2O: 7-12%, F: 6-10%, C 总 : 3-6%, MnO: 2-4%, Li2O: 0.5-1%, and the rest is other inevitable impurities. The crystallizer protection slag can significantly reduce the occurrence rate of crystallizer sticking alarm emergency speed reduction and the occurrence rate of leakage during continuous casting when used for casting high-hydrogen-content medium-carbon steel liquid steel. Thus, the high-hydrogen-content medium-carbon steel liquid steel can be directly subjected to continuous casting without additional dehydrogenation treatment, the production efficiency is improved, and the production cost is solved.

Description

Technical Field

[0001] This application relates to the field of continuous casting billet technology, specifically to a mold flux for casting high-hydrogen-content medium-carbon steel molten steel and its application. Background Technology

[0002] Adding scrap steel to the LF furnace can significantly reduce iron consumption and maximize steelmaking capacity and efficiency. However, the rust (xFeO·rFe3O4·2H2O) on the surface of the added scrap steel will increase the hydrogen content in the molten steel. Combined with rainy weather, the hydrogen content in the molten steel can reach as high as 7-14 ppm. The high hydrogen content in the molten steel will cause frequent adhesion alarms and emergency speed reductions. In severe cases, it can lead to serious production accidents such as steel leakage due to adhesion.

[0003] When medium carbon steel solidifies below its peritectic point, it produces a peritectic γ phase and excess liquid, thus exhibiting both crack susceptibility and adhesion susceptibility. In existing processes for casting medium carbon steels such as Q235B, Q355B, and USIBOR1500 with hydrogen content ranging from 7 to 14 ppm, the occurrence rate of adhesion alarms and emergency speed reductions in the continuous casting mold reaches 21.82%, and the incidence of adhesion-induced steel leakage reaches 0.536%, severely impacting the smooth operation of continuous casting production and product quality. Therefore, current technologies generally dehydrogenate the medium carbon steel before continuous casting; however, this significantly reduces production efficiency and increases production costs.

[0004] There is currently no mold flux for casting high-hydrogen-content medium-carbon steel molten steel. Summary of the Invention

[0005] This application provides a mold flux for casting high-hydrogen-content medium-carbon steel and its application. Using this mold flux to directly continuously cast high-hydrogen-content medium-carbon steel can effectively solve the technical problems of high incidence of sticking alarm and emergency speed reduction in continuous casting molds, and high incidence of sticking and steel leakage.

[0006] In a first aspect, this application provides a mold flux for casting high-hydrogen-content medium-carbon steel molten steel, the mass percentage of which is:

[0007] SiO2: 25%–32%,

[0008] CaO: 29%–36%,

[0009] Al2O3: 1%–4%,

[0010] MgO: 3%–6%,

[0011] Na2O: 7%–12%,

[0012] F: 6%–10%,

[0013] C 总 3% to 6%,

[0014] MnO: 2%–4%,

[0015] Li2O: 0.5%–1%,

[0016] The remainder consists of other unavoidable impurities.

[0017] In the technical solution of this application, 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 high-hydrogen-content medium-carbon steel can significantly reduce the incidence of mold sticking alarms and emergency speed reductions, as well as the rate of steel leakage during continuous casting. Therefore, it is possible to directly continuously cast high-hydrogen-content medium-carbon steel without additional dehydrogenation treatment, improving production efficiency and simultaneously reducing production costs.

[0018] In some embodiments of this application, the mass percentage of the chemical composition of the crystallizer protective slag is as follows:

[0019] SiO2: 26%–28%,

[0020] CaO: 31%–34%,

[0021] Al2O3: 2%–3%,

[0022] MgO: 4%–5%,

[0023] Na2O: 8%–10%,

[0024] F: 8%–10%,

[0025] C 总 3% to 6%,

[0026] MnO: 2%–3%,

[0027] Li2O: 0.5%–1%,

[0028] The remainder consists of other unavoidable impurities.

[0029] In some embodiments of this application, the basicity of the crystallizer protective slag is 1.02 to 1.22;

[0030] Optionally, the melting point of the crystallizer protective slag is 1010-1070℃, and the viscosity of the crystallizer protective slag at 1300℃ is 0.07-0.11 Pa·s.

[0031] In some embodiments of this application, the transition temperature of the crystallizer protective slag is 1070–1130°C.

[0032] In some embodiments of this application, 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.

[0033] Secondly, this application provides a method for preparing a mold flux, comprising the following steps:

[0034] S10: Provide raw materials prepared according to the chemical composition of the crystallizer protective slag according to any embodiment of the first aspect;

[0035] S20: The raw materials are mixed, pre-melted, cooled, and ground to obtain a powder;

[0036] S30: The grinding material is granulated to obtain the crystallizer protective slag.

[0037] In the technical solution of this application, a pre-melting method is used to prepare a mold protective slag with the chemical composition of any embodiment of the first aspect. The mold protective slag obtained in this way has good melting uniformity, fast slag formation speed, and no partial melting phenomenon. The mold protective slag obtained by this method is more conducive to improving the quality of the cast billet and the smooth progress of the process.

[0038] Thirdly, this application provides a method for preparing medium carbon steel billets, comprising the following steps:

[0039] Medium carbon steel billets are obtained by continuous casting of molten medium carbon steel using the mold flux prepared according to any embodiment of the first aspect or the preparation method described in any embodiment of the second aspect.

[0040] In the technical solution of this application, the mold flux prepared by the method of any embodiment of the first aspect or the preparation method of any embodiment of the second aspect is used to continuously cast medium carbon steel molten steel. During the continuous casting process, the occurrence rate of mold sticking alarm emergency speed reduction and the occurrence rate of steel leakage are low, the production efficiency is better, and there is no need to dehydrogenate the molten steel before continuous casting, resulting in lower cost.

[0041] In some embodiments of this application, the molten medium carbon steel contains 0.0007% to 0.0014% hydrogen by mass and 0.16% to 0.30% carbon by mass.

[0042] In some embodiments of this application, during the continuous casting process, the thickness of the liquid slag in the mold protective slag is 10-12 mm, and the consumption of the mold protective slag is 0.38-0.45 kg / t of molten steel.

[0043] In some embodiments of this application, during the continuous casting process, the crystallization temperature of the mold flux is 1050-1100°C, which is lower than the transition temperature, and the crystallization ratio of the mold flux is 40%-60%. Detailed Implementation

[0044] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0047] To save costs, scrap steel is added during the refining of molten steel using an LF furnace. However, the rust in the scrap steel increases the hydrogen content in the molten steel, and rainy weather can further raise the hydrogen content to 7–14 ppm. On the other hand, during the continuous casting of medium carbon steel, when the steel solidifies below the peritectic point, peritectic γ-phase and excess liquid are produced, making it susceptible to both cracking and adhesion. Generally, in existing technologies, the slag used in the continuous casting of medium carbon steel has high basicity and viscosity, resulting in a high crystallization rate and crystal ratio, more uniform heat transfer, and thus reduced longitudinal crack defects.

[0048] The inventors discovered that when casting medium-carbon steel molten steel with high hydrogen content, although the longitudinal crack defect is low when using traditional medium-carbon steel crystallizer continuous casting slag, the occurrence rate of crystallizer sticking alarm and emergency speed reduction and the occurrence rate of steel leakage are high during the continuous casting process, which seriously affects the smooth progress of production.

[0049] Specifically, during the casting of medium carbon steel with hydrogen content of 7-14 ppm, such as Q235B, Q355B, and USIBOR1500, at Lianggong Steel, the occurrence rate of sticking alarm and emergency speed reduction in the continuous casting crystallizer reached 21.82%, and the occurrence rate of sticking and steel leakage reached 0.536%, which seriously affected production efficiency and production costs.

[0050] Therefore, in response to the above problems, the inventors provide a mold protective slag for casting high-hydrogen-content medium-carbon steel molten steel and its application.

[0051] In a first aspect, this application provides a mold flux for casting high-hydrogen-content medium-carbon steel molten steel, the mass percentage of which is:

[0052] SiO2: 25%–32%,

[0053] CaO: 29%–36%,

[0054] Al2O3: 1%–4%,

[0055] MgO: 3%–6%,

[0056] Na2O: 7%–12%,

[0057] F: 6%–10%,

[0058] C 总 3% to 6%,

[0059] MnO: 2%–4%,

[0060] Li2O: 0.5%–1%,

[0061] The remainder consists of other unavoidable impurities.

[0062] In the technical solution of this application, by controlling the mass percentage of each chemical component in the mold flux, a mold flux with suitable basicity, melting point, viscosity, and transition temperature is obtained. Using this mold flux to cast high-hydrogen-content medium-carbon steel can significantly reduce the incidence of mold sticking alarms and emergency speed reductions, as well as the rate of steel leakage during continuous casting. Therefore, it is possible to directly continuously cast high-hydrogen-content medium-carbon steel without additional dehydrogenation treatment, improving production efficiency and simultaneously reducing production costs.

[0063] In the technical solution of this application, the design idea of ​​each chemical component of the mold flux is to reduce the impact of high hydrogen content on the continuous casting process by improving the basicity, melting point, viscosity and transition temperature of the mold flux, thereby determining the mass percentage of each chemical component of the mold flux.

[0064] During continuous casting, as the temperature of the molten steel decreases, it begins to solidify. The saturated solubility of hydrogen in the molten steel decreases, and hydrogen in the molten steel accumulates from the solidification front to the surface of the molten steel, and then enters the liquid protective slag layer. Gaseous hydrogen does not dissolve in the liquid protective slag, but it is likely to be captured in the form of hydrogen bubbles. The amount of hydrogen escaping from the molten steel increases, which in turn leads to an increase in the hydrogen content in the liquid protective slag. The hydrogen in the slag appears in the form of micropores, which increases the thermal resistance of the protective slag film layer and the viscosity of the liquid protective slag. At the same time, because the basicity and viscosity of the protective slag for medium carbon steel crystallization in the existing technology are relatively high, the heat conduction of the crystallizer is reduced and the lubrication performance of the protective slag is reduced. This makes it easy for crystallizer sticking alarms, emergency speed reductions, and steel leakage to occur.

[0065] Therefore, based on the above analysis, when casting medium carbon steel with high hydrogen content, the basicity and viscosity of the protective slag used for medium carbon steel crystallization in the prior art should be reduced to ensure appropriate heat conduction of the crystallizer and appropriate lubricity of the protective slag. This will reduce the occurrence of crystallizer sticking alarms, emergency speed reductions, and steel leakage, while ensuring that the medium carbon steel billet does not develop surface longitudinal cracks.

[0066] On the other hand, as continuous casting continues, the hydrogen content in the protective slag gradually increases, which may lead to the fusion of hydrogen micropores into larger bubbles. Since the thermal conductivity of bubbles is significantly lower than that of the protective slag, uneven heat transfer may occur, further resulting in surface longitudinal cracks in medium carbon steel billets, and in severe cases, even steel leakage. To address this problem, the inventors conceived of lowering the melting point of the protective slag, thereby increasing the renewal rate of the liquid slag film and ensuring that too many hydrogen micropores in the liquid slag film do not fuse, thus preventing surface longitudinal cracks in the medium carbon steel billets.

[0067] Based on the above ideas, the inventors controlled the basicity of the mold flux by adjusting the mass ratio of SiO2 to CaO. Higher CaO content resulted in higher basicity of the flux. Simultaneously, CaO disrupted the silicate network structure, reducing the viscosity of the molten flux, lowering steric hindrance for ion migration, increasing the crystallization temperature, increasing thermal resistance, and raising the crystallization rate. Considering the influence of hydrogen content during casting, to reduce the thermal resistance of the mold flux and increase the glassy proportion, the mass percentages of SiO2 and CaO were set to 25%–32% and 29%–36%, respectively.

[0068] Al₂O₃ in the protective slag can combine with oxygen ions to form complex anions, increasing the chain or network structure formed by the composite silicon-oxygen ions, making the silicate slag structure more compact and increasing the viscosity of the protective slag. This increases the steric hindrance for the migration of ions required for crystal formation, thus lowering the crystallization temperature of the protective slag. Based on the requirements for casting high-hydrogen-content medium-carbon steel, the mass percentage of Al₂O₃ in the protective slag is set to 1%–4%.

[0069] MgO, Na2O, F, MnO, and Li2O act as fluxes and fluxes, reducing the viscosity and melting point of the protective slag. The specific content of each component is adjusted according to the needs of casting high-hydrogen-content carbon steel molten steel. The mass percentages of MgO, Na2O, F, MnO, and Li2O are set to 3%–6%, 7%–12%, 6%–10%, 2%–4%, and 0.5%–1%, respectively, to obtain a mold protective slag with lower viscosity and lower melting point. This improves the slag consumption of the protective slag, increases the renewal rate of the liquid slag film, enhances the lubrication performance of the protective slag, and also helps control longitudinal cracks on the surface of the cast billet.

[0070] In continuous casting, carbon in the protective slag plays a crucial role in the framework and regulating its melting characteristics. When the protective slag comes into contact with molten steel, the carbon in it gradually burns, causing the slag to melt and form a liquid slag layer. As the amount of carbon material increases, the melting rate decreases. Melting speed is a critical characteristic of the protective slag and should be maintained at an appropriate value during production. If melting is too fast, the powdery slag layer is difficult to maintain, resulting in poor insulation; if melting is too slow, the liquid slag layer is too thin, leading to poor inclusion absorption and deterioration of the billet surface quality. Based on the requirements for casting high-hydrogen-content medium-carbon steel, the carbon content in the protective slag... 总 The mass percentage is set at 3% to 6%.

[0071] In some embodiments of this application, the mass percentage of the chemical composition of the crystallizer protective slag is as follows:

[0072] SiO2: 26%–28%,

[0073] CaO: 31%–34%,

[0074] Al2O3: 2%–3%,

[0075] MgO: 4%–5%,

[0076] Na2O: 8%–10%,

[0077] F: 8%–10%,

[0078] C 总 3% to 6%,

[0079] MnO: 2%–3%,

[0080] Li2O: 0.5%–1%,

[0081] The remainder consists of other unavoidable impurities.

[0082] In some of the above embodiments, the chemical composition of the mold flux is further optimized so that when it is used to cast medium carbon steel with high hydrogen content, it is less likely to cause mold sticking alarms, emergency speed reduction and steel leakage, while also controlling the defects of longitudinal cracks on the surface of medium carbon steel billets.

[0083] In some embodiments of this application, the basicity of the crystallizer protective slag is 1.02 to 1.22;

[0084] Optionally, the melting point of the mold flux is 1010–1070℃, and the viscosity of the mold flux at 1300℃ is 0.07–0.11 Pa·s.

[0085] In some of the above embodiments, the basicity of the mold flux is 1.02 to 1.22, which is lower than that of the mold flux used for medium carbon steel in the prior art. This is more conducive to reducing the thermal resistance of the mold flux and preventing the formation of hydrogen micropores in the mold flux layer due to hydrogen precipitation in the molten steel. This would lead to a further increase in the thermal resistance of the mold flux, an increase in the crystallization rate, and ultimately result in the occurrence of mold sticking alarm, emergency speed reduction and steel leakage.

[0086] Furthermore, the melting point of the mold flux is 1010–1070℃, and the viscosity at 1300℃ is 0.07–0.11 Pa·s. It should be noted that the melting point of the mold flux in this application refers to the hemispherical point temperature. Similarly, it has a lower melting point and viscosity than the mold flux used for medium carbon steel in the prior art. This is to increase the slag consumption of the mold flux during continuous casting, increase the renewal rate of the liquid slag film, and allow the liquid slag film containing hydrogen micropores to flow out quickly, preventing the hydrogen micropores from merging into hydrogen bubbles, which would lead to uneven heat transfer in the mold flux layer and cause longitudinal cracks on the surface of the medium carbon steel billet.

[0087] In some embodiments of this application, the transition temperature of the crystallizer protective slag is 1070–1130°C.

[0088] In some of the above embodiments, the transition temperature mentioned in this application refers to the temperature at which the viscosity of the protective slag rapidly increases when the temperature drops to a certain level, and the temperature at which the viscosity begins to increase dramatically is the transition temperature. When the slag temperature is higher than the transition temperature, the viscosity of the protective slag changes less with temperature; conversely, the viscosity increases and the slag loses its flowability when the temperature is lower. The transition temperature of the mold protective slag is 1070–1130°C. The transition temperature of the protective slag used for medium carbon steel in the prior art is even lower, which can provide a thicker liquid slag layer with lubricating ability. As a result, the liquid slag layer can accommodate a larger amount of hydrogen micropores. On the one hand, this can prevent the fusion of hydrogen micropores in the liquid slag layer; on the other hand, it can also prevent the crystallizer sticking alarm, emergency speed reduction, and steel leakage caused by the increase in viscosity of the liquid slag layer due to hydrogen micropores.

[0089] In some embodiments of this application, 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.

[0090] In some of the above embodiments, the raw materials are commonly used for preparing mold flux. The pre-melted material is the main raw material for the mold flux, serving as the primary source of SiO2, CaO, MgO, Na2O, and F. Glass powder provides SiO2 and Al2O3, manganese carbonate provides MnO, fluorite, sodium fluoride, and cryolite provide F, lithium carbonate provides Li2O, and carbon black provides C. The mold flux is obtained by proportioning the above raw materials according to the chemical composition of the mold flux. Compared to other carbonaceous materials, carbon black, with its excellent skeletal effect, can control the melting rate and melt structure of the mold flux, 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.

[0091] In some embodiments of this application, the raw materials for the crystallizer protective slag, by mass percentage, include:

[0092] Premelted material 60.0%–70.0%, glass powder 5.0%–9.0%, manganese carbonate 2.0%–4.0%, fluorite 10.0%–15.0%, lithium carbonate 2.0%–3.0%, sodium fluoride 3.0%–5.0%, cryolite 2.0%–4.0%, carbon black 1.0%–2.0%;

[0093] The chemical composition of the pre-melted material is as follows by mass percentage: SiO2: 30%–32%, CaO: 42%–44%, Na2O: 7.5%–8%, F: 8%–8.5%, MgO: 7%–8%, with the balance being other unavoidable impurities.

[0094] In some of the above embodiments, the raw materials for the mold protective slag are calculated based on the chemical composition of the required mold protective slag and the types of each raw material. The raw materials are then proportioned accordingly to obtain a mold protective slag for casting high-hydrogen-content medium-carbon steel molten steel.

[0095] Secondly, this application provides a method for preparing a mold flux, comprising the following steps:

[0096] S10: Provide raw materials prepared according to the chemical composition of the crystallizer protective slag according to any embodiment of the first aspect;

[0097] S20: The raw materials are mixed, pre-melted, cooled, and ground to obtain powder;

[0098] S30: Granulate the ground material to obtain crystallizer protective slag.

[0099] In the technical solution of this application, a pre-melting method is used to prepare a mold protective slag with the chemical composition of any embodiment of the first aspect. The mold protective slag obtained in this way has good melting uniformity, fast slag formation speed, and no partial melting phenomenon. The mold protective slag obtained by this method is more conducive to improving the quality of the cast billet and the smooth progress of the process.

[0100] In some embodiments of this application, step S20 specifically includes:

[0101] The raw materials are crushed to 100-150 mesh, dried at 200-250℃ and mixed evenly. The mixed raw materials are pre-melted at 1400-1460℃ and kept at that temperature for 20-30 minutes to obtain pre-melted raw materials. The pre-melted raw materials are cooled and then ground to obtain grinding powder with a particle size of 1-5μm.

[0102] In some embodiments of this application, step S30 specifically includes:

[0103] The ground material is fed into a spray granulation tower to obtain hollow particles with a particle size of 300-360 mesh, which are used as protective slag for the crystallizer.

[0104] In some of the above embodiments, the hollow structure of the mold flux has better heat insulation effect, can spread well on the surface of molten steel, thus giving the flux a good heat insulation effect and preventing the molten steel from being oxidized by air.

[0105] Thirdly, this application provides a method for preparing medium carbon steel billets, comprising the following steps:

[0106] Medium carbon steel billets are obtained by continuous casting of molten medium carbon steel using a mold flux prepared according to any embodiment of the first aspect or the preparation method of any embodiment of the second aspect.

[0107] In the technical solution of this application, the mold flux prepared by the method of any embodiment of the first aspect or the preparation method of any embodiment of the second aspect is used to continuously cast medium carbon steel molten steel. During the continuous casting process, the occurrence rate of mold sticking alarm emergency speed reduction and the occurrence rate of steel leakage are low, the production efficiency is better, and there is no need to dehydrogenate the molten steel before continuous casting, resulting in lower cost.

[0108] In some embodiments of this application, the mass percentage of hydrogen in the molten medium carbon steel is 0.0007% to 0.0014%, and the mass percentage of carbon is 0.16% to 0.30%.

[0109] In some of the above embodiments, when continuously casting medium carbon steel with the above-mentioned hydrogen and carbon content in the prior art, it is easy to encounter crystallizer sticking alarms, emergency speed reductions, and steel leakage. However, the method provided in this application is particularly suitable for casting medium carbon steel with high hydrogen content. During the process, it is less likely to encounter crystallizer sticking alarms, emergency speed reductions, and steel leakage, which can ensure the smooth progress of the process. At the same time, it avoids the process of dehydrogenating the molten steel before continuous casting, thereby avoiding logistics chaos in the steel plant.

[0110] In some embodiments of this application, during continuous casting, the thickness of the liquid slag in the mold protective slag is 10-12 mm, and the consumption of the mold protective slag is 0.38-0.45 kg / t of molten steel.

[0111] In some of the above embodiments, by using the mold flux provided in the first and second aspects, it is possible to ensure that the slag thickness is 10-12 mm during continuous casting. This ensures good lubricity even with hydrogen micropores in the slag layer, preventing mold sticking alarms, emergency speed reductions, and steel leakage. Simultaneously, the consumption of the mold flux is 0.38-0.45 kg / t of molten steel to ensure the renewal rate of the liquid slag film, thereby preventing uneven heat transfer caused by hydrogen micropore fusion and ultimately preventing longitudinal cracks on the surface of medium carbon steel slabs.

[0112] In some embodiments of this application, during continuous casting, the crystallization temperature of the mold flux is 1050-1100°C, which is lower than the turning point temperature, and the crystallization ratio of the mold flux is 40%-60%.

[0113] In some of the above embodiments, the protective slag film generally has a solid slag film and a liquid slag film. The solid slag film contains a glass layer and a crystalline layer. Due to the presence of crystals, the thermal resistance of the crystalline layer is relatively high. Therefore, adjusting the proportion of the crystalline layer in the slag film can regulate its heat transfer. When processing high-hydrogen medium-carbon steel molten steel, the presence of hydrogen micropores further increases the thermal resistance of the slag film, which can easily lead to crystallizer sticking alarms, emergency speed reductions, and steel leakage. Therefore, it is necessary to control the proportion of the crystalline layer in the slag film, i.e., reduce the crystallization ratio to reduce thermal resistance. By adjusting the transition temperature of the protective slag, it is easier for the protective slag to transform into a glassy state, increasing the proportion of the glassy state in the protective slag, and thus reducing the crystallization ratio of the protective slag, a suitable thermal resistance of the protective slag can be obtained, thereby reducing the occurrence rate of crystallizer sticking alarms, emergency speed reductions, and steel leakage.

[0114] In addition, by adjusting carbonaceous materials, lowering the melting point, and increasing viscosity to increase slag consumption, the number of pores formed in the slag film due to hydrogen evolution during the solidification process of molten steel can be reduced.

[0115] The following examples illustrate in more detail the mold flux for casting high-hydrogen-content medium-carbon steel and its application, but this application is by no means limited to these examples.

[0116] Example 1

[0117] Preparation method of mold flux for casting high-hydrogen-content medium-carbon steel:

[0118] Weigh out the following components by mass percentage: 66.4% premelted material, 7.0% glass powder, 3.0% manganese carbonate, 10.0% fluorite, 7.0% sodium fluoride, 3.0% cryolite, 1.6% lithium carbonate, and 2.0% carbon black, as raw materials.

[0119] The chemical composition of the pre-melted material is as follows (mass percentage): SiO2: 30%, CaO: 44%, Na2O: 7.5%, F: 8.5%, MgO: 8%, with the balance being other unavoidable impurities.

[0120] The raw materials are crushed to 120 mesh, dried at 220℃, mixed evenly, pre-melted at 1420℃, kept at the temperature for 30 minutes, cooled, and then ground into powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer with a particle size of 300 mesh.

[0121] The protective slag for crystallizer has an basicity of 1.16, a viscosity of 0.110 Pa·s at 1300℃, a melting point of 1065℃, a transition temperature of 1085℃, and the following mass percentage of its chemical composition:

[0122] SiO2: 26.8%,

[0123] CaO: 31.2%,

[0124] Al2O3: 2.5%,

[0125] MgO: 4.5%,

[0126] Na2O: 8.5%,

[0127] F: 8.2%,

[0128] Total C: 3.95%,

[0129] MnO: 3%,

[0130] Li2O: 0.55%,

[0131] The remainder consists of other unavoidable impurities.

[0132] The mold flux was used to continuously cast medium carbon steel of Q235B, Q355B, and USIBOR1500 series with hydrogen content of 0.0007-0.0014% and carbon content of 0.18-0.30%. During the continuous casting process, the occurrence rate of mold sticking alarm and emergency speed reduction was 3.78%, and the occurrence rate of steel leakage was 0.098%.

[0133] Example 2

[0134] Preparation method of mold flux for casting high-hydrogen-content medium-carbon steel:

[0135] Weigh out the following components by mass percentage: 68.0% premelted material, 6.8% glass powder, 2.0% manganese carbonate, 11.2% fluorite, 6.0% sodium fluoride, 2.5% cryolite, 2.0% lithium carbonate, and 1.5% carbon black, as raw materials.

[0136] The chemical composition of the pre-melted material is as follows (mass percentage): SiO2: 30%, CaO: 42%, Na2O: 7.5%, F: 8%, MgO: 7%, with the balance being other unavoidable impurities.

[0137] The raw materials are crushed to 100 mesh, dried at 220℃, mixed evenly, pre-melted at 1400℃, kept at the temperature for 20 minutes, cooled, and then ground into powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer with a particle size of 320 mesh.

[0138] The protective slag for crystallizer has an basicity of 1.19, a viscosity of 0.095 Pa·s at 1300℃, a melting point of 1070℃, a transition temperature of 1090℃, and the following mass percentage of its chemical composition:

[0139] SiO2: 27.9%,

[0140] CaO: 33.2%,

[0141] Al2O3: 2.2%,

[0142] MgO: 4.2%,

[0143] Na2O: 8.8%,

[0144] F: 8.8%,

[0145] C 总 3.3%,

[0146] MnO: 2.2%,

[0147] Li2O: 0.7%,

[0148] The remainder consists of other unavoidable impurities.

[0149] The mold flux was used to continuously cast medium carbon steel of Q235B, Q355B, and USIBOR1500 series with hydrogen content of 0.0007-0.0014% and carbon content of 0.18-0.30%. During the continuous casting process, the occurrence rate of mold sticking alarm and emergency speed reduction was 3.58%, and the occurrence rate of steel leakage was 0.076%.

[0150] Example 3

[0151] Preparation method of mold flux for casting high-hydrogen-content medium-carbon steel:

[0152] Weigh out the following components by mass percentage: 65.0% premelted material, 8.1% glass powder, 2.0% manganese carbonate, 12.0% fluorite, 6.0% sodium fluoride, 2.5% cryolite, 2.6% lithium carbonate, and 1.8% carbon black, as raw materials.

[0153] The chemical composition of the pre-melted material is as follows (mass percentage): SiO2: 31%, CaO: 43%, Na2O: 7.8%, F: 8.2%, MgO: 7.2%, with the balance being other unavoidable impurities.

[0154] The raw materials are crushed to 100 mesh, dried at 250℃, mixed evenly, pre-melted at 1410℃, kept at the temperature for 20 minutes, cooled and then ground to a powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer with a particle size of 320 mesh.

[0155] The protective slag for crystallizer protection has a basicity of 1.10, a viscosity of 0.108 Pa·s at 1300℃, a melting point of 1062℃, a transition temperature of 1077℃, and the following mass percentage of its chemical composition:

[0156] SiO2: 30.9%,

[0157] CaO: 34.0%,

[0158] Al2O3: 2.1%,

[0159] MgO: 4.1%,

[0160] Na2O: 8.7%,

[0161] F: 9.2%,

[0162] C 总 3.2%,

[0163] MnO: 2.1%,

[0164] Li2O: 0.95%,

[0165] The remainder consists of other unavoidable impurities.

[0166] The mold flux was used to continuously cast medium carbon steel of Q235B, Q355B, and USIBOR1500 series with hydrogen content of 0.0007-0.0014% and carbon content of 0.18-0.30%. During the continuous casting process, the occurrence rate of mold sticking alarm and emergency speed reduction was 2.62%, and the occurrence rate of steel leakage was 0.052%.

[0167] Comparative Example 1

[0168] Commercially available medium carbon steel crystallizer protective slag has a basicity of 1.25, a viscosity of 0.138 Pa·s at 1300℃, a melting point of 1127℃, and a transition temperature of 1163℃.

[0169] The commercially available medium carbon steel crystallizer protective slag was used to continuously cast Q235B, Q355B, and USIBOR1500 series medium carbon steel with hydrogen content of 0.0007-0.0014% and carbon content of 0.18-0.30%. During the continuous casting process, the occurrence rate of crystallizer sticking alarm and emergency speed reduction was 21.82%, and the occurrence rate of steel leakage was 0.536%.

[0170] As demonstrated in Examples 1-3 and Comparative Example 1, using the mold flux provided in this application for casting high-hydrogen-content medium-carbon steel significantly reduces the incidence of mold sticking alarms and emergency speed reductions, as well as the rate of steel leakage, during continuous casting. This ensures the smooth operation of the medium-carbon steel production process, eliminates the need for dehydrogenation treatment of the molten steel before continuous casting, improves the production efficiency of medium-carbon steel, and saves production costs for enterprises.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing medium carbon steel billets, characterized in that, Includes the following steps: Medium carbon steel billets are obtained by continuous casting of medium carbon steel molten steel using crystallizer protective slag, wherein the mass percentage of hydrogen in the medium carbon steel molten steel is 0.0007% to 0.0014%, and the mass percentage of carbon is 0.16% to 0.30%. The mass percentage of the chemical composition of the crystallizer protective slag is as follows: SiO2: 25%–32%, CaO: 29%–36%, Al2O3: 1%–4%, MgO: 3%–6%, Na2O: 7%–12%, F：6％～10％， C 总 ：3％～6％， MnO: 2%–4%, Li2O: 0.5%–1%, The remainder consists of other unavoidable impurities, wherein the basicity of the crystallizer protective slag is 1.1 to 1.22; the melting point of the crystallizer protective slag is 1010 to 1070°C; the viscosity of the crystallizer protective slag at 1300°C is 0.07 to 0.11 Pa·s; and the transition temperature of the crystallizer protective slag is 1070 to 1130°C.

2. The preparation method according to claim 1, characterized in that, Its chemical composition by mass percentage is: SiO2: 26%–28%, CaO: 31%–34%, Al2O3: 2%–3%, MgO: 4%–5%, Na2O: 8%–10%, F：8％～10％， C 总 ：3％～6％， MnO: 2%–3%, Li2O: 0.5%–1%, The remainder consists of other unavoidable impurities.

3. The preparation method according to claim 1, 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.

4. The preparation method according to claim 1, characterized in that, The method for preparing the crystallizer protective slag includes the following steps: S10: Raw materials for the chemical composition of the protective slag in the crystallizer; S20: The raw materials are mixed, pre-melted, cooled, and ground to obtain a powder; S30: The grinding material is granulated to obtain the crystallizer protective slag.

5. The preparation method according to claim 1, characterized in that, During continuous casting, the thickness of the liquid slag in the mold protective slag is 10-12 mm, and the consumption of the mold protective slag is 0.38-0.45 kg / t of molten steel.

6. The preparation method according to claim 1, characterized in that, During continuous casting, the crystallization temperature of the mold flux is 1050-1100℃, which is lower than the transition temperature, and the crystallization ratio of the mold flux is 40%-60%.