Heterogeneous carbon steel continuous casting mold flux and application thereof

Abstract

The application discloses a continuously cast mould flux for a shaped medium-carbon steel and application, wherein the continuously cast mould flux for the shaped medium-carbon steel has an alkalinity of 1.45-1.6, a melting point of 1160-1200 DEG C, a viscosity of 0.55-0.8 Pa.s at 1300 DEG C, a melting time of 32-40 s and a crystallization rate of 65-90%. The high alkalinity can ensure good adsorption and inclusion capacity, and meanwhile, the melting point of the mould flux is relatively high; the relatively high melting point can effectively ensure that a proper amount of liquid slag layer is melted when two water outlets pour molten steel under the condition of high liquid surface temperature and large liquid surface fluctuation; the viscosity can ensure that the thickness of the mould flux film between the liquid slag layer and the continuously cast mould is neither too thick nor too thin, and the mould flux can continuously flow in; and the crystallization rate can effectively control the thermal conductivity of the shaped medium-carbon steel at a meniscus, so that the heat transfer of each part of the shaped medium-carbon steel section is reduced, the temperature is relatively uniform, the shrinkage is relatively uniform, the stress is small, and the probability of crack generation is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of steelmaking auxiliary materials technology, and more specifically, to protective slag for continuous casting of carbon steel in shaped billets and its application. Background Technology

[0002] Due to the special characteristics of its cross-section, irregularly shaped billets have the following features:

[0003] 1. The cross-section of irregular billets is complex, and the heat dissipation conditions at various points on the cross-section are quite different. The web is a one-dimensional heat transfer plate, while the flanges are a two-dimensional heat transfer plate. Therefore, the temperature difference at various points on the cross-section is large. If the billet stays in the casting machine for too long, it will aggravate this temperature difference and easily cause crack defects.

[0004] 2. Since the irregular billet crystallizer has 8 faces, the requirements for the spreading performance of the protective slag are higher. This is because uneven thickness of the protective slag film in the crystallizer will lead to uneven cooling of the billet. Where the slag film is thicker, the billet shell is thinner and the strength is also poorer, making it easy to crack.

[0005] 3. Compared with other cast billets, the solidification structure of irregularly shaped billets has a more developed columnar crystal structure, and segregation is prone to occur between the coarse columnar crystals, in the web, and near the pouring point. During the solidification process, irregularly shaped billets are subjected to the combined effects of thermal stress, bulging stress, and mechanical stress. If these stresses exceed the plastic strength of the billet shell, initial cracks will occur in the weak parts of the billet shell.

[0006] 4. During the initial solidification of irregularly shaped billets in the crystallizer, micro-hot cracks are easily formed in the web and inner edge. If the hot cracks are not replenished by molten steel in time during the continued solidification of the billet, they will continue to expand under the action of thermal and mechanical stress, eventually extending to the surface of the billet shell to form surface cracks.

[0007] Due to the unique cross-sectional characteristics of shaped billets, continuous casting machines are among the most difficult to operate of all types. Currently, the continuous casting process for shaped billets is plagued by severe web cracking. While high-viscosity mold fluxes significantly improve web cracking, limitations in their physicochemical properties and raw materials mean that this type of flux, due to its thick sintered layer, easily forms slag rings, significantly impacting production flow. Ordinary high-basicity mold fluxes can meet production requirements, but they cannot effectively control web cracking. Furthermore, with increasing quality demands from downstream customers in the steel industry, existing continuous casting mold fluxes are unable to balance billet quality and production flow.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a protective slag for continuous casting of carbon steel in irregularly shaped billets and its application.

[0010] This invention is implemented as follows:

[0011] In a first aspect, the present invention provides a mold flux for continuous casting of carbon steel in shaped billets, with a basicity of 1.45-1.6, a melting point of 1160-1200℃, a viscosity of 0.55-0.8 Pa·s at 1300℃, a melting time of 32-40s, and a crystallization rate of 65-90%.

[0012] In an optional embodiment, the composition includes 30-36 parts by weight of CaO, 20-24 parts by weight of SiO2, 1.0-2.0 parts by weight of Fe2O3, 2.5-4 parts by weight of MgO, 8-13.5 parts by weight of Al2O3, 1-3 parts by weight of MnO, 3-5 parts by weight of R2O, 2.5-5 parts by weight of F, 1.44-2.52 parts by weight of B2O3, and 9-15 parts by weight of C, wherein R is Na or Li.

[0013] In an optional embodiment, the raw materials include 3-6 parts by weight of fluorite, 6.5-10.5 parts by weight of cement clinker, 1.5-3.5 parts by weight of industrial soda ash, 1.0-3.0 parts by weight of lithium carbonate, 1.0-2.5 parts by weight of imported carbon black, 1.5-2.5 parts by weight of Xinjiang carbon black, 8-14 parts by weight of earthy graphite, 0.5-2.5 parts by weight of sodium fluoride, 36.0-42.0 parts by weight of boron-containing premelted material, 6.0-10.0 parts by weight of calcite, 1.5-2.5 parts by weight of magnesia, 2.5-5.0 parts by weight of manganese carbonate, and 8.0-15.0 parts by weight of bauxite.

[0014] In an optional embodiment, the boron-containing premelted material contains 4-6 wt% boron oxide.

[0015] In an optional implementation, the mixture includes 2 parts by weight of imported carbon black, 2 parts by weight of Xinjiang carbon black, and 10 parts by weight of earthy graphite.

[0016] In an optional embodiment, the premelted material includes at least one of CaO, SiO2, Fe2O3, MgO, Al2O3, MnO, R2O, F, and C, and the premelted material also includes boron oxide.

[0017] Secondly, the present invention provides a method for continuous casting of carbon steel in irregularly shaped billets, using the protective slag described in any of the foregoing embodiments.

[0018] Thirdly, the present invention provides a carbon steel in a special-shaped billet, which is obtained by the method described in the foregoing embodiments.

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

[0020] This application sets the basicity at 1.45-1.6, the melting point at 1160-1200℃, the viscosity at 1300℃ at 0.55-0.8 Pa·s, the melting time at 32-40s, and the crystallization rate at 65-90%. The high basicity ensures good adsorption of inclusions, while also making the melting point of the protective slag relatively high. The relatively high melting point of the protective slag effectively ensures that a suitable amount of liquid slag layer is melted when pouring molten steel at both nozzles, under conditions of high liquid surface temperature and large liquid surface fluctuations. The viscosity of 0.55-0.8 Pa·s ensures that the thickness of the protective slag film between the billet and the crystallizer is neither too thick nor too thin, allowing for continuous flow. The crystallization rate of 65-90% effectively controls the thermal conductivity of the irregular billet at the meniscus, reducing heat transfer throughout the cross-section of the irregular billet, resulting in relatively uniform temperature, relatively uniform shrinkage, low stress, and a significantly reduced probability of cracking. Detailed Implementation

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

[0022] This embodiment provides a protective slag for continuous casting of carbon steel in special-shaped billets, with a basicity of 1.45-1.6, a melting point of 1160-1200℃, a viscosity of 0.55-0.8 Pa·s at 1300℃, a melting time of 32-40s, and a crystallization rate of 65-90%.

[0023] Regarding the design of the indicators, it should be noted that:

[0024] Basicity: In this application, the basicity of the protective slag is set at 1.45-1.6. Within this basicity range, the crystallization temperature of the protective slag is high, the crystallization ratio is large, and the glassy body is small, thereby reducing radiative heat transfer. In addition, the micropores and interfaces in the crystal body greatly weaken the lattice vibration, thereby weakening the heat conduction. This effectively solves the problem of web cracks caused by uneven heat transfer and stress concentration due to the complex cross-section of the irregular billet, the large temperature difference at various points on the cross-section, the high and wide flanges, and the thin web.

[0025] Melting temperature: Unlike ordinary slabs, shaped billets are mostly cast in a double-nozzle mode, and the heat exchange at the liquid surface of the crystallizer is more active than that of slabs. The melting temperature of carbon protective slag in general slabs is basically between 1080-1150℃, while the melting point of protective slag for shaped billets is higher than that for slabs. Taking all factors into consideration, this application sets the melting temperature at 1160-1200℃. Within this range, the liquid slag can flow quickly, appropriately and evenly into the gap between the billet shell and the crystallizer, maintaining a smooth liquid slag channel, and also obtaining protective slag with a higher transition temperature, thereby exerting the metallurgical effect of good lubrication and heat transfer control of the protective slag.

[0026] Viscosity: The slag film in contact with the billet shell exhibits viscous flow characteristics, which can be considered as fluid lubrication. Viscosity is an important factor affecting the lubrication effect of the protective slag. When the viscosity is low, the liquid slag will excessively form slag channels in some areas; while when the viscosity is high, the liquid slag will not flow smoothly into the meniscus, making it impossible to form a slag film of uniform thickness between the billet shell and the crystallizer, thus increasing the inhomogeneity of the billet shell. Both low and high viscosity protective slag will affect the uniformity of slag film formation, thereby affecting heat transfer and lubrication, leading to phenomena such as high friction, uneven liquid slag consumption, and unstable heat flow curves in shaped billets during casting. Therefore, it has characteristics similar to slabs. The viscosity of protective slag for ordinary slabs is mostly designed to be below 0.2, but due to the slower casting speed of shaped steel compared to slabs and the complex cross-section, this application sets the viscosity at 1300℃ to 0.55-0.8 Pa·s.

[0027] Crystallization rate: The crystallization rate is the percentage of crystals in the slag film. An excessively high crystal ratio will affect the lubrication effect of the slag film, while an excessively low crystal ratio will affect its heat transfer control effect. The protective slag for irregularly shaped billets inherently faces the challenge of simultaneously addressing both web cracking and lubrication. Considering the primary focus on resolving web cracking, and taking into account the inclusion of lithium oxide and boron oxide to refine grains and improve lubrication, this application sets the crystallization rate at 65-90%. Setting the crystallization rate within this range also maintains the glassiness (i.e., lubrication performance) of the protective slag, thus reasonably resolving the conflict between the two functions of lubrication and heat transfer control.

[0028] This application sets the basicity at 1.45-1.6, the melting point at 1160-1200℃, the viscosity at 1300℃ at 0.55-0.8 Pa·s, the melting time at 32-40s, and the crystallization rate at 65-90%. The high basicity ensures good adsorption of inclusions, while also making the melting point of the protective slag relatively high. The relatively high melting point of the protective slag effectively ensures that a suitable amount of liquid slag layer is melted when pouring molten steel at both nozzles, under conditions of high liquid surface temperature and large liquid surface fluctuations. The viscosity of 0.55-0.8 Pa·s ensures that the thickness of the protective slag film between the billet and the crystallizer is neither too thick nor too thin, allowing for continuous flow. The crystallization rate of 65-90% effectively controls the thermal conductivity of the irregular billet at the meniscus, reducing heat transfer throughout the cross-section of the irregular billet, resulting in relatively uniform temperature, relatively uniform shrinkage, low stress, and a significantly reduced probability of cracking.

[0029] In an optional embodiment, the composition includes 30-36 parts by weight of CaO, 20-24 parts by weight of SiO2, 1.0-2.0 parts by weight of Fe2O3, 2.5-4 parts by weight of MgO, 8-13.5 parts by weight of Al2O3, 1-3 parts by weight of MnO, 3-5 parts by weight of R2O, 2.5-5 parts by weight of F, 1.44-2.52 parts by weight of B2O3, and 9-15 parts by weight of C, wherein R is Na or Li.

[0030] Appropriate addition of fluorides, lithium oxide, borax and other components to the protective slag can make the crystallized protective slag have good density, a certain glassy state and good lubricity, and reduce the occurrence of poor lubrication problems that may be caused by excessive crystallization rate.

[0031] In an optional embodiment, the raw materials include 3-6 parts by weight of fluorite, 6.5-10.5 parts by weight of cement clinker, 1.5-3.5 parts by weight of industrial soda ash, 1.0-3.0 parts by weight of lithium carbonate, 1.0-2.5 parts by weight of imported carbon black, 1.5-2.5 parts by weight of Xinjiang carbon black, 8-14 parts by weight of earthy graphite, 0.5-2.5 parts by weight of sodium fluoride, 36.0-42.0 parts by weight of boron-containing premelted material, 6.0-10.0 parts by weight of calcite, 1.5-2.5 parts by weight of magnesia, 2.5-5.0 parts by weight of manganese carbonate, and 8.0-15.0 parts by weight of bauxite.

[0032] Using a pre-melted material containing 4-6% boron oxide as the base material, which has been treated in an electric furnace, the pre-melted material exhibits stable performance and fewer impurities. When using this boron-containing pre-melted material to produce protective slag, it can color the liquid slag film to a reddish-brown color, significantly reducing heat radiation and heat conduction, thus delaying heat transfer. The use of industrial soda ash, fluorite, sodium fluoride, lithium carbonate, and manganese carbonate as fluxes helps stabilize the performance of the protective slag. It is worth noting that lithium carbonate and manganese carbonate also help lower the melting point, and lithium carbonate further refines the slag film grains and improves the stability of the protective slag during use.

[0033] In an optional embodiment, the boron-containing premelted material contains 4-6 wt% boron oxide.

[0034] Existing technologies include adding B2O3 to protective slag to achieve its application. However, in actual production processes, limitations imposed by the protective slag manufacturing process mean that directly using borax, due to its poor water solubility, easily turns into white spheres upon heating during spray granulation, resulting in an excessive number of white spheres in the protective slag particles and thus affecting its performance. This application innovatively selects a boron-containing pre-melted material, which avoids the defect of white spheres easily formed by directly using borax. Furthermore, the pre-melted material has a more uniform composition, which is beneficial for improving the stability of the protective slag during use.

[0035] In an optional implementation, the mixture includes 2 parts by weight of imported carbon black, 2 parts by weight of Xinjiang carbon black, and 10 parts by weight of earthy graphite.

[0036] This application uses imported carbon black, Xinjiang carbon black, and earthy graphite. This composite carbon formulation significantly affects the three-layer structure of the protective slag: the liquid slag layer, the sintering layer, and the granular protective slag layer. The imported carbon black used has a large specific surface area, reaching 2.92 μm. 2 / g can effectively enhance the skeletal function of each component in the protective slag, enabling the protective slag to form a better three-layer structure after being added to the crystallizer, promoting the melting effect of the protective slag, significantly improving the heat preservation effect of the slag layer, reducing slag strip formation, obtaining a suitable melting rate, continuously providing liquid slag replenishment, and better ensuring the lubrication effect.

[0037] In this embodiment, by combining imported carbon black, Xinjiang carbon black, and earthy graphite, along with other components mentioned in the application, the thickness of the liquid slag layer can be maintained at approximately 6-10 mm. The amount of liquid slag layer filling between the billet and the crystallizer is kept within a reasonable range. If the liquid slag layer is too thick, it will affect the sintering layer and cause slag strips to form around the sintering layer. Too many slag strips will affect the liquid slag layer from reaching between the billet and the crystallizer. If the liquid slag layer is too thin, the amount of liquid slag layer filling between the billet and the crystallizer will be insufficient, which will easily cause the protective slag to stick.

[0038] In an optional embodiment, the premelted material includes at least one of CaO, SiO2, Fe2O3, MgO, Al2O3, MnO, R2O, F, and C, and the premelted material also includes boron oxide.

[0039] Pre-melted material is a material formed by melting raw materials such as fluorite and then quenching them in water to create small granules. Different pre-melted materials have different chemical compositions and contents due to the different raw materials added. Pre-melted materials can be selected by those skilled in the art based on their needs within the existing technology. After selecting a pre-melted material, those skilled in the art can add other raw materials to make up for any missing parts in the pre-melted material according to the composition ratio of the protective slag, thus obtaining a protective slag with a specified ratio. The advantages of using pre-melted materials are: the pre-melted material has been treated in an electric furnace, resulting in stable performance, fewer impurities, and full fusion of various substances, leading to a more uniform distribution of chemical composition and contributing to the overall stability of the protective slag's performance.

[0040] Using a pre-melted material containing 4-6% boron oxide as the base material, which has been treated in an electric furnace, the pre-melted material exhibits stable performance and fewer impurities. When using this boron-containing pre-melted material to produce protective slag, it can color the liquid slag film to a reddish-brown color, significantly reducing heat radiation and heat conduction, thus delaying heat transfer. The use of industrial soda ash, fluorite, sodium fluoride, lithium carbonate, and manganese carbonate as fluxes helps stabilize the performance of the protective slag. It is worth noting that lithium carbonate and manganese carbonate also help lower the melting point, and lithium carbonate further refines the slag film grains and improves the stability of the protective slag during use.

[0041] Secondly, the present invention provides a method for continuous casting of carbon steel in irregularly shaped billets, using the protective slag described in any of the foregoing embodiments.

[0042] Thirdly, the present invention provides a carbon steel in a special-shaped billet, which is obtained by the method described in the foregoing embodiments.

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

[0044] Example 1

[0045] A protective slag for a continuous casting crystallizer of carbon steel in a special-shaped billet, the raw materials and their weight composition are as follows: 4 parts by weight of fluorite, 9 parts by weight of cement clinker, 2 parts by weight of industrial soda ash, 2 parts by weight of lithium carbonate, 2 parts by weight of imported carbon black, 2 parts by weight of Xinjiang carbon black, 10 parts by weight of earthy graphite, 1.5 parts by weight of sodium fluoride, 41 parts by weight of boron-containing premelted material (of which boron oxide accounts for 5% of the total premelted material), 8 parts by weight of calcite, 1.5 parts by weight of magnesia, 5 parts by weight of manganese carbonate, and 12 parts by weight of bauxite.

[0046] The protective slag contains the following chemical composition (wt%): 35% CaO, 23% SiO2, 1.5% Fe2O3, 3.5% MgO, 11% Al2O3, 1.7% MnO, 2.2% Na2O, 0.8% Li2O, 2.05% B2O3, 3.5% F, and 12% C.

[0047] The above-mentioned protective slag has a binary basicity of 1.52, a melting point of 1170℃, a viscosity of 0.62 Pa·S at 1300℃, a melting time of 35 s, and a crystallization rate of 80%.

[0048] Example 2

[0049] A protective slag for a continuous casting crystallizer of carbon steel in a special-shaped billet, the raw materials and their weight composition are as follows: 3 parts by weight of fluorite, 8.5 parts by weight of cement clinker, 3 parts by weight of industrial soda ash, 2 parts by weight of lithium carbonate, 2 parts by weight of imported carbon black, 2 parts by weight of Xinjiang carbon black, 12 parts by weight of earthy graphite, 1.5 parts by weight of sodium fluoride, 37 parts by weight of boron-containing premelted material (of which boron oxide accounts for 6% of the total premelted material), 7 parts by weight of calcite, 2 parts by weight of magnesia, 5 parts by weight of manganese carbonate, and 15 parts by weight of bauxite.

[0050] The protective slag contains the following chemical composition (wt%) in weight percentages: 32% CaO, 22% SiO2, 2% Fe2O3, 3% MgO, 14% Al2O3, 1.7% MnO, 2.2% Na2O, 0.8% Li2O, 2.2% B2O3, 4% F, and 15% C.

[0051] The above-mentioned protective slag has a binary basicity of 1.45, a melting point of 1170℃, a viscosity of 0.75 Pa·S at 1300℃, a melting time of 39 s, and a crystallization rate of 65%.

[0052] Example 3

[0053] A protective slag for a continuous casting crystallizer of carbon steel in a special-shaped billet, the raw materials and their weight composition are as follows: 4.5 parts by weight of fluorite, 9 parts by weight of cement clinker, 2 parts by weight of industrial soda ash, 2 parts by weight of lithium carbonate, 2 parts by weight of imported carbon black, 2 parts by weight of Xinjiang carbon black, 10.5 parts by weight of earthy graphite, 1.5 parts by weight of sodium fluoride, 40 parts by weight of boron-containing premelted material (of which boron oxide accounts for 6% of the total premelted material), 9 parts by weight of calcite, 1.5 parts by weight of magnesia, 5 parts by weight of manganese carbonate, and 11 parts by weight of bauxite.

[0054] The protective slag contains the following chemical composition (wt%): 36% CaO, 22.5% SiO2, 1.3% Fe2O3, 3.6% MgO, 10% Al2O3, 1.7% MnO, 2.2% Na2O, 0.8% Li2O, 2.4% B2O3, 3.5% F, and 12% C.

[0055] The above-mentioned protective slag has a binary basicity of 1.6, a melting point of 1190℃, a viscosity of 0.58 Pa·S at 1300℃, a melting time of 36 s, and a crystallization rate of 90%.

[0056] Test case

[0057] I. Experimental conditions:

[0058] Cross section: BB2 type, 570*450*110mm; Test steel grade: Q355B; Tensioning speed: 0.8m / min-1.1m / min.

[0059] Test results

[0060] The protective slags prepared in Examples 1-3 were used to cast 20 heats of the above-mentioned steel grades respectively. The on-site usage of the casting was recorded, and the appearance and internal quality of the test steel grades were inspected. The comprehensive results are as follows:

[0061] Crystallizer condition: Observation shows that the protective slag reacts well in the crystallizer and can cover the surface of the molten steel evenly with the fluctuation of the molten steel surface; the flame is moderate and the crystallizer is relatively active; the slag is uniform and there are no irregular or obvious slag strips generated. This also shows that the protective slag has a strong ability to adsorb and contain inclusions and is well adapted to the on-site process.

[0062] Slag consumption: According to statistics, the slag consumption per ton of steel is between 0.4 and 0.6 kg / t. Generally speaking, the slag consumption per ton of steel is lower when the casting speed is high for small cross-sections, and higher when the casting speed is low for large cross-sections.

[0063] Liquid slag layer thickness: 6-10mm.

[0064] Ingot quality: Upon observation, the ingot surface is flat, smooth, and uniform, without defects such as cracks or pits, and the internal quality is good. The cold inspection pass rate of the ingot quality is over 99%, indicating that the protective slag can produce high-quality ingots that meet the requirements for ingot quality.

[0065] Continuing from the above, the ultra-high basicity molded slag for medium carbon (alloy) steel continuous casting obtained in Examples 1-3 of this invention can be applied to the continuous casting of low carbon steel in shaped billets. It can effectively solve the contradiction between heat transfer and lubrication between the billet shell and the copper plate of the mold during the continuous casting of shaped billets. It can effectively solve the problem of web cracks and the problem of large slag rings of conventional molded slag affecting the lubrication effect.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the composition of the protective slag is adjusted so that the binary basicity of the protective slag of the continuous casting crystallizer is 1.2, the melting point is 1130℃, the viscosity at 1300℃ is 0.5 Pa·S, the melting time is 30 s, and the crystallization rate is 20%.

[0068] Using the same experimental method, the results showed that the protective slag of Comparative Example 1 was significantly worse than that of Example 1. Specifically, the liquid slag layer in the crystallizer was very thin, the consumption was too large, and the surface cracks of the billet reached 98%.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the binary basicity of the continuous casting mold flux is 1.8, the melting point is 1220℃, the viscosity at 1300℃ is 2.5 Pa·S, the melting time is 50 s, and the crystallization rate is 80%.

[0071] Using the same experimental method, the results showed that the protective slag of Comparative Example 2 was significantly worse than that of Example 1. Specifically, the protective slag melting in the crystallizer was unstable, the liquid slag layer in the crystallizer was thin, the consumption was less than 0.2 kg / t, the slag bar was generated quickly, and the probability of steel leakage was very high.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that only Xinjiang carbon black and earthy graphite are used in the carbon formulation, with their proportions in the raw materials being 2.5 wt% and 10 wt%, respectively, thereby protecting the carbon content of the slag to be 12.5 wt%.

[0074] Using the same experimental method, the results showed that the protective slag of Comparative Example 3 was significantly worse than that of Example 1. Specifically, the main functions of carbon black and graphite in the protective slag are to control the three-layer structure and melting rate of the protective slag. When the amount of carbon black and graphite is too low, the protective slag melts too quickly in the crystallizer, the liquid slag layer is too thick, the slag strips are generated quickly, and the liquid slag channel is easily blocked. At the same time, the three-layer structure of the protective slag is also unreasonable, the workload of workers picking slag is large, and a slight oversight can easily lead to steel leakage. The main reason is that carbon black and graphite play a role in controlling the melting rate and maintaining the temperature in the protective slag. Carbon black has an amorphous structure and very fine particles, resulting in high dispersion and strong adsorption in the protective slag. It has a strong ability to separate the molten slag and to inhibit the flow and polymerization of the melt. The finer the carbon black, the stronger its separating ability. It can effectively control the melting rate of the protective slag in the low-temperature zone, but its effect is limited in the high-temperature zone. Graphite has a crystalline structure and relatively large particles. Its separating and inhibiting effects are poor, but it has a high initial melting temperature and a slow oxidation rate, and it has a significant skeletal effect. It has a strong ability to control the melting rate in the high-temperature zone. The combination of these two materials is more effective in controlling the three-layer structure.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Example 1 is that the pre-melted material does not contain boron oxide, and the same amount of boron oxide is directly added to the protective slag.

[0077] Using the same experimental method, the results showed that the protective slag of Comparative Example 3 was significantly worse than that of the protective slag of Example 1. Specifically, the protective slag was easily heated and turned into white balls during the spray granulation process, resulting in too many white balls in the protective slag particles. This led to a relatively large amount of powder and dust in the protective slag, which had an impact on the environment. In addition, the air permeability of the protective slag was relatively poor, and the escape of volatiles from the protective slag was hindered, which also had a slight impact on the performance of the protective slag.

[0078] In summary, the protective slag provided in the preferred embodiment of the present invention is used for casting carbon steel in shaped billets, which can effectively solve the contradiction between heat transfer and lubrication between the billet shell and the copper plate of the crystallizer during the continuous casting process of shaped billets. It can effectively solve both web cracks and lubrication problems.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A continuously cast bloom carbon steel mould powder, characterized in that, The basicity is 1.45-1.6, the melting point is 1160-1190 DEG C, the viscosity at 1300 DEG C is 0.55-0.8 Pa s, the melting time is 32-40 s, and the crystallization rate is 65-90 %; The continuous casting mold powder for the shaped blank medium carbon steel comprises CaO 30-36 parts by weight, SiO2 20-24 parts by weight, Fe2O3 1.0-2.0 parts by weight, MgO 2.5-4 parts by weight, Al2O3 8-13.5 parts by weight, MnO 1-3 parts by weight, R2O 3-5 parts by weight, F 2.5-5 parts by weight, B2O3 1.44-2.52 parts by weight, and C 9-15 parts by weight, wherein R is Na or Li; The source of C comprises 1.0-2.5 parts by weight of imported carbon black, 1.5-2.5 parts by weight of Xinjiang carbon black, and 8-14 parts by weight of earthy graphite.

2. The beam blank medium carbon steel continuous caster mould powder according to claim 1, characterized in that, The raw materials comprise 3-6 parts by weight of fluorite, 6.5-10.5 parts by weight of cement clinker, 1.5-3.5 parts by weight of industrial pure soda, 1.0-3.0 parts by weight of lithium carbonate, 1.0-2.5 parts by weight of imported carbon black, 1.5-2.5 parts by weight of Xinjiang carbon black, 8-14 parts by weight of earthy graphite, 0.5-2.5 parts by weight of sodium fluoride, 36.0-42.0 parts by weight of boron-containing pre-melted material, 6.0-10.0 parts by weight of calcite, 1.5-2.5 parts by weight of magnesia, 2.5-5.0 parts by weight of manganese carbonate, and 8.0-15.0 parts by weight of bauxite.

3. The beam blank medium carbon steel continuous caster mould powder according to claim 2, characterized in that, The boron-containing pre-melted material contains 4-6 wt% of boron oxide.

4. The beam blank medium carbon steel continuous caster mould powder according to claim 2, characterized in that, The pre-melted material comprises 2 parts by weight of imported carbon black, 2 parts by weight of Xinjiang carbon black, and 10 parts by weight of earthy graphite.

5. The beam blank medium carbon steel continuous caster mould powder according to claim 3, characterized in that, The pre-melted material comprises at least one of CaO, SiO2, Fe2O3, MgO, Al2O3, MnO, R2O, F, and C, and further comprises boron oxide.

6. A method of continuous casting of a medium carbon steel in a beam blank, characterized in that, The application of the continuous casting mold powder according to any one of claims 1-5.

7. A medium carbon steel in an ingot, characterized by, The shaped blank medium carbon steel continuous casting method according to claim 6.