Low-cost high-pulling-speed slab continuous casting covering slag

Abstract

The invention discloses a low-cost high-pulling-speed slab continuous casting covering slag which comprises the following components in percentage by weight: 14-23% of CaO, 33-43% of SiO2, 14-25% of CaF2, 9-13% of Na2O, 2-8% of Al2O3, less than or equal to 5% of MgO, 1.5-4% of C, 0.1-2.5% of nucleating agent and the balance of inevitable impurities, and the total amount of the impurities is less than or equal to 3%. The melting point of the nucleating agent is higher than 2000 DEG C, the solubility of slag formed after other components are completely molten is smaller than 3%, and the particle size of the nucleating agent is 25-50 microns. The casting powder has low viscosity, low melting point and good heat control capability, the melting point of the casting powder is 1000-1150 DEG C, the viscosity of the casting powder at 1300 DEG C is 0.1-0.4 Pa.s, the casting powder can meet continuous casting operation at the pulling speed of 2.0 m / min or above, and an obtained plate blank is good in quality and free of cracks. And the casting powder is completely lithium-free slag, so that the cost of the casting powder is reduced, and the low cost of the high-pulling-speed casting powder is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of auxiliary materials for steelmaking and continuous casting, and in particular to a low-cost and high-casting-speed slab continuous casting protective slag. Background Art

[0002] Continuous casting mold powder is a powdered or hollow, small-particle auxiliary material used in the continuous casting process. It coats the surface of the molten steel in the continuous casting mold. Under the high temperature of the molten steel, the mold powder forms two layers, solid and liquid. Next to the molten steel is a molten layer, which not only isolates the steel from air and prevents oxidation, but also effectively absorbs floating non-metallic inclusions, purifying the steel. Above the molten layer, the mold powder remains in its original granular or powdered form, providing excellent insulation and heat preservation, preventing excessive surface temperature drops and solidification.

[0003] Under the influence of the periodic vibration of the crystallizer, the molten layer will continuously flow into the gap between the crystallizer copper plate and the primary steel shell, lubricating the relative movement of the shell and the copper plate, thereby ensuring good surface quality of the cast billet. The mold slag flowing into the gap between the mold copper plate and the shell forms a 1-2 mm thick mold slag film, which is solid on the side close to the copper plate and liquid on the side close to the shell. The liquid phase acts as a lubricant, and the solid phase can effectively control the cooling capacity of the mold copper plate on the shell, thereby adjusting the cooling rate of the molten steel and achieving the effect of controlling heat transfer.

[0004] Therefore, protective slag is the last important technical means in the steelmaking process to control the smooth progress of the continuous casting process and the surface quality of the ingot. Protective slag with inappropriate performance will cause surface defects such as slag inclusions and cracks in the ingot. In severe cases, it may even cause the ingot shell to tear, thereby causing steel leakage accidents.

[0005] Polshing slag is typically composed primarily of a binary system of CaO and SiO2, supplemented with fluxes such as CaF2, Na2O, and Li2O. Its primary function is to lower the melting point and viscosity of the CaO and SiO2 binary system. Small amounts of Al2O3, MgO, MnO, and Fe2O3 are also added to achieve suitable metallurgical properties. Because the melting point of molten slag is approximately 400°C lower than the temperature of the molten steel, a certain amount of carbonaceous material must be incorporated to ensure that the relatively low-melting-point slag melts slowly on the steel surface. Carbonaceous materials have a high melting point and can effectively prevent the aggregation of slag droplets, thereby delaying their melting. Carbonaceous materials slowly burn into a gas, causing no pollution to the slag, making them a very practical skeletal material.

[0006] In order to effectively increase the output of casting machines and maximize benefits, continuous casting high-speed technology has always been the goal pursued by steelmaking, which places higher demands on mold slag technology. That is, it is necessary to ensure the proper lubrication function and prevent the crystallizer from dissipating heat too quickly. It is necessary to ensure that a shell of a certain thickness is quickly formed while preventing cracks. However, in order to achieve the ideal lubrication function, the mold slag is required to have a low melting point and viscosity, and a low alkalinity design is preferably adopted; but in order to prevent cracks caused by excessive heat transfer, the mold slag is required to have a certain heat control ability and the melting point cannot be too low, so a high alkalinity design is preferably adopted. For these performance requirements, the same point is that the viscosity needs to be reduced. The higher the casting speed, the lower the expected viscosity value. Usually, the following requirements are met:

[0007] Viscosity × pulling speed 2 = constant.

[0008] Conventional slab continuous casting machines typically operate at casting speeds between 1.0 and 1.5 m / min. To maximize profitability, further increasing casting speeds has become a key development direction for metallurgical enterprises. High casting speeds create greater friction in the mold, requiring more heat to be dissipated per unit time. As casting speeds increase, the gap between the mold copper plate and the primary billet shell narrows, reducing the amount of mold slag consumed. Therefore, to achieve adequate lubrication at high casting speeds, the mold slag must have a lower viscosity. As casting speeds increase, the amount of steel produced increases, requiring a greater supply of mold slag. This requires a faster melting rate and a less-than-ideal melting point. Therefore, to achieve the performance requirements of low viscosity and low melting point, a certain amount of Li2O is usually added to high-speed casting flux. This reacts with Al2O3 in the slag to form LiAlO2 crystals, which serve as nucleation sites for gunite. This facilitates proper thermal control under high casting speed conditions and prevents crack defects caused by excessively rapid cooling of the ingot. It is particularly suitable for casting flux with a basicity of less than 1. This type of casting flux is mainly suitable for low-carbon and ultra-low-carbon steel grades. These two types of steel have huge market demand and occupy a large position in steel mills in terms of production, resulting in a huge consumption of casting flux.

[0009] Chinese patents CN200810049028.9, "A Pre-melted Continuous Casting Mold Mold Flux and Its Preparation Method," and CN201610103385.3, "Mold Flux for Continuous Casting of Automotive Steel Sheets," both add a certain amount of Li2O to the mold slag to achieve the viscosity required for high casting speeds. The higher the casting speed, the more Li2O is needed. Li2O offers significant advantages in both viscosity reduction and heat management, making it a common mold slag component for high-speed continuous casting. However, Li2O is expensive, with each 0.5% addition doubling the price.

[0010] Chinese patents CN201610946639.8 disclose “High-speed billet continuous casting protective slag and its preparation method” and CN201610049064.X disclose “A protective slag for continuous casting of low-carbon steel and its application”. In the protective slag, B2O3 is added to reduce the viscosity. Although Li2O and B2O3 have a significant effect on reducing viscosity, B2O3 is a slag network structure former, which inhibits the formation of crystals and easily causes the primary billet shell to dissipate heat too quickly to form cracks.

[0011] In addition to viscosity requirements, high-speed continuous casting also has requirements for the heat control ability of the protective slag. Excessive heat dissipation can easily lead to cracks on the surface of the ingot. High-alkalinity and high-crystallization protective slag is a commonly used solution.

[0012] Chinese patents CN201210283898.9 disclose a "mold powder with high crystallinity and high lubricity for continuous casting" and CN201410068318.3 disclose an "ultra-high basicity mold powder for peritectic steel with high drawing speeds." Both utilize designs with high basicity and high crystallization properties. However, due to the high basicity, these powders have relatively high solidification temperatures, making them suitable only for medium-carbon steel or peritectic steel (carbon content 0.07-0.18%) with significant solidification shrinkage, and for drawing speeds not exceeding 2.0 m / min. For low-carbon steel (carbon content <0.07%), crack sensitivity is relatively low, and due to the minimal solidification shrinkage, a mold powder with a high solidification temperature is not suitable. Furthermore, to meet the drawing speed requirement of 2.0 m / min or higher, both the viscosity and the solidification temperature must be low. Low alkalinity is necessary, but there is no report on how to design a low-cost solution to achieve a good crystallization shape of the protective slag under low alkalinity conditions without adding Li2O. Summary of the Invention

[0013] The object of the present invention is to provide a low-cost, high-drawing-speed slab continuous casting protective slag, which has low viscosity, low melting point and good heat control ability. Its melting point is 1000-1150°C, and its viscosity is 0.1-0.4 Pa.s at 1300°C. It can meet the continuous casting operation with a drawing speed of more than 2.0 m / min, and the obtained slab is of good quality and free of cracks. Moreover, the protective slag is completely lithium-free, which reduces the cost of the protective slag, thereby realizing the low cost of the high-drawing-speed protective slag.

[0014] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0015] A low-cost, high-speed slab continuous casting protective slag comprises the following components by weight: CaO: 14-23%, SiO2: 33-43%, CaF2: 14-25%, Na2O: 9-13%, Al2O3: 2-8%, MgO≤5%, C: 1.5-4%, a nucleating agent: 0.1-2.5%, and the remainder being unavoidable impurities, with a total impurity amount of ≤3%. The nucleating agent has a melting point higher than 2000°C and a solubility of less than 3% in a slag formed after the other components are completely melted. The particle size of the nucleating agent is 25-50 μm.

[0016] Preferably, the protective slag does not contain non-ferrous metal oxides such as Nb, V, Mo, Ni, Cr, and Zn, and the total content of Fe2O3 and MnO shall not be higher than 1%.

[0017] Preferably, the nucleating agent is a carbide or a nitride, and the addition amount thereof is 0.1 to 0.5%.

[0018] Preferably, the amount of the nucleating agent added = (0.4×pulling speed - 0.5) ± 0.1, unit: weight percentage, wherein the pulling speed unit is m / min.

[0019] Preferably, the nucleating agent is an oxide, and its addition amount is 0.5-2.0%, preferably ZrO2.

[0020] Preferably, the amount of the nucleating agent added = (1.5×pulling speed - 1.8) ± 0.3, unit: weight percentage, wherein the pulling speed unit is m / min.

[0021] Preferably, the mold slag has a melting point of 1000-1150°C and a viscosity of 0.1-0.4 Pa.s at 1300°C.

[0022] In the mold slag of the present invention:

[0023] In the conventional slab continuous casting process, it takes about 6 to 8 minutes for the protective slag to melt into liquid and flow out of the crystallizer. Once the liquid protective slag enters the lubrication channel, assuming that the flow rate is synchronized with the billet pulling speed, taking the effective height of the crystallizer as an example, when the pulling speed is 1m / min, it stays for 48s, when it is 1.5m / min, it stays for 32s, and when it is 2.0m / min, it stays for only 24s. The liquid protective slag will then reach the crystallizer outlet to complete the lubrication function. The isothermal transformation TTT curve of the crystallization process of the protective slag for low carbon steel (such as Figure 1 As shown in the figure, the incubation time for crystal precipitation varies at different temperatures. It is fastest at 1210°C, but it still takes 66 seconds. Other temperatures show longer incubation times. This indicates that in order for the mold powder to achieve a certain thermal control function, the residence time of the liquid mold powder in the crystallizer must be greater than the incubation period of the crystal. Otherwise, the liquid mold powder will be discharged from the crystallizer before the crystals precipitate.

[0024] The faster the casting speed, the shorter the residence time of the liquid mold slag, and the greater the possibility that the residence time of the liquid mold slag will be less than the incubation time. For low-carbon steel, to ensure the proper lubrication function of the mold slag, an acidic slag design with low alkalinity is usually used, and the crystal incubation time is generally longer than that of high-alkalinity slag.

[0025] In order to make the acidic high-drawing speed protective slag have a certain rapid crystallization ability and meet the heat control function under high-drawing speed process conditions, the liquid protective slag needs to overcome the nucleation work before crystals can be precipitated during the initial crystallization process. For gun spar, high alkalinity and low viscosity are favorable conditions for its precipitation, and the nucleation work that needs to be overcome for precipitation under acidic conditions is greater. In order to improve the crystallization ability of the protective slag, the present invention specially introduces 0.1-2.5% nucleating agent, which can greatly reduce the nucleation work of gun spar precipitation, shorten the incubation time of the crystal, and make the molten protective slag have better heat control ability, avoiding excessive heat dissipation during high-drawing speed continuous casting, resulting in crack defects on the surface of the ingot.

[0026] Usually, the pouring temperature of molten steel produced in the continuous casting process is around 1550°C. In order to ensure that the nucleating agent remains in a solid phase within this temperature range, the melting point of the nucleating agent is usually significantly higher than 1550°C, at least not lower than 2000°C. In order to ensure that the nucleating agent has a nucleating function, the solubility of the nucleating agent in other molten components should be relatively small. The solubility in the slag formed after the other components are completely melted is less than 3%, and the dissolution rate is relatively slow.

[0027] From the perspective of protective slag, it needs to have good melting properties during use and be able to provide continuous and stable liquid slag for the continuous casting process. Adding a nucleating agent is equivalent to the appearance of a solid phase in a completely liquid phase, which destroys the slag morphology of the protective slag and is not conducive to the performance of various metallurgical functions. This negative effect is undesirable.

[0028] The various oxides and fluorides in the mold slag are melted to form liquid slag. Carbides and nitrides have poor solubility in the liquid slag. Among them, high-melting-point materials such as SiC, TiN, and BN have the conditions to act as nucleating agents. However, during the experiment, it was found that when carbides or nitrides are used as nucleating agents, although their solubility in the liquid slag is very low, they will slowly react with the free oxygen in the liquid slag as follows:

[0029] MC+3O=MO+CO2↑ (1)

[0030] 2MN+2O=2MO+N2↑ (2)

[0031] The gases produced during the reaction form microbubbles, which flow into the gap between the mold copper plate and the billet shell along with the liquid slag. While the liquid slag film quickly dissipates, the solid slag film is replaced very slowly. The resulting porous solid slag film is highly detrimental to stable heat transfer in the mold. To prevent the microbubbles produced by carbon and nitride nucleating agents from affecting heat transfer, the present invention strictly controls the amount of carbon and nitride nucleating agents added, keeping it within 0.1-0.5% and, more precisely, within (0.4 × casting speed - 0.5) ± 0.1%.

[0032] At the same time, in order to limit the decomposition reactions (1) and (2) of carbon and nitride nucleating agents in liquid slag, the activity of free oxygen O in the protective slag should be strictly controlled and the content of high oxygen potential oxides should be reduced.

[0033] After experimental comparison and research, the presence of non-ferrous metal oxides such as Nb, V, Mo, Ni, Cr, and Zn is prohibited in the protective slag material, and the sum of the Fe2O3 and MnO oxide contents shall not exceed 1%. Fe2O3 and MnO are common impurities. Although other non-ferrous metal oxides are not intentionally added and are almost not contained in natural minerals, more and more raw materials are now coming from industrial waste recycling and extraction, and it is inevitable that some will be brought in. This has little effect on conventional protective slag, but due to the addition of a nucleating agent in the present invention, there will be obvious negative effects, so it must be strictly controlled.

[0034] As the primary oxide in mold flux, SiO2 content also affects the activity of free oxygen in the flux to a certain extent. The higher the SiO2 content, the higher the free oxygen activity. Therefore, when the SiO2 content in the mold flux is higher than 40%, the nucleating agent should be added at the upper limit of the allowable range. When the SiO2 content in the mold flux is lower than 35%, the nucleating agent should be added at the lower limit of the allowable range to avoid gas generation and microbubbles that affect the stable heat transfer of the crystallizer.

[0035] Liquid slag has a high solubility for most oxides, such as CaO, Al2O3, and MgO. Although their melting points exceed 2000°C, they dissolve rapidly in the liquid slag and therefore lack the ability to form nuclei and cannot be used as nucleating agents. Research by the present inventors has found that ZrO2 is a poorly soluble oxide in liquid slag, with a solubility of approximately 2% and a very slow dissolution rate. The time required for dissolution far exceeds the incubation time for crystallization, making it suitable for use as a nucleating agent. Oxide nucleating agents dissolve slowly in the liquid slag but do not produce additional bubbles. The added amount should be appropriately increased, but should not exceed 2.5%. A more precise addition amount for oxide nucleating agents is (1.5 × casting speed - 1.8) ± 0.3%.

[0036] To ensure uniform nucleation of the mold slag, a higher amount of nucleating agent is preferred. However, to maximize the mold slag's inherent functionality, the addition of an external nucleating agent is undesirable. To achieve a balanced distribution of these two factors, optimizing the nucleating agent's particle size is crucial. Research has shown that optimal results are achieved when the particle size is controlled between 25 and 50 μm, or a standard sieve size of 300-500 mesh. Too large a particle size will not ensure sufficient nucleation points per unit volume, while too small a particle size will cause the nucleating agent to dissolve or decompose, preventing it from performing its nucleation function.

[0037] CaO and SiO2 form the mold slag's base system, accounting for approximately half of the mold slag's weight percentage. CaO content is lower than SiO2 to maintain the mold slag's acidic glassy properties, facilitating lubrication of the ingot under high casting speed conditions. Therefore, the mold slag of the present invention contains CaO at a level of 14-23%, and SiO2 at a level of 33-43%.

[0038] CaF2 is a common fluxing material that can quickly reduce the viscosity of the mold slag after melting, ensuring that the molten layer of mold slag can quickly flow into the gap between the crystallizer copper plate and the primary shell, preventing the high-temperature shell from adhering to the low-temperature copper plate and causing steel leakage accidents. More importantly, CaF2 can form gunite with CaO and SiO2. Its crystal properties are very consistent with the requirements of the molten mold slag to control heat transfer and maintain a certain lubricating effect. Too little CaF2 cannot reduce the viscosity of the molten mold slag to a reasonable range. Too much CaF2 will promote excessive precipitation of gunite, which is not conducive to smooth high-speed casting. Therefore, the CaF2 content in the mold slag of the present invention is controlled to 14-25%.

[0039] Na2O is another common flux in mold slag, effectively lowering its melting point. To ensure the melting point of the mold slag falls within the required range for this invention and to meet the high casting speed requirements of 2.0 m / min and above, the Na2O content in the mold slag is controlled between 9% and 13%.

[0040] Al2O3 is a common impurity component in mold flux raw materials, normally containing around 2%. Al2O3 is also a common component in mold flux, and its presence generally increases the viscosity of the flux and reduces its ability to crystallize. Taking into account the viscosity and crystallization ability of the mold flux of the present invention, the Al2O3 content should be controlled within 8%. Therefore, the Al2O3 content in the mold flux of the present invention is controlled within a range of 2-8%.

[0041] In addition, appropriate MgO can be added to the protective slag to reduce the viscosity of the molten protective slag, but the amount added should not be too high. When it exceeds 5%, not only will the crystallization tendency of the molten protective slag gradually increase, but the melting point will also increase.

[0042] Because the melting point of mold slag is approximately 400°C lower than that of molten steel, carbonaceous materials, such as carbon black, graphite, and coke, are essential additives to maintain stable melting of the mold slag on the steel surface and a certain thickness of the powder slag layer (which provides insulation and heat preservation). Carbon, with its high melting point, prevents small droplets of molten mold slag from agglomerating. Furthermore, carbon, upon combustion, turns into a gas, which does not contaminate the mold slag. For the mold slag used for high-speed slab continuous casting described herein, a carbon content of 1.5-4% is ideal.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] In order to meet the heat control function under high pulling speed conditions, the protective slag of the present invention adds a nucleating agent to reduce the nucleation work of the crystal, thereby shortening the incubation time of the crystal, making the incubation time of the crystal less than the residence time of the slag in the crystallizer, and achieving good heat control ability of the protective slag under high pulling speed conditions, thereby preventing crack defects in the ingot due to excessive cooling. Furthermore, by controlling the amount and particle size of the added nucleating agent, the influence of the added nucleating agent on the metallurgical properties of the slag is avoided. The protective slag of the present invention is based on the binary system of CaO and SiO2, and a certain amount of Na2O, CaF2 flux and other components such as MgO and Al2O3 are added to meet the glass characteristics of the acidic slag and meet the requirements of low viscosity and low melting point.

[0045] Production practice shows that the protective slag of the present invention can be applied to continuous casting at a casting speed of more than 1.5 m / min, especially to continuous casting at a casting speed of more than 2.0 m / min. The thickness of the slag layer reaches 8 to 16 mm, the consumption reaches 0.3 to 0.5 kg / t, and various usage indicators meet normal requirements. The temperature curve of the thermocouple of the crystallizer copper plate is stable, and no steel leakage alarm occurs. Moreover, because the protective slag does not contain Li2O at all, the price is only 30 to 50% of the protective slag containing lithium, and the cost per ton of steel can be reduced by 2 to 5 yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the isothermal transformation TTT curve of the crystallization process of protective slag for low carbon steel.

[0047] Figure 2 This is a photograph of the slag morphology formed after the protective slag of Example 5 of the present invention is cooled after being melted.

[0048] Figure 3 This is a photo of the slag morphology formed after the protective slag of Comparative Example 3 was cooled after melting. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0050] The components of the mold slag used in the examples and comparative examples of the present invention are shown in Table 1.

[0051] The raw materials of the protective slag in the embodiment of the present invention are: limestone, quartz, wollastonite, fluorite, magnesia, bauxite, soda ash, glass powder, cement powder, sodium fluoride, sodium silicate, carbon black, graphite, nucleating agent, etc.

[0052] The protective slag used in the embodiment of the present invention has both heat control and lubrication functions. Batch applications on conventional slab continuous casting machines show that it has good spreadability on the surface of the molten steel in the crystallizer. When the pulling speed exceeds 1.5m / min, a stable slag pool can be formed, and the thickness is always maintained at 8-15mm. The consumption per ton of steel is 0.3-0.5kg. The heat transfer of the crystallizer copper plate is stable, and the comprehensive heat transfer coefficient is 1100-1300kW / mK. The surface quality of the produced ingots is smooth, without batch slag inclusions, cracks and other quality defects, meeting the high pulling speed production requirements.

[0053] The metallurgical effects of the protective slag, such as the slag layer thickness, consumption, crystallizer heat transfer coefficient, surface quality of the produced ingot (incidence of defects such as slag inclusions and cracks), etc., have fully reached the level of traditional lithium-containing slag.

[0054] In Comparative Example 1, Li2O is added, which results in higher cost.

[0055] In Comparative Example 2, no nucleating agent or Li2O was added, and the thermal difference was controlled. When the pulling speed was below 1.5 m / min, the comprehensive heat transfer coefficient of the crystallizer copper plate reached the allowable upper limit of 1300 kW / mK. The heat transfer coefficient will increase with the increase of the pulling speed. Therefore, this protective slag is not suitable for high-speed continuous casting production with a pulling speed of more than 1.5 m / min.

[0056] Too much nucleating agent added in Comparative Example 3 will lead to excessive crystal precipitation, destroying the heat transfer performance of the slag. When the free oxygen activity in the slag is high, a large number of microbubbles will appear, the thermal control ability and stability will be greatly reduced, and the lubrication function will deteriorate.

[0057] Figure 2 This is a photo of the slag morphology formed after the mold slag of Example 5 of the present invention is cooled after being melted. Figure 3 This is a photograph of the slag morphology formed after cooling after melting in Comparative Example 3. As can be seen from the image, the mold slag of the present invention does not form microbubbles, while the mold slag in Comparative Example 3 contains too much nucleating agent, which causes gas generation and the formation of a large number of microbubbles after the mold slag solidifies.

[0058]

[0059]

Claims

1. A low-cost, high-speed slab continuous casting mold slag, comprising the following components by weight: CaO: 14-23%, SiO2: 33-43%, CaF2: 14-25%, Na2O: 9-13%, Al2O3: 2-8%, MgO ≤ 5%, C: 1.5-4%, a nucleating agent: 0.1-2.5%, and the remainder being unavoidable impurities, with a total impurity content of ≤ 3%; the nucleating agent having a melting point higher than 2000°C and a solubility of less than 3% in the slag formed after the other components are completely melted; and the particle size of the nucleating agent is 25-50 μm.

2. The low-cost, high-speed slab continuous casting mold flux according to claim 1, characterized in that: The protective slag does not contain non-ferrous metal oxides such as Nb, V, Mo, Ni, Cr, and Zn, and the total content of Fe2O3 and MnO shall not be higher than 1%.

3. The low-cost, high-speed slab continuous casting mold flux according to claim 1, characterized in that: The nucleating agent is carbide or nitride, and its addition amount is 0.1-0.5%.

4. The low-cost, high-speed slab continuous casting mold flux according to claim 3, characterized in that: The amount of the nucleating agent added = (0.4×pulling speed - 0.5) ± 0.1, unit: weight percentage, wherein the pulling speed unit is m / min.

5. The low-cost, high-speed slab continuous casting mold flux according to claim 1, characterized in that: The nucleating agent is an oxide, and its addition amount is 0.5-2.0%.

6. The low-cost, high-speed slab continuous casting mold flux according to claim 1, characterized in that: The nucleating agent is ZrO2.

7. The low-cost, high-speed slab continuous casting mold flux according to claim 5 or 6, characterized in that: The amount of the nucleating agent added = (1.5×pulling speed - 1.8) ± 0.3, unit: weight percentage, wherein the pulling speed unit is m / min.

8. The low-cost, high-speed slab continuous casting mold flux according to any one of claims 1 to 7, characterized in that: The protective slag has a melting point of 1000-1150° C. and a viscosity of 0.1-0.4 Pa.s at 1300° C.

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