Crystallizer casting powder for continuous casting of high-hydrogen-content medium carbon steel slab, preparation method and application

Abstract

The invention provides crystallizer casting powder for continuous casting of a high-hydrogen-content medium carbon steel slab, a preparation method and application, and the crystallizer casting powder for continuous casting of the high-hydrogen-content medium carbon steel slab comprises the following components in percentage by mass: 15-22% of CaO, 30-38% of SiO2, 9-14% of Na2O + K2O, 6-9% of F, 0.5-1.5% of Li2O, 1-3% of B2O3, 4-6% of C and the balance of inevitable impurities. Moreover, the preparation method is simple, convenient to operate and suitable for industrial large-scale production, and the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical continuous casting, and particularly relates to the mold flux for continuous casting of medium carbon steel slabs with high hydrogen content, its preparation method and application. Background Technology

[0002] Medium carbon steel (C 0.25-0.60%) conventional slab continuous casting is one of the largest-volume cast slab varieties, with end products covering key areas such as bridges, pressure vessels, long-distance pipelines, and automotive structural components. This type of steel undergoes a δ→γ peritectic phase transformation in the meniscus region of the crystallizer, with a linear shrinkage of 0.38-0.42%, belonging to the steel grade range with the highest incidence of sticking and leakage. In recent years, in order to reduce steelmaking costs and CO2 emissions, steel mills have generally increased the scrap ratio to ≥35%, resulting in a sharp increase in the hydrogen content of molten steel after secondary refining such as converter / electric furnace and LF / RH from the traditional ≤4ppm to 8-10ppm; while in the continuous casting process, due to the continuous air intake of the ladle, tundish, and submerged entry nozzle, the hydrogen content is difficult to remove further. Hydrogen has a solubility of up to 27 ppm at 1500℃, but it drops sharply to 4-5 ppm in the meniscus range of 1200-1250℃, with a supersaturation of 4-6 ppm, resulting in the instantaneous precipitation of microbubbles of 10-100 μm. These bubbles rise and penetrate the liquid protective slag film, causing "perforation" in the slag film, leading to uneven local heat transfer and fluctuations in billet shell thickness. The superposition of peritectic shrinkage and solidification lag induces adhesion alarms. Once the slag film ruptures, the friction coefficient μ jumps sharply from 0.2 to 0.7, slag consumption drops precipitously to <0.3 kg·t⁻¹, lubrication fails, the adhesion alarm rate increases exponentially, the finishing rate of the cast billet decreases, and economic losses are huge.

[0003] Furthermore, traditional medium-carbon steel protective slags employ high basicity (CaO / SiO2 = 0.9–1.3), with melting points of 1080–1150℃ and viscosity of 0.10–0.15 Pa·s at 1300℃. While high basicity is beneficial for adsorbing inclusions, the high melting point and low viscosity result in a slag film thickness of only 0.8–1.0 mm and low bubble penetration resistance. Simply increasing the Al2O3 and MgO content within this system can increase viscosity, but it also raises the melting point by 30–50℃, further deteriorating fluidity and creating a cycle of "higher viscosity, harder to melt," making it impossible to simultaneously achieve "low melting point + high viscosity." Therefore, this invention provides a mold protective slag for continuous casting of high-hydrogen-content medium-carbon steel slabs, its preparation method, and its application, aiming to solve the technical problems of slag film penetration and adhesion alarms during continuous casting under high-hydrogen conditions. Summary of the Invention

[0004] The main objective of this invention is to provide a mold protective slag for continuous casting of medium-carbon steel slabs with high hydrogen content, its preparation method, and its application, so as to solve the existing technical problems of slag film penetration and adhesion alarm during continuous casting under high hydrogen conditions.

[0005] To achieve the above objectives, the present invention provides a mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content. The composition of the mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content, by mass percentage, includes: CaO 15-22%, SiO2 30-38%, Na2O+K2O 9-14%, F 6-9%, Li2O 0.5-1.5%, B2O3 1-3%, C 4-6%, with the remainder being unavoidable impurities.

[0006] According to an embodiment of this application, the mass percentage of CaO and SiO2 in the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.5 to 0.7.

[0007] According to an embodiment of this application, the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a viscosity of 0.15 to 0.25 Pa·s at 1300°C.

[0008] The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a moisture content of ≤0.2% at 1300℃.

[0009] According to an embodiment of this application, the melting point of the mold protective slag used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 950–1050°C.

[0010] According to an embodiment of this application, the raw materials for the mold protective slag used in the continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass fraction, include: 33-37% pre-melted material, 10-14% quartz sand, 5-9% fluorite, 2-6% anhydrous borax, 7-11% sodium carbonate, 1-5% spodumene, 2.5-6.5% graphite, 1-3% carbon black, and 1-2% binder.

[0011] The basicity of the pre-melted material is 0.6 to 0.7.

[0012] This invention also provides a method for preparing a mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs, comprising the following steps:

[0013] S1: Provide raw materials for the mold flux used in the continuous casting of medium-carbon steel slabs with high hydrogen content, as described above.

[0014] S2: The raw materials are mixed and melted at 1400-1500°C, then quenched in water and vitrified, and then ground to obtain powder.

[0015] S3: The grinding material is made into a slurry and then granulated to obtain the granules of the mold protective slag used for continuous casting of high hydrogen content medium carbon steel slabs.

[0016] The particle size is 0.1 to 0.5 mm.

[0017] According to an embodiment of this application, the hydrogen content in the high-hydrogen-content medium-carbon steel slab is 8-10 ppm by mass; and the carbon content is 4-6% by mass.

[0018] The present invention also provides the application of the mold flux for continuous casting of high hydrogen content medium carbon steel slabs prepared according to the above-described mold flux for continuous casting or the above-described preparation method for continuous casting of high hydrogen content medium carbon steel slabs in the continuous casting process.

[0019] According to the embodiments of this application, the slag consumption of the mold protective slag used for continuous casting of high hydrogen content medium carbon steel slabs is 0.5 to 0.7 kg / t.

[0020] The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is applicable to steel grades including Q235B, Q355B, and HP295 steel.

[0021] The hydrogen content in the steel is 8-10 ppm.

[0022] According to the embodiments of this application, the number of adhesion alarms of the mold protective slag used for continuous casting of high hydrogen content medium carbon steel slabs is ≤1 time / 5000 tons of slabs.

[0023] The pass rate of the cast billets is ≥99%.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] The aforementioned mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content, its preparation method, and its application, achieve this by controlling the appropriate chemical composition of the mold flux, particularly by strictly controlling the content of CaO and SiO2, to create an ultra-low basicity slag system. This results in a "high viscosity-low melting point" coupling characteristic, enhancing the polymerization degree of silicon-oxygen composite anions and increasing the viscosity of the mold flux. This effectively strengthens its resistance to hydrogen bubble penetration, improving the stability and casting performance of the mold flux during continuous casting. It effectively solves the problem of slag film penetration under high hydrogen conditions, ensuring the continuity of the continuous casting process and the surface quality of the cast slab.

[0026] Furthermore, the introduction of B2O3 disrupts the chain-like framework structure of CaO-SiO2, promoting the formation of the eutectic phase and lowering the melting point of the protective slag. Simultaneously, it increases the superheat of the meniscus slag pool, inhibiting the nucleation and precipitation of hydrogen bubbles, reducing the amount of bubble precipitation, and further ensuring the surface quality of the cast billet. The high-viscosity protective slag significantly reduces the frequency of adhesion alarms, improves slag consumption and the billet yield. Moreover, the preparation method of this invention is simple, easy to operate, and reduces production costs, making it suitable for large-scale industrial production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 The image shows a slab used in the continuous casting of Q355B steel (H = 9.2 ppm) with the mold flux prepared in Example 1 of this invention for continuous casting of high hydrogen content medium carbon steel slabs.

[0029] Figure 2 This is a photograph of a slab used in the continuous casting of Q355B steel (H = 9.2 ppm) with the mold flux prepared by Comparative Example 1 of this invention for continuous casting of high hydrogen content medium carbon steel slabs. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0032] To achieve the above objectives, the present invention provides a mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content. The composition of the mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content, by mass percentage, includes: CaO 15-22%, SiO2 30-38%, Na2O+K2O 9-14%, F 6-9%, Li2O 0.5-1.5%, B2O3 1-3%, C 4-6%, with the remainder being unavoidable impurities.

[0033] In some embodiments, the composition of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass percentage, includes: CaO 15-20%, SiO2 32-35%, Na2O+K2O 10-12%, F 7-8%, Li2O 0.8-1.2%, B2O3 1.5-2.5%, C 4.5-5.5%, with the remainder being unavoidable impurities.

[0034] In some embodiments, by strictly controlling the CaO and SiO2 content, the mold flux used in the continuous casting of high-hydrogen-content carbon steel slabs is an ultra-low basicity slag system to increase its viscosity and enhance its resistance to hydrogen bubble penetration, thereby improving the casting performance of the mold flux. The addition of B2O3 lowers the melting point of the mold flux by 90–100°C, increases its viscosity, and significantly increases slag consumption, ultimately greatly reducing the number of sticking alarms and improving the slab qualification rate.

[0035] The aforementioned mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content achieves this by controlling the appropriate chemical composition, particularly the content of CaO and SiO2, to create an ultra-low basicity slag system. This results in a "high viscosity-low melting point" coupling characteristic, enhancing the polymerization degree of silicon-oxygen composite anions and increasing the viscosity of the flux. This effectively strengthens its resistance to hydrogen bubble penetration, improving its stability and casting performance during continuous casting. It effectively solves the problem of slag film penetration under high hydrogen conditions, ensuring the continuity of the continuous casting process and the surface quality of the cast slab.

[0036] Furthermore, the introduction of B2O3 disrupts the chain-like framework structure of CaO-SiO2, promoting the formation of the eutectic phase and lowering the melting point of the protective slag. Simultaneously, it increases the superheat of the meniscus slag pool, inhibiting the nucleation and precipitation of hydrogen bubbles, reducing the amount of bubble precipitation, and further ensuring the surface quality of the cast billet. The high-viscosity protective slag significantly reduces the number of adhesion alarms, improving slag consumption and the billet yield.

[0037] In some embodiments, the mass percentage of CaO to SiO2 in the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.5 to 0.7.

[0038] In some embodiments, the mass percentage of CaO to SiO2 in the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.55–0.65. A slag system with "low basicity, low viscosity, and low melting point" is used to counteract the damage to the performance of the mold flux caused by hydrogen precipitation in molten steel. First, because hydrogen in molten steel precipitates during solidification and remains in the liquid slag film in the form of micropores, these hydrogen micropores significantly increase the thermal resistance of the slag film, leading to uneven heat transfer. Controlling the CaO / SiO2 ratio, combined with the introduction of B2O3, can effectively reduce the basicity, melting point, and viscosity of the mold flux, making it easier to form a glassy state, thereby reducing the overall thermal resistance and making heat transfer more uniform. Second, the low melting point and low viscosity increase the consumption of the mold flux and accelerate the renewal rate of the liquid slag film, preventing the hydrogen micropores from merging into large bubbles, thus avoiding a sudden increase in thermal resistance and local heat transfer interruption caused by large bubbles. Finally, the low viscosity provides continuous and stable lubrication between the billet shell and the crystallizer wall, significantly reducing crystallizer sticking alarms caused by poor lubrication, and significantly reducing the sticking rate and the number of sticking alarms.

[0039] In some embodiments, the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a viscosity of 0.15–0.25 Pa·s at 1300°C.

[0040] The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a moisture content of ≤0.2% at 1300℃.

[0041] In some embodiments, the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a viscosity of 0.18–0.22 Pa·s at 1300°C.

[0042] The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a moisture content of ≤0.2% at 1300℃.

[0043] In some embodiments, low viscosity enables the protective slag to form a uniform liquid slag film between the crystallizer wall and the billet shell, reducing frictional resistance and preventing sticking and leakage of steel. This is especially suitable for high-hydrogen-content steels that are highly susceptible to hydrogen-induced cracking.

[0044] In some embodiments, extremely low moisture content can prevent hydrogen elements generated by decomposition at high temperatures from entering the molten steel, thus preventing hydrogen-induced defects (such as white spots and bubbles) caused by additional hydrogen absorption in high-hydrogen-content steels. Furthermore, low moisture content can eliminate slag layer pores formed by moisture vaporization, maintain slag film density, ensure heat transfer and lubrication stability, and prevent slag layer structure damage or liquid surface fluctuations caused by instantaneous gas expansion in the crystallizer.

[0045] In some embodiments, the melting point of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 950–1050°C.

[0046] In some embodiments, the melting point of the mold protective slag used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 960–1000°C.

[0047] In some embodiments, the melting point of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 970–990°C.

[0048] In some embodiments, the raw materials for the mold flux used in the continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass fraction, include: 33-37% pre-melted material, 10-14% quartz sand, 5-9% fluorite, 2-6% anhydrous borax, 7-11% sodium carbonate, 1-5% spodumene, 2.5-6.5% graphite, 1-3% carbon black, and 1-2% binder.

[0049] The basicity of the pre-melted material is 0.6 to 0.7.

[0050] In some embodiments, the raw materials for the mold flux used in the continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass fraction, include: 34-36% pre-melted material, 11-13% quartz sand, 6-8% fluorite, 3-5% anhydrous borax, 8-10% sodium carbonate, 3.5-5% spodumene, 4-5% graphite, 1-2% carbon black, and 1-1.5% binder.

[0051] The basicity of the pre-melted material is 0.65 to 0.7.

[0052] This invention also provides a method for preparing a mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs, comprising the following steps:

[0053] S1: Provide the raw materials for the mold flux used in the continuous casting of medium-carbon steel slabs with high hydrogen content, as described above. Design a slag system formulation with low H2O, low carbon, and low basicity to inhibit hydrogen from entering the molten steel and ensure subsequent glassization.

[0054] S2: The raw materials are mixed and melted at 1400-1500°C, then quenched in water and vitrified, and then ground to obtain powder.

[0055] S3: The grinding material is made into a slurry and then granulated to obtain the granules of the mold protective slag used for continuous casting of high hydrogen content medium carbon steel slabs.

[0056] The particle size is 0.1 to 0.5 mm.

[0057] In some embodiments, the hydrogen content in the high-hydrogen-content carbon steel slab is 8–10 ppm by mass; and the carbon content is 4–6% by mass.

[0058] In some embodiments, the hydrogen content in the high-hydrogen-content carbon steel slab is 8.5–9.5 ppm by mass; and the carbon content is 4–6% by mass.

[0059] The method for preparing mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs of the present invention is simple, easy to operate, reduces production costs, and is suitable for large-scale industrial production.

[0060] The present invention also provides the application of the mold flux for continuous casting of high hydrogen content medium carbon steel slabs prepared according to the above-described mold flux for continuous casting or the above-described preparation method for continuous casting of high hydrogen content medium carbon steel slabs in the continuous casting process.

[0061] In some embodiments, the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is used in continuous casting processes with a casting speed of 1.0 to 1.5 m / min.

[0062] In some embodiments, the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is used in continuous casting processes with a casting speed of 1.0 to 1.2 m / min.

[0063] In some embodiments, the slag consumption of the mold protective slag used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.5 to 0.7 kg / t.

[0064] The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is applicable to steel grades including Q235B, Q355B, and HP295 steel.

[0065] The hydrogen content in the steel is 8-10 ppm.

[0066] In some embodiments, the slag consumption of the mold protective slag used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.5 to 0.6 kg / t.

[0067] The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is applicable to steel grades including Q235B and Q355B steel.

[0068] The hydrogen content in the steel is 9 to 9.5 ppm.

[0069] In some embodiments, stable lubrication and heat transfer can be achieved within a slag consumption range of 0.5–0.7 kg / t, which is 30–40% lower than that of conventional medium carbon steel protective slag (slag consumption of 0.9–1.1 kg / t), saving 3–4 yuan in slag cost per ton of steel. Furthermore, it is directly compatible with high-hydrogen steel grades (Q235B, Q355B steel). Even if the hydrogen content in molten steel is as high as 8–10 ppm, the total hydrogen content in the billet can still be controlled within the range of ≤1.5 ppm, eliminating the need for additional vacuum degassing or hydrogen-expanding annealing, thus shortening the process flow.

[0070] In some embodiments, the number of adhesion alarms for the mold protective slag used in the continuous casting of high-hydrogen-content medium-carbon steel slabs is ≤1 per 5000 tons of slabs.

[0071] The pass rate of the cast billets is ≥99%.

[0072] In some embodiments, the use of the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs can significantly reduce the risk of production accidents and improve the safety of continuous casting operations; it can also reduce unplanned downtime and improve production efficiency; reduce equipment wear and maintenance costs caused by steel leakage; ensure the stability of the continuous casting process; and improve production continuity.

[0073] To further illustrate the present invention, the following examples are provided:

[0074] Example 1

[0075] The continuous casting speed for producing Q355B steel (with a hydrogen content of 9.2 ppm, hereinafter referred to as H = 9.2 ppm) (used for high-hydrogen-content medium-carbon steel) is 1.2 m / min. The composition of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass percentage, is: CaO 16.5%, SiO2 30%, Na2O + K2O 9%, F 8%, Li2O 1.0%, B2O3 2%, C 4%, with the remainder being unavoidable impurities. The mass percentage of CaO to SiO2 is 0.55.

[0076] The raw materials for the mold flux used in the continuous casting of medium-carbon steel slabs with high hydrogen content, by mass fraction, are: 35% pre-melted material, 12% quartz sand, 7% fluorite, 4% anhydrous borax, 9% sodium carbonate, 3% spodumene, 4.5% graphite, 1.5% carbon black, and 1% binder; wherein the basicity of the pre-melted material is 0.68.

[0077] The preparation method of mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs includes the following steps:

[0078] S1: Provide the raw materials for the mold protective slag used in the continuous casting of high-hydrogen-content medium-carbon steel slabs as described above.

[0079] S2: After mixing the raw materials, melt them at 1450℃, then quench them in water and vitrify them, and then grind them to obtain the powder.

[0080] S3: After the grinding material is made into a slurry, it is granulated to obtain the mold protective slag for continuous casting of medium carbon steel slabs with high hydrogen content; the particle size is 0.2 mm.

[0081] The hydrogen content in the high-hydrogen-content medium-carbon steel slab is 8.3 ppm by mass; the carbon content is 4.6% by mass.

[0082] The mold flux prepared in Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was used in the production of Q355B steel (H = 9.2 ppm). Tests showed that the melting point of the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs was 980℃; the viscosity at 1300℃ was 0.20 Pa·s; and the moisture content was 0.12%. The slag consumption of the mold flux prepared in Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was 0.58 kg / t; the number of adhesion alarms was 1 per 5000 tons of slabs; and the slab qualification rate was 99.70%.

[0083] The mold flux prepared in Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was used in the production of Q235B steel (H = 9.5 ppm). Tests showed that the melting point of the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs was 1050℃; the viscosity at 1300℃ was 0.18 Pa·s; and the moisture content was 0.2%. The slag consumption of the mold flux prepared in Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was 0.58 kg / t; the number of adhesion alarms was 1 per 5000 tons of slabs; and the slab qualification rate was 99.3%.

[0084] Example 2

[0085] Compared to Example 1, the composition of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs was changed.

[0086] The composition of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass percentage, is as follows: CaO 21.1%, SiO2 32%, Na2O+K2O 10%, F 6%, Li2O 1.2%, B2O 31.6%, C 4.5%, with the remainder being unavoidable impurities. The mass percentage of CaO to SiO2 is 0.66. Other steps are the same as in Example 1.

[0087] The mold flux prepared in Example 2 for continuous casting of high-hydrogen-content medium-carbon steel slabs was used in the production of Q355B steel (H = 9.2 ppm). Tests showed that the melting point of the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs was 980℃; the viscosity at 1300℃ was 0.16 Pa·s; and the moisture content was 0.14%. The slag consumption of the mold flux prepared in Example 2 for continuous casting of high-hydrogen-content medium-carbon steel slabs was 0.67 kg / t; the number of adhesion alarms was 1 per 5000 tons of slabs; and the slab qualification rate was 99.5%.

[0088] Comparative Example 1

[0089] Compared to Example 1, no B2O3 was added to the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs; and the mass percentage of CaO to SiO2 was 1.1. Other steps were the same as in Example 1.

[0090] The mold flux prepared in Comparative Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was used in the production of Q355B steel (H = 9.2 ppm). Tests showed that the melting point of the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs was 1080℃; the viscosity at 1300℃ was 0.10 Pa·s; and the moisture content was 0.26%. The slag consumption of the mold flux prepared in Comparative Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was 0.32 kg / t; the number of adhesion alarms was 12 times / 5000 tons of slabs; and the slab qualification rate was 97.50%.

[0091] Comparative Example 2

[0092] Compared to Example 1, no B2O3 was added to the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs; the mass percentage of CaO and SiO2 was 0.55. Other steps were the same as in Example 1.

[0093] The mold flux prepared in Comparative Example 2 for continuous casting of high-hydrogen-content medium-carbon steel slabs was used in the production of Q355B steel (H = 9.2 ppm). Tests showed that the melting point of the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs was 1080℃; the viscosity at 1300℃ was 0.11 Pa·s; and the moisture content was 0.27%. The slag consumption of the mold flux prepared in Comparative Example 1 for continuous casting of high-hydrogen-content medium-carbon steel slabs was 0.43 kg / t; the number of adhesion alarms was 4 times / 5000 tons of slabs; and the slab qualification rate was 98.2%.

[0094] Analysis example:

[0095] Figure 1 The image shows a slab used in the continuous casting of Q355B steel (H = 9.2 ppm) with the mold flux prepared in Example 1 of this invention for continuous casting of high hydrogen content medium carbon steel slabs. It can be seen that the surface of the slab is flat and free of cracks. Figure 2 The image shows a slab used in the continuous casting of Q355B steel (H = 9.2 ppm) with the mold flux prepared by Comparative Example 1 of this invention for continuous casting of medium carbon steel slabs with high hydrogen content. It can be seen that due to the frequent occurrence of adhesion alarms, the surface of the slab is uneven and has cracks.

[0096] As can be seen from Example 1 and Comparative Example 1, the mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs in Example 1 of the present invention contains a certain mass of B2O3. Compared with the mold flux without boron in Comparative Example 1, the melting point is reduced by 100°C, indicating that the addition of B2O3 has a significant effect on reducing the melting point of the mold flux. Moreover, the present invention uses an ultra-low basicity slag system with a CaO and SiO2 mass percentage of 0.5 to 0.7, which increases its viscosity, enhances its resistance to hydrogen bubble penetration, and improves the casting performance of the mold flux.

[0097] The aforementioned mold flux for continuous casting of medium-carbon steel slabs with high hydrogen content achieves this by controlling the appropriate chemical composition, particularly the content of CaO and SiO2, to create an ultra-low basicity slag system. This results in a "high viscosity-low melting point" coupling characteristic, enhancing the polymerization degree of silicon-oxygen composite anions and increasing the viscosity of the flux. This effectively strengthens its resistance to hydrogen bubble penetration, improving its stability and casting performance during continuous casting. It effectively solves the problem of slag film penetration under high hydrogen conditions, ensuring the continuity of the continuous casting process and the surface quality of the cast slab.

[0098] Furthermore, the introduction of B2O3 disrupts the chain-like framework structure of CaO-SiO2, promoting the formation of the eutectic phase and lowering the melting point of the protective slag. Simultaneously, it increases the superheat of the meniscus slag pool, inhibiting the nucleation and precipitation of hydrogen bubbles, reducing the amount of bubble precipitation, and further ensuring the surface quality of the cast billet. The high-viscosity protective slag significantly reduces the number of adhesion alarms, improving slag consumption and the billet yield.

[0099] The method for preparing mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs of the present invention is simple, easy to operate, reduces production costs, and is suitable for large-scale industrial production.

[0100] The above technical solutions of the present invention are merely preferred embodiments and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs, characterized in that, The composition of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass percentage, includes: CaO 15-22%, SiO2 30-38%, Na2O+K2O 9-14%, F 6-9%, Li2O 0.5-1.5%, B2O 31-3%, C 4-6%, with the remainder being unavoidable impurities.

2. The mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs according to claim 1, characterized in that, The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs contains CaO and SiO2 at a mass percentage of 0.5 to 0.7%.

3. The mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs according to claim 1, characterized in that, The viscosity of the mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.15–0.25 Pa·s at 1300°C. The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs has a moisture content of ≤0.2% at 1300℃.

4. The mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs according to claim 1, characterized in that, The melting point of the mold protective slag used for continuous casting of medium-carbon steel slabs with high hydrogen content is 950-1050℃.

5. The mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs according to claim 1, characterized in that, The raw materials for the mold protective slag used in the continuous casting of high-hydrogen-content medium-carbon steel slabs, by mass fraction, include: 33-37% pre-melted material, 10-14% quartz sand, 5-9% fluorite, 2-6% anhydrous borax, 7-11% sodium carbonate, 1-5% spodumene, 2.5-6.5% graphite, 1-3% carbon black, and 1-2% binder; The basicity of the pre-melted material is 0.6 to 0.

7.

6. A method for preparing a mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs according to any one of claims 1 to 5, characterized in that the step... include: S1: Provide raw materials for the mold flux used in the continuous casting of high-hydrogen-content medium-carbon steel slabs, which have the same composition as the mold flux used in the continuous casting of high-hydrogen-content medium-carbon steel slabs. S2: The raw materials are mixed and melted at 1400-1500°C, then quenched in water and vitrified, and then ground to obtain powder. S3: After the grinding material is made into a slurry, it is granulated to obtain the granules of the mold protective slag used for continuous casting of high hydrogen content medium carbon steel slabs; The particle size is 0.1 to 0.5 mm.

7. The method for preparing mold flux for continuous casting of high-hydrogen-content medium-carbon steel slabs according to claim 6, characterized in that, The hydrogen content in the high-hydrogen-content medium-carbon steel slab is 8–10 ppm; the carbon content is 4–6%.

8. The application of a mold flux as described in any one of claims 1 to 5 for continuous casting of high-hydrogen-content medium-carbon steel slabs, characterized in that, The application of the mold flux used in the continuous casting of high-hydrogen-content medium-carbon steel slabs in the continuous casting process.

9. The application of the mold flux according to claim 8 for continuous casting of high-hydrogen-content medium-carbon steel slabs, characterized in that, The slag consumption of the mold protective slag used for continuous casting of high-hydrogen-content medium-carbon steel slabs is 0.5-0.7 kg / t; The mold flux used for continuous casting of high-hydrogen-content medium-carbon steel slabs is applicable to steel grades including Q235B, Q355B, and HP295 steel. The hydrogen content in the steel is 8-10 ppm.

10. The application of the mold flux according to claim 8 for continuous casting of high-hydrogen-content medium-carbon steel slabs, characterized in that, The number of adhesion alarms for the mold protective slag used in the continuous casting of high hydrogen content medium carbon steel slabs is ≤1 time / 5000 tons of slabs. The pass rate of the cast billets is ≥99%.

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