Thin slab continuous casting method

Abstract

The invention provides a thin slab continuous casting method, and belongs to the field of continuous casting. The method comprises the steps that molten steel is cast, and in the casting process, the type of casting powder is determined according to the pulling speed of a casting machine; when the pulling speed of a casting machine is smaller than 4.5 m / min, the casting powder is first casting powder; the viscosity of the first casting powder at the temperature of 1,300 DEG C is 0.10 Pa.s to 0.20 Pa.s; when the pulling speed of the casting machine is larger than or equal to 4.5 m / min, the casting powder is second casting powder; and the viscosity of the second casting powder at the temperature of 1,300 DEG C is 0.04 Pa.s to 0.08 Pa.s. The casting powder is added in a two-section mode, the lubricating heat transfer effect at the low pulling speed can be achieved, and the casting powder consumption, heat transfer and liquid slag layer thickness at the high pulling speed can be achieved. Therefore, the lubricating performance and the heat transfer performance of the casting powder at different pulling speeds can be effectively balanced, and the surface quality of a casting blank is improved.

Description

Technical Field

[0001] The present application relates to the technical field of continuous casting, and in particular to a thin slab continuous casting method. Background Art

[0002] Shougang thin slab continuous casting and rolling equipment is a world-first third-generation thin slab continuous casting and rolling production line built on the basis of the existing second-generation TSCR technology, integrating the most cutting-edge technologies of today's continuous casting and rolling. It has multiple production modes including single-bill production, semi-headless production, and full headless production. The production line adopts headless rolling, mainly producing high-quality, high-strength, and ultra-thin products; it replaces cold with hot, and can produce high-end thin-gauge hot-rolled products, while also producing products with high surface quality, good plate shape, and uniform and stable properties in all directions. It mainly includes three categories: thin-gauge hot-rolled coils, hot-rolled pickled plates, and hot-base galvanized plates. The full headless rolling specifications are 0.8-4.0mm, and the varieties include: automotive structural steel, high-strength steel, weathering steel, pickled base plate, bidirectional steel, high-expansion steel, medium manganese steel, martensitic steel, and cold-rolled base material. The casting machine type of this equipment is straight arc type, with an arc radius of 5.5m, the ladle and tundish capacities are 200t and 70t respectively, the crystallizer is long funnel type, the billet specification range is (900~1600)×(110~123)mm, and the metallurgical length is 26.567m. The dual-mode fusion pressing technology is adopted, that is, the fan-shaped 0-1 section liquid core pressing and the solidification end light pressing are achieved to achieve the purpose of thinning and improving the internal quality.

[0003] However, due to the small cross-sectional thickness of the crystallizer of the thin slab continuous casting and rolling production line, as the pulling speed increases, the liquid level fluctuation intensifies, which can easily cause problems such as crystallizer sticking alarm, slag defective ingots, and surface cracks on the ingots. Summary of the invention

[0004] The present application provides a thin slab continuous casting method to solve the following technical problem: how to improve the surface quality of the cast slab.

[0005] The present application provides a thin slab continuous casting method, the method comprising:

[0006] Casting the molten steel, and during the casting process, determining the type of protective slag according to the casting speed of the casting machine;

[0007] When the casting speed is less than 4.5 m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300° C. is 0.10 Pa·s to 0.20 Pa·s;

[0008] When the casting machine casting speed is ≥4.5m / min, the protective slag is the second protective slag; the viscosity of the second protective slag at 1300°C is 0.04Pa·s to 0.08Pa·s.

[0009] Optionally, the chemical composition of the first protective slag includes, by mass fraction: CaO: 25.0% to 35.0%, SiO 2 :24.0%~28.0%,Al 2 O 3 : 4.0% ~ 8.0%, MgO: 5.0% ~ 9.0%, MnO: 1.0% ~ 3.0%, NaO 2 +K 2 O: 5.0% to 9.0%, LiO 2 <5.0%, C: 4.0%~6.0%, the remainder is inevitable impurities.

[0010] Optionally, the melting point of the first protective slag is 1000°C to 1100°C.

[0011] Optionally, the basicity of the first protective slag is 1.05-1.15.

[0012] Optionally, the chemical composition of the first mold slag is, by mass fraction, CaO: 30.0%, SiO 2 : 25.5%,Al 2 O 3 :5.8%, MgO: 6.8%, MnO: 1.63%, NaO 2 +K 2 O: 7.1%, LiO 2 : 0.66%, C: 5.65%, and the remainder is unavoidable impurities; the melting point of the first protective slag is 1038°C, the viscosity of the first protective slag at 1300°C is 0.10Pa·s, and the basicity of the first protective slag is 1.10.

[0013] Optionally, the chemical composition of the second protective slag includes, by mass fraction: CaO: 30.0% to 35.0%, SiO 2 :25.0%~30.0%,Al 2 O 3 : 4.0% ~ 8.0%, MgO: 6.0% ~ 8.0%, MnO: 0.05% ~ 0.20%, NaO 2 +K 2 O: 6.0%~10.0%, LiO 2 <5.0%, C: 4.0%~6.0%, the balance is inevitable impurities.

[0014] Optionally, the melting point of the second protective slag is 950°C to 1050°C.

[0015] Optionally, the basicity of the second protective slag is 1.25-1.35.

[0016] Optionally, the chemical composition of the second mold slag is, by mass fraction, CaO: 32.9%, SiO 2 : 27.2%, Al 2 O 3 :6.4%, MgO: 5.9%, MnO: 0.10%, NaO 2 +K 2 O: 8.2%, LiO 2 : 0.88%, C: 5.23%; the melting point of the second protective slag is 1005°C, the viscosity of the second protective slag at 1300°C is 0.06Pa·s, and the basicity of the second protective slag is 1.29.

[0017] Optionally, the molten steel is molten steel for low carbon steel.

[0018] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0019] The present application provides a thin slab continuous casting method, comprising: casting molten steel, and during the casting process, determining the type of protective slag according to the casting machine pulling speed; when the casting machine pulling speed is less than 4.5m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300°C is 0.10Pa·s to 0.20Pa·s; when the casting machine pulling speed is ≥4.5m / min, the protective slag is the second protective slag; the viscosity of the second protective slag at 1300°C is 0.04Pa·s to 0.08Pa·s. By adding protective slag in two stages, the lubrication and heat transfer effects at low pulling speeds can be met, and the protective slag consumption, heat transfer and liquid slag layer thickness at high pulling speeds can be met. Thereby, the lubrication performance and heat transfer performance of the protective slag at different pulling speeds can be effectively balanced, thereby improving the surface quality of the cast billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 A schematic flow chart of a thin slab continuous casting method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0024] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0025] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0026] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0027] High-speed thin slab continuous casting has attracted great attention and widespread concern in the steel industry due to its outstanding advantages such as short process, low investment, low cost, green energy saving and environmental protection. In order to achieve high efficiency of thin slab continuous casting and rolling, the demand for improving the efficiency of the casting machine is more urgent. Stably increasing the casting speed will provide important support for the economic benefits of the thin slab continuous casting and rolling production line.

[0028] There are significant differences between the protective slag of the thin slab continuous casting mold and the protective slag of the conventional slab continuous casting machine, which is mainly reflected in the higher pulling speed of the thin slab continuous casting, the lower slag consumption of the protective slag, the reduced slag film thickness, and the greater friction between the crystallizer and the billet; at the same time, the heat flux of the crystallizer at high pulling speed will also be significantly greater than that of the conventional slab continuous casting machine. Therefore, thin slab continuous casting puts forward higher requirements on the metallurgical properties of the protective slag, especially lubrication and heat transfer. The performance requirements of protective slag for continuous casting of thin slabs at different drawing speeds are also different. According to on-site analysis, when the drawing speed is ≥4.5m / min when casting low carbon steel, the thickness of the liquid slag layer is significantly thinned. The traditional process mostly uses one kind of protective slag from the start of casting to the end of casting, without considering the thickness of the protective slag liquid slag layer and slag consumption at different drawing speeds. This patent adopts two-stage low carbon steel protective slag according to the different drawing speeds during casting, so as to reasonably control the melting speed, melting point and viscosity of the protective slag, the thickness of the liquid slag layer and the crystallization performance of the protective slag within a reasonable range, so that the liquid slag can stably flow into the slag film channel, ensure lubrication performance, improve heat transfer, and play an important guiding role in increasing the drawing speed of thin slabs.

[0029] See also Figure 1 The present application provides a thin slab continuous casting method, the method comprising:

[0030] S1. Casting molten steel, and during the casting process, determining the type of protective slag according to the casting speed of the casting machine;

[0031] The present application can effectively balance the lubrication and heat transfer performance of the protective slag by using protective slags of different properties at different casting speeds, reduce problems such as mold sticking alarms and surface cracks of the ingot during the casting process, and provide guarantee for smooth production.

[0032] In some embodiments, the molten steel is molten steel for low carbon steel.

[0033] In the implementation mode of the present application, the casting process is specifically as follows: the secondary cooling water distribution system and the crystallizer vibration parameters are customized according to the characteristics of low-carbon steel to achieve uniform cooling and reduce internal cracks. The superheat of the tundish is strictly controlled at 20-35°C to ensure that the liquidus temperature is stable at 1531°C, laying the foundation for the subsequent high-quality ingot production. Before the formal casting, a detailed tundish preparation operation was carried out. The ladle slag detection was performed to ensure that the slag amount was appropriate. Then the ladle slide was opened and the molten steel was smoothly transferred to the tundish. In order to prevent the oxidation of the molten steel in the tundish, a high-alkalinity low-carbon steel covering agent was added to the stopper rod position when the molten steel volume was 24 tons. When the tundish reached 30 tons, the casting was officially started, and the molten steel was slowly injected into the crystallizer. A slow pouring speed of 0.8m / min was adopted in the initial stage, and this speed was maintained for 3 seconds to ensure the stable formation of the initial slag film. As the casting progresses, the pulling speed is directly increased from 0.8m / min to 3.5m / min and stabilized at this speed until the swing shear completes the first shearing. The pulling speed increase rate in this stage is 1.5m / min2, aiming to quickly reach the target pulling speed while ensuring that the quality of the billet is not affected. When the pulling speed stabilizes at 4.5m / min, the pulling speed is further increased to the target pulling speed of 5.6m / min according to production needs.

[0034] S2. When the casting speed of the casting machine is less than 4.5 m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300° C. is 0.10 Pa·s to 0.20 Pa·s;

[0035] In some embodiments, the first protective slag is added when the casting speed of the casting machine increases from 0 to 0.8 m / min.

[0036] In some embodiments, the chemical composition of the first mold slag includes, by mass fraction: CaO: 25.0% to 35.0%, SiO 2 :24.0%~28.0%,Al 2 O 3 : 4.0% ~ 8.0%, MgO: 5.0% ~ 9.0%, MnO: 1.0% ~ 3.0%, NaO 2 +K 2 O: 5.0% to 9.0%, LiO 2 <5.0%, C: 4.0%~6.0%, the balance is inevitable impurities.

[0037] In some embodiments, the melting point of the first mold slag is 1000°C to 1100°C.

[0038] In some embodiments, the basicity of the first protective slag is 1.05-1.15.

[0039] The present application reasonably designs the chemical composition of the first protective slag to ensure that the protective slag has good lubricity, melting point and viscosity. Under low pulling speed conditions (pulling speed within the range of <4.5m / min), good lubricity is still crucial to reduce the friction between the ingot and the crystallizer and prevent the occurrence of adhesion and cracks. At lower pulling speeds, the protective slag has more time to contact with the molten steel and should be able to effectively absorb non-metallic inclusions in the molten steel to improve the purity of the ingot. The melting temperature of the protective slag should not be too high to ensure the rapid formation of a uniform slag film, and the viscosity should be moderate to ensure good coverage and protection. Basicity (CaO / SiO 2 ) mainly plays a role in controlling the crystallization performance. When the pulling speed is high, the friction will increase. While reducing the risk of slag rolling, lubrication is ensured and heat transfer is properly controlled. The basicity of the first protective slag of the present invention is increased by increasing the content of CaO, increasing the crystallization temperature and the proportion of the crystal phase, and inhibiting heat transfer. For example, the content of CaO can be 25.0%, 27.0%, 29.0%, 30.0%, 32.0%, 34.0%, 35.0%, etc., SiO 2 The content of Al can be 24.0%, 25.0%, 26.0%, 27.0%, 28.0%, etc. 2 O 3 The content of O can be 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, etc., the content of MgO can be 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, etc., the content of MnO can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc., the content of NaO can be 2 With K 2 The sum of the contents of LiO can be 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, etc. 2 The content of may be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc., and the content of C may be 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, etc. The viscosity of the first protective slag at 1300°C may be 0.10Pa·s, 0.12Pa·s, 0.14Pa·s, 0.16Pa·s, 0.18Pa·s, 0.20Pa·s, etc., the melting point of the first protective slag may be 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, etc., and the basicity of the first protective slag may be 1.05, 1.07, 1.09, 1.10, 1.12, 1.14, 1.15, etc.

[0040] In some embodiments, the chemical composition of the first mold slag is, by mass fraction, CaO: 30.0%, SiO 2 : 25.5%,Al 2 O 3:5.8%, MgO: 6.8%, MnO: 1.63%, NaO 2 +K 2 O: 7.1%, LiO 2 : 0.66%, C: 5.65%, and the remainder is unavoidable impurities; the melting point of the first protective slag is 1038°C, the viscosity of the first protective slag at 1300°C is 0.10Pa·s, and the basicity of the first protective slag is 1.10.

[0041] S3. When the casting speed of the casting machine is ≥4.5 m / min, the protective slag is the second protective slag; the viscosity of the second protective slag at 1300°C is 0.04 Pa·s to 0.08 Pa·s.

[0042] In some embodiments, the chemical composition of the second mold slag includes, by mass fraction: CaO: 30.0% to 35.0%, SiO 2 :25.0%~30.0%,Al 2 O 3 : 4.0% ~ 8.0%, MgO: 6.0% ~ 8.0%, MnO: 0.05% ~ 0.20%, NaO 2 +K 2 O: 6.0%~10.0%, LiO 2 <5.0%, C: 4.0%~6.0%, the balance is inevitable impurities.

[0043] In some embodiments, the melting point of the second mold slag is 950°C to 1050°C.

[0044] In some embodiments, the basicity of the second protective slag is 1.25-1.35.

[0045] The present application reasonably designs the chemical composition of the second protective slag to ensure that the protective slag has a lower melting temperature and excellent fluidity, as well as maintains a low viscosity. Under high pulling speed conditions (pulling speed is in the range of 4.5m / min to 6.0m / min), the protective slag is required to have a lower melting temperature and excellent fluidity to quickly cover the surface of the crystallizer and form a stable slag film to cope with more violent liquid level disturbances. At high pulling speeds, the protective slag must maintain a low viscosity and be evenly distributed in the crystallizer to avoid cracks and steel sticking caused by local overheating or uneven cooling. Exemplarily, the CaO content can be 30.0%, 31.0%, 32.0%, 33.0%, 33.5%, 34.0%, 35.0%, etc., and SiO 2 The content of Al can be 25.0%, 26.0%, 27.0%, 28.0%, 29.0%, 30.0%, etc. 2 O 3The content of O can be 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, etc., the content of MgO can be 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, etc., the content of MnO can be 0.05%, 0.08%, 0.10%, 0.15%, 0.20%, etc., the content of NaO can be 2 With K 2 The sum of the contents of LiO can be 6.0%, 7.0%, 8.0%, 9.0%, 10.0%, etc. 2 The content of may be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc., and the content of C may be 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, etc. The viscosity of the second protective slag at 1300°C may be 0.04Pa·s, 0.05Pa·s, 0.06Pa·s, 0.07Pa·s, 0.08Pa·s, etc., the melting point of the second protective slag may be 950°C, 980°C, 1000°C, 1020°C, 1040°C, 1050°C, etc., and the basicity of the second protective slag may be 1.25, 1.27, 1.29, 1.30, 1.32, 1.34, 1.35, etc.

[0046] In some embodiments, the chemical composition of the second mold slag is, by mass fraction, CaO: 32.9%, SiO 2 : 27.2%, Al 2 O 3 :6.4%, MgO: 5.9%, MnO: 0.10%, NaO 2 +K 2 O: 8.2%, LiO 2 : 0.88%, C: 5.23%; the melting point of the second protective slag is 1005°C, the viscosity of the second protective slag at 1300°C is 0.06Pa·s, and the basicity of the second protective slag is 1.29.

[0047] In some embodiments, the preparation method of the first protective slag and the second protective slag includes the steps of batching, melting, cooling and crushing. First, various raw materials, such as basic slag, flux and regulator, are accurately weighed according to the required performance indicators; then, the mixed raw materials are placed in a melting furnace and heated to a high temperature to completely melt and evenly mix them; then, the molten protective slag is rapidly cooled to control its crystal morphology and glass content; finally, the cooled protective slag is crushed and sieved to a specified particle size to meet the use requirements in the high-speed continuous casting process of thin slabs.

[0048] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0049] Example 1

[0050] This embodiment adopts two-stage addition of mold slag. In terms of mass fraction, the chemical composition of the first mold slag is: CaO: 30.0%, SiO 2 : 25.5%,Al 2 O 3 :5.8%, MgO: 6.8%, MnO: 1.63%, NaO 2 +K 2 O: 7.1%, LiO 2 : 0.66%, C: 5.65%, the remainder is unavoidable impurities; the melting point of the first protective slag is 1038℃, the viscosity of the first protective slag at 1300℃ is 0.10Pa·s, and the basicity of the first protective slag is 1.10. In terms of mass fraction, the chemical composition of the second protective slag is: CaO: 32.9%, SiO 2 : 27.2%, Al 2 O 3 :6.4%, MgO: 5.9%, MnO: 0.10%, NaO 2 +K 2 O: 8.2%, LiO 2 : 0.88%, C: 5.23%; the melting point of the second protective slag is 1005°C, the viscosity of the second protective slag at 1300°C is 0.06Pa·s, and the basicity of the second protective slag is 1.29.

[0051] Based on the above protective slag, this embodiment also provides a thin slab continuous casting method, including the following steps: low-carbon SPHC steel is continuously cast, the secondary cooling water distribution adopts the low-carbon steel water distribution system, the crystallizer vibration parameters adopt the low-carbon steel vibration parameters, the superheat of the tundish is controlled to 20-35°C (liquidus 1531°C), the tundish is prepared before casting, the ladle slag is tested for 20% opening, the ladle slide is opened and the molten steel flows from the ladle into the tundish, after the pouring starts, when the tundish is 24 tons, a high-basicity low-carbon steel covering agent is added to the stopper rod, the tundish is started at 30 tons and the molten steel in the tundish is poured into the crystallizer, that is, the process from the start of pouring to the pulling speed rising to 0.8m / min, the first protective slag is pushed in, and when the pulling speed rises to 0.8m / min, the holding time is 3 seconds, and then it is directly increased from 0.8m / min to 3.5m / min and stabilized until the swing shear shearing ends, and the pulling speed increase rate is 1.5m / min 2When the pulling speed is increased to 4.5m / min, the protective slag liquid slag layer is at an ideal 11mm. When the pulling speed is greater than 4.5m / min, the pulling speed is further increased to 5.8m / min and the second protective slag is used. The thickness of the liquid slag layer is well controlled during the entire casting process and can still be maintained at an ideal 10mm. The liquid level fluctuation ratio of ±3mm is good. The surface quality of the final product is good, and no slag rolling defects are found.

[0052] Comparative Example 1

[0053] This comparative example adopts a one-step addition of mold slag. The chemical composition of the mold slag is as follows: CaO: 30.0%, SiO 2 : 25.5%,Al 2 O 3 :5.8%, MgO: 6.8%, MnO: 1.63%, NaO 2 +K 2 O: 7.1%, LiO 2 : 0.66%, C: 5.65%, and the balance is inevitable impurities; the melting point of the protective slag is 1038°C, the viscosity of the protective slag at 1300°C is 0.10Pa·s, and the basicity of the protective slag is 1.10.

[0054] Based on the above-mentioned protective slag, this embodiment also provides a thin slab continuous casting method, including the following steps: low-carbon SPHC steel is continuously cast, the secondary cooling water distribution adopts the low-carbon steel water distribution system, the crystallizer vibration parameters adopt the low-carbon steel vibration parameters, the tundish superheat is controlled to be 20-35°C (liquidus line 1531°C), the tundish is prepared before casting, the ladle slag is tested for 20% opening, the ladle slide is opened, the molten steel flows from the ladle into the tundish, and after the pouring starts, when the tundish is 24 tons, a high-basicity low-carbon steel covering agent is added to the stopper rod , the 30-ton tundish is started to pour, and the molten steel in the tundish is poured into the crystallizer, that is, from the start of pouring to the process of the pulling speed rising to 0.8m / min, the protective slag is pushed in. When the pulling speed rises to 0.8m / min, the holding time is 3 seconds, and the pulling speed is directly increased from 0.8m / min to 3.5m / min, and stabilized at this speed until the swing shear completes the first shearing. The pulling speed increase rate in this stage is 1.5m / min2, aiming to quickly reach the target pulling speed while ensuring that the quality of the ingot is not affected. When the pulling speed reaches 4.5m / min, the protective slag shows its excellent performance and maintains the thickness of the liquid slag layer at an ideal 11mm. After the casting speed stabilized at 4.5m / min, the casting speed was further increased to the target casting speed of 5.6m / min in accordance with production demand. The above-mentioned protective slag was still used, but its relatively high viscosity and specific melting point range were no longer applicable under high-speed casting conditions, resulting in the difficulty in maintaining the ideal 10mm thickness of the liquid slag layer. The thickness of the liquid slag layer was only 8mm, the liquid level fluctuation increased, and the difficulty of surface quality control increased, which affected the surface quality of the ingot and reduced the yield and product quality.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that the chemical composition of the second protective slag is: CaO: 33.0%, SiO 2 :25.5%、Al 2 O 3 :8.5%, MgO: 8.0%, MnO: 0.25%, NaO 2 +K 2 O: 7.0%, LiO 2 : 2.0%, C: 6.5%, the balance is inevitable impurities;

[0057] The melting point of the second protective slag is 1040° C., the viscosity of the second protective slag at 1300° C. is 0.11 Pa·s, and the basicity of the second protective slag is 1.29.

[0058] When the pulling speed reaches 4.5m / min, the first protective slag shows its excellent performance and maintains the thickness of the liquid slag layer at an ideal 11mm. After the pulling speed stabilizes at 4.5m / min, the pulling speed is further increased to the target pulling speed of 5.6m / min according to production needs, and the second protective slag is used, but its viscosity is 0.11Pa·s, which is not within the range of 0.04-0.08Pa·s, making it difficult for the liquid slag layer to maintain an ideal thickness of 10-12mm. The thickness of the liquid slag layer is only 8mm, the lubrication effect is poor, the friction resistance increases, the surface quality of the ingot is affected, and the yield and product quality are reduced.

[0059] In addition, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0060] In the embodiment of the present invention, low carbon steel protective slag is added in two stages, which can not only meet the lubrication and heat transfer effects at a pulling speed of less than 4.5m / min, but also meet the protective slag consumption, heat transfer and liquid slag layer thickness at a high pulling speed of ≥4.5m / min, which can ensure smooth continuous casting and improve product quality, while ensuring efficient production of the production line and product quality.

[0061] In the embodiment of the present invention, the thin slab continuous casting method provided is crucial to ensure smooth continuous casting and improve product quality, and can also ensure efficient production of the production line and product quality. It has high process application value, is easy to operate, and can ensure the stable improvement of the slab quality of the thin slab continuous casting machine.

[0062] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A thin slab continuous casting method, characterized in that: The method comprises: Casting the molten steel, and during the casting process, determining the type of protective slag according to the casting speed of the casting machine; When the casting speed is less than 4.5 m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300° C. is 0.10 Pa·s to 0.20 Pa·s; When the casting machine casting speed is ≥4.5m / min, the protective slag is the second protective slag; the viscosity of the second protective slag at 1300°C is 0.04Pa·s to 0.08Pa·s.

2. The method according to claim 1, characterized in that Measured in mass fraction, the chemical composition of the first protective slag includes: CaO: 25.0%~35.0%, SiO2: 24.0%~28.0%, Al2O3: 4.0%~8.0%, MgO: 5.0%~9.0%, MnO: 1.0%~3.0%, NaO2+K2O: 5.0%~9.0%, LiO2<5.0%, C: 4.0%~6.0%, and the remainder is unavoidable impurities.

3. The method according to claim 2, characterized in that The melting point of the first mold slag is 1000°C to 1100°C.

4. The method according to claim 3, characterized in that: The basicity of the first protective slag is 1.05-1.

15.

5. The method according to claim 2, characterized in that: In terms of mass fraction, the chemical composition of the first protective slag is: CaO: 30.0%, SiO2: 25.5%, Al2O3: 5.8%, MgO: 6.8%, MnO: 1.63%, NaO2+K2O: 7.1%, LiO2: 0.66%, C: 5.65%, and the remainder is unavoidable impurities; the melting point of the first protective slag is 1038°C, the viscosity of the first protective slag at 1300°C is 0.10Pa·s, and the basicity of the first protective slag is 1.

10.

6. The method according to claim 1, characterized in that Measured in mass fraction, the chemical composition of the second protective slag includes: CaO: 30.0%~35.0%, SiO2: 25.0%~30.0%, Al2O3: 4.0%~8.0%, MgO: 6.0%~8.0%, MnO: 0.05%~0.20%, NaO2+K2O: 6.0%~10.0%, LiO2<5.0%, C: 4.0%~6.0%, and the remainder is unavoidable impurities.

7. The method according to claim 6, characterized in that The melting point of the second mold slag is 950°C to 1050°C.

8. The method according to claim 7, characterized in that The basicity of the second protective slag is 1.25-1.

35.

9. The method according to claim 6, characterized in that In terms of mass fraction, the chemical composition of the second protective slag is: CaO: 32.9%, SiO2: 27.2%, Al2O3: 6.4%, MgO: 5.9%, MnO: 0.10%, NaO2+K2O: 8.2%, LiO2: 0.88%, C: 5.23%; the melting point of the second protective slag is 1005°C, the viscosity of the second protective slag at 1300°C is 0.06Pa·s, and the basicity of the second protective slag is 1.

29.

10. The method according to claim 1, characterized in that The molten steel is molten steel for low carbon steel.

Images