A method and apparatus for suppressing cracks in 20Mn23AlV low alloy steel slabs

Abstract

This invention provides a method and apparatus for suppressing cracks in 20Mn23AlV low-alloy steel slabs, comprising the following steps: introducing molten steel from a tundish into a crystallizer through an immersion nozzle in a sealed inert gas environment; adding protective slag to the molten steel in the crystallizer and cooling and continuously casting the molten steel to obtain 20Mn23AlV low-alloy steel slabs with a yield ≥94% and a crack rate ≤1.6%; the superheat of the molten steel in the tundish is 30~50℃. The above process steps and apparatus are simple in structure and easy to operate, improving yield, reducing production costs, and effectively suppressing cracks in 20Mn23AlV low-alloy steel slabs. This method is suitable for large-scale industrial production, effectively improving the continuous casting castability and production efficiency of 20Mn23AlV low-alloy steel.

Description

Technical Field

[0001] This invention belongs to the field of steel continuous casting production technology, and particularly relates to a method and apparatus for suppressing cracks in 20Mn23AlV low alloy steel slabs. Background Technology

[0002] In the field of low-alloy steel continuous casting technology, 20Mn23AlV steel, as a lightweight alloy steel with high aluminum and high manganese content, shows broad application potential in industries such as automobile manufacturing and construction machinery due to its high strength, low density, and wear resistance. However, slab cracks often occur during the continuous casting process of 20Mn23AlV steel, which seriously affect the surface quality and internal density of the slab. These cracks may lead to cracking, delamination, or fracture during subsequent rolling and processing, thereby affecting the performance and service life of the product. The presence of cracks also reduces the yield and production efficiency of the cast slab, and increases the costs of grinding and scrapping.

[0003] In existing technologies, while optimizing the basicity of the protective slag or adding fluxes such as Li2O can alleviate slag system modification, it cannot suppress the continuous enrichment of Al2O3. While electromagnetic stirring or light reduction techniques can improve the solidification structure, the equipment modification costs are high. Therefore, reducing slab cracks is crucial for improving billet quality, reducing production costs, and ensuring product performance. Based on this, this application provides a method and apparatus for suppressing cracks in 20Mn23AlV low-alloy steel slabs. Summary of the Invention

[0004] The main objective of this invention is to provide a method and apparatus for suppressing cracks in 20Mn23AlV low-alloy steel slabs, aiming to solve the technical problem that cracks easily appear on the surface of 20Mn23AlV low-alloy steel slabs during the continuous casting production process in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for suppressing cracks in 20Mn23AlV low-alloy steel slabs, comprising the following steps:

[0006] In a sealed, inert gas environment, molten steel from the tundish is introduced into the crystallizer through an immersion nozzle.

[0007] A protective slag is added to the molten steel in the crystallizer, and the molten steel is cooled and continuously cast to obtain 20Mn23AlV low alloy steel slabs with a yield of ≥94% and a crack rate of ≤1.6%.

[0008] The steel composition of the tundish, by mass fraction, includes: Mn 22~25%, Al 1~3%, C 0.18~0.25%, V 0.08~0.12%, P≤200 ppm, S≤50 ppm, N≤100 ppm, O≤15 ppm, with the balance being Fe and unavoidable impurities.

[0009] The superheat of the molten steel in the tundish is 30~50℃.

[0010] In some embodiments, the molten steel in the tundish is introduced into the crystallizer in a flow direction that allows the molten steel in the crystallizer to be cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone.

[0011] The first water flow rate of the first water cooling zone is 300~450 L / min, the second water flow rate of the second water cooling zone is 200~350 L / min, and the third water flow rate of the third water cooling zone is 100~250 L / min.

[0012] In some embodiments, a sealing cover is provided at the connection between the crystallizer and the intermediate package, and the sealing cover is filled with inert gas to form a sealed inert gas environment.

[0013] The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%.

[0014] The inner layer of the sealing cover is made of 310S heat-resistant stainless steel; the outer layer is made of aluminum silicate fiber insulation board with a thermal conductivity of ≤0.12 W / (m·K) and a thickness of 30~50 mm.

[0015] In some embodiments, the composition of the protective slag, by mass fraction, includes: 25-50% SiO2, 1-15% Al2O3, 20-40% CaO, 5-15% Na2O, 5-15% F, 3-10% C, and 3-8% Li2O.

[0016] The binary basicity of the protective slag, CaO / SiO2, is 0.5~1.

[0017] The melting point of the protective slag is 800~950℃.

[0018] The viscosity of the protective slag is 0.1~0.3 Pa·s.

[0019] In some embodiments, the thickness of the protective slag in the crystallizer is 3 to 10 mm, and the consumption of the protective slag is 0.3 to 0.6 kg / t of molten steel in the tundish.

[0020] In some embodiments, the continuous casting speed is 0.4~1.0 m / min, and the constant casting rate is ≥96%.

[0021] In some embodiments, the tilt angle of the crystallizer is 2 to 10°.

[0022] The crystallizer vibrates at a frequency of 140-160 times / min and has an amplitude of 3-5 mm.

[0023] In some embodiments, the immersion nozzle is a double-sided immersion nozzle with an insertion depth of 0.11~0.17m.

[0024] The inclination angle of the sprue is 10~30°.

[0025] The width of the side hole of the water inlet is 0.04~0.09 m.

[0026] The height of the side hole of the water inlet is 0.05~0.10 m.

[0027] In some embodiments, the side hole of the water inlet also includes 4 to 8 annular protective gas nozzles.

[0028] The protective gas is argon with a purity of ≥99.99%.

[0029] The gas flow rate of a single annular protective gas nozzle is 5~15 L / min.

[0030] The present invention also provides a device for suppressing cracks in 20Mn23AlV low alloy steel slabs, comprising:

[0031] The molten steel buffer vessel includes a tundish and an immersion nozzle. The bottom of the tundish is equipped with an electromagnetic induction heating module with a power density of 50~150 kW / m³. 2 It is used to maintain the superheat of molten steel at 30~50℃; in a sealed inert gas environment, molten steel in the tundish is introduced into the molten steel solidification and forming equipment through a submerged nozzle; the first end of the submerged nozzle is located in the tundish, the inclination angle of the second end of the submerged nozzle is 10~30°, and the insertion depth of the second end of the submerged nozzle is 0.11~0.17 m.

[0032] The molten steel solidification forming equipment is located below the molten steel buffer container. The molten steel solidification forming equipment is connected to the molten steel buffer container through an immersion nozzle, and protective slag is added to the molten steel solidification forming equipment to cool and solidify the molten steel therein.

[0033] The sealing cover is located at the connection between the molten steel buffer container and the molten steel solidification forming equipment. The sealing cover is filled with inert gas to form a sealed inert gas environment.

[0034] In this process, the molten steel in the solidification and forming equipment is cooled sequentially through the first water-cooling zone, the second water-cooling zone, and the third water-cooling zone, taking into account the flow direction of the molten steel.

[0035] The first water flow rate of the first water cooling zone is 300~450 L / min, the second water flow rate of the second water cooling zone is 200~350 L / min, and the third water flow rate of the third water cooling zone is 100~250 L / min.

[0036] The width of the side hole of the submersible water inlet is 0.04~0.09 m; the height of the side hole of the submersible water inlet is 0.05~0.10 m.

[0037] The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%; the inner layer of the sealing cover is made of 310S heat-resistant stainless steel; and the outer layer is made of aluminum silicate fiber insulation board.

[0038] The beneficial effects of this invention are:

[0039] The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs described in this invention effectively prevents secondary oxidation of aluminum in the molten steel during transport in a sealed inert gas environment, reduces the formation of Al2O3 and MnS inclusions, lowers crack sensitivity, and improves the cleanliness of the molten steel. By introducing appropriately composed 20Mn23AlV low-alloy steel from the tundish into the crystallizer through a submerged entry nozzle, and adding protective slag to improve slag film lubrication, reduces frictional resistance between the slab and the crystallizer, thereby effectively preventing crack formation. Subsequent cooling achieves differentiated cooling of the molten steel, alleviating the temperature gradient between the slab surface and core, thus reducing the tendency for solidification cracking. After continuous casting, a 20Mn23AlV low-alloy steel slab with a yield ≥94% and a crack rate ≤1.6% is obtained.

[0040] The above-mentioned process steps and equipment structure are simple and easy to operate, which improves the yield, reduces the production cost, and effectively suppresses cracks in 20Mn23AlV low alloy steel slabs. This method is suitable for large-scale industrial production and effectively improves the continuous casting castability and production efficiency of 20Mn23AlV low alloy steel. Attached Figure Description

[0041] 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.

[0042] Figure 1The image shows the 20Mn23AlV low-alloy steel slab obtained in Example 1;

[0043] Figure 2 The image shows the 20Mn23AlV low-alloy steel slab obtained in Example 2;

[0044] Figure 3 The image shows the 20Mn23AlV low-alloy steel slab obtained in Example 3;

[0045] Figure 4 The image shows the 20Mn23AlV low-alloy steel slab obtained in Comparative Example 1.

[0046] Figure 5 The image shows the 20Mn23AlV low-alloy steel slab obtained in Comparative Example 2.

[0047] Figure 6 This is a diagram of the device for suppressing cracks in 20Mn23AlV low alloy steel slabs in this invention;

[0048] Figure 7 The diagram shows the submersible nozzle in the apparatus for suppressing cracks in 20Mn23AlV low alloy steel slabs of the present invention; wherein, (a) is a diagram of the submersible nozzle apparatus; and (b) is a diagram of the annular protective gas nozzle on the side hole of the submersible nozzle.

[0049] Figure 8 This is a schematic diagram of the molten steel in the tundish of the device for suppressing cracks in 20Mn23AlV low alloy steel slabs in this invention being introduced into the crystallizer for cooling; wherein, (a) is a structural schematic diagram of the first water cooling zone, the second water cooling zone and the third water cooling zone; (b) is a water tank in the corner area and the face area.

[0050] The attached figures are labeled as follows: 11. molten steel buffer container; 12. molten steel solidification and forming equipment; 13. sealing cover; 21. tundish; 22. submersible nozzle; 23. inner layer of the sealing cover; 24. outer layer of the sealing cover; 25. annular protective gas nozzle; 26. angle of the submersible nozzle; 31. water tank in the corner area; 32. water tank in the face area.

[0051] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0052] 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.

[0053] 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.

[0054] To achieve the above objectives, the present invention provides a method for suppressing cracks in 20Mn23AlV low-alloy steel slabs, comprising the following steps:

[0055] In a sealed, inert gas environment, molten steel from the tundish is introduced into the crystallizer through an immersion nozzle.

[0056] A protective slag is added to the molten steel in the crystallizer, and the molten steel is cooled and continuously cast to obtain 20Mn23AlV low alloy steel slabs with a yield of ≥94% and a crack rate of ≤1.6%.

[0057] In some embodiments, operating in a sealed inert gas environment can prevent steel oxidation, ensure the purity of the steel, and thus improve the quality of 20Mn23AlV low-alloy steel slabs. Using an immersion nozzle to introduce molten steel from the tundish into the crystallizer effectively reduces splashing and oxidation. Adding a protective slag to the molten steel in the crystallizer coats the surface, preventing oxidation. Simultaneously, it serves a lubricating and heat-transfer function during crystallization.

[0058] The steel composition of the tundish, by mass fraction, includes: Mn 22~25%, Al 1~3%, C 0.18~0.25%, V 0.08~0.12%, P≤200 ppm, S≤50 ppm, N≤100 ppm, O≤15 ppm, with the balance being Fe and unavoidable impurities.

[0059] The superheat of the molten steel in the tundish is 30~50℃.

[0060] In some embodiments, the composition of the molten steel in the tundish, by mass fraction, includes: Mn 23.2~24.5%, Al 1.7~2.4%, C 0.18~0.25%, V 0.08~0.12%, P≤100 ppm, S≤30 ppm, N≤80 ppm, O≤15 ppm, with the balance being Fe and unavoidable impurities.

[0061] The superheat of the molten steel in the tundish is 30~45℃.

[0062] By controlling the steel composition in the tundish and coordinating it with the preparation process, the probability of surface cracks in 20Mn23AlV low-alloy steel slabs can be effectively reduced, while also improving the utilization rate of the steel. Controlling the overheating of the tundish helps the molten steel to quickly form a shell in the crystallizer, while avoiding overheating or undercooling that could affect the quality of the 20Mn23AlV low-alloy steel slab. Furthermore, controlling the steel composition in the tundish stage further improves the cleanliness of the molten steel, reducing the formation of inclusions such as Al2O3 and MnS, and lowering crack susceptibility.

[0063] The aforementioned method for suppressing cracks in 20Mn23AlV low-alloy steel slabs, under a sealed inert gas environment, effectively prevents secondary oxidation of aluminum in the molten steel during transport, reduces the formation of Al2O3 and MnS inclusions, lowers crack susceptibility, and improves the cleanliness of the molten steel. By introducing appropriately composed 20Mn23AlV low-alloy steel from the tundish into the crystallizer through a submerged entry nozzle, and adding protective slag, the lubrication effect of the slag film is improved, reducing the frictional resistance between the slab and the crystallizer, thereby effectively preventing crack formation. Subsequently, cooling with different water flow rates is performed to achieve differentiated cooling of the molten steel, alleviating the temperature gradient between the slab surface and core, thus reducing the tendency for solidification cracking. After continuous casting, 20Mn23AlV low-alloy steel slabs with a yield ≥94% and a crack rate ≤1.6% are obtained.

[0064] In some embodiments, the molten steel in the tundish is introduced into the crystallizer in a flow direction indicator, and the molten steel in the crystallizer is cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone.

[0065] The first water flow rate of the first water cooling zone is 300~450 L / min, the second water flow rate of the second water cooling zone is 200~350 L / min, and the third water flow rate of the third water cooling zone is 100~250 L / min.

[0066] In some embodiments, the molten steel in the crystallizer is cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone. The water tank depth in the first water-cooling zone is 35-45 mm, the water tank depth in the second water-cooling zone is 25-35 mm, and the water tank depth in the third water-cooling zone is 15-25 mm. The spacing between adjacent water tanks in the face region is 15-30 mm, and the spacing between adjacent water tanks in the corner regions is 5-15 mm.

[0067] In some embodiments, the first water flow rate of the first water-cooled zone is 330~420 L / min, the second water flow rate of the second water-cooled zone is 200~300 L / min, and the third water flow rate of the third water-cooled zone is 120~200 L / min.

[0068] In some embodiments, the molten steel in the crystallizer is cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone. The water tank depth in the first water-cooling zone is 37-44 mm, the water tank depth in the second water-cooling zone is 26-33 mm, and the water tank depth in the third water-cooling zone is 15-20 mm. The spacing between adjacent water tanks in the face region is 17-27 mm, and the spacing between adjacent water tanks in the corner regions is 5-13 mm.

[0069] In some specific embodiments, the first water flow rate of the first water-cooling zone is 400 L / min, and the water tank depth is 44 mm; the second water flow rate of the second water-cooling zone is 290 L / min, and the water tank depth is 35 mm; the third water flow rate of the third water-cooling zone is 150 L / min, and the water tank depth is 20 mm. The spacing between adjacent water tanks in the facial area is 25 mm, and the spacing between adjacent water tanks in the corner areas is 6 mm.

[0070] The molten steel in the crystallizer is cooled sequentially through the first, second, and third water-cooling zones. By controlling the water flow rate in each zone, the flow of molten steel is optimized, and differentiated cooling is achieved. This effectively alleviates the temperature gradient between the surface and core of the slab, thereby reducing the tendency for solidification cracks to occur.

[0071] In some embodiments, a sealing cover is provided at the connection between the crystallizer and the intermediate package, and the sealing cover is filled with inert gas to form a sealed inert gas environment.

[0072] The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%.

[0073] The inner layer of the sealing cover is made of 310S heat-resistant stainless steel; the outer layer is made of aluminum silicate fiber insulation board with a thermal conductivity of ≤0.12 W / (m·K) and a thickness of 30~50 mm.

[0074] In some embodiments, the outlet gas flow rate of the intermediate package is 35~45 L / min, and the gas flow rate of the crystallizer is 15~25 L / min.

[0075] In some specific embodiments, the outlet gas flow rate of the intermediate package is 45 L / min, and the gas flow rate of the crystallizer is 20 L / min.

[0076] In some embodiments, a sealing cover is provided at the connection between the crystallizer and the tundish, and filled with inert gas to form a sealed inert gas environment. This maintains a low-oxygen environment, effectively preventing secondary oxidation of aluminum in the molten steel during transport, reducing the formation of Al2O3 inclusions, and improving the purity and surface quality of the slab. Furthermore, the material design of the sealing cover contributes to improved durability. The inner layer is made of 310S heat-resistant stainless steel, which has excellent corrosion resistance and high-temperature resistance. The outer layer is made of aluminum silicate fiber insulation board, which effectively insulates heat, reduces heat loss, and improves energy efficiency, playing a crucial role in reducing energy consumption and saving production costs.

[0077] In some embodiments, the composition of the protective slag, by mass fraction, includes: 25-50% SiO2, 1-15% Al2O3, 20-40% CaO, 5-15% Na2O, 5-15% F, 3-10% C, and 3-8% Li2O.

[0078] The binary basicity of the protective slag, CaO / SiO2, is 0.5~1.

[0079] The melting point of the protective slag is 800~950℃.

[0080] The viscosity of the protective slag is 0.1~0.3 Pa·s.

[0081] In some embodiments, the composition of the protective slag, by mass fraction, includes: SiO2 30-45%, Al2O3 1-10%, CaO 25-35%, Na2O 5-15%, F 7-13%, C 3-8%, and Li2O 3-5%.

[0082] The binary basicity of the protective slag, CaO / SiO2, is 0.5~1.

[0083] The melting point of the protective slag is 820~930℃.

[0084] The viscosity of the protective slag is 0.1~0.25 Pa·s.

[0085] In some specific embodiments, the composition of the protective slag, by mass fraction, includes: 42% SiO2, 4% Al2O3, 28% CaO, 10% Na2O, 8% F, 3% C, and 5% Li2O. The binary basicity of the protective slag, CaO / SiO2, is 0.67, the melting point is 820℃, and the viscosity is 0.17 Pa·s.

[0086] In some embodiments, optimizing the control of the composition, viscosity and melting point of the protective slag can increase the lubrication between the billet and the mold during continuous casting, so as to maintain suitable fluidity and heat conduction properties during continuous casting, ensure uniform temperature on the surface of the billet, and further reduce thermal stress and cracking tendency.

[0087] Appropriate binary basicity can improve the lubricity of the protective slag, reduce friction between the billet and the crystallizer, and also help inclusions float to the surface in the molten steel, thus reducing the inclusion content in the billet.

[0088] In some embodiments, the thickness of the protective slag in the crystallizer is 3-10 mm, and the consumption of the protective slag is 0.3-0.6 kg / t of molten steel in the tundish. By adjusting the thickness of the protective slag, the lubrication effect can be improved, the frictional resistance between the billet and the crystallizer can be reduced, thereby effectively preventing crack formation.

[0089] In some embodiments, the thickness of the protective slag in the crystallizer is 7-8 mm, and the consumption of protective slag per ton of molten steel in the tundish is 0.49 kg.

[0090] In some embodiments, the continuous casting speed is 0.4~1.0 m / min, and the constant casting rate is ≥96%.

[0091] In some embodiments, the continuous casting speed is 0.56 m / min, and the constant casting rate is 98%. Appropriate continuous casting speed and constant casting rate help the billet achieve more uniform cooling, thereby reducing internal stress and segregation and improving the microstructure uniformity of the billet.

[0092] In some embodiments, the tilt angle of the crystallizer is 2~10°.

[0093] The crystallizer vibrates at a frequency of 140-160 times / min and has an amplitude of 3-5 mm.

[0094] In some embodiments, the tilt angle of the crystallizer is 3~8°.

[0095] In some specific embodiments, the crystallizer has an inclination angle of 8°.

[0096] In some embodiments, the immersion nozzle is a double-sided immersion nozzle with an insertion depth of 0.11~0.17m.

[0097] The inclination angle of the sprue is 10~30°.

[0098] The width of the side hole of the water inlet is 0.04~0.09 m.

[0099] The height of the side hole of the water inlet is 0.05~0.10 m.

[0100] In some embodiments, the insertion depth of the immersion nozzle is 0.12~0.16 m, the inclination angle of the nozzle is 10~25°, the width of the side hole of the nozzle is 0.05~0.08 m, and the height of the side hole of the nozzle is 0.06~0.09 m.

[0101] In some specific embodiments, the insertion depth of the immersion nozzle is 0.16 m, the inclination angle of the nozzle is 20°, the width of the side hole of the nozzle is 0.08 m, and the height of the side hole of the nozzle is 0.09 m.

[0102] In some embodiments, adjusting the insertion depth and inclination angle of the submerged nozzle can make the flow distribution of molten steel more uniform, effectively reducing flow deviation and local temperature fluctuations, thereby reducing the solidification thickness difference in the crystallizer and thus reducing thermal stress and slab cracks. At the same time, appropriately increasing the inclination angle of the nozzle can also suppress slag entrapment in molten steel, reducing the risk of protective slag being drawn into the molten steel and forming inclusions, thereby improving the cleanliness of the molten steel.

[0103] In some embodiments, the side hole of the water inlet further includes 4 to 8 annular protective gas nozzles.

[0104] The protective gas is argon with a purity of ≥99.99%.

[0105] The gas flow rate of a single annular protective gas nozzle is 5~15 L / min.

[0106] In some specific embodiments, the side hole of the sprue includes eight annular protective gas nozzles, each with a gas flow rate of 7 L / min. By setting annular protective gas nozzles on the side hole of the sprue and introducing argon gas, air entrapment can be effectively prevented, thus preventing secondary oxidation of the molten steel. Simultaneously, sprue blockage is reduced, effectively improving production efficiency.

[0107] The present invention also provides a device for suppressing cracks in 20Mn23AlV low-alloy steel slabs, comprising:

[0108] The molten steel buffer vessel includes a tundish and an immersion nozzle. The bottom of the tundish is equipped with an electromagnetic induction heating module with a power density of 50~150 kW / m³. 2 It is used to maintain the superheat of molten steel at 30~50℃; in a sealed inert gas environment, molten steel in the tundish is introduced into the molten steel solidification and forming equipment through a submerged nozzle; the first end of the submerged nozzle is located in the tundish, the inclination angle of the second end of the submerged nozzle is 10~30°, and the insertion depth of the second end of the submerged nozzle is 0.11~0.17 m.

[0109] The molten steel solidification forming equipment is located below the molten steel buffer container. The molten steel solidification forming equipment is connected to the molten steel buffer container through an immersion nozzle, and protective slag is added to the molten steel solidification forming equipment to cool and solidify the molten steel therein.

[0110] The sealing cover is located at the connection between the molten steel buffer container and the molten steel solidification forming equipment. The sealing cover is filled with inert gas to form a sealed inert gas environment.

[0111] In this process, the molten steel in the solidification and forming equipment is cooled sequentially through the first water-cooling zone, the second water-cooling zone, and the third water-cooling zone, taking into account the flow direction of the molten steel.

[0112] The first water flow rate of the first water cooling zone is 300~450 L / min, the second water flow rate of the second water cooling zone is 200~350 L / min, and the third water flow rate of the third water cooling zone is 100~250 L / min.

[0113] The width of the side hole of the submersible water inlet is 0.04~0.09 m; the height of the side hole of the submersible water inlet is 0.05~0.10 m.

[0114] The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%; the inner layer of the sealing cover is made of 310S heat-resistant stainless steel; and the outer layer is made of aluminum silicate fiber insulation board.

[0115] In some embodiments, the steel solidification forming equipment is a crystallizer located below the steel buffer container. The crystallizer is connected to the steel buffer container through an immersion nozzle, and protective slag is added to the crystallizer to cool and solidify the molten steel therein.

[0116] The above-mentioned device has a simple structure and is easy to operate. It improves the yield, reduces the production cost, and effectively suppresses cracks in 20Mn23AlV low alloy steel slabs. This method is suitable for large-scale industrial production and effectively improves the continuous casting castability and production efficiency of 20Mn23AlV low alloy steel.

[0117] To further illustrate the present invention, examples are given below.

[0118] Example 1

[0119] A method for suppressing cracks in 20Mn23AlV low-alloy steel slabs includes the following steps: introducing molten steel from a tundish into a crystallizer through an immersion nozzle in a sealed inert gas environment; adding protective slag to the molten steel in the crystallizer and cooling and continuously casting the molten steel to obtain 20Mn23AlV low-alloy steel slabs.

[0120] The composition of the molten steel in the tundish, by mass fraction, includes: Mn 24.2%, Al 2.1%, C 0.20%, V 0.10%, P 50 ppm, S 16 ppm, N 34 ppm, O ≤15 ppm, with the balance being Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 30°C.

[0121] A sealing cover is installed at the connection between the crystallizer and the tundish. The sealing cover is filled with inert argon gas to form a sealed inert gas environment. The crystallizer is tilted at an angle of 8°, and the molten steel in the crystallizer is cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone. Specifically, the first water-cooling zone has a first water flow rate of 400 L / min and a water tank depth of 44 mm; the second water-cooling zone has a second water flow rate of 290 L / min and a water tank depth of 35 mm; and the third water-cooling zone has a third water flow rate of 150 L / min and a water tank depth of 20 mm. The spacing between adjacent water tanks in the face area is 25 mm, and the spacing between adjacent water tanks in the corner areas is 6 mm. The outlet gas flow rate of the tundish is 45 L / min, and the gas flow rate of the crystallizer is 20 L / min.

[0122] The immersion nozzle is a double-sided immersion nozzle with an insertion depth of 0.16 m, an inclination angle of 20°, a side hole width of 0.08 m, and a side hole height of 0.09 m. The side holes of the nozzle also include eight annular protective gas nozzles, each with a gas flow rate of 7 L / min.

[0123] The composition of the protective slag, by mass fraction, includes: 42% SiO2, 34% Al2O3, 28% CaO, 10% Na2O, 8% F, 3% C, and 5% Li2O. The binary basicity of the protective slag, CaO / SiO2, is 0.67, the melting point is 820℃, and the viscosity is 0.17 Pa·s.

[0124] In the crystallizer, the thickness of the protective slag is 7-8 mm, and the consumption of the protective slag is 0.49 kg / t of molten steel in the tundish. The continuous casting speed is 0.56 m / min, and the constant casting rate is 98%.

[0125] Testing revealed that the optimized molten steel exhibited improved purity and the lowest inclusion content. Adjusting the submerged entry nozzle angle to 20° resulted in a more uniform flow field distribution, minimal temperature fluctuations, and a more consistent protective slag thickness. The low-melting-point, low-viscosity protective slag ensured a smooth, crack-free surface for the cast billet. The grinding rate was 5%, the crack rate was 0.5%, and the yield was 98%.

[0126] Example 2

[0127] A method for suppressing cracks in 20Mn23AlV low-alloy steel slabs includes the following steps: introducing molten steel from a tundish into a crystallizer through an immersion nozzle in a sealed inert gas environment; adding protective slag to the molten steel in the crystallizer and cooling and continuously casting the molten steel to obtain 20Mn23AlV low-alloy steel slabs.

[0128] The composition of the molten steel in the tundish, by mass fraction, includes: Mn 23.4%, Al 2.0%, C 0.23%, V 0.08%, P 80 ppm, S 25 ppm, N 70 ppm, O ≤15 ppm, with the balance being Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 35°C.

[0129] A sealing cover is installed at the connection between the crystallizer and the tundish. The sealing cover is filled with inert argon gas to form a sealed inert gas environment. The crystallizer is tilted at 5°, and the molten steel in the crystallizer is cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone. Specifically, the first water-cooling zone has a first water flow rate of 350 L / min and a water tank depth of 40 mm; the second water-cooling zone has a second water flow rate of 260 L / min and a water tank depth of 30 mm; and the third water-cooling zone has a third water flow rate of 150 L / min and a water tank depth of 18 mm. The spacing between adjacent water tanks in the face area is 20 mm, and the spacing between adjacent water tanks in the corner areas is 9 mm. The outlet gas flow rate of the tundish is 40 L / min, and the gas flow rate of the crystallizer is 20 L / min.

[0130] The immersion nozzle is a double-sided immersion nozzle with an insertion depth of 0.14 m, an inclination angle of 10°, a side hole width of 0.06 m, and a side hole height of 0.07 m. The side holes of the nozzle also include six annular protective gas nozzles, each with a gas flow rate of 8 L / min.

[0131] The composition of the protective slag, by mass fraction, includes: 42% SiO2, 34% Al2O3, 30% CaO, 10% Na2O, 7% F, 4% C, and 3% Li2O. The binary basicity of the protective slag, CaO / SiO2, is 0.714, the melting point is 900℃, and the viscosity is 0.25 Pa·s.

[0132] In the crystallizer, the thickness of the protective slag is 5-6 mm, and the consumption of the protective slag is 0.4 kg / t of molten steel in the tundish. The continuous casting speed is 0.57 m / min, and the constant casting rate is 97%.

[0133] Testing revealed improved steel purity, reduced inclusion content, and decreased thermal stress. Surface cracks in the 20Mn23AlV low-alloy steel slab were significantly reduced, resulting in improved surface quality. Specifically, the grinding rate was 15%, the crack rate was 1.6%, and the yield was 94%.

[0134] Example 3

[0135] A method for suppressing cracks in 20Mn23AlV low-alloy steel slabs includes the following steps: introducing molten steel from a tundish into a crystallizer through an immersion nozzle in a sealed inert gas environment; adding protective slag to the molten steel in the crystallizer and cooling and continuously casting the molten steel to obtain 20Mn23AlV low-alloy steel slabs.

[0136] The composition of the molten steel in the tundish, by mass fraction, includes: Mn 23.8%, Al 1.9%, C 0.18%, V 0.11%, P 70 ppm, S 20 ppm, N 60 ppm, O ≤15 ppm, with the balance being Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 32°C.

[0137] A sealing cover is installed at the connection between the crystallizer and the tundish. The sealing cover is filled with inert argon gas to form a sealed inert gas environment. The crystallizer is tilted at 6°, and the molten steel in the crystallizer is cooled sequentially through a first water-cooling zone, a second water-cooling zone, and a third water-cooling zone. Specifically, the first water flow rate in the first water-cooling zone is 380 L / min, and the water tank depth is 42 mm; the second water flow rate in the second water-cooling zone is 270 L / min, and the water tank depth is 32 mm; the third water flow rate in the third water-cooling zone is 180 L / min, and the water tank depth is 19 mm. The spacing between adjacent water tanks in the face area is 22 mm, and the spacing between adjacent water tanks in the corner areas is 7 mm. The outlet gas flow rate of the tundish is 45 L / min, and the gas flow rate of the crystallizer is 18 L / min.

[0138] The immersion nozzle is a double-sided immersion nozzle with an insertion depth of 0.15 m, an inclination angle of 15°, a side hole width of 0.07 m, and a side hole height of 0.08 m. The side holes of the nozzle also include eight annular protective gas nozzles, each with a gas flow rate of 9 L / min.

[0139] The composition of the protective slag, by mass fraction, includes: 40% SiO2, 32% Al2O, 32% CaO, 9% Na2O, 9% F, 4% C, and 4% Li2O. The binary basicity of the protective slag, CaO / SiO2, is 0.74, the melting point is 860℃, and the viscosity is 0.2 Pa·s.

[0140] In the crystallizer, the thickness of the protective slag is 5-7 mm, and the consumption of the protective slag is 0.45 kg / t of molten steel in the tundish. The continuous casting speed is 0.52 m / min, and the constant casting rate is 98%.

[0141] Testing revealed that the purity of the molten steel was further improved, and the content of inclusions was reduced. Adjustment of the submerged entry nozzle angle improved the uniformity of the flow field distribution and reduced flow deviation. The thickness of the protective slag was stable, effectively reducing friction between the billet and the mold. The grinding rate was 10%, the crack rate was 0.9%, and the yield was 96%.

[0142] Comparative Example 1

[0143] Molten steel from the tundish is introduced into the crystallizer through an immersion nozzle; protective slag is added to the molten steel in the crystallizer, and the molten steel is cooled and continuously cast to obtain 20Mn23AlV low alloy steel slab.

[0144] The composition of the molten steel in the tundish, by mass fraction, includes: Mn 22.5%, Al 2.6%, C 0.24%, V 0.08%, P 120 ppm, S 40 ppm, N 100 ppm, O ≤15 ppm, with the balance being Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 55°C.

[0145] No sealing cover was installed at the connection between the crystallizer and the tundish. The crystallizer was tilted at 2°, and the molten steel in the crystallizer was cooled without partitions at a water flow rate of 350 L / min.

[0146] The immersion nozzle is a double-sided hole immersion nozzle with an insertion depth of 0.10 m, an inclination angle of 5°, a side hole width of 0.04 m, and a side hole height of 0.05 m. There is no annular protective gas nozzle on the side holes of the nozzle.

[0147] The composition of the protective slag, by mass fraction, includes: 40% SiO2, 35% Al2O, 35% CaO, 5% Na2O, 7.8% F, 4.7% C, and 2.5% Li2O. The binary basicity of the protective slag, CaO / SiO2, is 0.875, the melting point is 946℃, and the viscosity is 0.35 Pa·s.

[0148] In the crystallizer, the thickness of the protective slag is 3-4 mm, and the consumption of the protective slag is 0.33 kg / t of molten steel in the tundish. The continuous casting speed is 0.42 m / min, and the constant casting rate is 92%.

[0149] Testing revealed that the molten steel had excessively high superheat and lacked a sealing cover at the connection between the crystallizer and the tundish, allowing direct contact with air and oxidation. A high level of inclusions was found, concentrated in the central segregation zone of the slab. Thermal stress was concentrated during solidification, resulting in noticeable longitudinal cracks and depressions on the surface. The protective slag film exhibited poor lubricity and high frictional resistance. The grinding rate was 35-40%, the surface crack rate was 4.2%, and the yield was 87%.

[0150] Comparative Example 2

[0151] Compared to Example 1, the composition of the molten steel in the tundish was changed.

[0152] The composition of the molten steel in the tundish, by mass fraction, includes: Mn 24.1%, Al 2.5%, C 0.15%, V 0.12%, P 100 ppm, S 62 ppm, N 133 ppm, O ≤25 ppm, with the balance being Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 34°C.

[0153] The other steps are the same as in Example 1.

[0154] The test results showed that the grinding rate was 19%, the surface crack rate was 3.3%, and the yield was 89%.

[0155] in, Figure 1 The image shows the 20Mn23AlV low-alloy steel slab obtained in Example 1; Figure 2 The image shows the 20Mn23AlV low-alloy steel slab obtained in Example 2; Figure 3 The image shows the 20Mn23AlV low-alloy steel slab obtained in Example 3; Figure 4 The image shows the 20Mn23AlV low-alloy steel slab obtained in Comparative Example 1. Figure 5 The image shows the 20Mn23AlV low-alloy steel slab obtained in Comparative Example 2. Figure 6 This is a diagram of the device for suppressing cracks in 20Mn23AlV low alloy steel slabs in this invention; Figure 7 This is a diagram of the submersible nozzle in the apparatus for suppressing cracks in 20Mn23AlV low-alloy steel slabs of the present invention; wherein, Figure 7 (a) is a diagram of an immersion nozzle device; Figure 7 (b) is a diagram of the annular protective gas nozzle on the side hole of the immersion nozzle; Figure 8 This is a schematic diagram illustrating the process of introducing molten steel from the tundish into the crystallizer for cooling in the apparatus for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to the present invention; wherein, Figure 8 (a) is a structural schematic diagram of the first water-cooled zone, the second water-cooled zone and the third water-cooled zone; Figure 8 (b) is the water tank for the corner and face areas.

[0156] As can be seen from Examples 1-3, through the coordination of components and various process steps, 20Mn23AlV low-alloy steel slabs with a yield ≥94% and a crack rate ≤1.6% are obtained. Among them, the 20Mn23AlV low-alloy steel slab obtained in Example 1 has a grinding rate of 5%, a crack rate of 0.5%, and a yield of 98%.

[0157] In Comparative Example 1, the superheat of the molten steel was too high, and no sealing cover was installed at the connection between the crystallizer and the tundish. The molten steel was in direct contact with air and oxidized, resulting in a high content of inclusions and obvious longitudinal cracks and depressions on the surface of the cast billet. In Comparative Example 2, the composition of the molten steel in the tundish was changed, which increased the crack rate of the 20Mn23AlV low alloy steel slab and reduced the yield.

[0158] Therefore, this invention introduces molten steel of suitable composition into the crystallizer through a submerged entry nozzle in a sealed inert gas environment. A protective slag is added to the molten steel in the crystallizer, and the steel is then cooled and continuously cast to obtain a 20Mn23AlV low-alloy steel slab. The sealed inert gas environment effectively prevents secondary oxidation of aluminum in the molten steel during transport, reduces the formation of Al2O3 and MnS inclusions, lowers crack susceptibility, and improves the cleanliness of the molten steel. The introduction of 20Mn23AlV low-alloy steel of suitable composition from the tundish into the crystallizer through the submerged entry nozzle, along with the addition of protective slag, enhances the slag film lubrication effect, reduces the frictional resistance between the slab and the crystallizer, and effectively prevents crack formation. Subsequent cooling and continuous casting achieve differentiated cooling of the molten steel, alleviating the temperature gradient between the slab surface and core, thereby reducing the tendency for solidification cracking.

[0159] The above-mentioned process steps and equipment structure are simple and easy to operate, which improves the yield, reduces the production cost, and effectively suppresses cracks in 20Mn23AlV low alloy steel slabs. This method is suitable for large-scale industrial production and effectively improves the continuous casting castability and production efficiency of 20Mn23AlV low alloy steel.

[0160] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for suppressing cracks in 20Mn23AlV low-alloy steel slabs, characterized in that, Includes the following steps: In a sealed inert gas environment, molten steel from the tundish is introduced into the crystallizer through an immersion nozzle; Add protective slag to the molten steel in the crystallizer and cool and continuously cast the molten steel to obtain 20Mn23AlV low alloy steel slabs with a yield of ≥94% and a crack rate of ≤1.6%. The composition of the protective slag, by mass fraction, includes: SiO2 25~50%, Al2O3 1~15%, CaO 20~40%, Na2O 5~15%, F 5~15%, C 3~10%, Li2O 3~8%; The protective slag has a binary basicity of CaO / SiO2 of 0.5~1, a melting point of 800~950℃, and a viscosity of 0.1~0.3 Pa·s; The composition of the molten steel in the tundish, by mass fraction, includes: Mn 22~25%, Al 1~3%, C 0.18~0.25%, V 0.08~0.12%, P≤200 ppm, S≤50 ppm, N≤100 ppm, O≤15 ppm, with the balance being Fe and unavoidable impurities; The superheat of the molten steel in the tundish is 30~50℃; Based on the flow direction of molten steel introduced from the tundish into the crystallizer, the molten steel in the crystallizer is cooled sequentially through the first water-cooling zone, the second water-cooling zone, and the third water-cooling zone. The first water flow rate of the first water cooling zone is 300~450 L / min, the second water flow rate of the second water cooling zone is 200~350 L / min, and the third water flow rate of the third water cooling zone is 100~250 L / min.

2. The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to claim 1, characterized in that, A sealing cover is provided at the connection between the crystallizer and the intermediate package. The sealing cover is filled with inert gas to form a sealed inert gas environment. The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%. The inner layer of the sealing cover is made of 310S heat-resistant stainless steel; the outer layer is made of aluminum silicate fiber insulation board with a thermal conductivity of ≤0.12 W / (m·K) and a thickness of 30~50 mm.

3. The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to claim 1, characterized in that, In the crystallizer, the thickness of the protective slag is 3~10 mm, and the consumption of the protective slag is 0.3~0.6 kg / t of molten steel in the tundish.

4. The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to claim 1, characterized in that, The continuous casting speed is 0.4~1.0 m / min, and the constant casting rate is ≥96%.

5. The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to claim 1, characterized in that, The tilt angle of the crystallizer is 2~10°; The crystallizer has a vibration frequency of 140~160 times / min and an amplitude of 3~5mm.

6. The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to claim 1, characterized in that, The immersion nozzle is a double-sided immersion nozzle with an insertion depth of 0.11~0.17 m; The inclination angle of the sluice gate is 10~30°; The width of the side hole of the water inlet is 0.04~0.09 m; The height of the side hole of the water inlet is 0.05~0.10 m.

7. The method for suppressing cracks in 20Mn23AlV low-alloy steel slabs according to claim 6, characterized in that, The side hole of the water inlet also includes 4 to 8 annular protective gas nozzles; The protective gas is argon with a purity of ≥99.99%. The gas flow rate of a single annular protective gas nozzle is 5~15 L / min.

8. An apparatus for using the method for suppressing cracks in 20Mn23AlV low-alloy steel slabs as described in any one of claims 1 to 7, characterized in that, include: A molten steel buffer vessel, comprising a tundish and an immersion nozzle, wherein the bottom of the tundish is equipped with an electromagnetic induction heating module with a power density of 50~150kW / m³. 2 It is used to maintain the superheat of molten steel at 30~50℃; in a sealed inert gas environment, molten steel in the tundish is introduced into the molten steel solidification and forming equipment through a submerged nozzle; the first end of the submerged nozzle is located in the tundish, the inclination angle of the second end of the submerged nozzle is 10~30°, and the insertion depth of the second end of the submerged nozzle is 0.11~0.17 m; The molten steel solidification forming equipment is located below the molten steel buffer container. The molten steel solidification forming equipment is connected to the molten steel buffer container through an immersion nozzle, and protective slag is added to the molten steel solidification forming equipment to cool and solidify the molten steel therein. A sealing cover is located at the connection between the molten steel buffer container and the molten steel solidification forming equipment. The sealing cover is filled with inert gas to form a sealed inert gas environment. In terms of the flow direction of the molten steel, the molten steel in the molten steel solidification and forming equipment is cooled sequentially through the first water cooling zone, the second water cooling zone, and the third water cooling zone. The first water flow rate of the first water cooling zone is 300~450 L / min, the second water flow rate of the second water cooling zone is 200~350 L / min, and the third water flow rate of the third water cooling zone is 100~250 L / min; The width of the side hole of the submersible inlet is 0.04~0.09 m; the height of the side hole of the submersible inlet is 0.05~0.10 m; The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%; the inner layer of the sealing cover is made of 310S heat-resistant stainless steel; and the outer layer is made of aluminum silicate fiber insulation board.

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