Method and device for inhibiting cracks of 20Mn23AlV low alloy steel slab

Abstract

The invention provides a method and device for inhibiting cracks of a 20Mn23AlV low alloy steel slab, and the method comprises the following steps: introducing molten steel in a tundish into a crystallizer through a submersed nozzle in a sealed inert gas environment; casting powder is added into the molten steel in the crystallizer, cooling and continuous casting are conducted on the molten steel, and a 20Mn23AlV low-alloy steel slab with the yield larger than or equal to 94% and the crack rate smaller than or equal to 1.6% is obtained; and the degree of superheat of the molten steel in the tundish is 30-50 DEG C. The process steps and the device are simple in structure and convenient to operate, the yield is increased, the production cost is reduced, cracks of the 20Mn23AlV low-alloy steel slab are effectively restrained, the method is suitable for large-scale industrial production, and the continuous casting castability and production efficiency of the 20Mn23AlV low-alloy steel are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel continuous casting production, and in particular relates to a method and a device for suppressing cracks in a 20Mn23AlV low alloy steel slab. Background Art

[0002] In the field of low alloy steel continuous casting technology, 20Mn23AlV steel, as a high aluminum, high manganese lightweight alloy steel, has shown wide application potential in industrial fields such as automobile manufacturing and engineering machinery due to its high strength, low density and wear resistance. However, during the continuous casting process of 20Mn23AlV steel, slab cracks often appear, which have a serious impact on the surface quality and internal density of the slab. These cracks may cause cracking, delamination or fracture during subsequent rolling and processing, thereby affecting the performance and service life of the product. The presence of cracks will also reduce the yield rate and production efficiency of the ingot, and increase the cost of grinding and scrapping.

[0003] In the prior art, although the modification of slag system can be alleviated by optimizing the basicity of protective slag or adding flux such as Li2O, the continuous enrichment of Al2O3 cannot be suppressed; although electromagnetic stirring or soft pressure reduction technology can improve the solidification structure, the equipment modification cost is high. Therefore, reducing slab cracks is the key to improving the quality of castings, reducing production costs and ensuring product performance. Based on this, the present application provides a method and device for suppressing cracks in 20Mn23AlV low alloy steel slabs. Summary of the invention

[0004] The main purpose of the present invention is to provide a method and device for suppressing cracks in 20Mn23AlV low alloy steel slabs, aiming to solve the technical problem that cracks are prone to appear on the surface of 20Mn23AlV low alloy steel slabs in the continuous casting production process of the prior art.

[0005] To achieve the above object, the present invention provides a method for inhibiting cracks in a 20Mn23AlV low alloy steel slab, comprising the following steps: In a sealed inert gas environment, the molten steel in the tundish is introduced into the crystallizer through an immersed nozzle.

[0006] Protective slag is added to the molten steel in the crystallizer, and the molten steel is cooled and continuously cast to obtain a 20Mn23AlV low alloy steel slab with a yield rate of ≥94% and a crack rate of ≤1.6%.

[0007] 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, and the balance is Fe and unavoidable impurities.

[0008] The superheat of the molten steel in the tundish is 30 to 50 °C.

[0009] In some embodiments, taking the flow direction of the molten steel in the tundish introduced into the mold as a reference, the molten steel in the mold is cooled successively through a first water cooling zone, a second water cooling zone, and a third water cooling zone.

[0010] Among them, the first water flow rate in the first water cooling zone is 300 to 450 L / min, the second water flow rate in the second water cooling zone is 200 to 350 L / min, and the third water flow rate in the third water cooling zone is 100 to 250 L / min.

[0011] In some embodiments, a sealing cover is provided at the connection between the mold and the tundish, and the sealing cover is filled with an inert gas to form a sealed inert gas environment.

[0012] Among them, the inert gas is argon, with a purity ≥ 99.99% and an oxygen content ≤ 0.5%.

[0013] The inner layer material of the sealing cover is 310S heat-resistant stainless steel; the outer layer material is a refractory fiber insulation board with a thermal conductivity ≤ 0.12 W / (m·K) and a thickness of 30 to 50 mm.

[0014] In some embodiments, the composition of the mold powder, by mass fraction, includes: SiO2 25 to 50%, Al2O3 1 to 15%, CaO 20 to 40%, Na2O 5 to 15%, F 5 to 15%, C 3 to 10%, Li2O 3 to 8%.

[0015] The binary basicity CaO / SiO2 of the mold powder is 0.5 to 1.

[0016] The melting point of the mold powder is 800 to 950 °C.

[0017] The viscosity of the mold powder is 0.1 to 0.3 Pa·s.

[0018] In some embodiments, in the mold, the thickness of the mold powder is 3 to 10 mm, and the consumption of the mold powder is 0.3 to 0.6 kg / t of the molten steel in the tundish.

[0019] In some embodiments, the casting speed of continuous casting is 0.4 to 1.0 m / min, and the constant casting speed rate ≥ 96%.

[0020] In some embodiments, the inclination angle of the mold is 2 to 10°.

[0021] The vibration frequency of the mold is 140 to 160 times / min, and the amplitude is 3 to 5 mm.

[0022] In some embodiments, the submerged entry nozzle is a double-side orifice submerged entry nozzle, and the insertion depth is 0.11 - 0.17 m.

[0023] The inclination angle of the nozzle is 10 - 30°.

[0024] The width of the side orifice of the nozzle is 0.04 - 0.09 m.

[0025] The height of the side orifice of the nozzle is 0.05 - 0.10 m.

[0026] In some embodiments, there are also 4 - 8 annular protective gas nozzles on the side orifice of the nozzle.

[0027] Among them, the protective gas is argon, and the purity is ≥99.99%.

[0028] The gas flow rate of a single annular protective gas nozzle is 5 - 15 L / min.

[0029] The present invention also provides a device for suppressing cracks in 20Mn23AlV low-alloy steel slab, including: The molten steel buffer container includes a tundish and a submerged entry nozzle. An electromagnetic induction heating module is arranged at the bottom of the tundish, and the power density is 50 - 150 kW / m 2 , which is used to maintain the superheat degree of the molten steel at 30 - 50°C; in a sealed inert gas environment, the molten steel in the tundish is introduced into the molten steel solidification forming equipment through the submerged entry nozzle; the first end of the submerged entry nozzle is located in the tundish, the inclination angle of the second end of the submerged entry nozzle is 10 - 30°, and the insertion depth of the second end of the submerged entry nozzle is 0.11 - 0.17 m.

[0030] 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 the submerged entry nozzle, and a protective slag is added in the molten steel solidification forming equipment to cool and solidify the molten steel therein.

[0031] 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 an inert gas to form a sealed inert gas environment.

[0032] Among them, in the direction of the molten steel flow, the molten steel in the molten steel solidification forming equipment sequentially passes through the first water cooling zone, the second water cooling zone, and the third water cooling zone for cooling.

[0033] The first water flow rate in the first water cooling zone is 300 - 450 L / min, the second water flow rate in the second water cooling zone is 200 - 350 L / min, and the third water flow rate in the third water cooling zone is 100 - 250 L / min.

[0034] The side hole width of the submerged nozzle is 0.04 - 0.09 m; the side hole height of the submerged nozzle is 0.05 - 0.10 m.

[0035] The inert gas is argon with a purity ≥ 99.99% and an oxygen content ≤ 0.5%; the inner layer material of the sealing cover is 310S heat-resistant stainless steel; the outer layer material is aluminosilicate fiber insulation board.

[0036] The beneficial effects of the present invention are as follows: The method for suppressing cracks in 20Mn23AlV low-alloy steel slab of the present invention can effectively prevent secondary oxidation of aluminum element in molten steel during the transmission process, reduce the generation of Al2O3 and MnS inclusions, lower the crack sensitivity, and improve the cleanliness of molten steel in a sealed inert gas environment. Through the submerged nozzle, the 20Mn23AlV low-alloy steel molten steel with appropriate components in the tundish is introduced into the mold, and mold powder is added to enhance the lubrication effect of the slag film and reduce the friction resistance between the slab and the mold, thereby effectively preventing crack generation. Then cooling is carried out to achieve differential cooling of the molten steel, relieve the temperature gradient between the surface and the core of the slab, and thus reduce the tendency of solidification cracks. After continuous casting, 20Mn23AlV low-alloy steel slabs with a yield rate ≥ 94% and a crack rate ≤ 1.6% are obtained.

[0037] The above process steps and device structure are simple, easy to operate, improve the yield rate, reduce the production cost, and effectively suppress cracks in 20Mn23AlV low-alloy steel slabs. This method is applicable to large-scale industrial production, effectively improves the castability and production efficiency of 20Mn23AlV low-alloy steel. Brief Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for description in the embodiments or in the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0039] Figure 1 It is a drawing of the 20Mn23AlV low-alloy steel slab obtained in Example 1; Figure 2 It is a drawing of the 20Mn23AlV low-alloy steel slab obtained in Example 2; Figure 3 It is a drawing of the 20Mn23AlV low-alloy steel slab obtained in Example 3; Figure 4 It is a drawing of the 20Mn23AlV low-alloy steel slab obtained in Comparative Example 1; Figure 5 It is a drawing of the 20Mn23AlV low-alloy steel slab prepared in Comparative Example 2; Figure 6 It is a drawing of the device for suppressing cracks in the 20Mn23AlV low-alloy steel slab in the present invention; Figure 7 It is a drawing of the submerged nozzle in the device for suppressing cracks in the 20Mn23AlV low-alloy steel slab in the present invention; among them, (a) is the drawing of the submerged nozzle; (b) is the drawing of the annular protective gas nozzle on the side hole of the submerged nozzle; Figure 8 It is a schematic diagram of introducing molten steel in the tundish into the crystallizer for cooling in the device for suppressing cracks in the 20Mn23AlV low-alloy steel slab in the present invention; among them, (a) is the schematic diagram of the structures of the first water-cooling zone, the second water-cooling zone and the third water-cooling zone; (b) is the water tank in the corner area and the face area.

[0040] The reference numerals are: 11, molten steel buffer container; 12, molten steel solidification forming equipment; 13, sealing cover; 21, tundish; 22, submerged nozzle; 23, inner layer of the sealing cover; 24, outer layer of the sealing cover; 25, annular protective gas nozzle; 26, inclination angle of the submerged nozzle; 31, water tank in the corner area; 32, water tank in the face area.

[0041] The realization, functional features and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the drawings. Specific Embodiments

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0043] Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] To achieve the above object, the present invention provides a method for suppressing cracks in a 20Mn23AlV low-alloy steel slab, including the following steps: In a sealed inert gas environment, introduce the molten steel in the tundish into the crystallizer through a submerged nozzle.

[0045] Add mold powder to the molten steel in the mold, and cool and continuously cast the molten steel therein to obtain a 20Mn23AlV low-alloy steel slab with a yield rate ≥ 94% and a crack rate ≤ 1.6%.

[0046] In some embodiments, operating in a sealed inert gas environment can prevent the oxidation of molten steel, ensure the purity of molten steel, and thus improve the quality of the 20Mn23AlV low-alloy steel slab. Using an immersion nozzle to introduce the molten steel from the tundish into the mold can effectively reduce the splashing and oxidation of molten steel. Adding mold powder to the molten steel in the mold can cover the surface of the molten steel to prevent the oxidation of molten steel. At the same time, it plays a role in lubrication and heat transfer during the crystallization process.

[0047] Among them, the chemical 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, and the balance is Fe and unavoidable impurities.

[0048] The superheat of the molten steel in the tundish is 30 - 50°C.

[0049] In some embodiments, the chemical 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, and the balance is Fe and unavoidable impurities.

[0050] The superheat of the molten steel in the tundish is 30 - 45°C.

[0051] By regulating the chemical composition of the molten steel in the tundish and cooperating with the preparation process, the probability of surface cracks in the 20Mn23AlV low-alloy steel slab can be effectively reduced, and at the same time, the utilization rate of steel is also improved. Regulating the superheat of the tundish helps the molten steel to quickly form a shell in the mold, and at the same time avoids the influence of overheating or overcooling on the quality of the 20Mn23AlV low-alloy steel slab. By regulating the chemical composition of the molten steel at the tundish stage, the cleanliness of the molten steel is further improved, the generation of inclusions such as Al2O3 and MnS is reduced, and the crack sensitivity is lowered.

[0052] The above method for suppressing cracks in 20Mn23AlV low-alloy steel slabs effectively prevents secondary oxidation of aluminum elements in molten steel during transportation in a sealed inert gas environment, reduces the generation of Al2O3 and MnS inclusions, lowers crack sensitivity, and improves the cleanliness of molten steel. Through the submerged nozzle, the 20Mn23AlV low-alloy molten steel with appropriate components in the tundish is introduced into the mold, and mold powder is added to enhance the lubrication effect of the slag film, reducing the frictional resistance between the slab and the mold, thereby effectively preventing crack generation. Subsequently, cooling with different water flow rates is carried out to achieve differential cooling of the molten steel, alleviating the temperature gradient between the surface and the core of the slab, and thus reducing the tendency of solidification cracks. After continuous casting, 20Mn23AlV low-alloy steel slabs with a yield rate ≥ 94% and a crack rate ≤ 1.6% are obtained.

[0053] In some embodiments, taking the flow direction of the molten steel in the tundish introduced into the mold as a reference, the molten steel in the mold is cooled successively through a first water cooling zone, a second water cooling zone, and a third water cooling zone.

[0054] Among them, the first water flow rate in the first water cooling zone is 300 - 450 L / min, the second water flow rate in the second water cooling zone is 200 - 350 L / min, and the third water flow rate in the third water cooling zone is 100 - 250 L / min.

[0055] In some embodiments, the molten steel in the mold is cooled successively through a first water cooling zone, a second water cooling zone, and a third water cooling zone. The water tank depth of the first water cooling zone is 35 - 45 mm, the water tank depth of the second water cooling zone is 25 - 35 mm, and the water tank depth of the third water cooling zone is 15 - 25 mm. Among them, the spacing between adjacent water tanks in the facial area is 15 - 30 mm, and the spacing between adjacent water tanks in the corner area is 5 - 15 mm.

[0056] In some embodiments, the first water flow rate in the first water cooling zone is 330 - 420 L / min, the second water flow rate in the second water cooling zone is 200 - 300 L / min, and the third water flow rate in the third water cooling zone is 120 - 200 L / min.

[0057] In some embodiments, the molten steel in the mold is cooled successively through a first water cooling zone, a second water cooling zone, and a third water cooling zone. The water tank depth of the first water cooling zone is 37 - 44 mm, the water tank depth of the second water cooling zone is 26 - 33 mm, and the water tank depth of the third water cooling zone is 15 - 20 mm. Among them, the spacing between adjacent water tanks in the facial area is 17 - 27 mm, and the spacing between adjacent water tanks in the corner area is 5 - 13 mm.

[0058] 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 area is 6 mm.

[0059] The molten steel in the crystallizer is cooled in turn through the first water cooling zone, the second water cooling zone and the third water cooling zone, and the water flow rate in different water cooling zones is regulated. This not only optimizes the flow of molten steel, but also achieves differentiated cooling, effectively alleviating the temperature gradient between the surface and the core of the slab, thereby reducing the tendency of solidification cracks.

[0060] In some embodiments, a sealing cover is provided at the connection between the crystallizer and the tundish, and the sealing cover is filled with an inert gas to form a sealed inert gas environment.

[0061] Wherein, the inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%.

[0062] The inner layer material of the sealing cover is 310S heat-resistant stainless steel; the outer layer material is an aluminum silicate fiber insulation board with a thermal conductivity of ≤0.12 W / (m·K) and a thickness of 30~50 mm.

[0063] In some embodiments, the outlet gas flow rate of the tundish is 35-45 L / min, and the gas flow rate of the crystallizer is 15-25 L / min.

[0064] In some specific embodiments, the outlet gas flow rate of the tundish is 45 L / min, and the gas flow rate of the crystallizer is 20 L / min.

[0065] In some embodiments, a sealing cover is provided at the connection between the crystallizer and the tundish and filled with an inert gas to form a sealed inert gas environment to maintain a low oxygen environment, effectively prevent the secondary oxidation of aluminum in the molten steel during the transmission process, reduce the formation of Al2O3 inclusions, and improve the purity and surface quality of the slab. In addition, the material design of the sealing cover helps to improve durability. Among them, the inner layer is 310S heat-resistant stainless steel, which has good corrosion resistance and high temperature resistance. The outer layer is an aluminum silicate fiber insulation board, which can effectively insulate, reduce heat loss, and improve energy efficiency, which plays an important role in reducing energy consumption and saving production costs.

[0066] In some embodiments, the composition of the mold powder, 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%.

[0067] The binary basicity CaO / SiO2 of the mold powder is 0.5-1.

[0068] The melting point of the mold powder is 800-950 °C.

[0069] The viscosity of the mold powder is 0.1-0.3 Pa·s.

[0070] In some embodiments, the composition of the mold powder, by mass fraction, includes: SiO2 30-45%, Al2O3 1-10%, CaO 25-35%, Na2O 5-15%, F 7-13%, C 3-8%, Li2O 3-5%.

[0071] The binary basicity CaO / SiO2 of the mold powder is 0.5-1.

[0072] The melting point of the mold powder is 820-930 °C.

[0073] The viscosity of the mold powder is 0.1-0.25 Pa·s.

[0074] In some specific embodiments, the composition of the mold powder, by mass fraction, includes: SiO2 42%, Al2O3 4%, CaO 28%, Na2O 10%, F 8%, C 3%, Li2O 5%. The binary basicity CaO / SiO2 of the mold powder is 0.67, the melting point is 820 °C, and the viscosity is 0.17 Pa·s.

[0075] In some embodiments, by optimizing the control of the composition, viscosity, and melting point of the mold powder, the lubricating effect between the billet and the mold can be increased during continuous casting, enabling it to maintain appropriate fluidity and heat conduction performance during continuous casting, ensuring uniform temperature on the surface of the billet, and further reducing thermal stress and crack tendency.

[0076] Appropriate binary basicity can improve the lubricity of the mold powder, reduce the friction between the billet and the mold, and also help the inclusions to float in the molten steel, reducing the inclusion content in the billet.

[0077] In some embodiments, in the mold, the thickness of the mold powder is 3-10 mm, and the consumption of the mold powder is 0.3-0.6 kg / t of the molten steel in the tundish. By adjusting the thickness of the mold powder, the lubricating effect can be enhanced, and the frictional resistance between the billet and the mold can be reduced, thereby effectively preventing crack generation.

[0078] In some embodiments, in the mold, the thickness of the mold powder is 7 - 8 mm, and the consumption of the mold powder corresponding to the molten steel in each tundish is 0.49 kg per ton.

[0079] In some embodiments, the casting speed of the continuous casting is 0.4 - 1.0 m / min, and the constant casting speed rate ≥ 96%.

[0080] In some embodiments, the casting speed of the continuous casting is 0.56 m / min, and the constant casting speed rate is 98%. Appropriate continuous casting speed and constant casting speed rate help the cast slab to obtain more uniform cooling, thereby reducing internal stress and segregation, and improving the tissue uniformity of the cast slab.

[0081] In some embodiments, the inclination angle of the mold is 2 - 10°.

[0082] The vibration frequency of the mold is 140 - 160 times / min, and the amplitude is 3 - 5 mm.

[0083] In some embodiments, the inclination angle of the mold is 3 - 8°.

[0084] In some specific embodiments, the inclination angle of the mold is 8°.

[0085] In some embodiments, the submerged nozzle is a double - side - hole submerged nozzle, and the insertion depth is 0.11 - 0.17 m.

[0086] The inclination angle of the nozzle is 10 - 30°.

[0087] The width of the side hole of the nozzle is 0.04 - 0.09 m.

[0088] The height of the side hole of the nozzle is 0.05 - 0.10 m.

[0089] In some embodiments, the insertion depth of the submerged 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.

[0090] In some specific embodiments, the insertion depth of the submerged 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.

[0091] In some embodiments, adjusting the insertion depth and inclination angle of the submerged nozzle can make the flow distribution of the molten steel more uniform, effectively reduce the cross-flow and local temperature fluctuations, thereby reducing the difference in solidification thickness in the mold, and thus reducing the thermal stress and slab cracks. At the same time, appropriately increasing the inclination angle of the nozzle can also inhibit the slag entrainment phenomenon of the molten steel, reduce the risk of the protective slag being entrained into the molten steel to form inclusions, and improve the cleanliness of the molten steel.

[0092] In some embodiments, there are also 4 - 8 annular protective gas nozzles on the side holes of the nozzle.

[0093] Among them, the protective gas is argon with a purity ≥ 99.99%.

[0094] The gas flow rate of a single annular protective gas nozzle is 5 - 15 L / min.

[0095] In some specific embodiments, there are 8 annular protective gas nozzles on the side holes of the nozzle, and the gas flow rate of a single annular protective gas nozzle is 7 L / min. By arranging annular protective gas nozzles on the side holes of the nozzle and introducing the protective gas argon, it can effectively prevent air from being entrained and prevent the secondary oxidation of the molten steel. At the same time, it reduces the nozzle blockage and effectively improves the production efficiency.

[0096] The present invention also provides a device for suppressing cracks in 20Mn23AlV low-alloy steel slab, including: The molten steel buffer container includes a tundish and a submerged nozzle. An electromagnetic induction heating module with a power density of 50 - 150 kW / m 2 is configured at the bottom of the tundish to maintain the superheat of the molten steel at 30 - 50°C; in a sealed inert gas environment, the molten steel in the tundish is introduced into the molten steel solidification forming equipment through the 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.

[0097] 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 the submerged nozzle, and a protective slag is added in the molten steel solidification forming equipment to cool and solidify the molten steel therein.

[0098] 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 an inert gas to form a sealed inert gas environment.

[0099] Among them, in the direction of the molten steel flow, the molten steel in the molten steel solidification forming equipment sequentially passes through the first water-cooling zone, the second water-cooling zone, and the third water-cooling zone for cooling.

[0100] 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.

[0101] The side hole width of the submerged water outlet is 0.04-0.09 m; the side hole height of the submerged water outlet is 0.05-0.10 m.

[0102] The inert gas is argon with a purity of ≥99.99% and an oxygen content of ≤0.5%; the inner layer material of the sealing cover is 310S heat-resistant stainless steel; and the outer layer material is an aluminum silicate fiber insulation board.

[0103] In some embodiments, the molten steel solidification and molding equipment uses a crystallizer, which is located below the molten steel buffer container. The crystallizer is connected to the molten steel buffer container through an immersion water inlet, and protective slag is added to the crystallizer to cool and solidify the molten steel therein.

[0104] The above-mentioned device has a simple structure and is easy to operate, which improves the yield rate, reduces the production cost, and effectively suppresses the cracks in the 20Mn23AlV low alloy steel slab. The method is suitable for large-scale industrial production and effectively improves the continuous casting castability and production efficiency of 20Mn23AlV low alloy steel.

[0105] In order to further understand the present invention, examples are given.

[0106] Example 1 A method for suppressing cracks in a 20Mn23AlV low alloy steel slab comprises the following steps: in a sealed inert gas environment, introducing molten steel in a tundish into a crystallizer through an immersed nozzle; adding protective slag to the molten steel in the crystallizer, and cooling and continuously casting the molten steel to obtain a 20Mn23AlV low alloy steel slab.

[0107] 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, and the remainder is Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 30°C.

[0108] A sealing cover is provided at the connection between the crystallizer and the tundish, and the sealing cover is filled with inert gas argon to form a sealed inert gas environment. The inclination angle of the crystallizer is 8°, and the molten steel in the crystallizer is cooled in turn through the first water cooling zone, the second water cooling zone and the third water cooling zone. Among them, 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 area 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.

[0109] The submerged nozzle is a double-side hole submerged 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 8 annular protective gas nozzles, and the gas flow rate of a single annular protective gas nozzle is 7 L / min.

[0110] The components of the protective slag, by mass fraction, include: SiO2 42%, Al2O 34%, CaO 28%, Na2O 10%, F8%, C 3%, Li2O 5%. The binary basicity CaO / SiO2 of the protective slag is 0.67, the melting point is 820°C, and the viscosity is 0.17 Pa·s.

[0111] 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 pulling rate is 98%.

[0112] After testing, the purity of the optimized molten steel composition is improved, and the inclusion content is the lowest. The inclination angle of the submerged nozzle is adjusted to 20°, the flow field distribution is more uniform, the temperature fluctuation is minimal, and the thickness of the protective slag is uniform. The protective slag with low melting point and low viscosity makes the surface of the ingot smooth and crack-free. Among them, the grinding rate is 5%, the crack rate is 0.5%, and the yield rate is 98%.

[0113] Example 2 A method for suppressing cracks in a 20Mn23AlV low alloy steel slab comprises the following steps: in a sealed inert gas environment, introducing molten steel in a tundish into a crystallizer through an immersed nozzle; adding protective slag to the molten steel in the crystallizer, and cooling and continuously casting the molten steel to obtain a 20Mn23AlV low alloy steel slab.

[0114] 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, and the remainder is Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 35°C.

[0115] A sealing cover is provided at the connection between the crystallizer and the tundish, and the sealing cover is filled with inert gas argon to form a sealed inert gas environment. The inclination angle of the crystallizer is 5°, and the molten steel in the crystallizer is cooled in turn through the first water cooling zone, the second water cooling zone and the third water cooling zone. Among them, the first water flow rate of the first water cooling zone is 350 L / min, and the water tank depth is 40 mm; the second water flow rate of the second water cooling zone is 260 L / min, and the water tank depth is 30 mm; the third water flow rate of the third water cooling zone is 150 L / min, and the water tank depth is 18 mm. The spacing between adjacent water tanks in the facial area is 20 mm, and the spacing between adjacent water tanks in the corner area 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.

[0116] The submerged nozzle is a double-side hole submerged 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 6 annular protective gas nozzles, and the gas flow rate of a single annular protective gas nozzle is 8 L / min.

[0117] The components of the protective slag, by mass fraction, include: SiO2 42%, Al2O 34%, CaO 30%, Na2O 10%, F7%, C 4%, Li2O 3%. The binary basicity CaO / SiO2 of the protective slag is 0.714, the melting point is 900°C, and the viscosity is 0.25 Pa·s.

[0118] 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 pulling rate is 97%.

[0119] After testing, the purity of molten steel was improved, the inclusion content was reduced, the thermal stress was reduced, the surface cracks of 20Mn23AlV low alloy steel slabs were significantly reduced, and the surface quality was improved. Among them, the grinding rate was 15%, the crack rate was 1.6%, and the yield rate was 94%.

[0120] Example 3 A method for suppressing cracks in 20Mn23AlV low-alloy steel slab billets, the steps including: in a sealed inert gas environment, introducing the molten steel in the tundish into the mold through a submerged nozzle; adding mold powder into the molten steel in the mold, and performing continuous casting with cooling on the molten steel therein to obtain 20Mn23AlV low-alloy steel slab billets.

[0121] Among them, the chemical 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, and the balance is Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 32°C.

[0122] A sealing cover is provided at the connection between the mold and the tundish, and the sealing cover is filled with inert gas argon to form a sealed inert gas environment. The inclination angle of the mold is 6°, and the molten steel in the mold passes through the first water cooling zone, the second water cooling zone, and the third water cooling zone in sequence for cooling. Among them, 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 facial area is 22 mm, and the spacing between adjacent water tanks in the corner area is 7 mm. The outlet gas flow rate of the tundish is 45 L / min, and the gas flow rate of the mold is 18 L / min.

[0123] The submerged nozzle is a double-side hole submerged nozzle, the insertion depth is 0.15 m, the inclination angle of the nozzle is 15°, the width of the side hole of the nozzle is 0.07 m, and the height of the side hole of the nozzle is 0.08 m. There are also 8 annular protective gas nozzles on the side hole of the nozzle, and the gas flow rate of a single annular protective gas nozzle is 9 L / min.

[0124] The chemical composition of the mold powder, by mass fraction, includes: SiO2 40%, Al2O3 2%, CaO 32%, Na2O 9%, F 9%, C 4%, Li2O 4%. The binary basicity CaO / SiO2 of the mold powder is 0.74, the melting point is 860°C, and the viscosity is 0.2 Pa·s.

[0125] In the mold, the thickness of the mold powder is 5 - 7 mm, and the consumption of the mold powder is 0.45 kg / t of the molten steel in the tundish. The casting speed of continuous casting is 0.52 m / min, and the constant casting speed rate is 98%.

[0126] After testing, the purity of molten steel was further improved and the inclusion content was reduced. After the inclination of the submerged nozzle was adjusted, the uniformity of the flow field distribution was improved and the deviation phenomenon was weakened. The thickness of the protective slag was stable, which effectively reduced the friction between the ingot and the crystallizer. Among them, the grinding rate was 10%, the crack rate was 0.9%, and the yield rate was 96%.

[0127] Comparative Example 1 The molten steel in the tundish is introduced into the crystallizer through an immersed nozzle; protective slag is added to the molten steel in the crystallizer, and the molten steel is cooled and continuously cast to obtain a 20Mn23AlV low alloy steel slab.

[0128] 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, and the remainder is Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 55°C.

[0129] No sealing cover is provided at the connection between the crystallizer and the tundish. The inclination angle of the crystallizer is 2°, the cooling of the molten steel in the crystallizer is non-zone cooling, and the water flow rate is 350 L / min.

[0130] The submerged nozzle is a double-side hole submerged 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 hole of the nozzle.

[0131] The components of the protective slag, by mass fraction, include: SiO2 40%, Al2O 35%, CaO 35%, Na2O 5%, F 7.8%, C 4.7%, Li2O 2.5%. The binary basicity CaO / SiO2 of the protective slag is 0.875, the melting point is 946°C, and the viscosity is 0.35 Pa·s.

[0132] 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 pulling rate is 92%.

[0133] After testing, it was found that the molten steel was in direct contact with air and oxidized due to the high superheat of the molten steel and the lack of a sealing cover at the connection between the crystallizer and the tundish. It was found that the inclusion content was relatively high and the inclusions were concentrated in the central segregation zone of the slab. When the ingot solidified, thermal stress concentrated and there were obvious longitudinal cracks and depressions on the surface. The slag film of the protective slag had poor lubricity and large friction resistance. Among them, the grinding rate was 35~40%, the surface crack rate was 4.2%, and the yield rate was 87%.

[0134] Comparative Example 2 Compared with Example 1, the composition of the molten steel in the tundish was changed.

[0135] The composition of the molten steel in the tundish, by mass fraction, includes: Mn 24.1%, Al 2.5%, C 0.15, V0.12%, P 100 ppm, S 62 ppm, N 133 ppm, O≤25 ppm, and the remainder is Fe and unavoidable impurities; the superheat of the molten steel in the tundish is 34°C.

[0136] The other steps are the same as in Example 1.

[0137] After testing, the grinding rate was 19%, the surface crack rate was 3.3%, and the yield rate was 89%.

[0138] in, Figure 1 This is a diagram of a 20Mn23AlV low alloy steel slab prepared in Example 1; Figure 2 This is a diagram of a 20Mn23AlV low alloy steel slab prepared in Example 2; Figure 3 This is a diagram of a 20Mn23AlV low alloy steel slab prepared in Example 3; Figure 4 This is a diagram of a 20Mn23AlV low alloy steel slab prepared in Comparative Example 1; Figure 5 This is a diagram of a 20Mn23AlV low alloy steel slab prepared in Comparative Example 2; Figure 6 A diagram of a device for suppressing cracks in a 20Mn23AlV low alloy steel slab in the present invention; Figure 7 The device diagram of the submerged nozzle in the device for suppressing cracks in 20Mn23AlV low alloy steel slab in the present invention; wherein, Figure 7 (a) is the installation diagram of the submerged nozzle; Figure 7 (b) is a diagram of the annular protective gas nozzle on the side hole of the submerged nozzle; Figure 8 The schematic diagram of the device for suppressing cracks in 20Mn23AlV low alloy steel slabs of the present invention is that the molten steel in the tundish is introduced into the molten steel in the crystallizer for cooling; wherein, Figure 8 (a) is a schematic diagram of the structures of the first water cooling zone, the second water cooling zone and the third water cooling zone; Figure 8 (b) The sinks in the corner area and the face area.

[0139] It can be seen from Examples 1 to 3 that, through the coordination of components and process steps, a 20Mn23AlV low alloy steel slab with a yield rate of ≥94% and a crack rate of ≤1.6% is obtained. Among them, the grinding rate of the 20Mn23AlV low alloy steel slab prepared in Example 1 is 5%, the crack rate is 0.5%, and the yield rate is 98%.

[0140] In Comparative Example 1, the superheat of the molten steel was too high, and no sealing cover was set at the connection between the crystallizer and the tundish, so the molten steel directly contacted the air and oxidized, the inclusion content was high, and obvious longitudinal cracks and depressions existed on the surface of the ingot. In Comparative Example 2, the composition of the molten steel in the tundish was changed, the crack rate of the 20Mn23AlV low alloy steel slab was increased, and the yield rate was reduced.

[0141] It can be seen that the present invention introduces molten steel of suitable components in a sealed inert gas environment, and introduces the molten steel in the tundish into the crystallizer through an immersion nozzle; adds protective slag to the molten steel in the crystallizer, and cools and continuously casts the molten steel to obtain a 20Mn23AlV low-alloy steel slab. Among them, the sealed inert gas environment effectively prevents the secondary oxidation of the aluminum element in the molten steel during the transmission process, reduces the formation of Al2O3 and MnS inclusions, reduces crack sensitivity, and improves the cleanliness of the molten steel. Through the immersion nozzle, the 20Mn23AlV low-alloy molten steel of suitable components in the tundish is introduced into the crystallizer, and protective slag is added to improve the lubrication effect of the slag film, reduce the friction resistance between the ingot and the crystallizer, and effectively prevent the generation of cracks. After that, cooling and continuous casting are carried out to achieve differentiated cooling of the molten steel, alleviate the temperature gradient between the surface and the core of the slab, and thus reduce the tendency of solidification cracks.

[0142] The above-mentioned process steps and device structure are simple, easy to operate, improve the yield rate, reduce the production cost, and effectively suppress the cracks of 20Mn23AlV low alloy steel slabs. The method is suitable for large-scale industrial production and effectively improves the continuous casting castability and production efficiency of 20Mn23AlV low alloy steel.

[0143] In summary, the above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for suppressing cracks in 20Mn23AlV low alloy steel slab, characterized in that, It includes the following steps: In a sealed inert gas environment, introduce the molten steel in the tundish into the mold through a submerged entry nozzle; Add mold powder to the molten steel in the mold, and perform continuous casting with cooling on the molten steel therein to obtain a 20Mn23AlV low-alloy steel slab with a yield rate ≥ 94% and a crack rate ≤ 1.6%; Among them, 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, and the balance is Fe and unavoidable impurities; The superheat of the molten steel in the tundish is 30 - 50°C.

2. The method for suppressing the cracks of 20Mn23AlV low alloy steel slab according to claim 1, wherein Taking the flow direction of the molten steel introduced from the tundish into the mold as the reference, the molten steel in the mold is cooled successively through a first water cooling zone, a second water cooling zone, and a third water cooling zone; Among them, the first water flow rate in the first water cooling zone is 300 - 450 L / min, the second water flow rate in the second water cooling zone is 200 - 350 L / min, and the third water flow rate in the third water cooling zone is 100 - 250 L / min.

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

4. The method for suppressing cracks in 20Mn23AlV low alloy steel slab according to claim 1, characterized in that, The composition of the mold powder, 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 binary basicity CaO / SiO2 of the mold powder is 0.5 - 1; The melting point of the mold powder is 800 - 950°C; The viscosity of the mold powder is 0.1 - 0.3 Pa·s.

5. The method for suppressing cracks in 20Mn23AlV low alloy steel slab according to claim 4, characterized in that, In the mold, the thickness of the mold powder is 3 - 10 mm, and the consumption of the mold powder is 0.3 - 0.6 kg / t of the molten steel in the tundish.

6. The method for suppressing cracks in 20Mn23AlV low-alloy steel slab according to claim 1, characterized in that, The casting speed of the continuous casting is 0.4 - 1.0 m / min, and the constant casting speed rate ≥ 96%; 7. The method for suppressing cracks in 20Mn23AlV low alloy steel slab according to claim 1, characterized in that, The inclination angle of the mold is 2 - 10°; The vibration frequency of the mold is 140 - 160 times / min, and the amplitude is 3 - 5 mm.

8. The method for suppressing cracks in 20Mn23AlV low-alloy steel slab according to claim 1, characterized in that, The submerged entry nozzle is a double-side hole submerged entry nozzle, and the insertion depth is 0.11 - 0.17 m; The inclination angle of the nozzle is 10 - 30°; The width of the side hole of the nozzle is 0.04 - 0.09 m; The height of the side hole of the nozzle is 0.05 - 0.10 m.

9. The method for suppressing the cracks of 20Mn23AlV low alloy steel slab according to claim 8, characterized in that There are also 4 - 8 annular protective gas nozzles on the side hole of the nozzle; Among them, the protective gas is argon, with a purity ≥ 99.99%; The gas flow rate of a single annular protective gas nozzle is 5 - 15 L / min.

10. An apparatus for the method of suppressing cracks in 20Mn23AlV low-alloy steel slabs as described in any one of claims 1 to 9, characterized in that, It includes: The molten steel buffer container includes a tundish and a submerged nozzle. An electromagnetic induction heating module with a power density of 50 - 150 kW / m is configured at the bottom of the tundish 2 , which is used to maintain the superheat degree of the molten steel at 30 - 50 °C; in a sealed inert gas environment, the molten steel in the tundish is introduced into the molten steel solidification forming equipment through the 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 a submerged nozzle, and a protective slag is added to the molten steel solidification forming equipment to cool and solidify the molten steel therein; 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 an inert gas to form a sealed inert gas environment; Among them, in the flowing direction of the molten steel, the molten steel in the molten steel solidification forming equipment sequentially passes through the first water cooling zone, the second water cooling zone and the third water cooling zone for cooling; The first water flow rate in the first water cooling zone is 300 - 450 L / min, the second water flow rate in the second water cooling zone is 200 - 350 L / min, and the third water flow rate in the third water cooling zone is 100 - 250 L / min; The side hole width of the submerged nozzle is 0.04 - 0.09 m; the side hole height of the submerged nozzle is 0.05 - 0.10 m; The inert gas is argon, with a purity ≥ 99.99% and an oxygen content ≤ 0.5%; the inner layer material of the sealing cover is 310S heat-resistant stainless steel; the outer layer material is aluminum silicate fiber insulation board.

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