Method for efficiently removing microscopic inclusions through long nozzle hydrogen / nitrogen blowing

Abstract

The invention belongs to the technical field of continuous casting, and particularly relates to a method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen into a long nozzle, which comprises the following steps: blowing hydrogen, nitrogen, hydrogen-argon mixed gas or hydrogen-nitrogen mixed gas into the long nozzle in high flow in continuous casting production to form a large amount of dispersed tiny bubbles in molten steel to promote removal of the inclusions in the molten steel; and especially, the method can be used for removing microscopic inclusions (inclusions less than 5 microns) with relatively small sizes.

Description

Technical Field

[0001] The present invention relates to the technical field of continuous casting, and specifically provides a method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle. Background Art

[0002] High-quality steel has strict requirements for inclusions in the steel. The efficient and deep removal of inclusions in the steel has always been a bottleneck technical problem for high-quality steel. In steel production, an off-line refining process that is time-consuming and energy-consuming is often used to purify the molten steel. After refining, the cleanliness of the molten steel is significantly improved. However, during the subsequent pouring process, the cleanliness of the molten steel easily decreases due to the absorption of air by the molten steel, reaction with refractories and slag, etc.

[0003] In continuous casting production after refining, argon is often blown through the long nozzle for protective pouring. The blown argon mainly prevents external air from entering the molten steel flowing rapidly downward in the long nozzle through the interface gap between the long nozzle and the submerged nozzle of the slide gate, controls the secondary oxidation of the molten steel, prevents the generation of secondary oxidation inclusions in the steel, and ensures that the molten steel maintains a high cleanliness. However, this method cannot remove inclusions in the steel.

[0004] There are also methods of blowing argon in the turbulence inhibitor in the tundish or setting a diffused porous plug in the tundish to blow argon, attempting to remove inclusions in the steel by bubbles in the tundish. However, due to the relatively large size of the generated bubbles, the ability of the bubbles to capture inclusions is limited, and the removal effects are not ideal. Generating a large number of diffused and tiny bubbles in the tundish molten steel can promote the removal effect of inclusions in the tundish molten steel. However, how to generate a large number of diffused and tiny bubbles in the tundish has always been a technical problem in tundish metallurgy.

[0005] Predecessors have proposed a method of blowing argon through the long nozzle to generate tiny bubbles to remove inclusions. However, the size of the generated argon bubbles is still relatively large, often several hundred micrometers or several millimeters. Bubbles of this size have a good effect on removing inclusions in the steel larger than 5 μm, especially larger than 10 μm, but their ability to remove inclusions in the steel smaller than 5 μm is very low. The smaller the bubble size, the stronger its ability to capture microscopic inclusions. How to generate smaller bubbles in the tundish molten steel to promote the removal of microscopic inclusions has always been a difficult point in the field of inclusion control. Summary of the Invention

[0006] To solve the problems existing in this technology, the main object of the present invention is to propose a method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle.

[0007] According to one aspect of the present invention, the present invention provides the following technical solution:

[0008] A method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle. During continuous casting production, hydrogen, nitrogen, a hydrogen-argon mixed gas, or a hydrogen-nitrogen mixed gas is blown into the long nozzle at a large flow rate. The blown gas is guided by a gas conduction channel to the rapidly flowing molten steel in the long nozzle, forming a large number of bubbles inside the molten steel. The highly turbulent molten steel flowing downward in the long nozzle breaks the bubbles into dispersed and tiny bubbles, generating a large number of dispersed and tiny bubbles in the turbulent zone of the tundish. Hydrogen and / or nitrogen in the bubbles continuously dissolve into the molten steel, making the bubble size even smaller and more dispersed. A large number of tiny and dispersed bubbles capture the inclusions in the steel, promoting the floating of the inclusions into the tundish covering agent. At the same time, the position of the steel-passing through hole of the dam between the turbulent zone and the pouring zone in the tundish is lowered, so that the bubbles entering the pouring zone are more dispersed in the pouring zone. By using this method, more dispersed and tinier bubbles can be generated in the long nozzle and the tundish, suppressing the exposure of the molten steel caused by the concentrated floating of bubbles near the long nozzle in the turbulent zone of the tundish and enhancing the ability of the bubbles to capture inclusions. At the same time, blowing gas at a large flow rate can generate more bubbles, further improving the inclusion removal effect. This method can significantly improve the removal effect of microscopic inclusions with smaller sizes (inclusions less than 5 μm) in the molten steel and can be applied to the cleanliness and quality control of some steels that are insensitive to hydrogen and / or nitrogen.

[0009] The beneficial effects of the present invention are as follows:

[0010] The present invention provides a method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle. During continuous casting production, hydrogen, nitrogen, a hydrogen-argon mixed gas, or a hydrogen-nitrogen mixed gas is blown into the long nozzle at a large flow rate, forming a large number of dispersed and tiny bubbles inside the molten steel, promoting the removal of inclusions in the molten steel, especially the removal of microscopic inclusions with smaller sizes (inclusions less than 5 μm). BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or 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 also be obtained based on the structures shown in these drawings.

[0012] Figure 1 Schematic diagram of a device for implementing the method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle of the present invention.

[0013] Figure 2 Schematic diagram of another device for implementing the method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle of the present invention.

[0014] Figure 3 Schematic diagram of yet another device for implementing the method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle of the present invention.

[0015] In the figure, 1 - skateboard nozzle for molten steel discharging, 2 - gas injection hole of long nozzle, 3 - gas injection channel of long nozzle, 4 - long nozzle, 5 - gasket, 6 - gas guiding ring groove of skateboard nozzle for molten steel discharging, 7 - gas guiding groove, 8 - air vent hole of gasket, 9 - gas vent hole of skateboard nozzle for molten steel discharging, 10 - turbulent zone, 11 - pouring zone, 12 - molten steel passing through hole, 13 - stopper rod, 14 - submerged nozzle.

[0016] The realization of the purpose, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific embodiments

[0017] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] According to one aspect of the present invention, the present invention provides the following technical solution:

[0019] As Figures 1-3 shown, a method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen into a long nozzle. In continuous casting production, hydrogen, nitrogen, hydrogen-argon mixed gas or hydrogen-nitrogen mixed gas is blown into the long nozzle 4 in a large flow rate; the blown gas is guided by the gas guiding channel 3 to the molten steel flowing rapidly downward in the long nozzle 4, and a large number of bubbles are formed inside the molten steel; the highly turbulent molten steel flowing downward in the long nozzle 4 breaks the bubbles into dispersed and tiny bubbles, and a large number of dispersed and tiny bubbles are generated in the turbulent zone 10 of the tundish. Hydrogen and / or nitrogen in the bubbles continuously dissolve into the molten steel, and the bubble size becomes even more tiny and dispersed; a large number of tiny and dispersed bubbles capture the inclusions in the steel, promoting the floating of the inclusions into the tundish covering flux. At the same time, the position of the molten steel passing through hole 12 of the dam between the turbulent zone 10 and the pouring zone 11 in the tundish is lowered, so that the bubbles entering the pouring zone 11 are more dispersed in the pouring zone. Then, the molten steel is discharged through the submerged nozzle 14 provided with the stopper rod 13. By adopting this method, more dispersed and tinier bubbles can be generated in the long nozzle 4 and the tundish, suppressing the exposure of the molten steel caused by the concentrated floating of the bubbles near the long nozzle 4 in the turbulent zone 10 of the tundish and enhancing the ability of the bubbles to capture inclusions; at the same time, by blowing gas in a large flow rate, more bubbles can be generated, further enhancing the inclusion removal effect. This method can significantly improve the removal effect of microscopic inclusions with smaller sizes (inclusions less than 5 μm) in the molten steel and can be applied to the cleanliness and quality control of some steels that are insensitive to hydrogen and / or nitrogen.

[0020] Preferably, the flow rate of hydrogen, nitrogen, hydrogen-argon mixed gas or hydrogen-nitrogen mixed gas blown into the long nozzle 4 is 60 - 1000 L / min, and the pressure is 0.3 - 1.3 MPa. Specifically, the flow rate can be, for example, any one of 60 L / min, 100 L / min, 200 L / min, 300 L / min, 400 L / min, 500 L / min, 600 L / min, 700 L / min, 800 L / min, 900 L / min, 1000 L / min or the range between any two of them; the pressure can be, for example, any one of 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa or the range between any two of them. Further preferably, the volume content of hydrogen in the hydrogen-argon mixed gas or hydrogen-nitrogen mixed gas is 50 - 100%. Specifically, the volume content of hydrogen can be, for example, any one of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% or the range between any two of them.

[0021] Preferably, as Figure 1 shown, to implement a device for the method of efficiently removing microscopic inclusions by blowing hydrogen / nitrogen into the long nozzle of the present invention, a gas guiding channel is provided on the submerged nozzle 1 of the slide plate and the long nozzle 4. The gas guiding channel successively includes a long nozzle gas blowing hole 2, a long nozzle gas blowing channel 3, a gasket ventilation hole 8, a submerged nozzle gas guiding ring groove 6 of the slide plate, and a gas guiding groove 7 starting from the submerged nozzle gas guiding ring groove 6 of the slide plate and extending downward; among them, the long nozzle gas blowing hole 2, the long nozzle gas blowing channel 3, the gasket ventilation hole 8, and the submerged nozzle gas guiding ring groove 6 of the slide plate are at the same height in the height direction. The hydrogen, nitrogen, hydrogen-argon mixed gas or hydrogen-nitrogen mixed gas blown into the long nozzle 4 through the long nozzle gas blowing hole 2 is first annularly distributed around the submerged nozzle 1 of the long nozzle 4 in the upper part of the long nozzle 4 through the submerged nozzle gas guiding ring groove 6 of the slide plate, inhibiting the entry of external air into the long nozzle 4 from the upper end of the long nozzle 4 and preventing the secondary oxidation of the molten steel in the long nozzle 4 by the air; at the same time, the blown gas in the submerged nozzle gas guiding ring groove 6 of the slide plate can be guided to the molten steel flowing rapidly downward inside the long nozzle 4 through the gas guiding groove 7 starting from the submerged nozzle gas guiding ring groove 6 of the slide plate.

[0022] Further preferably, the diameters of the long nozzle gas injection holes 2 and the long nozzle gas injection channels 3 are 5 - 20 mm; the gasket ventilation holes 8 are holes opened at the height position of the gasket directly opposite the long nozzle gas injection holes 2, with a horizontal length of 15 - 60 mm around the annular nozzle and a width of 10 - 25 mm in the longitudinal height. The horizontal center line of the holes is at the same height as the center lines of the long nozzle gas injection holes 2, the long nozzle gas injection channels 3, and the slide gate nozzle gas guiding ring groove 6; the cross-sections of the annular slide gate nozzle gas guiding ring groove 6 and the gas guiding grooves 7 provided on the slide gate nozzle 1 are semi-circular, semi-elliptical, or rectangular. The depth of the slide gate nozzle gas guiding ring groove 6 is 5 - 20 mm and the width is 5 - 20 mm, the depth of the gas guiding grooves 7 is 3 - 15 mm and the width is 3 - 15 mm, and the number of the gas guiding grooves 7 is 1 - 5.

[0023] Preferably, as Figure 2 shown, another device for implementing the method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through the long nozzle of the present invention is provided with a gas guiding channel on the slide gate nozzle 1 and the long nozzle 4. The gas guiding channel sequentially includes the long nozzle gas injection holes 2, the long nozzle gas injection channels 3, the gasket ventilation holes 8, the slide gate nozzle gas guiding ring groove 6, and several gas guiding holes 9 distributed along the slide gate nozzle gas guiding ring groove 6 and leading into the slide gate nozzle 1. The gas blown into the slide gate nozzle gas guiding ring groove 6 is blown into the molten steel poured into the water inlet through several gas guiding holes 9 distributed along the slide gate nozzle gas guiding ring groove 6.

[0024] Further preferably, the diameters of the long nozzle gas injection holes 2 and the long nozzle gas injection channels 3 are 5 - 20 mm; the gasket ventilation holes 8 are holes opened at the height position of the gasket directly opposite the long nozzle gas injection holes 2, with a horizontal length of 15 - 60 mm around the annular nozzle and a width of 10 - 25 mm in the longitudinal height. The horizontal center line of the holes is at the same height as the center lines of the long nozzle gas injection holes 2, the long nozzle gas injection channels 3, and the slide gate nozzle gas guiding ring groove 6; the cross-section of the annular slide gate nozzle gas guiding ring groove 6 provided on the slide gate nozzle 1 is semi-circular, semi-elliptical, or rectangular. The depth of the slide gate nozzle gas guiding ring groove 6 is 5 - 20 mm and the width is 5 - 20 mm. The gas guiding holes 9 can be arranged as needed, for example, perpendicular to the slide gate nozzle pipe wall, or in other ways beneficial to gas introduction (such as at a certain angle with the slide gate nozzle pipe wall along the horizontal and / or vertical directions); the gas guiding holes 9 are evenly distributed along the slide gate nozzle gas guiding ring groove 6, the number of which is 1 - 10, and the diameter is 1 - 6 mm.

[0025] Preferably, the gas guiding groove 7 starting from the gas guiding ring groove 6 at the ladle nozzle and several gas guiding holes 9 distributed along the gas guiding ring groove 6 of the ladle nozzle and leading into the ladle nozzle 1 can exist simultaneously. The gas blown into the gas guiding ring groove 6 of the ladle nozzle can be guided to the molten steel flowing rapidly inside the submerged entry nozzle 4 through the gas guiding groove 7 starting from the gas guiding ring groove 6 at the ladle nozzle and several gas guiding holes 9 distributed along the gas guiding ring groove 6 of the ladle nozzle and leading into the ladle nozzle 1.

[0026] Preferably, the size and distribution of the generated bubbles are adjusted by the volume content of hydrogen in the mixed gas. The higher the hydrogen content in the blown gas, the smaller the size of the generated bubbles and the more dispersed the distribution. When the volume content of hydrogen exceeds 70%, a large number of bubbles smaller than 100 μm can be generated. These small bubbles can follow the molten steel into the tundish casting area 11. The interaction time between the bubbles and the molten steel is long, the bubbles are more widely distributed in the molten steel, and the effect of removing inclusions is better.

[0027] Preferably, the smaller the size of the bubbles in the tundish molten steel, the stronger the ability to remove microscopic inclusions with smaller sizes. A large number of bubbles smaller than 100 μm generated in the tundish molten steel significantly improve the ability to remove inclusions smaller than 5 μm in the molten steel. More specifically, a large number of bubbles smaller than 100 μm generated in the tundish molten steel significantly improve the ability to remove inclusions of 2 - 5 μm in the molten steel.

[0028] Preferably, as Figure 3 shown, in order to realize another device for the method of efficiently removing microscopic inclusions by blowing hydrogen / nitrogen into the submerged entry nozzle of the present invention, the position of the steel - passing through hole 12 of the dam between the turbulent flow area 10 and the casting area 11 in the tundish is lowered, so that the distribution of the bubbles entering the casting area 11 is more dispersed in the casting area.

[0029] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] A certain steel plant produces the DC06 steel grade by slab continuous casting. This steel grade has no strict requirements for hydrogen. The original continuous casting process is as follows: a traditional submerged entry nozzle is used, the argon - blowing flow rate of the submerged entry nozzle is 30 NL / min, the steel - passing rate is controlled at 6.9 t / min, and the total oxygen in the cast slab after continuous casting is 25×10 -6 , and the number of inclusions of 2 - 10 μm in the steel is 3.7 pieces / mm 2 .

[0032] In this example, the improvements described in the present invention are made to the argon - blowing structure of the submerged entry nozzle, the gasket, and the tundish dam, specifically including:

[0033] Before continuous casting starts, improve the gas blowing structure of the long nozzle and the tundish slide gate. Extend the existing argon blowing holes into the long nozzle to form a long nozzle gas blowing channel, so that the blown hydrogen-argon mixed gas can directly reach the inside of the long nozzle. The diameter of the long nozzle gas blowing channel is the same as that of the argon blowing holes. Place a refractory gasket on the inner wall of the bowl of the long nozzle. A ventilation hole is opened at the position of the refractory gasket facing the gas blowing channel. The ventilation hole is 30 mm long in the horizontal direction and 18 mm high in the vertical direction. At the horizontal position of the long nozzle gas blowing channel, a gas guiding ring groove is horizontally opened along the outside of the tundish slide gate, and 5 downward gas guiding grooves are opened downward on the outside of the slide nozzle under the slide plate from the gas guiding ring groove. The upper end of the gas guiding groove is connected to the gas guiding ring groove. The width of the gas guiding ring groove is 10 mm, the depth is 8 mm, and the cross-section is semi-circular. The width of the gas guiding groove is 8 mm, the depth is 6 mm, and the cross-section is semi-circular.

[0034] Before continuous casting starts, move the position of the steel-passing through hole of the dam in the turbulence zone and the pouring zone in the tundish downward by 100 mm from the original 200 mm from the bottom of the tundish to 100 mm from the bottom, while keeping the original cross-sectional size and shape unchanged.

[0035] During continuous casting, blow a hydrogen-argon mixed gas into the long nozzle through the long nozzle gas blowing holes and the modified gas guiding channel. The gas flow rate is 400 L / min, the blowing pressure is 0.6 MPa, and the hydrogen volume content is 80%.

[0036] In this embodiment, the average size of the bubbles generated in the tundish molten steel is 89 μm, and the total oxygen in the molten steel after continuous casting is \(10\times10\) -6 ; the number of inclusions with a size of 2 - 10 μm in the steel is 2.7 per \(mm\) 2 , the number of inclusions larger than 5 μm decreases by 40%, and the number of inclusions larger than 10 μm decreases by 95%.

[0037] Example 2

[0038] A certain steel plant produces the steel grade M3A35 by slab continuous casting. This steel grade has no strict requirements for hydrogen. The original continuous casting process is as follows: use a traditional long nozzle, the argon blowing flow rate of the long nozzle is 25 NL / min, the steel passing rate is controlled at 8.6 t / min, and the total oxygen in the cast slab after continuous casting is \(23\times10\) -6 , the number of inclusions with a size of 2 - 10 μm is 3.2 per \(mm\) 2 .

[0039] In this embodiment, the improvements described in the present invention are made to the long nozzle gas blowing structure, the gasket, and the tundish dam, specifically including:

[0040] Before continuous casting starts, improve the gas-blowing structure of the long nozzle and the tundish slide gate. Extend the existing argon-blowing hole into the long nozzle to form a long-nozzle gas-blowing channel, so that the blown hydrogen-argon mixed gas can directly reach the inside of the long nozzle. The diameter of the long-nozzle gas-blowing channel is the same as that of the argon-blowing hole. Place a refractory sealing gasket on the inner wall of the bowl of the long nozzle. A ventilation hole is opened at the position of the refractory sealing gasket facing the gas-blowing channel. The ventilation hole is 30 mm long in the horizontal direction and 18 mm high in the vertical direction. At the horizontal position of the long-nozzle gas-blowing channel, a gas-guiding ring groove is horizontally opened along the outside of the tundish slide gate. The cross-section of the gas-guiding ring groove is rectangular, with a width of 10 mm and a depth of 5 mm. Five gas-guiding holes with a diameter of 3 mm are drilled into the submerged nozzle inside the slide plate in this gas-guiding ring groove.

[0041] Before continuous casting starts, move the position of the steel-passing through hole of the dam in the turbulence area and the pouring area in the tundish downward by 150 mm from the original 250 mm from the bottom of the tundish to 100 mm from the bottom, while keeping the original cross-sectional size and shape unchanged.

[0042] During continuous casting, blow a hydrogen-argon mixed gas into the long nozzle through the long-nozzle gas-blowing hole and the modified gas-guiding channel. The gas flow rate is 600 L / min, the gas-blowing pressure is 0.55 MPa, and the hydrogen volume content is 90%.

[0043] In this embodiment, the average size of the bubbles generated in the tundish molten steel is 95 μm, and the total oxygen in the molten steel after continuous casting is 9×10 -6 ; the number of inclusions with a size of 2 - 10 μm in the steel is 2.0 pieces / mm 2 , the number of inclusions larger than 5 μm decreases by 45%, and the number of inclusions larger than 10 μm decreases by 93%.

[0044] Example 3

[0045] A certain steel plant produces the St13 steel grade by slab continuous casting. This steel grade has no strict requirements for hydrogen. The original continuous casting process is as follows: Use a traditional long nozzle, the argon-blowing flow rate of the long nozzle is 30 NL / min, the steel-passing amount is controlled at 6.9 t / min, and the total oxygen in the continuous-cast slab is 22×10 -6 , and the number of inclusions with a size of 2 - 10 μm is 4.5 pieces / mm 2 .

[0046] In this embodiment, the improvements described in the present invention are made to the long-nozzle argon-blowing structure, the sealing gasket, and the tundish dam, specifically including: y

[0047] Before continuous casting starts, improve the gas-blowing structure of the long nozzle and the tundish slide gate. Extend the existing argon-blowing hole into the long nozzle to form a long-nozzle gas-blowing channel, so that the blown hydrogen can directly reach the inside of the long nozzle. The diameter of the long-nozzle gas-blowing channel is the same as that of the argon-blowing hole. Place a refractory gasket on the inner wall of the bowl part of the long nozzle. The refractory gasket is provided with a vent hole at the position facing the gas-blowing channel. The vent hole is 30 mm long in the horizontal direction and 18 mm high in the vertical direction. At the horizontal position of the long-nozzle gas-blowing channel, a gas-guiding ring groove is horizontally opened along the outside of the tundish slide gate, and 4 downward gas-guiding grooves are opened downward on the outside of the submerged nozzle from this gas-guiding ring groove. The upper end of the gas-guiding groove is connected to the gas-guiding ring groove. The width of the gas-guiding ring groove is 10 mm, the depth is 6 mm, and the cross-section is rectangular. The width of the gas-guiding groove is 8 mm, the depth is 6 mm, and the cross-section is rectangular.

[0048] Before continuous casting starts, move the position of the steel-passing through hole of the dam in the turbulence area and the pouring area in the tundish downward by 120 mm from the original 220 mm from the bottom of the tundish to 100 mm from the bottom, while keeping the original cross-sectional size and shape unchanged.

[0049] During continuous casting, hydrogen is blown into the long nozzle through the long-nozzle gas-blowing hole and the modified gas-guiding channel. The gas flow rate is 800 L / min, and the blowing pressure is 0.6 MPa.

[0050] In this embodiment, the average size of the bubbles generated in the tundish molten steel is 100 μm, and the total oxygen in the molten steel after continuous casting is 8×10 -6 ; the number of inclusions with a size of 2 - 10 μm in the steel is 2.5 per mm 2 , the number of inclusions larger than 5 μm decreases by 40%, and the number of inclusions larger than 10 μm decreases by 95%.

[0051] Example 4

[0052] For the square billet production of electrode flat steel of steel grade YT2 in a certain steel plant, this steel grade has no strict requirement for nitrogen content. The original continuous casting process is as follows: use a traditional long nozzle, the argon-blowing flow rate of the long nozzle is 20 NL / min, the steel-passing rate is controlled at 3.3 t / min, and the total oxygen in the cast billet after continuous casting is 39×10 -6 , the number of inclusions with a size of 2 - 10 μm is 4.7 per mm 2 .

[0053] In this embodiment, the improvements described in the present invention are made to the long-nozzle gas-blowing structure, the gasket, and the tundish dam, specifically including:

[0054] Before continuous casting starts, improve the gas blowing structure of the long nozzle and the tundish slide gate. Extend the existing argon blowing hole into the long nozzle to form a long nozzle gas blowing channel, so that the blown gas can directly reach the inside of the long nozzle. The diameter of the long nozzle gas blowing channel is the same as that of the argon blowing hole. Place a refractory sealing gasket on the inner wall of the bowl of the long nozzle. An air vent hole is opened at the position of the refractory sealing gasket facing the gas blowing channel. The air vent hole is 30 mm long in the horizontal direction and 15 mm high in the vertical direction. At the horizontal position of the long nozzle gas blowing channel, a gas guiding ring groove is horizontally opened along the outside of the tundish slide gate. The cross-section of the gas guiding ring groove is rectangular, with a width of 10 mm and a depth of 5 mm. Four gas guiding holes with a diameter of 2 mm are drilled from the gas guiding ring groove into the submerged nozzle.

[0055] Before continuous casting starts, move the position of the through-steel through-hole of the baffle in the turbulence zone and the pouring zone in the tundish downward by 120 mm from the original 230 mm from the bottom of the tundish to 110 mm from the bottom, while keeping the original cross-sectional size and shape unchanged.

[0056] During continuous casting, nitrogen is blown into the long nozzle through the long nozzle gas blowing hole and the modified gas guiding channel. The gas flow rate is 300 L / min, and the blowing pressure is 0.55 MPa. In this embodiment, the average size of the bubbles generated in the tundish molten steel is 130 μm, and the total oxygen in the molten steel after continuous casting is 15×10 -6 ; the number of inclusions with a size of 2 - 10 μm in the steel is 2.7 per mm 2 , the number of inclusions larger than 5 μm decreases by 30%, and the number of inclusions larger than 10 μm decreases by 85%.

[0057] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made using the content of the specification of the present invention under the inventive concept of the present invention, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a long nozzle, characterized in that, Inject hydrogen, nitrogen, hydrogen-argon mixture gas or hydrogen-nitrogen mixture gas into the long nozzle during continuous casting production; the injected gas is guided by the gas guiding channel into the rapidly flowing molten steel in the long nozzle, forming a large number of bubbles inside the molten steel; the highly turbulent molten steel flowing in the long nozzle breaks the bubbles into dispersed and tiny bubbles, generating a large number of dispersed and tiny bubbles in the turbulent zone of the tundish. The hydrogen and / or nitrogen in the bubbles continuously dissolve into the molten steel, and the bubble size becomes even smaller and more dispersed; a large number of tiny and dispersed bubbles capture the inclusions in the steel, promoting the floating of the inclusions into the tundish covering agent, and significantly improving the removal effect of inclusions smaller than 5μm in the molten steel.

2. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 1, characterized in that, The flow rate of the hydrogen, nitrogen, hydrogen-argon mixture gas or hydrogen-nitrogen mixture gas injected into the long nozzle is 60 - 1000 L / min, and the pressure is 0.3 - 1.3 MPa.

3. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 1, characterized in that, The volume content of hydrogen in the hydrogen-argon mixture gas or hydrogen-nitrogen mixture gas is 50 - 100%.

4. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 1, characterized in that, A gas guiding channel is set on the submerged nozzle of the slide plate and the long nozzle. The gas guiding channel successively includes a long nozzle blowing hole, a long nozzle blowing channel, a gasket vent hole, a submerged nozzle gas guiding ring groove of the slide plate, and a gas guiding groove starting from the submerged nozzle gas guiding ring groove of the slide plate and extending downward. Among them, the long nozzle blowing hole, the long nozzle blowing channel, the gasket vent hole, and the submerged nozzle gas guiding ring groove of the slide plate are at the same height in the height direction. The hydrogen, nitrogen, hydrogen-argon mixture gas or hydrogen-nitrogen mixture gas injected into the long nozzle through the long nozzle blowing hole is first annularly distributed around the submerged nozzle of the slide plate at the upper part of the long nozzle through the submerged nozzle gas guiding ring groove of the slide plate, inhibiting the entry of external air into the long nozzle from the upper end of the long nozzle and preventing the secondary oxidation of the molten steel in the long nozzle by air; at the same time, the injected gas in the submerged nozzle gas guiding ring groove of the slide plate is guided into the rapidly flowing molten steel inside the long nozzle through the gas guiding groove starting from the submerged nozzle gas guiding ring groove of the slide plate and extending downward.

5. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 1, characterized in that, A gas guiding channel is set on the submerged nozzle of the slide plate and the long nozzle. The gas guiding channel successively includes a long nozzle blowing hole, a long nozzle blowing channel, a gasket vent hole, a submerged nozzle gas guiding ring groove of the slide plate, a gas guiding groove starting from the submerged nozzle gas guiding ring groove of the slide plate and extending downward, and several gas guiding holes distributed along the submerged nozzle gas guiding ring groove of the slide plate and leading into the submerged nozzle. The gas blown into the submerged nozzle gas guiding ring groove of the slide plate is blown into the molten steel flowing inside the nozzle through the gas guiding groove starting from the submerged nozzle gas guiding ring groove of the slide plate and extending downward and several gas guiding holes distributed along the submerged nozzle gas guiding ring groove of the slide plate and leading into the submerged nozzle.

6. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 1, wherein A gas guiding channel is set on the submerged nozzle of the slide plate and the long nozzle. The gas guiding channel successively includes a long nozzle blowing hole, a long nozzle blowing channel, a gasket vent hole, a submerged nozzle gas guiding ring groove of the slide plate, and several gas guiding holes distributed along the submerged nozzle gas guiding ring groove of the slide plate and leading into the submerged nozzle. The gas blown into the submerged nozzle gas guiding ring groove of the slide plate is blown into the molten steel flowing inside the nozzle through the several gas guiding holes distributed along the submerged nozzle gas guiding ring groove of the slide plate and leading into the submerged nozzle.

7. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to any one of claims 4-6, characterized in that, The diameters of the long nozzle gas injection holes and the long nozzle gas injection channels are 5 - 20 mm; the gasket vent hole is a hole opened directly opposite the long nozzle gas injection hole at the height position of the gasket. The length in the horizontal direction around the annular nozzle is 15 - 60 mm, and the width in the longitudinal height is 10 - 25 mm. The horizontal center line of the hole is at the same height as the center lines of the long nozzle gas injection hole, the long nozzle gas injection channel, and the gas guiding ring groove of the submerged nozzle of the slide plate. The cross-section of the annular gas guiding ring groove provided on the submerged nozzle of the slide plate is semi-circular, semi-elliptical or rectangular, and the depth of the gas guiding ring groove of the submerged nozzle of the slide plate is 5 - 20 mm and the width is 5 - 20 mm.

8. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 4 or 6, characterized in that, The cross-section of the gas guiding groove is semi-circular, semi-elliptical or rectangular, the depth of the gas guiding groove is 3 - 15 mm, the width is 3 - 15 mm, and the number of the gas guiding grooves 7 is 1 - 5.

9. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 5 or 6, characterized in that, The number of the gas guiding holes is 1 - 10, and the diameter is 1 - 6 mm.

10. The method for efficiently removing microscopic inclusions by blowing hydrogen / nitrogen through a submerged entry nozzle according to claim 1, characterized in that, Lower the position of the steel passing through hole of the dam between the turbulent zone and the casting zone in the tundish so that the bubbles entering the casting zone are more diffusely distributed in the casting zone.

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