Method for efficiently removing inclusions in molten steel through long-nozzle large-flow blowing

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a method for efficiently removing inclusions in molten steel through long-nozzle large-flow blowing. During continuous casting, a long nozzle with a gas guide structure is adopted, large-flow argon blowing is adopted, and blown argon is broken into a large number of dispersed tiny bubbles through torrential steel flow in the long nozzle; a flow guide device is installed in a tundish flow injection area right opposite to an outlet of a long nozzle, molten steel containing a large number of tiny bubbles is guided to expand in all directions in the tundish flow injection area, and the situation that the tiny bubbles are gathered and float upwards at the position of the long nozzle, and the molten steel around the long nozzle is exposed is avoided; meanwhile, the thickness of a molten steel covering agent in a flow injection area is properly increased, and molten steel exposure in the flow injection area is inhibited; the fine bubbles are distributed in a tundish flow injection area in a dispersed mode, the bubbles collide with the inclusions and capture the inclusions, after the bubbles capture the inclusions, the inclusions are carried by the bubbles to float upwards to enter a covering agent above the molten steel, and efficient removal of the inclusions in the molten steel is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate. Background Art

[0002] Controlling inclusions in steel is an important issue in the production of high-quality steel. There are many measures to control inclusions in steel, including quality control of raw and auxiliary materials, converter endpoint control, converter slag control, deoxidation process optimization, off-furnace refining technology optimization, nitrogen enhancement and nitrogen precipitation technology, hydrogen enhancement and hydrogen precipitation technology, etc. These technologies have played a good role, but the cost is relatively high. The technology of efficiently removing inclusions by blowing argon at a long shroud to generate tiny bubbles has the advantages of low cost and easy operation, but because the generated bubbles may float up in a concentrated manner near the long shroud in the injection area, causing the molten steel to be exposed near the long shroud, and then causing secondary oxidation of the molten steel, this technology has not been effectively promoted and applied. The use of small-flow argon blowing can prevent the problem of molten steel being exposed in the injection area of ​​the long shroud blowing, but the number of tiny bubbles generated by small-flow argon blowing in the molten steel in the tundish is small, and the inclusion removal effect is difficult to achieve satisfactory results. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate.

[0004] According to one aspect of the present invention, the present invention provides the following technical solution:

[0005] A method for efficiently removing inclusions in molten steel by blowing air with a large flow rate through a long shroud, wherein during continuous casting, a long shroud with an air guiding structure directed inward and downward is used to blow argon with a large flow rate, the argon is blown into the interior of the long shroud and guided to the rapidly pouring steel flow in the interior, and the turbulent pouring steel flow in the long shroud is used to break the blown argon into a large number of dispersed tiny bubbles; the steel flow impacts a flow guiding device installed in a tundish pouring area directly facing the long shroud outlet, or by increasing the depth of the turbulent area of ​​the tundish or increasing the volume of the turbulent area, so as to avoid the formation of tiny bubbles. The molten steel containing a large number of tiny bubbles is guided to expand in all directions in the injection area of ​​the tundish, forming dispersed tiny bubbles that are evenly distributed in the injection area of ​​the tundish, avoiding the tiny bubbles from gathering and floating at the long nozzle position and causing the molten steel around the long nozzle to be exposed; at the same time, the thickness of the covering agent of the molten steel in the injection area is appropriately increased to inhibit the exposure of the molten steel in the injection area; the bubbles collide with the inclusions in the molten steel and capture the inclusions. After the bubbles capture the inclusions, they carry the inclusions to float into the covering agent above the molten steel, thereby realizing the efficient removal of the inclusions.

[0006] As a preferred embodiment of the method for efficiently removing inclusions in molten steel by blowing air at a long shroud with a large flow rate, the method comprises: a long shroud with an air guiding structure to the inside and below is used during continuous casting, and the argon blowing hole extends to the inside of the long shroud, so that the blown argon gas can directly reach the inside of the long shroud. An air guiding ring groove is provided in the horizontal direction along the inner wall of the long shroud bowl; a plurality of air guiding grooves are provided in the vertical or oblique downward direction on the inner wall of the long shroud; the upper end of the air guiding groove is connected to the air guiding ring groove, and the lower end of the air guiding groove is lower than the lower edge of the refractory sealing pad provided on the inner wall of the long shroud bowl. The width of the air guiding ring groove is 5-20mm, the depth is 5-15mm, and the cross-section is semicircular, elliptical or rectangular. The air guide ring groove is connected to the argon blowing channel extending horizontally from the outside of the long shroud to the inner wall of the long shroud bowl; and a vent is opened at the position of the refractory sealing pad opposite to the argon blowing channel. The size of the vent is slightly larger than the size of the argon blowing channel to ensure that part of the argon gasket can enter the contact interface between the refractory sealing pad and the sliding sprue of the ladle through the vent, thereby enhancing the protection of the pouring effect. The depth of the air guide groove is 2-10mm, the width of the air guide groove is 2-20mm, and the number of air guide grooves is 4-8. The lower end of the air guide groove is 3-10mm lower than the lower edge of the refractory sealing pad set on the inner wall of the long shroud bowl. The air guide grooves are unevenly distributed around the inner wall of the long shroud bowl, and more air guide grooves are arranged on the side away from the argon blowing channel.

[0007] As a preferred embodiment of the method for efficiently removing inclusions in molten steel by blowing air at a large flow rate through a long shroud according to the present invention, during the continuous casting process, the flow rate of argon gas blown into the long shroud is greater than 70 NL / min, and the argon pressure is (2-10)×10 5 Pa, argon is blown into the shroud, sucked into the molten steel by the rapidly downward flowing molten steel in the shroud, and broken into dispersed tiny bubbles by the turbulent molten steel. The bubble size is generally 50-1000 microns; the bubble size is small, and the bubbles are easily dispersed in the injection area of ​​the tundish with the flow of molten steel; increasing the casting speed and increasing the continuous casting steel throughput are conducive to promoting the breakage and dispersed distribution of bubbles.

[0008] As a preferred embodiment of the method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate described in the present invention, the maximum argon blowing amount of the long shroud is determined according to a water model experiment or a production experiment, the critical argon blowing amount is the maximum argon blowing amount in continuous casting production, which is the maximum argon blowing amount that does not cause exposure of molten steel in the injection zone during the continuous casting process, and in actual production, argon is blown according to 50-90% of the critical argon blowing amount, and the slag surface in the injection zone is monitored. If molten steel is exposed in the injection zone, the argon blowing amount is appropriately reduced, or a covering agent is appropriately added to increase the covering agent thickness of the molten steel in the injection zone.

[0009] As a preferred embodiment of the method for efficiently removing inclusions in molten steel by blowing with a long water nozzle and a large flow rate described in the present invention, the flow guide device is a circular turbulence inhibitor with a larger diameter or a polygonal turbulence inhibitor with a larger horizontal area, and the height of the turbulence inhibitor is 50-300mm; the existing turbulence inhibitor in the turbulence zone of the tundish can be improved, and the generated tiny bubbles can be made more diffuse in the turbulence zone of the tundish by expanding the bottom area and reducing the height; the aggregation and concentrated floating of the generated tiny bubbles can also be avoided by increasing the depth of the turbulence zone of the tundish or increasing the volume of the turbulence zone.

[0010] Or the guide device is a guide pile or a guide seat, the diameter of the guide pile or the guide seat is 50-500mm, the height is 50-300mm, and it is a variable diameter conical guide pile or guide seat with a smaller upper diameter and a larger lower diameter. The top of the guide pile or the guide seat is in the shape of a flat spherical crown, the radius of the spherical crown is 100-500mm, and the height of the spherical crown is 20-100mm; the central axis of the guide pile or the guide seat is consistent with or close to the central axis of the long water nozzle, so as to ensure that the gas-liquid two-phase flow stream injected from the long water nozzle directly impacts the upper end of the guide pile or the guide seat, and is separated from the center by the guide pile or the guide seat, and then flows downward and expands around the guide pile or the guide seat; or by increasing the depth of the turbulent zone of the tundish or increasing the volume of the turbulent zone, bubbles are prevented from concentrating in the center of the injection zone and floating up. The guide device is made of impact-resistant refractory material and is built at the bottom of the injection zone.

[0011] As a preferred solution of the method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate described in the present invention, the thickness of the covering agent of the molten steel in the injection zone is ≥10 mm.

[0012] As a preferred embodiment of the method for efficiently removing inclusions in molten steel by blowing air through a long shroud with a large flow rate described in the present invention, argon gas is blown into the long shroud with a large flow rate through the argon blowing hole before continuous casting begins, and the argon blowing flow rate is controlled at 500-1000NL / min to remove air from the long shroud.

[0013] The beneficial effects of the present invention are as follows:

[0014] The invention provides a method for efficiently removing inclusions in molten steel by blowing air at a long shroud with a large flow rate. During continuous casting, a long shroud with an air guiding structure toward the inside and the bottom is used, and argon is blown at a large flow rate. The turbulent steel flow in the long shroud is utilized to break the blown argon into a large number of dispersed tiny bubbles. A flow guide device is installed in a tundish injection area directly opposite to the outlet of the long shroud to guide the molten steel containing a large number of tiny bubbles to expand in all directions in the tundish injection area, or by increasing the depth of the turbulent area of ​​the tundish or the volume of the turbulent area, to avoid the tiny bubbles from gathering and floating at the position of the long shroud and causing the molten steel around the long shroud to be exposed. At the same time, the thickness of the molten steel covering agent in the injection area is appropriately increased to inhibit the molten steel from being exposed in the injection area. The tiny bubbles are dispersedly distributed in the tundish injection area, and the bubbles collide with and capture the inclusions. After the bubbles capture the inclusions, they float up with the inclusions and enter the covering agent above the molten steel. Due to the use of large-flow argon blowing, a large number of bubbles are generated, which can achieve efficient removal of inclusions; at the same time, the coordinated use of diversion devices and the appropriate increase in the thickness of the molten steel covering agent in the injection area can avoid the exposure of the molten steel in the injection area and prevent the secondary oxidation of the molten steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0016] Figure 1 It is a technical principle diagram of the present invention.

[0017] Figure 2 It is a structural schematic diagram of the long shroud of the present invention.

[0018] In the figure, 1- ladle, 11- sliding nozzle, 12- argon blowing hole, 2- tundish, 21- long nozzle, 211- air guide ring groove, 212- air guide groove, 213- refractory sealing pad, 3- flow guide device.

[0019] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0020] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The present invention proposes a method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate, such as Figure 1-2 As shown, Figure 2 Shown Figure 1 In the enlarged view of the circled area, before the continuous casting starts, the long water nozzle 21 is connected to the sliding water nozzle 11 of the ladle 1, and a refractory sealing pad 213 is set on the inner wall of the bowl of the long water nozzle 21; during the continuous casting process, argon gas is introduced into the long water nozzle 21 through the air guide ring groove 211 and the air guide groove 212. By utilizing the relatively high argon blowing pressure of the long shroud 21, the negative pressure of the area below the refractory sealing pad 213 provided in the bowl of the long shroud, and the effect of the air inlet groove 212, most of the argon blown into the long shroud 21 is guided to the area below the refractory sealing pad 213 provided in the bowl of the long shroud through the air inlet groove 212; the downwardly introduced argon contacts with the ultra-low carbon molten steel flowing rapidly downward in the long shroud 21, the molten steel sucks the argon, and argon bubbles are generated in the molten steel, and the argon bubbles move downward together with the molten steel; the molten steel forms strong turbulent kinetic energy in the long shroud 21 and in the injection area near the outlet of the long shroud 21, the turbulent ultra-low carbon molten steel shears and crushes the argon bubbles involved in the molten steel, and the inclusions in the molten steel continuously impact and scratch the argon bubbles, further crushing the argon bubbles, and promoting the argon bubbles to be broken into smaller argon bubbles, most of which are 50-1000 microns in size. The tiny dispersed argon bubbles collide with the inclusions in the molten steel and capture the inclusions in the steel, forming a combination of bubbles and inclusions, driving the inclusions in the molten steel to float up and enter the tundish covering agent of the tundish 2, thereby promoting the removal of inclusions in the molten steel. In order to prevent the bubbles from floating up in the vicinity of the long water nozzle 21, causing the molten steel to be exposed near the long water nozzle in the injection area, a guide device 3 is placed directly below the long water nozzle in the injection area to promote the rapid expansion of the molten steel in all directions of the injection area and prevent the bubbles from floating up in the vicinity of the long water nozzle; at the same time, by appropriately increasing the amount of covering agent input at the molten steel level in the injection area, the exposure of the molten steel is suppressed. The method of the present invention can significantly promote the removal of inclusions in molten steel in continuous casting production, reduce inclusions in ultra-low carbon molten steel, and improve the cleanliness of ultra-low carbon steel.

[0022] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0023] Example 1

[0024] A steel plant produces DC06 steel with a carbon content of ≤0.0030wt% by continuous casting. The original continuous casting process is: using a traditional long shroud, the argon blowing flow rate of the long shroud is 30NL / min, the steel flow rate is controlled at 6.9t / min, and the total oxygen in the slab after continuous casting is 25×10 -6 .

[0025] This embodiment makes improvements to the argon blowing structure, argon blowing flow rate, sealing gasket, turbulent zone structure and covering agent addition amount of the long shroud, which specifically includes the following steps:

[0026] S1. Before continuous casting begins, connect the long shroud with an inward and downward air guide structure to the sliding shroud of the ladle, set a refractory sealing pad on the inner wall of the bowl of the long shroud, and set a vent hole on the refractory sealing pad facing the argon blowing channel; and the argon blowing hole extends into the inside of the long shroud so that the blown argon can directly reach the inside of the long shroud. Set an air guide ring groove horizontally along the inner wall of the bowl of the long shroud; set several vertical air guide grooves on the inner wall of the long shroud; the upper end of the air guide groove is connected to the air guide ring groove, and the lower end of the air guide groove is lower than the lower edge of the refractory sealing pad set on the inner wall of the bowl of the long shroud. The width of the air guide ring groove is 15mm, the depth is 12mm, and the cross-section is rectangular. The air guide ring groove is connected to the argon blowing channel extending horizontally from the outside of the long nozzle to the inner wall of the long nozzle bowl; and a vent is opened at the position of the refractory sealing pad facing the argon blowing channel. The size of the vent is slightly larger than the size of the argon blowing channel to ensure that part of the argon gas can enter the contact interface between the refractory sealing pad and the sliding nozzle of the ladle through the vent, thereby enhancing the protection of the pouring effect. The depth of the air guide groove is 10mm, the width of the air guide groove is 10mm, and the number of air guide grooves is 4. The lower end of the air guide groove is 5mm lower than the lower edge of the refractory sealing pad set on the inner wall of the long nozzle bowl. A guide device is placed directly below the long nozzle in the injection area. The guide device is a guide seat. The bottom diameter of the guide seat is 400mm and the height is 200mm. It is a variable diameter conical guide seat with a smaller upper diameter and a larger lower diameter. The top of the guide seat is in the shape of a flat spherical crown with a spherical crown radius of 300mm and a spherical crown height of 50mm. The central axis of the guide seat is consistent with the central axis of the long nozzle.

[0027] S2. Blow argon gas into the long nozzle at a high flow rate through the argon blowing hole. The argon blowing flow rate is controlled to 600NL / min to remove the air in the long nozzle.

[0028] S3, 2-3 seconds later, adjust the argon blowing rate to 30NL / min, open the sliding gate, and start continuous casting production;

[0029] S4, when pouring the first furnace of continuous casting, as the height of molten steel in the injection zone of the tundish rises, gradually increase the argon blowing amount to 200NL / min; when changing the ladles for continuous casting, after the injection is stable, increase the argon blowing amount to 300NL / min;

[0030] S5. Check the condition of the covering agent in the injection area, add covering agent in the injection area, and control the thickness of the covering agent to be greater than 20mm.

[0031] The total oxygen in the molten steel after continuous casting in this embodiment is 12×10 -6 ; The number of inclusions larger than 5 microns in steel decreased by 30%, and the number of inclusions larger than 10 microns decreased by 90%.

[0032] Example 2

[0033] A steel plant produces M3A35 steel with a carbon content of ≤0.0020wt% by continuous casting. The original continuous casting process is: using a traditional long shroud, the argon blowing flow rate of the long shroud is 25NL / min, the steel flow rate is controlled at 8.6t / min, and the total oxygen in the slab after continuous casting is 23×10 -6 .

[0034] This embodiment adopts the long shroud with the gas guiding structure toward the inside and downwards of the present invention for production, and improves the turbulent zone structure of the tundish and the amount of covering agent added, including the following steps:

[0035] S1. Before continuous casting begins, connect the long shroud with an inward and downward air guide structure to the sliding shroud of the ladle, set a refractory sealing pad on the inner wall of the bowl of the argon-blowing long shroud, and set a vent hole on the refractory sealing pad directly opposite the argon blowing channel; and the argon blowing hole extends into the inside of the long shroud so that the blown argon can directly reach the inside of the long shroud. Set an air guide ring groove horizontally along the inner wall of the bowl of the long shroud; set several vertical air guide grooves on the inner wall of the long shroud; the upper end of the air guide groove is connected to the air guide ring groove, and the lower end of the air guide groove is lower than the lower edge of the refractory sealing pad set on the inner wall of the bowl of the long shroud. The width of the air guide ring groove is 18mm, the depth is 12mm, and the cross-section is rectangular. The air guide ring groove is connected to the argon blowing channel that extends horizontally from the outside of the long shroud to the inner wall of the long shroud bowl; and a vent is opened at the position of the refractory sealing pad opposite to the argon blowing channel. The size of the vent is slightly larger than that of the argon blowing channel to ensure that part of the argon gas can enter the contact interface between the refractory sealing pad and the sliding sprue of the ladle through the vent, thereby enhancing the protection of the pouring effect. The depth of the air guide groove is 6mm, the width of the air guide groove is 10mm, and the number of air guide grooves is 5. The lower end of the air guide groove is 5mm lower than the lower edge of the refractory sealing pad set on the inner wall of the long shroud bowl. The original turbulent zone depth (the original turbulent zone depth is 1000mm) is increased by 200mm, and the original turbulent zone turbulence suppressor is improved to expand the bottom area (originally 90000mm 2 ) is 250000mm 2 , reduce the original height (250mm) by 50mm;

[0036] S2. Blow argon gas into the long nozzle at a high flow rate through the argon blowing hole. The argon blowing flow rate is controlled to 650NL / min to remove air from the long nozzle.

[0037] S3, 2-3 seconds later, adjust the argon blowing rate to 30NL / min, open the sliding gate, and start continuous casting production;

[0038] S4, when continuous casting starts pouring the first furnace, as the height of molten steel in the injection zone of the tundish rises, gradually increase the argon blowing amount to 220NL / min; when changing the ladles for continuous casting, after the injection is stable, increase the argon blowing amount to 250NL / min;

[0039] S5. Check the condition of the covering agent in the injection area, add covering agent in the injection area, and control the thickness of the covering agent to be greater than 22mm.

[0040] The total oxygen in the molten steel after continuous casting in this embodiment is 11×10 -6 ; The number of inclusions larger than 5 microns in steel decreased by 35%, and the number of inclusions larger than 10 microns decreased by 92%.

[0041] Example 3

[0042] A steel plant produces St13 steel with a carbon content of ≤0.0030wt% by continuous casting. The original continuous casting process is: using a traditional long shroud, the argon blowing flow rate of the long shroud is 30NL / min, the steel flow rate is controlled at 6.9t / min, and the total oxygen in the slab after continuous casting is 22×10 -6 .

[0043] This embodiment adopts the long shroud with the inward and downward air guiding structure of the present invention for production, and improves the structure of the injection area. It includes the following steps:

[0044] S1. Before continuous casting begins, connect the long shroud with an inward and downward air guide structure to the sliding shroud of the ladle, set a refractory sealing pad on the inner wall of the bowl of the argon-blowing long shroud, and set a vent hole on the refractory sealing pad directly opposite the argon blowing channel; and the argon blowing hole extends into the inside of the long shroud so that the blown argon can directly reach the inside of the long shroud. Set an air guide ring groove horizontally along the inner wall of the bowl of the long shroud; set several vertical air guide grooves on the inner wall of the long shroud; the upper end of the air guide groove is connected to the air guide ring groove, and the lower end of the air guide groove is lower than the lower edge of the refractory sealing pad set on the inner wall of the bowl of the long shroud. The width of the air guide ring groove is 16mm, the depth is 12mm, and the cross-section is rectangular. The air guide ring groove is connected to the argon blowing channel extending horizontally from the outside of the long nozzle to the inner wall of the long nozzle bowl; and a vent hole is opened at the position of the refractory sealing pad facing the argon blowing channel. The size of the vent hole is slightly larger than the size of the argon blowing channel to ensure that part of the argon gas can enter the contact interface between the refractory sealing pad and the sliding nozzle of the ladle through the vent hole to enhance the protection of the pouring effect. The depth of the air guide groove is 8mm, the width of the air guide groove is 10mm, and the number of air guide grooves is 6. The lower end of the air guide groove is 5mm lower than the lower edge of the refractory sealing pad set on the inner wall of the long nozzle bowl. The injection area (the original injection area depth is 1200mm) is deepened by 150mm, and a guide pile is set at the bottom of the injection area. The diameter of the bottom of the guide pile is 350mm and the height is 300mm. It is a variable diameter conical guide pile with a smaller upper diameter and a larger lower diameter. The top of the guide pile is in the shape of a flat spherical crown with a spherical crown radius of 300mm and a spherical crown height of 40mm.

[0045] S2. Blow argon gas into the long nozzle at a high flow rate through the argon blowing hole. The argon blowing flow rate is controlled to 600NL / min to remove the air in the long nozzle.

[0046] S3, 2-3 seconds later, adjust the argon blowing rate to 30NL / min, open the sliding gate, and start continuous casting production;

[0047] S4, when pouring the first furnace of continuous casting, as the height of molten steel in the injection zone of the tundish rises, gradually increase the argon blowing amount to 200NL / min; when changing the ladles for continuous casting, increase the argon blowing amount to 200NL / min after the injection is stable;

[0048] S5. Check the condition of the covering agent in the injection area, add covering agent in the injection area, and control the thickness of the covering agent to be greater than 20mm.

[0049] In this embodiment, the total oxygen in the molten steel after continuous casting is 12×10 -6 ; The number of inclusions larger than 5 microns in steel decreased by 30%, and the number of inclusions larger than 10 microns decreased by 90%.

[0050] Example 4

[0051] A steel plant produces electrode flat steel YT2 steel with a carbon content of ≤0.0080wt%. The original continuous casting process is: using a traditional long shroud, the argon blowing flow rate of the long shroud is 20NL / min, the steel flow rate is controlled at 3.3t / min, and the total oxygen in the billet after continuous casting is 39×10 -6 .

[0052] The production is carried out by using the long water nozzle with the gas guiding structure toward the inside and downward and the large flow argon blowing technology of the present invention, including the following steps:

[0053] S1. Before continuous casting begins, connect the long shroud with an inward and downward air guide structure to the sliding shroud of the ladle, set a refractory sealing pad on the inner wall of the bowl of the argon-blowing long shroud, and set a vent hole on the refractory sealing pad directly opposite the argon blowing channel; and the argon blowing hole extends into the inside of the long shroud so that the blown argon can directly reach the inside of the long shroud. Set an air guide ring groove horizontally along the inner wall of the bowl of the long shroud; set several vertical air guide grooves on the inner wall of the long shroud; the upper end of the air guide groove is connected to the air guide ring groove, and the lower end of the air guide groove is lower than the lower edge of the refractory sealing pad set on the inner wall of the bowl of the long shroud. The width of the air guide ring groove is 16mm, the depth is 12mm, and the cross-section is rectangular. The air guide ring groove is connected to the argon blowing channel that extends horizontally from the outside of the long shroud to the inner wall of the long shroud bowl; and a vent is opened at the position of the refractory sealing pad opposite to the argon blowing channel. The size of the vent is slightly larger than that of the argon blowing channel to ensure that part of the argon gas can enter the contact interface between the refractory sealing pad and the sliding sprue of the ladle through the vent, thereby enhancing the protection of the pouring effect. The depth of the air guide groove is 8mm, the width of the air guide groove is 10mm, and the number of air guide grooves is 3. The lower end of the air guide groove is 5mm lower than the lower edge of the refractory sealing pad set on the inner wall of the long shroud bowl. The original turbulent zone of the tundish (the original turbulent zone depth of the tundish is 700mm) is deepened by 100mm;

[0054] S2. Blow argon gas into the long nozzle at a high flow rate through the argon blowing hole. The argon blowing flow rate is controlled to 550NL / min to remove air from the long nozzle.

[0055] S3, 2-3 seconds later, adjust the argon blowing rate to 20NL / min, open the sliding gate, and start continuous casting production;

[0056] S4. When pouring the first furnace of continuous casting, as the height of molten steel in the injection zone of the tundish rises, the argon blowing amount is gradually increased to 180NL / min; when changing the ladles for continuous casting, after the injection is stable, the argon blowing amount is increased to 180NL / min;

[0057] S5. Check the condition of the covering agent in the injection area, add covering agent in the injection area, and control the thickness of the covering agent to be greater than 20mm.

[0058] The total oxygen in the molten steel after continuous casting in this embodiment is 15×10 -6 ; The number of inclusions larger than 5 microns in steel decreased by 40%, and the number of inclusions larger than 10 microns decreased by 90%.

[0059] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive 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 efficiently removing inclusions from molten steel by blowing air with a long shroud and a large flow rate, characterized in that: During the continuous casting process, a long shroud with an air-guiding structure is used to blow argon at a large flow rate. Argon is blown into the long shroud and guided to the rapidly pouring steel flow inside. The steel flow impacts the guide device installed in the injection area of ​​the tundish opposite to the long shroud outlet, and at the same time increases the covering agent thickness of the molten steel in the injection area, thereby achieving efficient removal of inclusions.

2. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1 is characterized in that: During continuous casting, a long shroud with an inward and downward air guiding structure is used, and the argon blowing hole extends into the long shroud so that the blown argon gas can directly reach the inside of the long shroud; an air guiding ring groove is opened horizontally along the inner wall of the long shroud bowl; a number of air guiding grooves are opened vertically or obliquely downward on the inner wall of the long shroud; the upper end of the air guiding groove is connected to the air guiding ring groove, and the lower end of the air guiding groove is lower than the lower edge of the refractory sealing pad arranged on the inner wall of the long shroud bowl.

3. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 2 is characterized in that: The width of the air guide ring groove is 5-20mm, the depth is 5-15mm, and the cross-section is semicircular, elliptical or rectangular; the depth of the air guide groove is 2-10mm, the width of the air guide groove is 2-20mm, and the number of air guide grooves is 4-8.

4. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1 is characterized in that: During the continuous casting process, the argon flow rate of the long nozzle is greater than 70NL / min, and the argon pressure is (2-10)×10 5 Pa.

5. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1 is characterized in that: The maximum argon blowing amount of the long shroud is determined based on water model experiments or production experiments. The critical argon blowing amount is the maximum argon blowing amount in continuous casting production, which is the maximum argon blowing amount that does not cause exposure of molten steel in the injection zone during the continuous casting process. In actual production, argon is blown at 50-90% of the critical argon blowing amount, and the slag surface in the injection zone is monitored. If molten steel is exposed in the injection zone, the argon blowing amount is appropriately reduced or a covering agent is appropriately added to increase the covering agent thickness of the molten steel in the injection zone.

6. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1 is characterized in that: The flow guide device is a circular or polygonal turbulence inhibitor, and the height of the turbulence inhibitor is 50-300mm.

7. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1 is characterized in that: The guide device is a guide pile or a guide seat. The diameter of the guide pile or the guide seat is 50-500mm and the height is 50-300mm. It is a variable diameter conical guide pile or guide seat with a smaller upper diameter and a larger lower diameter. The top of the guide pile or the guide seat is in the shape of a flat spherical crown with a radius of 100-500mm and a height of 20-100mm. The central axis of the guide pile or the guide seat is consistent with or close to the central axis of the long water outlet to ensure that the gas-liquid two-phase flow injected in the long water outlet directly impacts the upper end of the guide pile or the guide seat, and is separated from the center by the guide pile or the guide seat, and then flows downward and expands to the surrounding areas along the four sides of the guide pile or the guide seat to avoid bubbles concentrating in the center of the injection area and floating up.

8. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 7 is characterized in that: The guide device is made of impact-resistant refractory material and is built at the bottom of the injection area.

9. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1 is characterized in that: The thickness of the covering agent for molten steel in the injection zone is ≥10mm.

10. The method for efficiently removing inclusions in molten steel by blowing air with a long shroud and a large flow rate according to claim 1, characterized in that: Before continuous casting begins, argon is blown into the shroud at a high flow rate, and the argon flow rate is controlled at 500-1000NL / min to remove air from the shroud.

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