Efficient decarburization and denitrification method for RH refining of ultra-low carbon steel

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to an ultra-low carbon steel RH refining efficient decarburization and denitrification method which comprises the steps that after RH refining starts, hydrogen-argon mixed gas is blown into an ascending pipe, hydrogen-argon mixed gas or hydrogen is blown into the side portion and / or the bottom of a vacuum chamber, and hydrogen is blown into molten steel in a descending pipe; the dissolution of hydrogen in the molten steel in the RH decarburization and denitrification refining process is promoted, the content of hydrogen in the molten steel in the vacuum chamber in the RH decarburization and denitrification refining process is increased, and the decarburization and denitrification reaction of the molten steel in the vacuum chamber is promoted; after decarburization is finished, a deoxidizing agent is added into the molten steel for molten steel deoxidation, a large number of dispersed inclusions are generated in the molten steel, and bubbles in the molten steel are further refined through the inclusions in the molten steel; and after decarburization and denitrification are finished, the blown-in gas is switched into argon gas to achieve combined blowing, mass transfer of the vacuum chamber is promoted, more bubbles are generated in the molten steel, and dehydrogenation of the molten steel is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for high-efficiency decarbonization and denitrification of ultra-low carbon steel through RH refining. Background Art

[0002] RH refining is an important means of vacuum refining of high-quality steel, which has the functions of decarburization, removal of inclusions, degassing (hydrogen, nitrogen), desulfurization, etc. However, due to the short production time and high oxygen and sulfur content in the steel, the RH refining process of ultra-low carbon steel has the problem of difficult to remove dissolved nitrogen in the steel efficiently and deeply. At the same time, the carbon content in the steel is less than 30×10 -6 After that, the decarburization rate is significantly reduced, and it is difficult to quickly reduce the carbon content in steel to 10×10 -6 the following.

[0003] With the development of low-carbon steel metallurgy, electric furnace steelmaking accounts for an increasing proportion. The nitrogen content in the steel obtained by electric furnace steelmaking is relatively high. The RH refining process of ultra-low carbon steel produced by the electric furnace process encounters the problem of difficult efficient and deep removal of nitrogen in steel. The Chinese patent application with publication number CN113621759A discloses a method of using hydrogen to improve the RH refining effect. By using hydrogen instead of argon as a lifting gas in the RH refining process, vacuum decarburization is promoted and inclusions in the steel are removed; however, due to the small molecular weight of hydrogen, the hydrogen flow has a small penetration depth in the molten steel, which causes problems such as slow circulation of the molten steel, poor hydrogen stirring effect, and less dissolution of hydrogen in the molten steel; on the other hand, only using hydrogen instead of argon as a lifting gas in the RH riser to improve the RH refining effect is limited, especially the problem of efficient denitrification encountered in ultra-low carbon production is more difficult to solve. Hydrogen is blown into the RH riser, and part of the hydrogen can be dissolved in the molten steel, but due to the large bubble size, short contact time between the bubble and the molten steel, and the molten steel immediately undergoes vacuum treatment, the hydrogen content in the molten steel increases slowly. In order to further increase the dissolved hydrogen content in molten steel and give full play to the role of hydrogen in steel in vacuum refining decarbonization and denitrification, it is necessary to develop more efficient molten steel hydrogenation technology. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining.

[0005] According to one aspect of the present invention, the present invention provides the following technical solution:

[0006] The invention discloses an ultra-low carbon steel RH refining high-efficiency decarburization and denitrification method. After the RH refining starts, hydrogen-argon mixed gas is blown into an ascending pipe, hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of a vacuum chamber, and hydrogen is blown into molten steel in a descending pipe; the dissolution of hydrogen in molten steel is promoted during RH decarburization and denitrification refining, the hydrogen content in the molten steel in the vacuum chamber during RH decarburization and denitrification refining is increased, and the decarburization and denitrification reactions of the molten steel in the vacuum chamber are promoted; after decarburization, a deoxidizer is added to the molten steel to deoxidize the molten steel, a large amount of dispersed inclusions are generated in the molten steel, and the inclusions in the molten steel are used to further refine the bubbles in the molten steel; after decarburization and denitrification are completed, the blowing gas is switched to argon, argon is blown into the ascending pipe, argon is blown into the side and / or bottom of the vacuum chamber, and argon is blown into the molten steel in the descending pipe to realize composite blowing, promote mass transfer in the vacuum chamber, generate more bubbles in the molten steel, and promote dehydrogenation of the molten steel.

[0007] As a preferred embodiment of the method for efficient decarburization and denitrification by RH refining of ultra-low carbon steel described in the present invention, when vacuum refining starts in RH refining, a hydrogen-argon mixed gas is blown into the riser as a lifting gas, and a hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of the vacuum chamber. After the riser is blown for 0.5-1 min, when the flow rate of the molten steel in the downcomer is ≥0.3 m / s, hydrogen is blown into the molten steel through the downcomer blowing element.

[0008] As a preferred embodiment of the method for efficient decarbonization and denitrification of ultra-low carbon steel RH refining described in the present invention, the downcomer blowing element is one of a metal tube, a straight-through refractory pore, a dispersed air-permeable brick, and a breathable plug; the diameter of the metal tube and the straight-through refractory pore is controlled to be 0.2-3.0 mm, and the average pore size of the dispersed air-permeable brick and the breathable plug is 5-1000 μm.

[0009] As a preferred embodiment of the method for efficient decarburization and denitrification of ultra-low carbon steel RH refining described in the present invention, the blowing element at the bottom of the vacuum chamber adopts a dispersed air-permeable brick or an air-permeable plug, and the average pore size of the dispersed air-permeable brick and the air-permeable plug is 5-1000 μm; the blowing element on the side of the vacuum chamber is a high-speed nozzle.

[0010] As a preferred embodiment of the method for high-efficiency decarburization and denitrification of ultra-low carbon steel RH refining described in the present invention, the volume proportion of hydrogen in the hydrogen-argon mixed gas is 30-100%.

[0011] As a preferred embodiment of the method for efficient decarburization and denitrification of ultra-low carbon steel RH refining described in the present invention, the blowing flow rate at the side and / or bottom of the vacuum chamber is 20-100% of the blowing flow rate of the riser, and the blowing flow rate of the downcomer is 1-20% of the blowing flow rate of the riser.

[0012] The beneficial effects of the present invention are as follows:

[0013] The present invention proposes a method for high-efficiency decarburization and denitrification of ultra-low carbon steel RH refining. After the RH refining starts, hydrogen-argon mixed gas is blown into the ascending pipe, hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of the vacuum chamber, and hydrogen is blown into the molten steel through the downcomer. The present invention can not only promote the dissolution of hydrogen in the molten steel through multi-position composite blowing, but also make full use of the effects of the fast-flowing molten steel in the vacuum chamber and the downcomer and the effects of inclusions to refine the blown bubbles, and generate fine bubbles in the molten steel through the bottom blowing of the vacuum chamber and the downcomer, which promotes the dissolution of hydrogen. The generated fine hydrogen bubbles move with the molten steel, have a long contact time with the molten steel, and are more easily dissolved in the molten steel. The hydrogen blown into the downcomer enters the ladle downwards and does not enter the vacuum chamber, has a longer contact time with the molten steel, and is more easily dissolved in the molten steel. Composite argon blowing after decarburization and denitrification can efficiently dehydrogenate. The fine argon bubbles generated by the argon blowing at the bottom of the vacuum chamber and the downcomer are dispersed in the molten steel in the vacuum chamber, and the denitrification effect is better. The invention is green and low-carbon, has low production cost and high efficiency, is conducive to promotion and application in the production of ultra-low carbon steel, and solves the problem of difficulty in efficient deep decarbonization and denitrification in the production of ultra-low carbon steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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.

[0015] Figure 1 It is a schematic diagram of the method for efficient decarburization and denitrification by RH refining of ultra-low carbon steel of the present invention.

[0016] In the figure, 1-vacuum chamber, 2-riser pipe, 3-blowing element on the side of the vacuum chamber, 4-ladle, 5-down pipe.

[0017] 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

[0018] 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.

[0019] The present invention provides a method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining, such as Figure 1As shown, after the RH refining starts, a hydrogen-argon mixed gas is blown into the riser 2, a hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of the vacuum chamber 1, and hydrogen is blown into the molten steel through the downcomer 5; the dissolution of hydrogen in the molten steel during the RH decarburization and denitrification refining process is promoted, the hydrogen content in the molten steel in the vacuum chamber 1 during the RH decarburization and denitrification refining process is increased, and the decarburization and denitrification reactions of the molten steel in the vacuum chamber 1 are promoted; after the decarburization is completed, a deoxidizer is added to the molten steel to deoxidize the molten steel, a large number of dispersed inclusions are generated in the molten steel, and the inclusions in the molten steel are used to further refine the bubbles in the molten steel; after the decarburization and denitrification are completed, the blown gas is switched to argon, argon is blown into the riser 2, argon is blown into the side and / or bottom of the vacuum chamber 1, and argon is blown into the molten steel through the downcomer 5 to achieve composite blowing, promote mass transfer in the vacuum chamber, generate more bubbles in the molten steel, and promote dehydrogenation of the molten steel.

[0020] The hydrogen gas blown into the RH downcomer 5 is quickly separated from the blowing element under the shearing effect of the steel flow rapidly downward in the downcomer 5, the collision and traction of the inclusions in the steel, and the dissolution of the bubble root in the molten steel, producing relatively small hydrogen bubbles, which move downward together with the molten steel; during the downward movement of the bubbles, the turbulence of the molten steel, the collision and traction of the inclusions, and the static pressure of the molten steel further refine the hydrogen bubbles; these small hydrogen bubbles quickly dissolve in the molten steel, increasing the hydrogen content in the molten steel. The hydrogen-argon mixed gas or hydrogen gas is blown into the bottom of the vacuum chamber 1, and is quickly separated from the blowing element under the shearing effect of the steel flow rapidly flowing in the vacuum chamber 1, the collision and traction of the inclusions in the steel, and the dissolution of the bubble root in the molten steel, producing relatively small hydrogen bubbles, which are further refined by the turbulence of the molten steel, the collision and traction of the inclusions, and the static pressure of the molten steel; at the same time, these small bubbles quickly dissolve in the molten steel, increasing the content of dissolved hydrogen in the molten steel relatively quickly. A large number of dispersed inclusions generated in the molten steel continuously collide with bubbles, and at the same time, the inclusions and bubbles adhere to each other, reducing the interfacial tension between the bubbles and the molten steel; the irregular movements of the inclusions on and near the bubble surface, such as rotation and vibration, pull and break the bubbles; under these actions, the dispersed inclusions in the steel refine the bubbles and promote the generation of fine bubbles. After decarburization and denitrification refining, argon is blown into the riser 2, argon is blown into the side and / or bottom of the vacuum chamber 1, and argon is blown into the molten steel in the downcomer 5 to achieve composite blowing, which promotes the efficient removal of hydrogen in the molten steel; blowing argon in the downcomer 5 and the bottom of the vacuum chamber can generate dispersed tiny argon bubbles in the molten steel, which can promote the removal of hydrogen in the molten steel.

[0021] Preferably, when RH refining starts vacuum refining, a hydrogen-argon mixed gas is blown into the riser 2 as a lifting gas, and a hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of the vacuum chamber 1. After the riser 2 is blown for 0.5-1 min, when the flow rate of the molten steel in the downcomer 5 is ≥0.3 m / s, hydrogen is blown into the molten steel through the blowing element of the downcomer 5.

[0022] Preferably, the blowing element of the downcomer 5 is one of a metal tube, a straight-through refractory pore, a diffused air brick, and a breathable plug. The diameter of the metal tube and the straight-through refractory pore is controlled to be 0.2-3.0 mm, and the average pore size of the diffused air brick and the breathable plug is 5-1000 μm.

[0023] Preferably, the blowing element at the bottom of the vacuum chamber is a diffused air-permeable brick or an air-permeable plug, and the average pore size of the diffused air-permeable brick or the air-permeable plug is 5-1000 μm; the blowing element 3 at the side of the vacuum chamber is a high-speed nozzle.

[0024] Preferably, the volume proportion of hydrogen in the hydrogen-argon mixed gas is 30-100%.

[0025] Preferably, the blowing flow rate at the side and / or bottom of the vacuum chamber 1 is 20-100% of the blowing flow rate of the riser 2 , and the blowing flow rate of the downcomer 5 is 1-20% of the blowing flow rate of the riser 2 .

[0026] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0027] Example 1

[0028] A domestic steel plant has a 210tRH refining unit, which uses RH to smelt ultra-low carbon steel. The target nitrogen content of the molten steel is 30ppm and the carbon content is 10ppm.

[0029] After the RH refined molten steel enters the station, the temperature, carbon and oxygen content of the molten steel are measured; the ladle is lifted so that the RH immersion tube is inserted into the ladle; vacuuming begins to quickly reduce the pressure in the vacuum chamber, and at the same time, a hydrogen-argon mixed gas is blown into the molten steel at the bottom of the riser and the vacuum chamber, with the volume proportion of hydrogen in the mixed gas being 90%; the riser has 16 nozzles, and the total flow rate of the hydrogen-argon mixed gas in the riser during decarburization and denitrogenation refining is 4500NL / min; 6 air permeable plugs are installed at the bottom of the vacuum chamber, and the bottom blowing flow rate of the hydrogen-argon mixed gas is 2000NL / min; the downcomer is equipped with 4 stainless steel blowing holes with an aperture of 0.8mm. After vacuuming for 0.5min, the molten steel flow rate in the downcomer reaches 0.4m / s, and hydrogen is blown into the molten steel through them, with a total blowing flow rate of 600NL / min; RH is blown into the molten steel The hydrogen-argon mixed gas and the hydrogen in the hydrogen partially dissolved in the molten steel, which promoted the RH decarburization and denitrification reactions; after RH refining treatment for 12 minutes, the carbon concentration in the molten steel was reduced to 8ppm, meeting the carbon control requirements of ultra-low carbon steel, and aluminum was added for deoxidation. The aluminum oxide inclusions generated in the molten steel further promoted the formation of fine hydrogen bubbles in the molten steel, which promoted the denitrification reaction of the molten steel; after RH refining treatment for 15 minutes, the nitrogen content in the molten steel was reduced to 26ppm, and the denitrification refining was ended. Argon dehydrogenation refining was carried out, and the argon blowing flow rate of the riser was adjusted to 3000NL / min, the argon blowing flow rate of the vacuum chamber bottom was adjusted to 1800NL / min, and the argon blowing flow rate of the downcomer was 600NL / min. After dehydrogenation refining for 5 minutes, the dissolved hydrogen content in the molten steel was 0.7ppm at the end of RH refining.

[0030] Example 2

[0031] In a domestic steel plant's 210tRH refining unit, the target nitrogen content of RH refined ultra-low carbon steel liquid is 25ppm and the carbon content is 10ppm.

[0032] After the RH refined molten steel enters the station, the temperature, carbon and oxygen content of the molten steel are measured; the ladle is lifted so that the RH immersion tube is inserted into the ladle; vacuuming begins to quickly reduce the pressure in the vacuum chamber, and at the same time, a hydrogen-argon mixed gas is blown into the molten steel at the bottom of the riser and the vacuum chamber, with the volume proportion of hydrogen in the mixed gas being 90%; the RH riser has 16 nozzles, and the total flow rate of the hydrogen-argon mixed gas in the riser during decarburization and denitrogenation refining is 4500NL / min; 10 air permeable plugs are installed at the bottom of the RH, and the total flow rate of the bottom-blown hydrogen-argon mixed gas is 2500NL / min; the downcomer is equipped with 8 stainless steel blowing holes with an aperture of 0.5mm. After vacuuming for 1min, the molten steel flow rate in the downcomer reaches 0.5m / s, and hydrogen is blown into the molten steel through them, with a total blowing flow rate of 800NL / min; RH is blown into the molten steel The hydrogen-argon mixed gas and the hydrogen in the hydrogen partially dissolved in the molten steel, which promoted the RH decarburization and denitrification reactions; after RH refining treatment for 11 minutes, the carbon concentration in the molten steel was reduced to 8ppm, meeting the carbon control requirements of ultra-low carbon steel, and aluminum was added for deoxidation. The aluminum oxide inclusions generated in the molten steel further promoted the formation of fine hydrogen bubbles in the molten steel, which promoted the denitrification reaction of the molten steel; after RH refining treatment for 15 minutes, the nitrogen content in the molten steel was reduced to 23ppm, and the denitrification refining was ended. Argon dehydrogenation refining was carried out, and the argon blowing flow rate of the riser was adjusted to 3200NL / min, the argon blowing flow rate of the vacuum chamber bottom was adjusted to 1800NL / min, and the argon blowing flow rate of the downcomer was 800NL / min. Dehydrogenation refining was carried out for 5 minutes. At the end of RH refining, the dissolved hydrogen content in the molten steel was 0.6ppm.

[0033] In the RH refining process, the present invention blows hydrogen-argon mixed gas into the ascending pipe, blows hydrogen-argon mixed gas or hydrogen into the side and / or bottom of the vacuum chamber, and blows hydrogen into the molten steel through the descending pipe; promotes the dissolution of hydrogen in the molten steel during the RH decarburization and denitrification refining process, increases the hydrogen content in the molten steel in the vacuum chamber during the RH decarburization and denitrification refining process, and promotes the decarburization and denitrification reactions of the molten steel in the vacuum chamber; after decarburization, adds a deoxidizer to the molten steel to deoxidize the molten steel, generates a large number of dispersed inclusions in the molten steel, and further refines the bubbles in the molten steel by using the inclusions in the molten steel; after decarburization and denitrification, switches the blown gas to argon, blows argon into the ascending pipe, blows argon into the side and / or bottom of the vacuum chamber, and blows argon into the molten steel through the descending pipe to realize composite blowing, promotes mass transfer in the vacuum chamber, generates more bubbles in the molten steel, and promotes dehydrogenation of the molten steel.

[0034] 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 high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining, characterized in that: After RH refining begins, a hydrogen-argon mixed gas is blown into the riser, a hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of the vacuum chamber, and hydrogen is blown into the molten steel in the downcomer; after decarburization and denitrification are completed, the blown gas is switched to argon to achieve composite blowing.

2. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: When RH refining starts vacuum refining, hydrogen-argon mixed gas is blown into the riser as lifting gas, and hydrogen-argon mixed gas or hydrogen is blown into the side and / or bottom of the vacuum chamber. After the riser is blown for 0.5-1min, when the flow rate of the molten steel in the downcomer is ≥0.3m / s, hydrogen is blown into the molten steel through the downcomer blowing element.

3. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: The downcomer blowing element is one of a metal tube, a straight-through refractory air hole, a diffused air brick, and an air plug.

4. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 3, characterized in that: The diameter of the pores of metal tubes and straight-through refractory materials is controlled to be 0.2-3.0mm.

5. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 3, characterized in that: The average pore size of diffused air bricks and air plugs is 5-1000μm.

6. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: The blowing element at the bottom of the vacuum chamber adopts a diffused air brick or a permeable plug, and the average pore size of the diffused air brick and the permeable plug is 5-1000μm.

7. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: The blowing element on the side of the vacuum chamber is a high-speed nozzle.

8. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: The volume proportion of hydrogen in the hydrogen-argon mixed gas is 30-100%.

9. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: The blowing air flow rate at the side and / or bottom of the vacuum chamber is 20-100% of the blowing air flow rate of the riser.

10. The method for high-efficiency decarburization and denitrification of ultra-low carbon steel by RH refining according to claim 1, characterized in that: The blowing flow rate of the downcomer is 1-20% of the blowing flow rate of the upcomer.

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