Ultra-low carbon steel RH refining denitrification method

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to an ultra-low carbon steel RH refining denitrification method, which adopts the modes of hydrogen increasing decarburization denitrification in the early stage of RH refining, hydrogen evolution denitrification in the middle stage of RH refining and argon blowing dehydrogenation in the later stage of RH refining, and performs composite blowing of hydrogen and argon mixed gas in the RH refining of ultra-low carbon steel, the circulating flowing speed of molten steel can be increased, the stirring effect is good, and hydrogen is promoted to be dissolved in the molten steel; by combining vacuum treatment, oxygen control and sulfur control treatment, micro-bubble denitrification and the like, ultra-low carbon steel RH deep denitrification can be well realized; in the refining process, it is guaranteed that the gas supply main pipeline is in the gas supply state all the time in the gas adjusting process, and pipeline blockage caused by the fact that molten steel flows backwards to the gas supply pipeline in the gas adjusting and switching process is avoided. The method is easy to operate, low in production cost, high in efficiency and beneficial to industrial large-scale production, popularization and application.

Description

Technical Field

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

[0002] RH refining is an important means of vacuum refining of high-quality steel, which has refining functions such as decarburization, removal of inclusions, degassing (hydrogen, nitrogen), and desulfurization. However, in the RH refining production of ultra-low carbon steel, due to the short time and high oxygen and sulfur content in the liquid steel, there is a problem that it is difficult to remove liquid nitrogen from the steel efficiently and deeply. With the development of low-carbon steel metallurgy, electric furnace steelmaking accounts for an increasing proportion, and the liquid nitrogen content of steel obtained from electric furnace steelmaking is relatively high. The RH refining process of producing ultra-low carbon steel using the electric furnace process encounters the problem that it is difficult to remove liquid nitrogen from the steel efficiently and deeply. A Chinese patent application with publication number CN113621759A discloses a method for improving the RH refining effect by using hydrogen, which comprises using hydrogen instead of argon as a lifting gas in the RH refining process, vacuum decarburization, switching the lifting gas to argon, vacuum degassing and removing inclusions, and finally adding aluminum for deoxidation; however, due to the small molecular weight of hydrogen, the hydrogen flow has a small penetration depth in the molten steel during hydrogen blowing, thereby causing problems such as slow circulation of the molten steel, poor hydrogen stirring effect, and less dissolution of hydrogen in the molten steel; more seriously, problems such as clogging of the blowing element may occur during the process of switching hydrogen to argon in the later stage of refining. 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 RH refining and denitrification of ultra-low carbon steel.

[0004] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0005] The invention discloses a method for RH refining and denitrification of ultra-low carbon steel, which comprises the following steps: hydrogenation decarburization and denitrification in the early stage of RH refining, hydrogenation denitrification in the middle stage of RH refining, and argon blowing dehydrogenation in the late stage of RH refining.

[0006] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the hydrogenation, decarburization and denitrification in the early stage of RH refining are specifically as follows:

[0007] 2-3 minutes after the start of refining, the vacuum degree of the vacuum chamber is reduced to below 8000Pa; while starting vacuum refining, a hydrogen-argon mixed gas is blown into the riser as a lifting gas, and a hydrogen-argon mixed gas is blown into the molten steel at the bottom and / or side of the vacuum chamber to achieve hydrogenation, decarburization and denitrification.

[0008] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, an argon pipeline and a hydrogen pipeline are connected in parallel to provide gas to the RH riser, the bottom and / or the side of the vacuum chamber, and are merged into a main pipeline before entering the riser blowing nozzle, the bottom and / or the side blowing element of the vacuum chamber; the argon pipeline and the hydrogen pipeline are respectively provided with a pressure gauge, a flow meter and a control valve.

[0009] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, independent gas supply systems are used for the riser, the bottom of the vacuum chamber, and the side of the vacuum chamber to achieve independent and flexible regulation of the gas flow and composition of each part.

[0010] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the pressure of the hydrogen pipeline is ≥ the pressure of the argon pipeline -0.2×10 6 Pa.

[0011] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, when hydrogen-argon mixed gas is mixed and supplied, the hydrogen flow rate / total flow rate of hydrogen-argon mixed gas is 30-100%; during the denitrification period, the total flow rate of rising pipe blowing and the total flow rate of side blowing or bottom blowing in the vacuum chamber are controlled according to equations (1) and (2), respectively.

[0012] Q 氢氩上升管 =n 喷嘴 ×q 1 (1)

[0013] In the formula, Q 氢氩上升管 is the total air flow rate of the riser, NL / min; n 喷嘴 is the number of rising pipe blowing nozzles, q 1 =200-500NL / min;

[0014] Q 氢氩侧吹 / 底吹 =n 元件 ×q 2 (2)

[0015] In the formula, Q 氢氩侧吹 / 底吹 is the total flow rate of side blowing or bottom blowing in the vacuum chamber, NL / min; n 元件 is the number of side blowing or bottom blowing elements in the vacuum chamber, q 2 =300-1000NL / min.

[0016] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the gas supply main pipeline is ensured to be in a gas supply state during the gas regulation process during the refining process to avoid pipeline blockage caused by backflow of molten steel into the gas supply pipeline during gas adjustment and switching.

[0017] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the hydrogen evolution and denitrification in the middle stage of RH refining is specifically as follows:

[0018] After RH vacuum treatment for 5-6 minutes, the pressure in the vacuum chamber drops to less than 150Pa. At this time, the hydrogen dissolved in the molten steel precipitates a large number of tiny diffuse hydrogen bubbles in the molten steel in the vacuum chamber. The tiny diffuse hydrogen bubbles promote the nitrogen in the molten steel to precipitate nitrogen in the tiny diffuse hydrogen bubbles; the partially dissolved hydrogen reacts with oxygen and sulfur in the molten steel on the surface of the molten steel in the vacuum chamber, increases the nitrogen concentration on the surface of the molten steel, and promotes the nitrogen in the molten steel in the vacuum chamber to precipitate into the vacuum on the surface of the molten steel in the vacuum chamber.

[0019] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the carbon content of the molten steel during the RH refining process is measured or calculated. After the carbon content reaches the control requirement of ultra-low carbon steel, aluminum is added for deoxidation to reduce the oxygen content in the molten steel and further promote denitrification. At this time, the denitrification of the molten steel mainly relies on the denitrification of hydrogen bubbles and the denitrification of the molten steel surface in the vacuum chamber.

[0020] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the argon blowing dehydrogenation in the later stage of RH refining is specifically as follows: after the nitrogen content reaches the control requirement of ultra-low carbon steel, the flow rate of the argon supply pipe is adjusted to ensure that the argon flow rate in the total gas supply pipeline is greater than the critical blockage flow rate of the pipeline; then the hydrogen pipeline control valve is closed, the argon supply intensity is adjusted, and dehydrogenation is carried out.

[0021] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the critical blocking flow rate is Q 氢氩上升管 or Q 氢氩侧吹 / 底吹 10% of.

[0022] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the hydrogen pipeline control valve is closed, the argon supply intensity is adjusted, dehydrogenation is carried out, and the total flow rate of argon blowing in the riser and the total flow rate of argon blowing in the side or bottom of the vacuum chamber are controlled according to the relationship (3) and (4), respectively.

[0023] Q Ar上升管 =n 喷嘴 ×q 3 (3)

[0024] In the formula, Q Ar上升管 is the total argon blowing flow rate of the riser, NL / min; n 喷嘴 is the number of rising pipe blowing nozzles, q 3 =200-300NL / min;

[0025] Q Ar侧吹 / 底吹 =n 元件 ×q 4 (4)

[0026] In the formula, Q Ar侧吹 / 底吹 is the total flow rate of argon gas for side blowing or bottom blowing in the vacuum chamber, NL / min; n 元件 is the number of side blowing or bottom blowing elements in the vacuum chamber, q 4 =300-1500NL / min.

[0027] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the dissolved oxygen content in the molten steel is controlled to be 300-700 ppm, the sulfur content is 30-120 ppm, the carbon content is 300-600 ppm, and the nitrogen content is 40-80 ppm before RH refining.

[0028] As a preferred embodiment of the method for RH refining and denitrification of ultra-low carbon steel described in the present invention, the dissolved hydrogen content in the molten steel after RH refining is 0.5-2.0 ppm, and the nitrogen content is 25-40 ppm.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention proposes a method for RH refining and denitrification of ultra-low carbon steel, which adopts the method of hydrogenation decarbonization and denitrification in the early stage of RH refining, hydrogenation denitrification in the middle stage of RH refining, and argon blowing dehydrogenation in the late stage of RH refining. By compounding hydrogen and argon mixed gas in the RH refining of ultra-low carbon steel, the penetration depth of hydrogen and argon mixed gas in molten steel is large, which can accelerate the circulation flow speed of molten steel, have good stirring effect and promote the dissolution of hydrogen in molten steel; combined with vacuum treatment, oxygen and sulfur control treatment, micro-bubble denitrification, etc., RH deep denitrification of ultra-low carbon steel can be better achieved; during the refining process, it is ensured that the gas supply main pipeline is always in a gas supply state during the gas adjustment process, so as to avoid the pipeline blockage caused by the backflow of molten steel into the gas supply pipeline during the gas adjustment and switching process. The present invention is simple to operate, low in production cost, high in efficiency, and conducive to large-scale industrial production and popularization. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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.

[0032] Figure 1 It is a schematic diagram of the method for RH refining and denitrification of ultra-low carbon steel of the present invention.

[0033] Among them: 1-vacuum chamber, 2-rising tube, 3-vacuum chamber side blowing tube, 4-ladle.

[0034] The realization of the effects, 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

[0035] 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.

[0036] like Figure 1 As shown, the present invention proposes a method for RH refining and denitrification of ultra-low carbon steel, which includes hydrogenation decarburization and denitrification in the early stage of RH refining, hydrogen evolution denitrification in the middle stage of RH refining, and argon blowing dehydrogenation in the late stage of RH refining.

[0037] After the ladle trolley is driven to the molten steel receiving position, the RH refining device ladle 4 is lifted, so that the ascending tube 2 and the descending tube are simultaneously inserted into the molten steel in the ladle 4 of the RH refining device.

[0038] Preferably, the hydrogenation, decarbonization and denitrification in the early stage of RH refining are specifically as follows:

[0039] 2-3 minutes after the start of refining, the vacuum degree of vacuum chamber 1 is reduced to below 8000Pa; while vacuum refining begins, hydrogen-argon mixed gas is blown into riser 2 as lifting gas, and hydrogen-argon mixed gas is blown into the molten steel at the bottom and / or side of the vacuum chamber (vacuum chamber side blowing pipe 3) to achieve hydrogenation, decarburization and denitrification.

[0040] Preferably, an argon pipeline and a hydrogen pipeline are connected in parallel to provide gas to the RH riser, the bottom and / or the side of the vacuum chamber, and are merged into a main pipeline before entering the riser blowing nozzle, the bottom and / or the side blowing elements of the vacuum chamber; the argon pipeline and the hydrogen pipeline are respectively provided with a pressure gauge, a flow meter and a control valve.

[0041] Preferably, the riser, the bottom of the vacuum chamber, and the side of the vacuum chamber each use independent gas supply systems to achieve independent and flexible regulation of the gas flow and composition of each part.

[0042] Preferably, the pressure of the hydrogen pipeline is ≥ the pressure of the argon pipeline - 0.2×10 6 Pa.

[0043] Preferably, when the mixed gas is supplied, the hydrogen flow rate / the total flow rate of the hydrogen-argon mixed gas is 30-100%; during the denitrification period, the total flow rate of the riser blowing, the total flow rate of the side blowing or the bottom blowing in the vacuum chamber are controlled according to the relationship (1) and (2), respectively.

[0044] Q 氢氩上升管 =n 喷嘴 ×q 1(1)

[0045] In the formula, Q 氢氩上升管 is the total air flow rate of the riser, NL / min; n 喷嘴 is the number of rising pipe blowing nozzles, which can be set as needed, for example, 10 to 20; q 1 =200-500NL / min;

[0046] Q 氢氩侧吹 / 底吹 =n 元件 ×q 2 (2)

[0047] In the formula, Q 氢氩侧吹 / 底吹 is the total flow rate of side blowing or bottom blowing in the vacuum chamber, NL / min; n 元件 is the number of side blowing or bottom blowing elements in the vacuum chamber, which can be set as needed, for example, 2 to 20; q 2 =300-1000NL / min.

[0048] Preferably, during the refining process, it is ensured that the main gas supply pipeline is always in a gas supply state during the gas regulation process to avoid pipeline blockage caused by the backflow of molten steel into the gas supply pipeline during gas adjustment and switching.

[0049] The hydrogen in the hydrogen-argon mixed gas blown into the molten steel partially dissolves in the molten steel, and partially reacts with the oxygen and sulfur in the molten steel on the surface of the bubble, reducing the oxygen and sulfur concentration in the molten steel on the surface of the hydrogen-argon bubble, increasing the nitrogen concentration in the molten steel on the surface of the bubble, and promoting the chemical reaction of nitrogen dissolved in the molten steel on the surface of the bubble; the hydrogen partially dissolved in the molten steel precipitates into the CO bubbles generated by decarburization in the molten steel, reducing the nitrogen concentration in CO, and reacts with the oxygen and sulfur in the molten steel on the surface of the CO bubble, promoting the denitrification of the CO bubble. In the RH refining and denitrification process, hydrogen-argon mixed gas is blown into the molten steel at the same time in the riser, at the bottom or side of the vacuum chamber. Blowing hydrogen-argon mixed gas can not only reduce the danger of explosion caused by the violent reaction of hydrogen and oxygen, but also increase the density of the mixed gas and the penetration depth of the mixed gas when it is blown into the molten steel, ensuring the good circulation of the RH refined molten steel, the good stirring of the molten steel in the vacuum chamber, and the dissolution of hydrogen in the mixed gas into the molten steel.

[0050] Preferably, the hydrogen evolution and denitrification in the middle stage of RH refining is specifically as follows:

[0051] After RH vacuum treatment for 5-6 minutes, the pressure in the vacuum chamber drops to less than 150Pa. At this time, the hydrogen dissolved in the molten steel precipitates a large number of tiny diffuse hydrogen bubbles in the molten steel in the vacuum chamber. The tiny diffuse hydrogen bubbles promote the nitrogen in the molten steel to precipitate nitrogen in the tiny diffuse hydrogen bubbles; the partially dissolved hydrogen reacts with oxygen and sulfur in the molten steel on the surface of the molten steel in the vacuum chamber, increases the nitrogen concentration on the surface of the molten steel, and promotes the nitrogen in the molten steel in the vacuum chamber to precipitate into the vacuum on the surface of the molten steel in the vacuum chamber.

[0052] Preferably, the carbon content of the molten steel during the RH refining process is measured or calculated. After the carbon content reaches the control requirement for ultra-low carbon steel, aluminum is added for deoxidation to reduce the oxygen content in the molten steel and further promote denitrification; at this time, the denitrification of the molten steel mainly relies on denitrification by hydrogen bubble precipitation and denitrification on the surface of the molten steel in the vacuum chamber.

[0053] Preferably, argon blowing and dehydrogenation in the later stage of RH refining are specifically as follows: after the nitrogen content reaches the control requirement of ultra-low carbon steel, the flow rate of the argon supply pipe is adjusted to ensure that the argon flow rate in the main gas supply pipeline is greater than the critical blockage flow rate of the pipeline; then the hydrogen pipeline control valve is closed, the argon supply intensity is adjusted, and dehydrogenation is carried out.

[0054] Preferably, the critical blockage flow is Q 氢氩上升管 or Q 氢氩侧吹 / 底吹 10% of.

[0055] Preferably, after denitrification is completed, the hydrogen pipeline control valve is closed, the argon supply intensity is adjusted, and dehydrogenation is performed. The total flow rate of argon supplied by the riser and the total flow rate of argon gas blown sideways or bottom-blown in the vacuum chamber are controlled according to equations (3) and (4), respectively.

[0056] Q Ar上升管 =n 喷嘴 ×q 3 (3)

[0057] In the formula, Q Ar上升管 is the total argon blowing flow rate of the riser, NL / min; n 喷嘴 is the number of rising pipe blowing nozzles, q 3 =200-300NL / min;

[0058] Q Ar侧吹 / 底吹 =n 元件 ×q 4 (4)

[0059] In the formula, Q Ar侧吹 / 底吹 is the total flow rate of argon gas for side blowing or bottom blowing in the vacuum chamber, NL / min; n 元件 is the number of side blowing or bottom blowing elements in the vacuum chamber, q 4 =300-1500NL / min.

[0060] Preferably, if the oxygen and sulfur in the molten steel are too high, the effect of the blown hydrogen is limited. At the same time, too high oxygen and sulfur in the molten steel will also affect the concentration of hydrogen dissolved in the molten steel. Therefore, before RH refining, the dissolved oxygen content in the molten steel should be controlled to be 300-700ppm, the sulfur content to be 30-120ppm, the carbon content to be 300-600ppm, and the nitrogen content to be 40-80ppm according to the demand for oxygen in the molten steel by the vacuum decarburization reaction, the demand for controlling oxygen and sulfur in the molten steel by the denitrification reaction, the production characteristics of ultra-low carbon steel and the cost control requirements.

[0061] Preferably, the dissolved hydrogen content in the molten steel after RH refining is 0.5-2.0 ppm, and the nitrogen content is 25-40 ppm.

[0062] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0063] Example 1

[0064] In a domestic steel plant's 210tRH refining unit, the RH inlet ultra-low carbon steel has an oxygen content of 550ppm, a sulfur content of 72ppm, a carbon content of 380ppm, and a nitrogen content of 61ppm. The target nitrogen content is 30ppm and the carbon content is 30ppm.

[0065] RH refining uses argon and hydrogen pipelines in parallel to supply gas to the RH riser and the side of the vacuum chamber. Finally, the argon and hydrogen pipelines are combined into a main pipeline to connect to the RH riser blowing nozzle and the blowing element on the side of the vacuum chamber to provide gas. The argon and hydrogen pipelines are respectively equipped with pressure gauges, flow meters and control valves; the gas supply channels, pressure gauges, flow meters and control valves on the RH riser and the side of the vacuum chamber each constitute an independent system and can be independently regulated.

[0066] In the early stage of refining, hydrogenation, decarbonization and denitrification were carried out. The vacuum degree of the vacuum chamber was rapidly reduced to 3000Pa 3 minutes after the start of RH refining. At the beginning of vacuum refining, hydrogen-argon mixed gas was blown into the molten steel from the riser and the side of the vacuum chamber. The volume proportion of hydrogen in the mixed gas was 90%. The RH riser had 16 nozzles. During the denitrification refining, the total flow rate of hydrogen-argon mixed gas in the riser was 4500NL / min, and the pressure of the hydrogen pipeline was 0.89×10 6 Pa, the pressure of the argon pipeline is 0.82×10 6 Pa; the RH vacuum chamber has two nozzles for side blowing, the total flow rate of the side blowing hydrogen-argon mixed gas is 2000NL / min, and the pressure of the hydrogen pipeline is 0.78×10 6 Pa, the pressure of the argon pipeline is 0.72×10 6Pa; RH The hydrogen in the hydrogen-argon mixed gas blown into the molten steel partially dissolves in the molten steel, and partially reacts with the oxygen and sulfur in the molten steel on the surface of the bubble, reducing the oxygen and sulfur concentrations in the molten steel on the surface of the hydrogen-argon bubble, and promoting the chemical reaction of the dissolved nitrogen in the molten steel on the surface of the bubble to precipitate nitrogen; Part of the hydrogen dissolved in the molten steel precipitates into the CO bubbles generated in the molten steel, reducing the nitrogen concentration in CO, and reacts with the oxygen and sulfur in the molten steel on the surface of the CO bubble, promoting the denitrification of the CO bubbles. As the hydrogen content in the molten steel in the vacuum chamber increases, the hydrogen dissolved in the molten steel gradually precipitates tiny diffuse hydrogen bubbles in the molten steel in the vacuum chamber, and the tiny diffuse hydrogen bubbles promote the nitrogen in the molten steel to precipitate nitrogen in the tiny diffuse hydrogen bubbles; Part of the dissolved hydrogen reacts with the oxygen and sulfur in the molten steel on the surface of the molten steel in the vacuum chamber, promoting the nitrogen in the molten steel in the vacuum chamber to precipitate into the vacuum on the surface of the molten steel in the vacuum chamber;

[0067] After RH vacuum treatment for 6 minutes, the vacuum chamber pressure dropped to 60Pa, and denitrification continued; after RH refining treatment for 10 minutes, the carbon concentration in the molten steel was measured to be reduced to 12ppm, meeting the carbon control requirements of ultra-low carbon steel, and aluminum was added for deoxidation to further reduce the oxygen content in the molten steel, while hydrogen-argon mixed gas was continued for denitrification;

[0068] After RH refining treatment for 15 minutes, the nitrogen content in the molten steel was reduced to 28ppm, and the denitrification refining was ended. The argon flow rate of the riser was adjusted to 1000NL / min, and the argon flow rate of the vacuum chamber side blowing was adjusted to 500NL / min. Then, the hydrogen pipeline control valves of the riser and vacuum chamber side blowing gas supply systems were closed, and the argon flow rates of the riser and vacuum chamber side blowing were adjusted to 4500NL / min and 2500NL / min, respectively, for dehydrogenation. At the end of RH refining, the dissolved hydrogen content in the molten steel was 0.8ppm.

[0069] Example 2

[0070] In a domestic steel plant's 210tRH refining unit, the RH incoming ultra-low carbon steel has an oxygen content of 600ppm, a sulfur content of 62ppm, a carbon content of 400ppm, and a nitrogen content of 65ppm. The target nitrogen content is 30ppm and the carbon content is 25ppm.

[0071] RH refining uses argon and hydrogen pipelines in parallel to supply gas to the RH riser and the side of the vacuum chamber. Finally, the argon and hydrogen pipelines are combined into a main pipeline to connect to the RH riser blowing nozzle and the blowing element on the side of the vacuum chamber to provide gas. The argon and hydrogen pipelines are respectively provided with pressure gauges, flow meters and control valves; the gas supply channels, pressure gauges, flow meters and control valves on the RH riser and the side of the vacuum chamber each constitute an independent system and can be independently regulated.

[0072] In the early stage of refining, hydrogenation, decarbonization and denitrification were carried out. The vacuum degree of the vacuum chamber dropped rapidly to 4200Pa 2.5min after the start of RH refining. At the beginning of vacuum refining, hydrogen-argon mixed gas was blown into the molten steel from the riser and the side of the vacuum chamber. The volume proportion of hydrogen in the mixed gas was 90%. The RH riser had 16 nozzles. During the denitrification refining, the total flow rate of hydrogen-argon mixed gas in the riser was 5000NL / min, and the pressure of the hydrogen pipeline was 1.08×10 6 Pa, the pressure of the argon pipeline is 1.12×10 6 Pa; the RH vacuum chamber has six side blowing nozzles, the total flow rate of the side blowing hydrogen-argon mixed gas is 3000NL / min, and the pressure of the hydrogen pipeline is 0.98×10 6 Pa, the pressure of the argon pipeline is 1.02×10 6 Pa; RH The hydrogen in the hydrogen-argon mixed gas blown into the molten steel partially dissolves in the molten steel, and partially reacts with the oxygen and sulfur in the molten steel on the surface of the bubble, reducing the oxygen and sulfur concentrations in the molten steel on the surface of the hydrogen-argon bubble, and promoting the chemical reaction of the dissolved nitrogen in the molten steel on the surface of the bubble to precipitate nitrogen; Part of the hydrogen dissolved in the molten steel precipitates into the CO bubbles generated in the molten steel, reducing the nitrogen concentration in CO, and reacts with the oxygen and sulfur in the molten steel on the surface of the CO bubble, promoting the denitrification of the CO bubbles. As the hydrogen content in the molten steel in the vacuum chamber increases, the hydrogen dissolved in the molten steel gradually precipitates tiny diffuse hydrogen bubbles in the molten steel in the vacuum chamber, and the tiny diffuse hydrogen bubbles promote the nitrogen in the molten steel to precipitate nitrogen in the tiny diffuse hydrogen bubbles; Part of the dissolved hydrogen reacts with the oxygen and sulfur in the molten steel on the surface of the molten steel in the vacuum chamber, promoting the nitrogen in the molten steel in the vacuum chamber to precipitate into the vacuum on the surface of the molten steel in the vacuum chamber;

[0073] After RH vacuum treatment for 6 minutes, the vacuum chamber pressure dropped to 50Pa, and denitrification continued; after RH refining treatment for 11 minutes, the carbon concentration in the molten steel was measured to be reduced to 20ppm, meeting the carbon control requirements of ultra-low carbon steel, aluminum was added for deoxidation to further reduce the oxygen content in the molten steel, and hydrogen-argon mixed gas was continued for denitrification;

[0074] After 15 minutes of RH refining treatment, the nitrogen content in the molten steel was reduced to 27ppm, and the denitrification refining was ended. The argon flow rate of the riser was adjusted to 980NL / min, and the argon flow rate of the vacuum chamber side blowing was adjusted to 550NL / min. Then, the hydrogen pipeline control valves of the riser and vacuum chamber side blowing gas supply systems were closed, and the argon supply intensities of the riser and vacuum chamber side blowing were adjusted to 4500NL / min and 2800NL / min, respectively, for dehydrogenation. At the end of RH refining, the dissolved hydrogen content in the molten steel was 0.6ppm.

[0075] The present invention adopts the method of increasing hydrogen, decarbonizing and denitrifying in the early stage of RH refining, denitrifying by hydrogenation in the middle stage of RH refining, and dehydrogenating by argon blowing in the late stage of RH refining. By compounding hydrogen and argon mixed gas in the RH refining of ultra-low carbon steel, the penetration depth of hydrogen and argon mixed gas in molten steel is large, which can accelerate the circulation flow speed of molten steel, have good stirring effect and promote the dissolution of hydrogen in molten steel; combined with vacuum treatment, oxygen and sulfur control treatment, micro bubble denitrification, etc., RH deep denitrification of ultra-low carbon steel can be well achieved; during the refining process, it is ensured that the gas supply main pipeline is always in the gas supply state during the gas adjustment process, so as to avoid the pipeline blockage caused by the backflow of molten steel into the gas supply pipeline during the gas adjustment and switching process. The present invention is simple to operate, has low production cost, high efficiency, and is conducive to industrial large-scale production and popularization.

[0076] 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 RH refining and denitrification of ultra-low carbon steel, characterized in that: It is a method of adding hydrogen to decarbonize and denitrify in the early stage of RH refining, denitrifying by hydrogen evolution in the middle stage of RH refining, and dehydrogenating by argon blowing in the late stage of RH refining.

2. The method for RH refining and denitrification of ultra-low carbon steel according to claim 1, characterized in that: The specific steps of hydrogenation, decarbonization and denitrification in the early stage of RH refining are as follows: 2-3 minutes after the start of refining, the vacuum degree of the vacuum chamber is reduced to below 8000Pa; while starting vacuum refining, a hydrogen-argon mixed gas is blown into the riser as a lifting gas, and a hydrogen-argon mixed gas is blown into the molten steel at the bottom and / or side of the vacuum chamber to achieve hydrogenation, decarburization and denitrification.

3. The method for RH refining and denitrification of ultra-low carbon steel according to claim 2, characterized in that: Argon and hydrogen pipelines are connected in parallel to provide gas to the RH riser, the bottom and / or the side of the vacuum chamber, and are merged into a main pipeline before entering the riser blowing nozzle, the bottom and / or the side blowing elements of the vacuum chamber; the argon and hydrogen pipelines are respectively provided with pressure gauges, flow meters and control valves.

4. The method for RH refining and denitrification of ultra-low carbon steel according to claim 2, characterized in that: When the hydrogen-argon mixed gas is supplied, the hydrogen flow rate / the total flow rate of the hydrogen-argon mixed gas is 30-100%; during the denitrification period, the total flow rate of the riser blowing, the total flow rate of the side blowing or the bottom blowing in the vacuum chamber are controlled according to the relationship (1) and (2), respectively. Q 氢氩上升管 =n 喷嘴 ×q1 (1) In the formula, Q 氢氩上升管 is the total air flow rate of the riser, NL / min; n 喷嘴 is the number of rising pipe blowing nozzles, pcs; q1 = 200-500NL / min; Q 氢氩侧吹 / 底吹 =n 元件 ×q2 (2) In the formula, Q 氢氩侧吹 / 底吹 is the total flow rate of side blowing or bottom blowing in the vacuum chamber, NL / min; n 元件 is the number of side blowing or bottom blowing elements in the vacuum chamber, pieces; q2=300-1000NL / min.

5. The method for RH refining and denitrification of ultra-low carbon steel according to claim 2, characterized in that: During the refining process, ensure that the main gas supply pipeline is always in a gas supply state during the gas regulation process.

6. The method for RH refining and denitrification of ultra-low carbon steel according to claim 1, characterized in that: The specific steps of hydrogen evolution and denitrification in the middle stage of RH refining are as follows: After RH vacuum treatment for 5-6 minutes, the pressure in the vacuum chamber drops to less than 150Pa. At this time, the hydrogen dissolved in the molten steel precipitates a large number of tiny diffuse hydrogen bubbles in the molten steel in the vacuum chamber. The tiny diffuse hydrogen bubbles promote the nitrogen in the molten steel to precipitate nitrogen in the tiny diffuse hydrogen bubbles; the partially dissolved hydrogen reacts with oxygen and sulfur in the molten steel on the surface of the molten steel in the vacuum chamber, increases the nitrogen concentration on the surface of the molten steel, and promotes the nitrogen in the molten steel in the vacuum chamber to precipitate into the vacuum on the surface of the molten steel in the vacuum chamber.

7. The method for RH refining and denitrification of ultra-low carbon steel according to claim 6, characterized in that: Measure or calculate the carbon content of molten steel during RH refining. When the carbon content reaches the control requirement of ultra-low carbon steel, aluminum is added for deoxidation to reduce the oxygen content in the molten steel and further promote denitrification. At this time, denitrification of molten steel mainly relies on denitrification by hydrogen bubble precipitation and denitrification on the surface of molten steel in the vacuum chamber.

8. The method for RH refining and denitrification of ultra-low carbon steel according to claim 1, characterized in that: The specific steps of argon blowing and dehydrogenation in the later stage of RH refining are as follows: after the nitrogen content reaches the control requirement of ultra-low carbon steel, the flow rate of the argon supply pipe is adjusted to ensure that the argon flow rate in the total gas supply pipeline is greater than the critical blockage flow rate of the pipeline; then the hydrogen pipeline control valve is closed, the argon supply intensity is adjusted, and dehydrogenation is carried out.

9. The method for RH refining and denitrification of ultra-low carbon steel according to claim 8, characterized in that: Close the hydrogen pipeline control valve, adjust the argon supply intensity, and carry out dehydrogenation. The total flow rate of argon blowing in the riser and the total flow rate of argon blowing from the side or bottom of the vacuum chamber are controlled according to equations (3) and (4), respectively. Q Ar上升管 =n 喷嘴 ×q3 (3) In the formula, Q Ar上升管 is the total argon blowing flow rate of the riser, NL / min; n 喷嘴 is the number of rising pipe blowing nozzles, pcs; q3 = 200-300NL / min; Q Ar侧吹 / 底吹 =n 元件 ×q4 (4) In the formula, Q Ar侧吹 / 底吹 is the total flow rate of side blowing or bottom blowing in the vacuum chamber, NL / min; n 元件 The number of side blowing or bottom blowing elements in the vacuum chamber, q4 = 300-1500NL / min.

10. The method for RH refining and denitrification of ultra-low carbon steel according to claim 1, characterized in that: Before RH refining, the dissolved oxygen content in the molten steel is controlled to be 300-700ppm, the sulfur content is 30-120ppm, the carbon content is 300-600ppm, and the nitrogen content is 40-80ppm; after RH refining, the dissolved hydrogen content in the molten steel is 0.5-2.0ppm, and the nitrogen content is 25-40ppm.

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