Ultra-low carbon steel RH refining decarburization and denitrification synergistic method

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to an ultra-low carbon steel RH refining decarburization and denitrification coordinated method, which comprises the following steps: controlling oxygen and sulfur in molten steel before RH refining, quickly reducing the pressure of a vacuum chamber after the refining is started, and then realizing the decarburization and denitrification coordination through a process of blowing hydrogen or hydrogen-argon mixed gas into an ascending pipe in coordination with oxygen top blowing or aluminum oxygen control. And after the carbon in the steel is reduced to the ultra-low carbon steel RH refining control requirement, aluminum is added for final deoxidation, then denitrification is continued, after denitrification is completed, ascending pipe blowing is adjusted to argon blowing, dehydrogenation is further conducted, and inclusions are removed. According to the method, the problem that in the prior art, RH deep denitrification is difficult can be solved, and nitrogen in the steel after RH refining can be reduced to 25-40 ppm.

Description

Technical Field

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

[0002] Electric furnace steelmaking and large scrap ratio steelmaking are the development direction of low-carbon metallurgical technology, but both technologies have problems such as high nitrogen content in steel and difficulty in removing nitrogen in steel. The Chinese patent application with publication number CN113621759A discloses a method of using hydrogen instead of argon as a lifting gas in the RH refining process for vacuum decarburization to achieve steel liquid temperature increase, promote decarburization, promote inclusion floating, improve steel liquid cleanliness, replace part of argon, and reduce refining costs, but it does not mention how to promote RH efficient denitrification; the Chinese patent application with publication number CN117512273A discloses a method of blowing hydrogen through the RH riser and the side or bottom of the vacuum chamber, which can enhance the functions of decarburization, removal of inclusions, and denitrification in the RH refining process, but this method requires composite hydrogen blowing, and the gas blown in is single, and the safety control and refining effect in the refining process are limited. 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 propose a method for RH refining decarburization and synergistic 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] A method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel, comprising: controlling oxygen and sulfur in molten steel before RH refining, rapidly reducing the pressure of a vacuum chamber after refining begins, and then blowing hydrogen or a hydrogen-argon mixed gas through a riser to coordinate top blowing of oxygen or an aluminum oxygen control process to achieve coordinated decarburization and denitrification; after the carbon in the steel is reduced to the control requirement for RH refining of ultra-low carbon steel, aluminum is added for final deoxidation, and then denitrification is continued; after denitrification is completed, the riser blowing is adjusted to argon blowing to further dehydrogenate and remove inclusions.

[0006] As a preferred embodiment of the method for RH refining, decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the dissolved oxygen content in the molten steel is controlled to be 50-150ppm and the sulfur content in the molten steel is controlled to be 10-100ppm before RH refining.

[0007] As a preferred embodiment of the method for RH refining, decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the vacuum chamber pressure is reduced to below 10,000 Pa within 0.5 minutes after the start of refining, hydrogen or a hydrogen-argon mixed gas is blown in through the riser, and the vacuum chamber pressure continues to be rapidly reduced.

[0008] As a preferred embodiment of the method for RH refining, decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the vacuum chamber pressure is reduced to below 3000Pa 2-3min after the molten steel enters the vacuum chamber, thereby promoting the carbon-oxygen reaction in the molten steel and promoting denitrification of the molten steel at the same time; during the refining process, as the carbon content in the molten steel decreases, the vacuum chamber pressure is further reduced, and the pressure in the vacuum chamber drops to below 126Pa 4-6min after the start of refining.

[0009] As a preferred embodiment of the method for RH refining, decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the volume concentration of hydrogen in the hydrogen-argon mixed gas is greater than 50%.

[0010] As a preferred embodiment of the method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, wherein: during the refining process, the oxygen in the molten steel is determined by an oxygen meter to obtain the dissolved oxygen in the molten steel or the dissolved oxygen in the molten steel is calculated by a model, and top-blowing oxygen or aluminum oxygen control process is performed according to the dissolved oxygen content in the molten steel, so that the dissolved oxygen content in the molten steel in the vacuum chamber is 80-150ppm. It is necessary to avoid the dissolved oxygen content in the molten steel in the vacuum chamber being reduced to below 50ppm to affect the decarburization and denitrification effect; at the same time, in the aluminum oxygen control process, aluminum reacts with oxygen in the molten steel to generate aluminum oxide inclusions, which promotes the nucleation and precipitation of CO bubbles and hydrogen bubbles in the molten steel and promotes denitrification.

[0011] As a preferred embodiment of the method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, wherein: if the dissolved oxygen content in the molten steel is lower than 80 ppm, oxygen is blown into the molten steel in the vacuum chamber by a top gun to provide an oxygen source for the molten steel, thereby promoting decarburization and denitrification of the molten steel;

[0012] If the dissolved oxygen in the molten steel is higher than 150ppm, add aluminum to the molten steel to control oxygen.

[0013] As a preferred embodiment of the method for RH refining, decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, when aluminum is added to the molten steel to control oxygen, a small amount of aluminum is added to the molten steel each time, and the amount of aluminum added each time is 0.00005-0.00012 times the mass of the treated molten steel.

[0014] As a preferred embodiment of the method for RH refining, decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the gas flow rate of each blowing nozzle of the riser is 200-500NL / min, which promotes the circulation of molten steel and the dissolution of hydrogen in the molten steel, and generates a large number of dispersed and fine hydrogen bubbles in the molten steel in the vacuum chamber to promote denitrification and decarburization.

[0015] As a preferred embodiment of the method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the dissolved oxygen content in the steel is reduced to below 6 ppm after final deoxidation by adding aluminum.

[0016] As a preferred embodiment of the method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel described in the present invention, the nitrogen content in the molten steel after denitrification is 25-40 ppm.

[0017] The beneficial effects of the present invention are as follows:

[0018] The present invention proposes a method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel. Before RH refining, the steel liquid controls oxygen and sulfur. After refining starts, the vacuum chamber pressure is quickly reduced. Then, hydrogen or hydrogen-argon mixed gas is blown into the riser to coordinate top blowing of oxygen or aluminum oxygen control process to achieve coordination of decarburization and denitrification. After the carbon in the steel is reduced to the ultra-low carbon steel RH refining control requirement, aluminum is added for final deoxidation, and then denitrification is continued. After denitrification is completed, the riser blowing is adjusted to argon blowing to further dehydrogenate and remove inclusions. The present invention can solve the problem of RH deep denitrification difficulty in the prior art, and the nitrogen in the steel can be reduced to 25-40ppm after RH refining. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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.

[0020] Figure 1 It is a schematic diagram of the method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel of the present invention.

[0021] Among them: 1-top gun, 2-vacuum chamber, 3-riser tube, 4-ladle.

[0022] 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

[0023] 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.

[0024] like Figure 1As shown, the present invention proposes a method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel. Before RH refining, oxygen and sulfur are controlled in the molten steel. After the refining starts, the pressure of the vacuum chamber 2 is quickly reduced, and then hydrogen or a hydrogen-argon mixed gas is blown into the riser 3 to coordinate with top blowing of oxygen or aluminum oxygen control process to achieve coordinated decarburization and denitrification. After the carbon in the steel is reduced to the control requirement of RH refining of ultra-low carbon steel, aluminum is added for final deoxidation, and then denitrification is continued. After denitrification is completed, the rising pipe blowing is adjusted to argon blowing to further dehydrogenate and remove inclusions.

[0025] After the ladle trolley of the present invention is driven to the molten steel receiving position, the ladle 4 is lifted so that the riser 4 and the downcomer are simultaneously inserted into the molten steel of the ladle 4 of the RH refining device, and hydrogen or a hydrogen-argon mixed gas is blown in through the riser 3 to coordinate with the top blowing of oxygen or the aluminum oxygen control process, which not only ensures the rapid circulation of the molten steel in the RH refining process, but also effectively controls the dissolved oxygen content in the molten steel, thereby achieving the coordination of decarburization and efficient denitrification; fully utilizes the CO bubbles generated by the decarburization of the molten steel in the vacuum chamber and the H2 bubbles precipitated by the dissolved hydrogen for denitrification, promotes the mass transfer of nitrogen in the molten steel to the gas-liquid interface, and promotes the denitrification reaction at the gas-liquid interface.

[0026] Preferably, before RH refining, the dissolved oxygen content in the molten steel is controlled to be 50-150 ppm, and the sulfur content in the molten steel is controlled to be 10-100 ppm.

[0027] Preferably, the pressure of the vacuum chamber 2 is reduced to below 10000 Pa within 0.5 min after the start of refining, hydrogen or a hydrogen-argon mixed gas is blown in through the riser, and the pressure of the vacuum chamber is continued to be rapidly reduced.

[0028] Preferably, the pressure of the vacuum chamber 2 is reduced to below 3000Pa 2-3min after the molten steel enters the vacuum chamber, so as to promote the carbon-oxygen reaction in the molten steel and promote denitrification of the molten steel; during the refining process, as the carbon content in the molten steel decreases, the pressure of the vacuum chamber 2 is further reduced, and the pressure in the vacuum chamber 2 drops to below 126Pa 4-6min after the start of refining.

[0029] Preferably, during the refining process, the oxygen content of the molten steel is determined by an oxygen meter to obtain the dissolved oxygen in the molten steel or the dissolved oxygen in the molten steel is calculated by a model, and top blowing oxygen or aluminum oxygen control process is performed according to the dissolved oxygen content of the molten steel, so that the dissolved oxygen content in the molten steel in the vacuum chamber 2 is 80-150ppm. It is necessary to avoid the dissolved oxygen content in the molten steel in the vacuum chamber 2 being reduced to below 50ppm to affect the decarburization and denitrification effect; at the same time, in the aluminum oxygen control process, aluminum reacts with oxygen in the molten steel to generate aluminum oxide inclusions, which promotes the nucleation and precipitation of CO bubbles and H2 bubbles in the molten steel and promotes denitrification.

[0030] Preferably, the volume concentration of hydrogen in the hydrogen-argon mixed gas is greater than 50%.

[0031] Preferably, if the dissolved oxygen content in the molten steel is lower than 80 ppm, oxygen is blown into the molten steel in the vacuum chamber by a top gun 1 to provide an oxygen source to the molten steel, thereby promoting decarburization of the molten steel and also denitrification of the molten steel;

[0032] If the dissolved oxygen in the molten steel is higher than 150ppm, add aluminum to the molten steel to control oxygen.

[0033] Preferably, when aluminum is added to the molten steel to control oxygen, a small amount of aluminum is added to the molten steel each time, and the amount of aluminum added each time is 0.00005-0.00012 times the mass of the treated molten steel.

[0034] Preferably, the gas flow rate of each blowing nozzle of the riser 3 is 200-500 NL / min, which promotes the circulation of the molten steel and the dissolution of hydrogen in the molten steel, and generates a large number of dispersed fine hydrogen bubbles in the molten steel in the vacuum chamber 2 to promote denitrification and decarburization. The number of blowing nozzles can be set as needed, for example, 10 to 20.

[0035] Preferably, the dissolved oxygen content in the steel is reduced to below 6 ppm after final deoxidation by adding aluminum.

[0036] Preferably, the nitrogen content in the molten steel after denitrification is 25-40 ppm.

[0037] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0038] Example 1

[0039] In a domestic steel plant's 210tRH refining unit, the dissolved oxygen content of the RH inlet ultra-low carbon steel liquid is 140ppm, the sulfur content is 60ppm, and the nitrogen content is 61ppm. The refining target nitrogen content is 30ppm and the carbon content is 30ppm. After the ladle trolley is driven to the steel liquid receiving position, the RH refining device ladle is lifted, and the RH riser and RH down pipe are simultaneously inserted into the steel liquid of the RH refining device ladle, and the insertion depth of the RH immersion pipe is 500mm; start the vacuum system, evacuate, and raise the liquid level of the steel liquid; 0.5min later, the pressure in the vacuum chamber is 9800Pa, and the hydrogen and argon mixed gas is immediately blown into the steel liquid through the RH riser blowing nozzle. There are 16 blowing nozzles in the RH riser, and the total flow rate of the mixed gas is 3800NL / min, and the volume concentration of hydrogen in the mixed gas is 80%; after refining for 2min, the vacuum chamber pressure drops to 2500Pa; after refining for 2.5min, the dissolved oxygen content in the steel liquid is reduced to 65ppm, and the top gun of the RH refining vacuum chamber is used to start top blowing of oxygen, and the oxygen blowing is 80m 3 , the dissolved oxygen content in the steel was 148ppm, oxygen blowing was stopped, and vacuum treatment was continued, with the vacuum chamber pressure of 500Pa; after refining for 5min, the dissolved oxygen content in the steel decreased to 55ppm, and top oxygen blowing was started using the top gun of the RH refining vacuum chamber, and the oxygen blowing was 80m3 , the dissolved oxygen content in the steel was 142ppm, oxygen blowing was stopped, and vacuum treatment was continued, with the vacuum chamber pressure of 100Pa; after 9min of refining, the dissolved oxygen content in the steel decreased to 60ppm, and top oxygen blowing was started using the top gun of the RH refining vacuum chamber, with oxygen blowing of 120m 3 , the dissolved oxygen content in the steel was 180ppm, aluminum was added to control oxygen, 12kg of aluminum particles were added from the RH silo, the dissolved oxygen content in the steel was adjusted to 130ppm, and vacuum treatment was continued, and the pressure in the vacuum chamber was 50Pa; after 11 minutes of refining, the carbon content in the steel dropped to 25ppm, aluminum was added for final deoxidation, the dissolved oxygen content in the steel dropped to 3ppm, and vacuum denitrification was continued; after 15 minutes of vacuum treatment, the nitrogen in the steel reached 28ppm; the RH riser was changed to argon blowing, and vacuum dehydrogenation and removal of inclusions were continued.

[0040] Example 2

[0041] In a domestic steel plant's 210tRH refining unit, the dissolved oxygen content of the RH inlet ultra-low carbon steel liquid is 150ppm, the sulfur content is 70ppm, and the nitrogen content is 70ppm. The refining target nitrogen content is 35ppm and the carbon content is 30ppm. After the ladle trolley is driven to the molten steel receiving position, the RH refining device ladle is lifted, and the RH riser and RH down pipe are simultaneously inserted into the molten steel of the RH refining device ladle, and the insertion depth of the RH immersion tube is 500mm; the vacuum system is started, vacuum is drawn, and the liquid level of the molten steel is raised; 0.4 minutes later, the pressure in the vacuum chamber is 9200Pa, and a mixed gas of hydrogen and argon is immediately blown into the molten steel through the blowing nozzle of the RH riser. There are 16 blowing nozzles in the RH riser, and the total flow rate of the mixed gas is 4000NL / min, and the volume concentration of hydrogen in the mixed gas is 90%; after refining for 2 minutes, the pressure in the vacuum chamber drops to 1800Pa, and the vacuum is continued to be drawn quickly to reduce the vacuum pressure in the vacuum chamber; at the same time, the dissolved oxygen content in the molten steel is reduced to 55ppm, and the top gun of the RH refining vacuum chamber is used to start top blowing of oxygen, and the oxygen blowing is 100m 3 , the dissolved oxygen content in the steel was 145ppm, oxygen blowing was stopped, and vacuum treatment was continued, with the vacuum chamber pressure of 300Pa; after refining for 5min, the dissolved oxygen content in the steel decreased to 52ppm, and top oxygen blowing was started using the top gun of the RH refining vacuum chamber, with oxygen blowing of 85m 3 , the dissolved oxygen content in the steel was 140ppm, oxygen blowing was stopped, and vacuum treatment was continued, with the vacuum chamber pressure of 80Pa; after 9min of refining, the dissolved oxygen content in the steel decreased to 53ppm, and top oxygen blowing was started using the top gun of the RH refining vacuum chamber, and the oxygen blowing was 80m 3, the dissolved oxygen content in the steel was 142ppm, oxygen blowing was stopped, and vacuum treatment was continued with a vacuum chamber pressure of 40Pa; after 12 minutes of refining, the carbon content in the steel dropped to 25ppm, aluminum was added for final deoxidation, the dissolved oxygen content in the steel dropped to 3ppm, and vacuum denitrification was continued; after 14 minutes of vacuum treatment, the nitrogen in the steel reached 31ppm; the RH riser was changed to argon blowing, and vacuum dehydrogenation and removal of inclusions were continued.

[0042] The present invention controls oxygen and sulfur in molten steel before RH refining, quickly reduces the pressure of the vacuum chamber after refining begins, and then blows hydrogen or hydrogen-argon mixed gas through a riser to coordinate top-blown oxygen or aluminum oxygen control process to achieve coordination of decarburization and denitrification. After the carbon in the steel is reduced to the control requirement of ultra-low carbon steel RH refining, aluminum is added for final deoxidation, and then denitrification is continued. After denitrification is completed, the rising pipe blowing is adjusted to argon blowing, and further dehydrogenation and inclusion removal are performed. The present invention can solve the problem of RH deep denitrification difficulty in the prior art, and the nitrogen in the steel can be reduced to 25-40ppm after RH refining.

[0043] 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, decarburization and coordinated denitrification of ultra-low carbon steel, characterized in that: Before RH refining, oxygen and sulfur are controlled in the molten steel. After refining begins, the pressure in the vacuum chamber is quickly reduced. Then, hydrogen or a hydrogen-argon mixed gas is blown into the riser to coordinate with top blowing of oxygen or aluminum oxygen control process to achieve synergy of decarburization and denitrification. After the carbon in the steel is reduced to the RH refining control requirement of ultra-low carbon steel, aluminum is added for final deoxidation, and then denitrification is continued. After denitrification is completed, the riser blowing is adjusted to argon blowing to further dehydrogenate and remove inclusions.

2. The method for RH refining decarburization and coordinated 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 50-150ppm, and the sulfur content in the molten steel is controlled to be 10-100ppm.

3. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 1, characterized in that: Within 0.5 minutes after the start of refining, the pressure in the vacuum chamber is reduced to below 10,000 Pa, hydrogen or a hydrogen-argon mixed gas is blown in through the riser, and the pressure in the vacuum chamber continues to be rapidly reduced.

4. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 3, characterized in that: The pressure in the vacuum chamber is reduced to below 3000Pa 2-3 minutes after the molten steel enters the vacuum chamber, and the pressure in the vacuum chamber is reduced to below 126Pa 4-6 minutes after the start of refining.

5. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 1, characterized in that: The volume concentration of hydrogen in the hydrogen-argon mixed gas is greater than 50%.

6. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 1, characterized in that: During the refining process, top blowing oxygen or aluminum oxygen control process is carried out according to the dissolved oxygen content of the molten steel, so that the dissolved oxygen content in the molten steel in the vacuum chamber is 80-150ppm.

7. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 1, characterized in that: If the dissolved oxygen content in the molten steel is lower than 80ppm, oxygen is blown into the molten steel in the vacuum chamber using a top gun; if the dissolved oxygen content in the molten steel is higher than 150ppm, aluminum is added to the molten steel to control oxygen.

8. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 7, characterized in that: When adding aluminum to the molten steel to control oxygen, a small amount of aluminum is added to the molten steel each time, and the amount of aluminum added each time is 0.00005-0.00012 times the mass of the molten steel to be treated.

9. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 1, characterized in that: The gas flow rate of each blowing nozzle of the riser is 200-500NL / min.

10. The method for RH refining decarburization and coordinated denitrification of ultra-low carbon steel according to claim 1, characterized in that: After final deoxidation by adding aluminum, the dissolved oxygen content in the steel is reduced to below 6ppm; after denitrification is completed, the nitrogen content in the molten steel is 25-40ppm.

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