Production method of RH single clean steel

Abstract

The invention belongs to the technical field of steelmaking, and relates to a method for producing RH single clean steel. The method comprises the following steps: (1) transforming an RH circulation gas lifting device; (2) producing a steel grade smelted in an RH single process; (3) smelting in a converter; and (4) RH lifting gas control. In the decarburization period of the RH smelting stage, the total standard flow of oxygen is controlled within the range of 1500-2500 NL / min, after the decarburization period is finished, oxygen is switched into argon, and argon is introduced in the subsequent whole process till RH smelting is completed. The method provided by the invention can effectively prevent the molten steel from being peroxided, reduce the temperature drop in the RH smelting process, reduce the generation of inclusions in the smelting process and improve the cleanliness of the molten steel.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology and is a method for producing RH single-stage clean steel, which can effectively prevent steel over-oxidation, reduce temperature drop during RH smelting, reduce the formation of inclusions in the smelting process, and improve the cleanliness of molten steel. Background Technology

[0002] With the development of RH multi-functional smelting technology, RH steelmaking technology has gradually begun to dominate the field of high-quality, low-cost secondary refining.

[0003] Low-carbon cold-rolled base plate steels such as IF steel, electrical steel, ultra-thin strip ultra-low carbon steel, and DC01 are smelted by RH single-stage smelting. Except for a very few special steels that are silicon deoxidized, they are generally aluminum killed steels. Al2O3 inclusions are generated during the smelting process. The above steels have certain requirements for the cleanliness of molten steel.

[0004] Automotive steels such as IF steel have high requirements for product surface quality and strict requirements for large-size inclusions. Inclusions in electrical steel can inhibit grain growth, cause lattice distortion, and hinder the movement of magnetic domains and domain walls, affecting the texture composition and deteriorating the magnetic properties of electrical steel.

[0005] Improving the cleanliness of molten steel in the single-process RH smelting and ensuring smooth steel casting have become one of the main challenges in RH smelting.

[0006] Patent document 201610134591.0 discloses a low-cost, high-efficiency RH production process, which modifies the RH booster gas to a switchable driving gas of oxygen and argon. Due to cost considerations, this patent does not address improving the cleanliness of the molten steel. Its implementation examples do not clearly specify the coordination between processes, nor does it clarify how the converter process creates optimal smelting conditions for the RH process. The proposed solution does not specify how to switch between oxygen and argon or provide detailed usage methods. Summary of the Invention

[0007] Based on the above background technology, the purpose of this invention is to provide a method for producing clean steel using a single-stage RH process. Through simple equipment modification and optimization of the production process, the method aims to prevent steel over-oxidation, reduce the temperature drop during the RH process, and improve the cleanliness of the steel. The processing method includes: (1) Modification of the RH lifting gas device. Modify the RH circulating lifting gas device, changing the original lifting gas system that switches between nitrogen and argon to a lifting gas system that can switch between nitrogen, argon, and oxygen; (2) High-carbon steel tapping in the converter, controlling the carbon content of the steel at the end point at 0.35-0.50% and the oxygen content at the end point at 400-700ppm to prevent steel over-oxidation; (3) During the decarburization period of RH smelting, a mixture of oxygen and argon is introduced through the lifting gas device. On the one hand, it serves as the lifting gas, and on the other hand, the introduction of oxygen can force decarburization of the steel. On the other hand, the secondary combustion of oxygen and carbon monoxide releases a large amount of heat, which can effectively reduce the temperature drop during the RH process. This significantly improves the cleanliness of the steel.

[0008] More specifically, the present invention adopts the following technical solution.

[0009] According to one aspect of the present invention, a method for producing RH single-unit clean steel is provided, characterized in that the method comprises the following steps:

[0010] (1) Modify the RH circulating lifting gas device: Modify the original lifting gas system that switches between nitrogen and argon into a lifting gas system that can switch between nitrogen, argon and oxygen.

[0011] (2) Steel grades produced by RH single-process smelting: The steel grades produced by RH single-process smelting include: ultra-low carbon steel grades, whose finished carbon content is less than 0.005% and steel grades that have undergone RH process decarburization and carbon replenishment, whose finished carbon content is higher than 0.01% and lower than 0.03%;

[0012] (3) Converter smelting: high carbon steel is tapped from the converter. The carbon content at the end of the converter blowing process is controlled at 0.35-0.50%, and the oxygen content at the end is controlled at 400-700ppm.

[0013] (4) RH boost gas control:

[0014] In the non-RH smelting stage, nitrogen gas is used for ventilation, and

[0015] During the decarburization period of the RH smelting stage, oxygen is used as the booster gas in the circulating pipeline. For a 180tRH unit, the standard total oxygen flow rate is controlled within the range of 1500-2500 NL / min. The standard total oxygen flow rate is adjusted according to the carbon and oxygen content of the molten steel entering the RH plant. After the decarburization period, the oxygen is switched to argon, and argon is subsequently introduced throughout the entire process until the RH smelting is completed.

[0016] After the RH smelting is completed, the booster gas will be changed to nitrogen.

[0017] The method for producing high-strength thin strip steel with surface indentation according to the present invention, wherein, preferably, in step (2), the ultra-low carbon steel includes IF steel and electrical steel.

[0018] The method for improving the twin-roll casting process of the present invention for producing surface indentation of high-strength thin strip steel is preferably, in step (2), the steel grade that is decarburized and then recarburized in the RH process includes DC01.

[0019] According to the method of improving the twin-roll casting process for producing high-strength thin strip steel surface indentation according to the present invention, preferably, in step (4), when the [O]-[C] in the molten steel entering the station is ≥350ppm, argon is used as the lifting gas throughout the RH smelting process.

[0020] According to the method of improving the twin-roll casting process for producing high-strength thin strip steel surface indentation of the present invention, preferably, in step (4), when the molten steel entering the station has 200 < [O] - [C] < 350 ppm, oxygen is used as the lifting gas during the decarburization period of RH smelting, wherein in the first stage of the decarburization period, the total oxygen flow rate is 1500-2000 NL / min, and in the second stage of the decarburization period, the total oxygen flow rate is 2000-2500 NL / min, wherein the standard total oxygen flow rate is determined based on the difference between the [O] content and the [C] content entering the station.

[0021] According to the present invention, the method for improving the twin-roll casting process for producing high-strength thin strip steel surface indentation is preferably, in step (4), when the [O]-[C] in the molten steel entering the station is ≤200ppm, oxygen is used as the lifting gas during the decarburization period of RH smelting, wherein the total oxygen flow rate is 2000NL / min in the first stage of the decarburization period and 2500NL / min in the second stage of the decarburization period.

[0022] By modifying the RH (Reverse Hydrocarbon) gas lifting device as described above, its function is expanded from simply lifting gas for molten steel to a multi-functional device encompassing gas delivery, forced oxygen decarburization, and secondary CO combustion. Combined with high-carbon tapping in the converter, forced oxygen decarburization is achieved through the circulating pipeline during the decarburization stage of RH smelting, thereby producing clean steel. This method involves simple equipment modification, is economical and efficient, and avoids over-oxidation during converter tapping. It also reduces temperature drop during the RH process, minimizing inclusions generated by the aluminum-oxygen reaction during RH smelting, thus significantly improving the cleanliness of the molten steel.

[0023] Beneficial technical effects

[0024] To address the problems of poor RH single-stage steel cleanliness leading to nozzle blockage and inclusion defects in the product, a method for producing clean RH single-stage steel is proposed. This method expands the function of the RH circulating gas lifting device from a single function of lifting gas for molten steel to a multi-functional device encompassing gas delivery, forced oxygen decarburization, and secondary CO combustion. Forced oxygen decarburization is performed through the circulating pipeline during the decarburization stage of RH smelting. This method involves simple equipment modification and is economical and efficient. Using this invention, over-oxidation at converter tapping can be avoided, and the temperature drop during the RH process can be reduced, minimizing the formation of inclusions due to the temperature rise caused by the aluminum-oxygen reaction during RH smelting, thereby significantly improving the cleanliness of the molten steel. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0026] Figure 1 This is a modified diagram of the circulating gas lifting system device of the present invention (taking 12 circulating small tubes as an example).

[0027] Figure 2 This is a process flow diagram of a single-unit clean steel production method according to the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0030] The purpose of this invention is to provide a method for producing clean steel using a single-stage RH process. Through simple equipment modifications and optimized production processes, it achieves the effects of preventing steel over-oxidation, reducing the temperature drop during the RH process, and improving the cleanliness of the molten steel. The method includes: 1. Modification of the RH lifting gas device. The original nitrogen-argon switching lifting gas system is modified to a system that can switch between nitrogen, argon, and oxygen; 2. High-carbon tapping in the converter, controlling the final carbon content of the molten steel at 0.35-0.50% and the final oxygen content at 400-700 ppm to prevent steel over-oxidation; 3. Forced oxygen blowing for decarburization of RH smelting steel, changing the oxygen blowing method from the top lance system to the lifting gas system. During the decarburization period of RH smelting, a mixture of oxygen and argon is introduced through the lifting gas device. This serves as both the lifting gas and the oxygen for forced decarburization of the molten steel. Furthermore, the secondary combustion of oxygen and carbon monoxide releases a large amount of heat, effectively reducing the temperature drop during the RH process. This significantly improves the cleanliness of the molten steel. During RH decarburization, the lifting gas is primarily supplied with oxygen, supplemented by argon. Oxygen control is adjusted based on the carbon and oxygen content and temperature of the molten steel entering the plant, while argon flow rate serves as a supplementary gas to ensure effective steel lifting. After the decarburization period, argon is used as the lifting gas until the end of smelting. By combining two methods—high-carbon converter tapping and RH circulating lifting gas device modification—high-carbon, low-oxygen tapping of the converter prevents over-oxidation of the molten steel. During the RH decarburization period, forced oxygen blowing is performed through the circulating pipe for decarburization, thus enabling the production of RH single-stage low-inclusion clean steel.

[0031] 1. RH Gas Boosting System Modification. The original function of the RH gas boosting system was: during the non-steel smelting stage, a low flow rate of nitrogen was introduced to prevent clogging of the circulating nozzle. During the RH smelting stage, argon was switched to the system, with different flow rates for different smelting stages. This stage was generally automatically controlled using a table-based system. In the initial smelting stage, due to the intense carbon-oxygen reaction and the tendency for molten steel to splash, the argon flow rate was slightly lower. After 5 minutes of RH treatment, the argon flow rate was gradually increased until the maximum flow rate was reached, at which point it switched back to a low flow rate of nitrogen until the RH smelting was completed. The RH gas boosting system modification involved converting the gas path from only nitrogen and argon to a system with three gas paths: nitrogen, oxygen, and argon. During the non-steel smelting stage, a low flow rate of nitrogen was introduced to prevent clogging of the circulating nozzle. During the RH smelting stage, a mixture of oxygen and argon is introduced during the decarburization period. This serves two purposes: firstly, it provides the conventional boosting of the molten steel; secondly, the introduced oxygen forces decarburization of the steel, producing carbon monoxide as the carbon-oxygen reaction product—a crucial principle in RH smelting for clean steel production. Furthermore, the secondary combustion reaction of oxygen and carbon monoxide releases a significant amount of heat, effectively reducing the temperature drop during the RH process, minimizing the temperature rise during the aluminum-oxygen reaction, and reducing the formation of Al2O3 inclusions. After the decarburization period, the mixture is switched to argon until the smelting process is complete. Afterward, a low-flow nitrogen gas is introduced to prevent clogging of the circulating nozzle.

[0032] 2. Steel grades produced. Steel grades that require decarburization treatment in RH single-layer steel production, including ultra-low carbon steels such as IF steel and electrical steel, as well as low carbon steels for cold-rolled substrates.

[0033] 3. High-carbon tapping in the converter prevents over-oxidation of molten steel. Because RH smelting requires a certain amount of residual oxygen in the molten steel for decarburization, converter tapping is done via boiling tapping, resulting in a high oxygen content in the molten steel. During converter tapping, the top slag in the ladle undergoes tempering. Due to the excessive oxygen content in the steel, the top slag is continuously oxidized during the process from converter tapping to the end of RH decarburization. After RH decarburization, the oxidizing properties of the top slag continuously re-oxygenate into the molten steel, thus deteriorating the cleanliness of the steel. By using high-carbon tapping in the converter, the final carbon content in the molten steel is controlled at 0.35-0.50%, and the final oxygen content is controlled at 400-650 ppm. This effectively prevents over-oxidation of the molten steel, thereby reducing the degree of oxidation of the top slag and minimizing the re-oxygenation from the top slag into the molten steel after the RH decarburization period, ultimately reducing the total oxygen content in the steel.

[0034] 4. Control of RH circulating gas. During non-smelting stages, a low flow rate of nitrogen is introduced to prevent the circulating pipes from being covered and clogged by dripping cold steel from the trough. During the decarburization period (RH treatment 0-18 min), oxygen is generally used as the lifting gas during high-carbon steel tapping from the converter, serving as the oxygen source for forced decarburization and secondary combustion of carbon monoxide. In the early stages of RH treatment, the carbon-oxygen reaction is intense, resulting in severe steel splashing; therefore, the decarburization period is divided into two sub-stages: 0-5 min and 5-18 min. The flow rate during decarburization is selected between 1500-2500 NL / min, determined based on the actual carbon [C] and oxygen [O] content of the incoming steel. The specific implementation plan is as follows: ① When the [O]-[C] content in the molten steel entering the plant is ≥350ppm, argon is used as the lifting gas throughout the RH smelting process; ② When the [O]-[C] content in the molten steel entering the plant is 200 < 350ppm, oxygen is used as the lifting gas during the decarburization period (0-18min) of RH smelting. Specifically, the total oxygen flow rate is 1500-2000 NL / min during the 0-5min stage and 2000-2500 NL / min during the 5-18min smelting stage. The specific total flow rate is determined based on the difference between the [O] and [C] content at the incoming plant. ③ When the [O]-[C] content in the molten steel entering the plant is ≤200ppm, oxygen is used as the lifting gas during the decarburization period (0-18min) of RH smelting. Specifically, the total oxygen flow rate is 2000 NL / min during the 0-5min stage and 2500 NL / min during the 5-18min smelting stage. A maximum of 42.5 Nm³ of oxygen can be introduced during this stage. 3This corresponds to approximately 300 ppm [O] (high oxygen recovery rate; the oxygen recovery rate of the top-lance oxygen blowing method is about 70%, while the oxygen recovery rate of this method is higher than 90%). The oxygen blowing flow rate and time can be adjusted according to the actual conditions at the station. Depending on the actual situation of the molten steel, more oxygen can also be blown in, and the excess oxygen is used for the alumino-oxygen reaction to raise the temperature of the molten steel. It should be noted that the above oxygen flow rate values ​​are based on a 180t RH equipment as an example; the boosting gas flow rate can be adjusted proportionally for RH equipment of different tonnages.

[0035] To address the problems of poor RH single-stage steel cleanliness leading to nozzle blockage and inclusion defects in the product, a method for producing clean RH single-stage steel is proposed. This method expands the function of the RH circulating gas lifting device from a single function of lifting gas for molten steel to a multi-functional device encompassing gas delivery, forced oxygen decarburization, and secondary CO combustion. Forced oxygen decarburization is performed through the circulating pipeline during the decarburization stage of RH smelting. This method involves simple equipment modification and is economical and efficient. Using this invention, over-oxidation at converter tapping can be avoided, and the temperature drop during the RH process can be reduced, minimizing the formation of inclusions due to the temperature rise caused by the aluminum-oxygen reaction during RH smelting, thereby significantly improving the cleanliness of the molten steel.

[0036] The following are embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention. All other embodiments that can be obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] The technical solution of the present invention will be further described in detail below through specific embodiments and comparative examples.

[0038] Example

[0039] A method for producing RH-treated single-unit clean steel includes the following key operational points: Modification of the RH booster gas equipment, adding an oxygen blowing branch to the existing argon and nitrogen gas source pipelines. High-carbon steel is tapped from the converter, with low oxygen and high carbon content in the molten steel to prevent over-oxidation. During tapping, the top slag is modified to reduce total iron content and prevent high oxygen levels in the slag from contaminating the molten steel later. When RH gas is introduced into the smelting plant, the flow rate and timing of oxygen and argon in the booster gas are rationally controlled based on the molten steel conditions, ultimately achieving low-cost RH-treated single-unit clean steel production. Specific implementation examples are shown in Table 1.

[0040] Table 1. Lifting gas settings and implementation effects under different entry conditions

[0041]

[0042] The above description is only a specific embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing RH single-unit clean steel, characterized in that, The method includes the following steps: (1) Modify the RH circulating lifting gas device: Modify the original lifting gas system that switches between nitrogen and argon into a lifting gas system that can switch between nitrogen, argon and oxygen. (2) Steel grades produced by RH single-process smelting: The steel grades produced by RH single-process smelting include: ultra-low carbon steel grades, whose finished carbon content is less than 0.005% and steel grades that have undergone RH process decarburization and carbon replenishment, whose finished carbon content is higher than 0.01% and lower than 0.03%; (3) Converter smelting: high carbon steel is tapped from the converter. The carbon content at the end of the converter blowing process is controlled at 0.35-0.50%, and the oxygen content at the end is controlled at 400-700ppm. (4) RH boost gas control: In the non-RH smelting stage, nitrogen gas is used for ventilation, and During the decarburization period of the RH smelting stage, oxygen is used as the booster gas in the circulating pipeline. For a 180t RH unit, the standard total oxygen flow rate is controlled within the range of 1500-2500 NL / min. This standard total oxygen flow rate is adjusted according to the carbon and oxygen content of the molten steel entering the RH plant. After the decarburization period, the oxygen is switched to argon, and argon is subsequently introduced throughout the entire process until the RH smelting is completed. After the RH smelting is completed, the booster gas will be changed to nitrogen.

2. The method for improving the surface indentation of high-strength thin strip steel produced by twin-roll casting and rolling process according to claim 1, characterized in that: In step (2), the ultra-low carbon steel grades include IF steel and electrical steel.

3. The method for improving the surface indentation of high-strength thin strip steel produced by twin-roll casting and rolling process according to claim 1, characterized in that: In step (2), the steel grade that undergoes decarburization followed by carbon replenishment in the RH process includes DC01.

4. The method for improving the surface indentation of high-strength thin strip steel produced by twin-roll casting and rolling process according to claim 1, characterized in that: In step (4), when the [O]-[C] in the molten steel entering the station is ≥350ppm, argon is used as the lifting gas throughout the RH smelting process.

5. The method for improving the surface indentation of high-strength thin strip steel produced by twin-roll casting and rolling process according to claim 1, characterized in that: In step (4), when the molten steel entering the station has 200 < [O] - [C] < 350 ppm, oxygen is used as the boosting gas during the decarburization period of RH smelting. In the first stage of the decarburization period, the total oxygen flow rate is 1500-2000 NL / min, and in the second stage of the decarburization period, the total oxygen flow rate is 2000-2500 NL / min. The standard total oxygen flow rate is determined based on the difference between the [O] content and the [C] content entering the station.

6. The method for improving the surface indentation of high-strength thin strip steel produced by twin-roll casting and rolling process according to claim 1, characterized in that: In step (4), when the [O]-[C] in the molten steel entering the station is ≤200ppm, oxygen is used as the boosting gas during the decarburization period of RH smelting. In the first stage of the decarburization period, the total oxygen flow rate is 2000NL / min, and in the second stage of the decarburization period, the total oxygen flow rate is 2500NL / min.

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