A method for removing nitrogen from steel

Abstract

The application relates to the technical field of steel smelting, in particular to a method for removing nitrogen in steel. The method comprises the following steps in sequence: in an EAF stage, low-nitrogen scrap steel and slagging materials are selected, low-power short-arc and foamed slag operation are adopted, and the tapping temperature is controlled to be 1600-1650 DEG C; in an LF stage, a ladle is covered, deoxidizers are added in batches, and argon blowing and stirring are carried out, and the refining temperature is less than or equal to 1650 DEG C; in a VOD stage, gradient vacuum and argon stirring are adopted, the vacuum degree is 5000-8000 Pa in the early stage, large-flow argon blowing is matched, the vacuum degree is less than or equal to 0.5 torr in the later stage, small-flow argon blowing is matched, argon is cut off before breaking the vacuum, and lime is covered for tapping. Through the whole-process cooperation of EAF source nitrogen control, LF nitrogen absorption inhibition and VOD deep nitrogen removal, the nitrogen removal effect is remarkably improved.

Description

Technical Field

[0001] This application relates to the field of iron and steel smelting technology, and more specifically, to a method for removing nitrogen from steel. Background Technology

[0002] Carbon steel and low alloy steel are the most widely used steel products in industrial production. During their smelting process, nitrogen is mainly introduced into the molten steel through raw materials (scrap steel, alloys, slag-forming materials, etc.), smelting process, and technological operations.

[0003] Excessive nitrogen can lead to defects in steel components such as porosity, age embrittlement, and cold brittleness, significantly reducing the mechanical and processing properties of steel and severely impacting product quality and service life. This makes it impossible to meet the purity requirements of high-end machinery manufacturing and precision instruments. Currently, commonly used smelting equipment in steelmaking includes EAF, LF, and VOD furnaces. However, in existing technologies, each furnace type often operates independently, lacking a comprehensive, coordinated design. This results in problems such as low denitrification efficiency, unstable nitrogen content control, and a tendency for secondary nitrogen absorption. Furthermore, existing denitrification processes lack sufficient control over the nitrogen content of raw materials and auxiliary materials, further affecting the stability of the denitrification effect and failing to meet the stringent nitrogen content requirements of different steel grades (especially high-end carbon steel and low-alloy steel).

[0004] Therefore, there is a need for a method to remove nitrogen from steel that can achieve efficient and stable removal of nitrogen, ensure that the final liquid steel has the required nitrogen content, improve steel quality, and meet the application requirements of different steel grades. Summary of the Invention

[0005] The nitrogen removal method in steel provided in this application is based on the characteristics of three smelting methods: EAF, LF, and VOD, and achieves efficient nitrogen removal through collaborative operation throughout the entire process.

[0006] A method for removing nitrogen from steel, the method comprising, in sequence, an EAF smelting stage, an LF smelting stage, and a VOD smelting stage: EAF smelting stage: Select scrap steel with nitrogen content ≤0.0050% and slag-forming material with nitrogen content ≤0.0400%; adopt low-power short-arc power supply and foam slag submerged arc operation; control the temperature of oxygen blowing decarburization stage at 1620~1680℃; reduce the molten steel before tapping, control the tapping temperature at 1600~1650℃, and the tapping time ≤2min; LF smelting stage: The ladle is covered and Si and Al deoxidizers are added in batches; Argon gas is continuously blown from the bottom for stirring, and the refining temperature is controlled to be ≤1650℃; VOD smelting stage: Gradient vacuum control and argon gas stirring are used in combination; the gradient vacuum control includes: controlling the vacuum degree at 5000~8000Pa in the early stage and maintaining it for 15-20min, and then increasing the vacuum degree to ≤0.5tor and maintaining it for more than 10min in the later stage; the argon gas stirring is: the flow rate is 250~400L / min in the early stage of low vacuum degree, and the flow rate is 80~150L / min in the later stage of high vacuum degree; the argon gas is turned off before the VOD breaks the vacuum, and lime is added to cover the molten steel when tapping.

[0007] Preferably, during the EAF smelting stage, after oxygen blowing and decarburization, lime is added at a ratio of 0.2~0.5 kg / t of molten steel to form a thin slag.

[0008] Preferably, during the LF smelting stage, fluorite is added during refining to reduce slag viscosity.

[0009] Preferably, during the LF smelting stage, the alloy used in the smelting needs to be baked before use, with a baking temperature of 250~350℃ and a baking time of not less than 1.5h.

[0010] Preferably, during the VOD smelting stage, the VOD furnace temperature is controlled at 1650℃~1680℃.

[0011] Preferably, during the VOD smelting stage, after the high vacuum is completed, lime and Al particles are added, and the argon flow rate is increased and stirred for 5-10 minutes.

[0012] Preferably, during the VOD smelting stage, lime is added to cover the molten steel at a ratio of 1~2 kg / t during tapping, and argon gas is not used for stirring during the transfer process.

[0013] Preferably, the VOD smelting stage adopts a double bottom-blowing argon design.

[0014] The nitrogen removal method in steel provided in this application adopts a synergistic denitrification process using EAF, LF, and VOD furnaces. EAF controls nitrogen at the source to reduce nitrogen introduction, LF inhibits nitrogen absorption to prevent nitrogen content from rising, and VOD deep denitrification ensures that nitrogen content meets the standards. This method is significantly better than the denitrification effect of existing single furnace types. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of the nitrogen removal method in steel provided in the embodiments of this application; Figure 2 This is a schematic diagram of EAF furnace smelting provided in the embodiments of this application. Detailed Implementation

[0016] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0017] This invention provides a method for removing nitrogen from steel, employing a synergistic denitrification process using EAF, LF, and VOD furnaces. EAF controls nitrogen at the source to reduce nitrogen carryover, LF inhibits nitrogen absorption to prevent nitrogen content rebound, and VOD provides deep denitrification to ensure nitrogen content meets standards. This method is significantly superior to existing single-furnace denitrification methods. The invention will be further described in detail below with reference to specific embodiments.

[0018] Please refer to Figures 1-2 , Figure 1 This is a schematic flowchart of the nitrogen removal method in steel provided in the embodiments of this application; Figure 2 This is a schematic diagram of EAF furnace smelting provided in an embodiment of this application. Figure 2 In the middle: 1-EAF furnace, 2-molten steel, 3-electrode, 4-foam slag.

[0019] The specific steps for removing nitrogen from steel are as follows: S1: EAF (Electric Arc Furnace) Smelting Stage EAF, as the initial stage of smelting, is primarily responsible for melting the furnace charge and adjusting its composition. In this application, nitrogen control at the source and preliminary denitrification are simultaneously achieved, laying the foundation for subsequent refining. The specific process is as follows: This embodiment optimizes the furnace charge structure to control nitrogen at the source: scrap steel with a nitrogen content ≤0.0050% and slag-forming materials with a nitrogen content ≤0.0400% are selected. In some implementations, high-quality Class A scrap steel with a nitrogen content ≤0.0030% is preferred, combined with pure iron with a nitrogen content of 0.0020~0.0030%. Scrap steel with a nitrogen content ≥0.0080% is prohibited from being fed into the furnace during all-scrap steel smelting. Low-nitrogen carbon powder, lime, and other slag-forming materials are selected to ensure that the nitrogen content of the auxiliary materials is ≤0.0400%, and the slag-forming materials are pre-dried to remove moisture and adsorbed nitrogen. During smelting, the furnace cover is tightly closed, and a single-feeding mode is adopted to shorten the furnace cover opening time and reduce air intrusion and nitrogen absorption caused by air ionization from the electric arc.

[0020] During the melting and heating period, the carbon content of the molten steel is controlled to promote the CO reaction (C+O→CO↑), utilizing CO bubbles to carry nitrogen atoms from the molten steel out; for example... Figure 2The schematic diagram of EAF furnace smelting shown shows that the smelting power supply process requires the use of foam slag 4 for submerged arc operation. Electrode 3 is inserted under foam slag 4, and low-power power supply is provided to isolate the electric arc from the air and optimize the temperature distribution of the molten pool. Before tapping, the molten steel is fully reduced and the tapping temperature is controlled at 1600~1650℃. The steel is tapped quickly, and the tapping time is shortened to ≤2min to avoid secondary nitrogen absorption during the tapping process.

[0021] S2: LF (Ladle Refining Furnace) Smelting Stage The LF furnace is used for fine-tuning the composition of molten steel, homogenizing the temperature, and removing inclusions. Its core function is to suppress nitrogen absorption in the molten steel and prevent the nitrogen content from rising again. The specific process is as follows: During the smelting process, Si and Al deoxidizers are added in batches to maintain a reducing atmosphere in the furnace, and prolonged refining under an oxidizing atmosphere is prohibited. Low-power, short-arc operation is used as much as possible during power supply to avoid frequent electrode lifting and reduce nitrogen absorption by the arc-ionized air. The ladle is covered, argon gas is used for smelting, a slight positive pressure is maintained inside the ladle, and the nitrogen increase is controlled to ≤6×10⁻⁶. -6 Low-nitrogen alloys are selected as raw materials for smelting, and the alloys are dried in advance and added slowly to avoid violently disturbing the molten steel.

[0022] Bottom-blown argon gas stirring is used with moderate stirring intensity and a stirring time of 15-25 minutes. The nitrogen atoms are carried out by the flotation effect of argon gas bubbles. The slag basicity R is adjusted to 3.0-4.0, and an appropriate amount of fluorite is added to reduce the slag viscosity and promote the transfer of nitrogen from the molten steel to the slag. The refining temperature is controlled at 1580-1620℃ to avoid the increase in nitrogen solubility due to high temperature. The temperature is not raised for a long time in the later stage of refining.

[0023] S3: VOD (Vacuum Oven) Smelting Stage The VOD furnace utilizes a vacuum environment combined with oxygen blowing for decarburization to achieve deep denitrification, which is a key step in nitrogen removal. The specific process is as follows: Vacuum control employs gradient vacuum operation, maintaining the vacuum level at 50~100Pa in the early stage of decarburization and increasing it to ≤0.5torr (approximately 68Pa) in the later stage of decarburization to ensure good sealing of the vacuum tank and maintain stable vacuum level.

[0024] Oxygen blowing and stirring were optimized by adjusting the oxygen flow rate according to the carbon content of the molten steel to promote the carbon-oxygen reaction, utilizing CO bubbles to adsorb nitrogen atoms and release them, and rationally adjusting the position of the oxygen blowing gun; a double bottom-blowing argon design was adopted, increasing the argon stirring flow rate to 500~800L / min, matching the stirring intensity with the vacuum degree and oxygen blowing flow rate; and the boiling denitrification time was controlled to 10~15min.

[0025] Temperature and composition control: The VOD furnace inlet temperature is controlled at 1620℃~1680℃, and the temperature is kept stable during the refining process; the initial carbon content of the molten steel is controlled to ensure sufficient carbon-oxygen reaction, while the content of surface-active elements such as oxygen and sulfur is controlled. During the high vacuum stage, the argon flow rate is appropriately increased to improve the degassing capacity. After the high vacuum ends, lime, Al particles, etc. are added, the argon flow rate is increased, and stirring is carried out for 5~10 minutes to increase the reducing properties of the molten steel. The argon gas in the ladle is turned off before the lid is opened after VOD to prevent the molten steel from absorbing nitrogen. During tapping, a large amount of lime needs to be added to cover the molten steel, and the argon gas should not be turned on to stir to prevent nitrogen addition during the transfer process.

[0026] This application adopts a full-process synergistic denitrification process using EAF, LF, and VOD furnaces. EAF controls nitrogen at the source to reduce nitrogen introduction, LF inhibits nitrogen absorption to prevent nitrogen content from rising, and VOD deep denitrification ensures that nitrogen content meets the standards, which is significantly better than the denitrification effect of existing single furnace types.

[0027] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0028] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for removing nitrogen from steel, characterized in that, The method includes, in sequence, the EAF smelting stage, the LF smelting stage, and the VOD smelting stage: EAF smelting stage: Select scrap steel with nitrogen content ≤0.0050% and slag-forming material with nitrogen content ≤0.0400%; adopt low-power short-arc power supply and foam slag submerged arc operation; control the temperature of oxygen blowing decarburization stage at 1620~1680℃; reduce the molten steel before tapping, control the tapping temperature at 1600~1650℃, and the tapping time ≤2min; LF smelting stage: The ladle is covered and Si and Al deoxidizers are added in batches; Argon gas is continuously blown from the bottom for stirring, and the refining temperature is controlled to be ≤1650℃; VOD smelting stage: Gradient vacuum control and argon gas stirring are used in combination. The gradient vacuum control includes: initially controlling the vacuum level at 5000~8000Pa and maintaining it for 15~20min, and later increasing the vacuum level to ≤0.5tor and maintaining it for more than 10min; the argon gas stirring is: the flow rate is 250~400L / min in the initial low vacuum stage and 80~150L / min in the later high vacuum stage; the argon gas is turned off before VOD is broken, and lime is added to cover the molten steel when tapping.

2. The method for removing nitrogen from steel according to claim 1, characterized in that, During the EAF smelting stage, after oxygen blowing and decarburization, lime is added at a ratio of 0.2~0.5 kg / t of molten steel to form a thin slag.

3. The method for removing nitrogen from steel according to claim 1, characterized in that, During the LF smelting stage, fluorite is added during refining to reduce slag viscosity.

4. The method for removing nitrogen from steel according to claim 1, characterized in that, During the LF smelting stage, the alloy used in the smelting needs to be baked before use. The baking temperature is 250~350℃ and the baking time is not less than 1.5h.

5. The method for removing nitrogen from steel according to claim 1, characterized in that, During the VOD smelting stage, the VOD furnace temperature is controlled at 1650℃~1680℃.

6. The method for removing nitrogen from steel according to claim 1, characterized in that, During the VOD smelting stage, after the high vacuum is completed, lime and Al particles are added, and the argon flow rate is increased and stirred for 5-10 minutes.

7. The method for removing nitrogen from steel according to claim 1, characterized in that, During the VOD smelting stage, lime is added to cover the molten steel at a ratio of 1~2 kg / t during tapping, and argon gas is not used for stirring during the transfer process.

8. The method for removing nitrogen from steel according to claim 1, characterized in that, The VOD smelting stage employs a double bottom-blowing argon design.

Images