A method for preparing high-nitrogen steel with high efficiency and high cleanliness by pressurizing bottom blowing of ammonia gas and pressurizing nitrogen gas on the surface of molten steel

Abstract

The present application relates to the technical field of high-nitrogen stainless steel smelting, in particular to a high-efficiency high-nitrogen high-purity high-nitrogen steel preparation method by pressurizing bottom blowing of ammonia gas and pressurizing nitrogen gas on the surface of molten steel, comprising the following steps: vacuumizing the alloy material, filling argon, vacuumizing again after the raw material is completely melted, filling nitrogen gas into the furnace cavity of the pressurized induction furnace to the target nitrogen pressure, entering the molten steel surface gas phase nitrogen enrichment stage, controlling the bottom blowing ammonia gas pressure by adjusting the output pressure of the ammonia gas cylinder, entering the pressurized bottom blowing ammonia gas and molten steel surface pressurized nitrogen gas collaborative nitrogen enrichment stage, switching the bottom blowing ammonia gas to bottom blowing nitrogen gas, entering the molten steel surface pressurized and bottom blowing nitrogen gas collaborative nitrogen enrichment stage, and completing the preparation of high-efficiency precise nitrogen enrichment and high-purity high-nitrogen steel. The present application solves the problem of high cost caused by adding nitriding alloy in the traditional preparation process, avoids the problem of inclusions caused by adding deoxidizing and desulfurizing agents, reduces the content of oxygen and sulfur in the steel, and meets the demand of high-end equipment manufacturing for high-purity high-nitrogen steel products.

Description

A method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom blowing ammonia gas and pressurized nitrogen gas on the surface of molten steel. Technical Field

[0001] This invention relates to the field of high-nitrogen stainless steel smelting technology, specifically to a method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel. Background Technology

[0002] Nitrogen, as a strong austenitic stabilizer, can stabilize the austenitic phase up to 18 times that of nickel, and can simultaneously improve the strength and corrosion resistance of materials. Therefore, the development of high-nitrogen austenitic stainless steel has become a cutting-edge research direction in the field of stainless steel. However, in industrial applications, the nitrogen alloying process has long been limited by thermodynamic conditions: under normal pressure, the solubility of nitrogen in austenitic stainless steel is extremely low, less than 0.4 wt.%, and problems such as nitrogen escape, nitrogen porosity, and severe segregation are prone to occur, which seriously restricts the quality and performance of high-nitrogen stainless steel.

[0003] In 1956, Zackey et al. achieved a breakthrough in nitrogen content to 0.75% in Fe-Cr-Mn stainless steel by combining centrifugal casting with high-pressure solidification, thus verifying for the first time the effect of high-nitrogen pressure environment on nitrogen solubility. In recent years, high-pressure metallurgical preparation technology has made significant progress. Industrial-scale pressurized electroslag remelting equipment has reached a scale of 20 tons, with the highest working pressure increased to 6 MPa. Under this high-nitrogen pressure condition, the nitrogen solubility limit in austenitic stainless steel is significantly improved, with the highest measured nitrogen content reaching 2.11 wt%, laying the foundation for the industrial application of high-nitrogen stainless steel.

[0004] Nitrogen solubility in steel under normal pressure is low, far below the design requirements for high-performance high-nitrogen steel. Therefore, breakthroughs in pressurized nitrogen smelting technology are crucial. However, to achieve high levels of nitrogen alloying, the smelting process must be carried out under extremely high nitrogen pressure, which places extremely stringent requirements on high-pressure smelting equipment and its control system, resulting in high equipment investment costs. Furthermore, in the process of high-pressure nitrogen vapor-phase nitriding of high-nitrogen steel, deoxidizing and desulfurizing agents need to be added during smelting to improve the cleanliness of the molten steel. These deoxidizing and desulfurizing elements themselves may form endogenous inclusions. For example, while Al effectively reduces the oxygen content of the molten steel, it also generates aluminum nitride and alumina inclusions. These inclusions remain in the steel ingot, posing a significant threat to the purity, mechanical properties, and corrosion resistance of the material.

[0005] In the field of gas-phase nitrogen enrichment technology for molten steel, scholars have proposed and verified a new method using ammonia instead of nitrogen as the nitriding medium. Experimental studies have shown that, under normal pressure, blowing NH3 into molten steel through an immersion blowpipe can significantly improve nitrogen enrichment efficiency by utilizing its coupling reaction with surface-active elements such as [O] and [S] in the molten steel. Laboratory simulations have confirmed that, at the same blowing flow rate, blowing NH3 increases the nitrogen absorption rate by 18-75% compared to blowing N2, and the final nitrogen content is closer to the theoretical saturation value. The nitrogen enrichment effect of ammonia is far superior to that of nitrogen. However, while increasing nitrogen with ammonia, it also increases the hydrogen content in the molten steel, which can lead to hydrogen embrittlement. In addition, thermodynamic calculations show that ammonia has extremely strong deoxidation and desulfurization capabilities under high pressure, which can solve the problem of the deoxidation and desulfurization elements themselves potentially forming endogenous inclusions at the source. However, the issues of efficient deoxidation and desulfurization with ammonia under high pressure and the control of hydrogen content are still in the unexplored stage.

[0006] Currently, there are few reports on ammonia nitrogen enrichment and precise control of nitrogen content. Moreover, the high-nitrogen steel preparation method based on pressurized gas-phase nitriding and bottom-blowing nitrogen efficient and precise nitrogen enrichment disclosed in Chinese patent CN119710136A cannot directly derive a precise control method for ammonia nitrogen enrichment and nitrogen content through simple substitution. There are still many technical problems that need to be solved.

[0007] In summary, the problems of ammonia nitrogen enrichment and precise control of nitrogen content, as well as the problems of efficient ammonia deoxidation and desulfurization under high pressure and hydrogen content control, have limited the development of ammonia as a substitute for nitrogen as a nitriding medium in the field of gas-phase nitrogen enrichment of molten steel. Therefore, solving the above problems is of great significance for realizing the industrial preparation of high-quality high-nitrogen steel. Summary of the Invention

[0008] Objective: This invention proposes a highly efficient and clean method for preparing high-nitrogen steel using pressurized bottom-blown ammonia and pressurized nitrogen on the surface of molten steel. The aim is to address the problems of low nitrogen enrichment efficiency, poor cleanliness, and high cost in existing high-nitrogen steel smelting processes. Specifically, by employing a pressurized induction furnace and introducing ammonia as a highly efficient nitrogen enrichment medium, the nitrogen enrichment efficiency is significantly improved, while simultaneously achieving cleanliness control for deoxidation and desulfurization of the molten steel. Furthermore, a kinetic prediction model for nitrogen enrichment is established to precisely control the nitrogen content of the molten steel, simplifying the smelting process and reducing smelting costs.

[0009] Technical solution:

[0010] The first aspect of this invention proposes a method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blowing ammonia gas and pressurized nitrogen gas on the surface of molten steel, characterized by comprising the following steps:

[0011] Step 1: Evacuate the alloy material to 0-2 Pa, maintain the vacuum until the raw material begins to melt, then fill with argon gas to make the pressure inside the furnace reach 20-60 kPa. After the raw material is completely melted, evacuate the vacuum again to 0-2 Pa.

[0012] Step 2: After vacuuming, stabilize the smelting temperature at 1550–1650℃, and fill the pressure induction furnace chamber with nitrogen to the target nitrogen pressure. Then, the process enters the gas phase nitrogen enrichment stage on the surface of the molten steel. Based on the nitrogen content of the molten steel at time t during surface nitrogen enrichment, the nitrogen enrichment level in this stage is determined to be 5% to 10% of the target nitrogen content.

[0013] Step 3: Adjust the output pressure of the ammonia cylinder Controlling the pressure of bottom-blown ammonia, a stage of synergistic nitrogen enhancement using pressurized bottom-blown ammonia and pressurized nitrogen on the surface of molten steel is implemented. Based on the nitrogen content of the molten steel at time t of the bottom-blown ammonia, the nitrogen content is determined to be increased to 75% to 85% of the target nitrogen content during this stage.

[0014] Step 4: Switch from bottom-blown ammonia to bottom-blown nitrogen, entering the stage of synergistic nitrogen enhancement through surface pressurization and bottom-blown nitrogen. This agitates the bubbles and removes reaction byproducts (H2, H2O, H2S, etc.). Based on the nitrogen content of the molten steel at time t during bottom-blown nitrogen, determine and enhance the nitrogen to 98%–102% of the target nitrogen content. Finally, determine the minimum bottom-blowing time based on the hydrogen content in the molten steel. This enables the preparation of highly efficient and precise nitrogen-enriched, high-purity, high-nitrogen steel.

[0015] In steps 2 to 4, the nitrogen content in the molten steel is controlled by a nitrogen solubility calculation formula based on kinetic prediction.

[0016] Furthermore, regarding the gas-phase nitriding process in step 2, to accurately calculate the process time required to increase the nitrogen content of the molten steel to 5% to 10% of the target nitrogen content, this study constructs a kinetic model of the change in the nitrogen content of the molten steel over time during this stage. The formula for calculating the nitrogen content of the molten steel at time t during surface nitriding is as follows:

[0017] ;

[0018] in, Let be the nitrogen content of the molten steel at time t; For the reaction in molten steel Balanced nitrogen content; Let be the nitrogen content of the molten steel at time t-1; is the mass transfer coefficient of nitrogen atoms in the liquid boundary layer at the surface of molten steel; ρ is the surface area of ​​the molten steel; W is the weight of the molten steel; ρ is the density of the molten steel.

[0019] Preferably, in step 2, the duration of the gas phase nitrogen enrichment stage on the surface of the molten steel is 2 to 5 minutes.

[0020] Furthermore, in step 3, the nitrogen content in the molten steel at time t during the synergistic nitrogen enhancement stage of pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of the molten steel is calculated based on the nitrogen content of the molten steel at time t of the bottom-blown ammonia gas. The formula for calculating the nitrogen content of the molten steel at time t of the bottom-blown ammonia gas is as follows:

[0021] ;

[0022] in, Let t be the nitrogen content in the molten steel. For the reaction in molten steel Balanced nitrogen content; For the reaction in molten steel Balanced nitrogen content; For the reaction in molten steel Balanced nitrogen content; For the surface reaction of molten steel Balanced nitrogen content; This represents the nitrogen content in the molten steel at time t-1. The mass transfer coefficient of nitrogen atoms in the gas-liquid boundary layer during the bottom-blown ammonia nitrogen enhancement stage; ρ is the surface area of ​​bubbles generated in the molten steel per unit time during the high-pressure bottom blowing ammonia process; ρ is the density of the molten steel. W is the surface area of ​​the molten steel; W is the weight of the molten steel.

[0023] Preferably, in step 3, the flow rate of the bottom-blown ammonia is 0.5 to 1.0 L / (min·kg), and the bottom-blowing time is 15 to 25 min.

[0024] Furthermore, in step 4, the nitrogen content in the molten steel at time t during the synergistic nitrogen enhancement stage of surface pressurization and bottom-blown nitrogen is calculated based on the nitrogen content of the molten steel at time t using bottom-blown ammonia. The formula for calculating the nitrogen content of the molten steel at time t using bottom-blown ammonia is as follows:

[0025] ;

[0026] in, Let t be the nitrogen content in the molten steel. For the surface reaction of molten steel Balanced nitrogen content; This represents the nitrogen content in the molten steel at time t-1. It represents the mass transfer coefficient of nitrogen atoms in the gas-liquid boundary layer during the bottom-blown nitrogen enrichment stage.

[0027] Furthermore, in step 4, the formula for calculating the minimum bottom blowing time in the stage of synergistic nitrogen enhancement of molten steel surface pressurization and bottom blowing is:

[0028] ;

[0029] in, The mass transfer coefficient of hydrogen atoms in the gas-liquid boundary layer during the bottom-blown nitrogen enrichment stage; ρ represents the surface area of ​​bubbles generated in the molten steel per unit time during bottom-blowing nitrogen gas; W represents the density of the molten steel; and W represents the weight of the molten steel. The required hydrogen content in the molten steel; This represents the hydrogen content in the molten steel after bottom blowing of ammonia.

[0030] Furthermore, the hydrogen content in the molten steel after the bottom-blowing ammonia gas is applied is based on the nitrogen content during the synergistic nitrogen enrichment stage of pressurized bottom-blowing ammonia gas and pressurized nitrogen gas on the surface of the molten steel in step 3. The formula for calculating the hydrogen content is as follows:

[0031] ;

[0032] in, For the reaction The equilibrium constant; For the reaction The equilibrium constant; R is the ideal gas constant; T is the reaction temperature; Standard atmospheric pressure; V furnace cavity volume; is the activity coefficient of hydrogen; is the activity coefficient of nitrogen; The target nitrogen content is 75% to 85%.

[0033] Preferably, in step 4, the rate of bottom-blowing nitrogen is 0.5 to 1.0 L / (min·kg), and the bottom-blowing time is 5 to 15 min.

[0034] A second aspect of the present invention also provides a high-nitrogen steel prepared by the preparation method described above, wherein the high-nitrogen steel has a nitrogen content ranging from 0.9% to 1.5%, an oxygen content ≤15ppm, a sulfur content ≤10ppm, and a hydrogen content ≤3.5ppm.

[0035] This invention provides several calculation formulas, offering a kinetic prediction basis for high-pressure gas-phase nitriding and precise nitrogen enhancement with bottom-blown ammonia, enabling relatively accurate prediction and control of the nitrogen content in molten steel without relying on real-time nitrogen content detection methods.

[0036] Beneficial effects:

[0037] This invention achieves efficient and precise nitrogen enrichment and the preparation of high-purity, high-nitrogen steel through a series of process steps, including vacuum gas washing, gas-phase nitrogen enrichment on the molten steel surface, synergistic nitrogen enrichment with pressurized bottom-blowing ammonia and pressurized nitrogen on the molten steel surface, and synergistic nitrogen enrichment with pressurized nitrogen on the molten steel surface and bottom-blowing. It utilizes high-pressure ammonia and nitrogen for efficient gas-phase nitriding, while leveraging the strong deoxidizing and desulfurizing effects of ammonia to achieve high-purity smelting. Precise control of nitrogen content is achieved by controlling the nitrogen and ammonia pressures, the ammonia bottom-blowing flow rate, and determining the minimum nitrogen bottom-blowing time based on the hydrogen content in the molten steel. This invention not only solves the problem of high costs caused by adding nitriding alloys in the traditional preparation of high-nitrogen steel, but also avoids the problem of inclusions generated by adding deoxidizing and desulfurizing agents, reducing the oxygen content in the steel to below 15 ppm and the sulfur content to below 10 ppm, thereby meeting the urgent demand of high-end equipment manufacturing for a new generation of high-purity, high-nitrogen steel products.

[0038] In the stage of pressurized bottom-blowing ammonia and pressurized nitrogen on the surface of molten steel for synergistic nitrogen enhancement, the provided high-pressure smelting process utilizes high-pressure bottom-blowing ammonia to couple the deoxidation and desulfurization reactions. and This significantly enhances the removal efficiency of ammonia for oxygen and sulfur impurities, reducing the oxygen content to below 15 ppm and the sulfur content to below 10 ppm.

[0039] Furthermore, by employing a nitrogen solubility calculation formula based on kinetic prediction, the surface nitrogen pressure, cylinder output pressure, nitrogen content in the molten steel at different stages (time t), and minimum nitrogen bottom blowing time can be calculated according to the target nitrogen content. This provides a kinetic prediction basis for the entire high-pressure nitrogen enhancement process, enabling relatively accurate prediction and control of the nitrogen content in the molten steel without relying on real-time nitrogen content detection methods. Ultimately, the nitrogen content control error in the molten steel is ≤0.005wt%. This also effectively avoids the drawback of hydrogen embrittlement caused by increasing the hydrogen content in the steel when using ammonia for nitrogen enhancement.

[0040] Through the above process, the present invention successfully achieves high cleanliness control and precise regulation of nitrogen content in high-nitrogen steel, which not only shortens the traditional high-nitrogen steel smelting process, but also effectively reduces production costs. Detailed Implementation

[0041] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0042] This invention utilizes bottom-blowing ammonia gas, enabling more efficient contact between ammonia and molten steel for nitrogen enrichment and cleanliness control. Simultaneously, it enhances steel agitation, providing favorable kinetic conditions and achieving efficient and uniform nitrogen enrichment, deoxidation, and desulfurization. This effectively avoids the difficulties in nitrogen content control and uneven distribution caused by adding nitriding alloys, as well as the introduction of foreign impurities through the addition of deoxidizers and desulfurizers. This invention precisely controls the pressure and amount of nitrogen and ammonia in stages. In step 2, a small amount of nitrogen is introduced to lay the foundation. Step 3 performs efficient nitrogen enrichment, deoxidation, and desulfurization, improving the cleanliness of the molten steel while maintaining the nitrogen content close to the target value. Step 4 removes byproducts from the ammonia reaction from the molten steel and fine-tunes the nitrogen content to precisely reach the target value. This effectively avoids the drawbacks of using ammonia for nitrogen enrichment, which can increase the hydrogen content in the steel and cause hydrogen embrittlement, and allows for more precise control of the nitrogen content in the molten steel. By rationally arranging these three steps and targeting nitrogen enrichment at different stages, the preparation cycle is effectively shortened.

[0043] Specifically, embodiments of the present invention provide a method for preparing high-nitrogen steel through efficient nitrogen enrichment and high-purity smelting using pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, comprising:

[0044] Step 1: After loading the alloy material into the crucible, heat it and evacuate it to 0-2 Pa. Maintain the high vacuum state until the material begins to melt. Then, fill the furnace with argon gas to increase the pressure inside the furnace to 20-60 kPa and continue heating. When the material is completely melted, evacuate it to 0-2 Pa again to complete one gas washing operation.

[0045] The gas washing and vacuuming steps before smelting can remove the original air in the furnace and the water vapor and other gases adsorbed in the raw materials, reducing the impact of the original gases on subsequent smelting.

[0046] Step 2: After vacuuming is completed, stabilize the smelting temperature to 1550-1650℃, and fill the pressure induction furnace cavity with nitrogen to the target nitrogen pressure. Then, the process enters the gas phase nitrogen enrichment stage on the surface of the molten steel, which lasts for 2 to 5 minutes. Based on the nitrogen content of the molten steel at time t during surface nitrogen enrichment, the nitrogen enrichment in this stage is determined to reach 5% to 10% of the target nitrogen content, and then the nitrogen filling is stopped.

[0047] The furnace cavity is filled with nitrogen gas at the target pressure to increase the surface nitrogen content of the molten steel in the gas phase. This serves as the basis for further high-pressure bottom blowing of ammonia gas, preventing severe splashing of the molten steel due to excessive bottom blowing pressure and insufficient surface pressure. Simultaneously, it avoids denitrification of the molten steel surface due to low nitrogen pressure during high-pressure bottom blowing, which would lead to inaccurate control of the nitrogen content. The amount of nitrogen added in this stage is 5% to 10% of the target nitrogen content, allowing for precise control of the nitrogen content.

[0048] The formula for calculating the target nitrogen pressure during the smelting process in a pressurized induction furnace is as follows:

[0049] [1]

[0050] In formula [1], Target nitrogen pressure (Pa); P 0 [Standard atmospheric pressure (Pa); [%N] represents the target nitrogen content; is the equilibrium constant for nitrogen dissolution reaction; T is the smelting temperature (K). is the first-order interaction coefficient of nitrogen with itself; Let N be the first-order interaction coefficient of element i with respect to N; Let be the second-order interaction coefficient between element i and N; Let represent the content of element i in the steel. 'i' is used as an iterative superscript to iterate through all alloying elements (or solute elements) in the molten steel except for the matrix element iron (Fe), such as carbon (C), manganese (Mn), chromium (Cr), nickel (Ni), and molybdenum (Mo). In the summation term... In this context, i represents each alloying element except for the subscript element N, along with its content [%i] and corresponding interaction coefficient. Together, they quantified the effect of this element on the nitrogen (N) activity coefficient.

[0051] Equation [1] is used to calculate the target nitrogen pressure in the smelting process of the pressurized induction furnace. Taking into account factors such as standard atmospheric pressure, target nitrogen content, nitrogen dissolution reaction equilibrium constant, smelting temperature and the interaction coefficients of various elements in steel with nitrogen, the appropriate nitrogen pressure to be injected into the furnace cavity in step 2 can be determined by this formula, so as to achieve precise control of the initial nitrogen increase and lay the foundation for the subsequent nitrogen increase process.

[0052] In step 2, during the gas-phase nitriding stage on the surface of the molten steel, the formula for calculating the nitrogen content of the molten steel at time t during surface nitriding is:

[0053] [2]

[0054] In formula [2], Let be the nitrogen content of the molten steel at time t during the vapor-phase nitrogen enrichment stage on the surface of the molten steel; let be Reaction in molten steel Balanced nitrogen content; The nitrogen content of the molten steel at time t-1 during the vapor-phase nitrogen enrichment stage on the surface of the molten steel. is the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer at the surface of molten steel (m / s). The area of ​​the molten steel surface (m²) 2 W is the weight of the molten steel (kg); ρ is the density of the molten steel (kg / m³). 3 ).

[0055] Equation [2] is used to calculate and predict the nitrogen content at time t during the gas phase nitrogen increase stage on the surface of molten steel under nitrogen pressure in smelting, according to Fick's first law and controlled by a first-order equation. The formula involves parameters such as the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer, the area of ​​the molten steel surface, the weight of the molten steel, and the nitrogen content in the molten steel at time t-1. These parameters can help determine the change in nitrogen content of the molten steel in step 2, thereby achieving control over the amount of nitrogen increase in this stage.

[0056] Step 3: Adjust the output pressure of the ammonia cylinder Control the pressure of bottom-blown ammonia gas, and carry out a stage of synergistic nitrogen enhancement by pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel. Simultaneously adjust the bottom-blown flow rate to 0.5-1.0 L / (min·kg) and the bottom-blown time to 15-25 min. Based on the nitrogen content of molten steel at time t of bottom-blown ammonia gas, determine the nitrogen enhancement to 75% to 85% of the target nitrogen content in this stage.

[0057] High-pressure bottom-blowing ammonia gas utilizes the advantages of large contact area between bottom-blowing bubbles and molten steel, high mass transfer driving force, and enhanced uniformity of molten pool composition. This is combined with the higher nitrogen enrichment efficiency of ammonia compared to nitrogen gas and the coupled deoxidation and desulfurization reactions. and This method improves the cleanliness of molten steel while efficiently increasing nitrogen content.

[0058] In step 3 of this technical solution, the formula for calculating the output pressure of the ammonia cylinder during bottom-blowing ammonia nitrogen enhancement is as follows:

[0059] [3]

[0060] In formula [3], The output pressure (Pa) of the bottom-blowing vent plug; The pressure loss (Pa) in the bottom blowing pipeline is 0.28–0.32 MPa. The nitrogen pressure inside the furnace cavity (Pa); The static pressure of molten steel, ρ is the density of molten steel (kg / m³). 3 g is the acceleration due to gravity (N / kg), and h is the depth of the molten steel (m).

[0061] Equation [3] is used to calculate the output pressure of the ammonia cylinder and the bottom blowing pressure. Taking into account factors such as nitrogen pressure in the furnace cavity, static pressure of molten steel, density of molten steel, gravitational acceleration, depth of molten steel and ammonia pressure loss in the bottom blowing pipeline, the appropriate output pressure of the ammonia cylinder and the bottom blowing pressure can be determined by this formula when high-pressure bottom blowing of ammonia is carried out in step 3, so as to achieve an efficient bottom blowing nitrogen enhancement process.

[0062] In step 3, during the synergistic nitrogen enrichment stage of pressurized bottom-blown ammonia and pressurized nitrogen on the surface of molten steel, the formula for calculating the nitrogen content in the molten steel at time t using bottom-blown ammonia is:

[0063] [4]

[0064] In formula [4], The nitrogen content in the molten steel at time t during the stage of synergistic nitrogen enhancement by pressurized bottom blowing ammonia and pressurized nitrogen on the surface of molten steel; For the reaction in molten steel Balanced nitrogen content; For the reaction in molten steel Balanced nitrogen content; For the reaction in molten steel Balanced nitrogen content; For the surface reaction of molten steel Balanced nitrogen content; The nitrogen content in the molten steel at time t-1 during the stage of synergistic nitrogen enhancement by pressurized bottom blowing ammonia and pressurized nitrogen on the surface of molten steel; The mass transfer coefficient (m / s) of nitrogen atoms in the gas-liquid boundary layer during the bottom-blown ammonia nitrogen enhancement stage. The surface area (m²) of bubbles generated in molten steel per unit time during bottom-blown ammonia gas process. 2 ); ρ is the density of molten steel (kg / m³) 3 ); The area of ​​the molten steel surface (m²) 2 W represents the weight of the molten steel (kg).

[0065] Equation [4] is used to calculate the nitrogen content of bottom-blown ammonia at time t during the high-pressure vapor phase nitriding and bottom-blown ammonia nitrogen enhancement stages. It includes two nitrogen enhancement methods: vapor phase nitriding of nitrogen on the steel surface and vapor phase nitriding of bottom-blown ammonia. Among them, the nitrogen enhancement method of bottom-blown ammonia vapor phase nitriding mainly considers , and Three reaction pathways are employed. To achieve precise control of nitrogen addition, multiple complex reaction pathways triggered by ammonia decomposition must be comprehensively considered, while simultaneously coupling factors such as the equilibrium nitrogen content of four reactions, the mass transfer coefficient of nitrogen atoms on the steel surface, the mass transfer coefficient of nitrogen atoms in bubbles, the surface area of ​​the steel, the surface area of ​​the bubbles, and the nitrogen content in the steel at time t-1. This helps determine the change in nitrogen content in the steel during step 3, thereby enabling control of nitrogen addition at this stage. This method establishes a novel multi-reaction-multi-phase mass transfer coupling control pathway based on ammonia, overcoming the limitations of single gas-phase mass transfer in traditional nitrogen addition, and demonstrating significant progress in introducing ammonia into high-temperature metallurgical reactors and achieving precise control of nitrogen content.

[0066] Step 4: Switch from bottom-blown ammonia to bottom-blown nitrogen, entering the stage of synergistic nitrogen enhancement through surface pressurization of molten steel and bottom-blown nitrogen. Simultaneously adjust the bottom-blowing flow rate to 0.5–1.0 L / (min·kg) and the bottom-blowing time to 5–15 min, allowing the bubbles to agitate and expel reaction byproducts (H2, H2O, H2S, etc.). Based on the nitrogen content of the molten steel at time t during bottom-blown nitrogen blowing, determine and enhance the nitrogen content to 98%–102% of the target nitrogen content. Determine the minimum bottom-blowing time based on the hydrogen content in the molten steel. This enables the preparation of highly efficient and precise nitrogen-enriched, high-purity, high-nitrogen steel.

[0067] Bottom-blown nitrogen mainly utilizes bottom-blown bubbles to create turbulent flow and agitate the molten steel, thereby expelling the byproducts (H2, H2O, H2S, etc.) generated by bottom-blown ammonia in step 3 from the molten steel, thus improving the cleanliness of the molten steel and further increasing nitrogen content.

[0068] In step 4, to better reduce the hydrogen content in the molten steel to the required value, the minimum time t for bottom-blowing nitrogen is determined. min The calculation formula is:

[0069] [5]

[0070] In formula [5], The mass transfer coefficient (m / s) of hydrogen atoms in the gas-liquid boundary layer during the bottom-blown nitrogen enrichment stage. The surface area (m²) of bubbles generated in molten steel per unit time during bottom-blown nitrogen process. 2 ); The required hydrogen content in the molten steel; The hydrogen content in the molten steel after bottom blowing of ammonia is completed is calculated using the following formula:

[0071] [6]

[0072] In equation [6], K1 is the reaction The equilibrium constant; K2 is the reaction constant. The equilibrium constant; R is the ideal gas constant (R = 8.314 m). 3 •Pa / (mol∙K)); T is the reaction temperature (K); Standard atmospheric pressure (Pa); V furnace cavity volume (m³) 3 ); is the activity coefficient of hydrogen; is the activity coefficient of nitrogen; The target nitrogen content is 75% to 85%.

[0073] Equation [6] is used to calculate the hydrogen content at the initial stage of high-pressure gas-phase nitriding and bottom-blowing nitrogen enhancement. Considering the various reaction pathways of hydrogen atoms being expelled from the molten steel and the influencing factors under the ammonia atmosphere, the hydrogen content in the steel after bottom-blowing ammonia is completed can be calculated, providing a calculation basis for accurately calculating the minimum bottom-blowing nitrogen time.

[0074] In step 4, during the high-pressure gas-phase nitriding and bottom-blown nitrogen enrichment stages, the formula for calculating the nitrogen content in the molten steel at time t during bottom-blown nitrogen is:

[0075] [7]

[0076] In formula [7], The nitrogen content in the molten steel at time t during the high-pressure vapor phase nitriding and bottom-blown nitrogen enrichment stages; For the surface reaction of molten steel Balanced nitrogen content; The nitrogen content in the molten steel at time t-1 during the high-pressure vapor phase nitriding and bottom-blown nitrogen enrichment stages; The mass transfer coefficient (m / s) of nitrogen atoms in the gas-liquid boundary layer during the bottom-blown nitrogen enrichment stage is given.

[0077] Equation [7] is used to calculate the nitrogen content of the bottom-blown nitrogen at time t during the high-pressure gas phase nitriding and bottom-blown nitrogen addition stages. It involves parameters such as the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer and the nitrogen content at time t-1, which can accurately predict the change of nitrogen content in the molten steel in step 4, so as to achieve accurate control of the amount of nitrogen added in this stage.

[0078] Based on the thermodynamics of nitrogen dissolution under high pressure, the kinetics of gas-phase nitrogen enrichment, and the influence of high-pressure bottom blowing on the nitrogen dissolution surface area, this invention designs the smelting temperature, smelting nitrogen pressure, bottom blowing ammonia pressure, and the time of each gas-phase nitriding stage to achieve efficient and precise nitrogen enrichment throughout the entire high-nitrogen steel production process. This allows for relatively accurate prediction and control of the nitrogen content of molten steel without relying on real-time nitrogen content detection methods.

[0079] To better understand the technical solution, exemplary embodiments of the present invention will be described in more detail below.

[0080] Example 1

[0081] Example 1 uses the P900 series (20 kg) as a specific example. The P900 composition content requirements are shown in Table 1 below. Alloy raw materials are used: iron rod, electrolytic manganese and metallic chromium. The composition of the alloy raw materials is shown in Table 2 below.

[0082] Table 1. Component content of P900

[0083]

[0084] Table 2 Alloy Raw Material Composition

[0085]

[0086] The smelting equipment used is a 25 kg pressurized induction furnace with a maximum operating pressure of 3.5 MPa and a furnace loading of 20 kg.

[0087] Based on Equations [1], [2], [3], [4], [5], [6] and [7], the target nitrogen content, smelting temperature, ammonia pressure during the nitrogen addition and deoxidation stage, nitriding time, bottom blowing pressure and bottom blowing flow rate are reasonably matched: The target nitrogen content of P900 high nitrogen steel is 0.98%, the smelting temperature throughout the process is about 1550 ℃, the nitrogen pressure for gas phase nitrogen addition on the surface of the molten steel under smelting pressure is 0.31 MPa, the nitrogen addition amount in step 2 is 0.05%, the ammonia cylinder output pressure during bottom blowing is 0.63 MPa, the bottom blowing flow rate is 12 L / min, the nitrogen addition amount in step 3 is 0.83%, the bottom blowing time is 15 min, the nitrogen addition amount in step 4 is 0.10%, the bottom blowing flow rate is 15 L / min, the minimum bottom blowing time is 4 min, and the bottom blowing time is 9 min.

[0088] Detailed operation steps:

[0089] Raw material processing in this invention includes turning iron bars to remove the outer layer of iron oxide scale, and crushing other raw materials to the required particle size (diameter 1cm-3cm). Traditional processing methods well-known in the art can be used for raw material processing, and there are no special requirements. The prepared raw materials are then placed into the furnace in a specific order. In this invention, there are no special requirements regarding the order in which the raw materials are placed into the furnace; traditional feeding methods well-known in the art can be used.

[0090] In this invention, after the raw materials are loaded into the furnace and sealed, the furnace temperature is slowly increased while a vacuum is applied. When the furnace pressure drops from atmospheric pressure (101 kPa) to 2 Pa, a high vacuum is maintained and the power is increased until the raw materials begin to melt. After the raw materials begin to melt, argon gas is injected into the furnace to bring the furnace pressure to 20 kPa. The argon gas purity is 99.99%. The negative pressure and power are maintained until the raw materials are completely melted. After the molten steel is completely melted, the vacuum is evacuated again to 2 Pa. During this process, the power is maintained to prevent the molten steel from solidifying.

[0091] After the vacuuming is completed, nitrogen is introduced into the furnace chamber to raise the internal pressure to 0.31 MPa. Ammonia is then introduced into the furnace by opening the bottom-blowing vent plug, controlling the ammonia cylinder output pressure to 0.63 MPa, the bottom-blowing flow rate to 12 L / min, and the bottom-blowing time to 15 min.

[0092] After the bottom blowing of ammonia is completed, the bottom blowing gas is switched to nitrogen, and the output pressure of the nitrogen cylinder is controlled at 0.63 MPa, the bottom blowing flow rate is 15 L / min, and bottom blowing continues for 9 minutes.

[0093] After bottom blowing is completed, casting is performed.

[0094] After smelting, the steel ingot was removed and subjected to compositional analysis. The results showed that the nitrogen content was 0.984%, the oxygen content was 15 ppm, the sulfur content was 10 ppm, and the hydrogen content was 3.4 ppm. The test results met expectations and satisfied the required compositional content for P900.

[0095] Example 2

[0096] Example 2 uses the P900 series (20kg) as a specific example, and the raw material composition is shown in Table 1.

[0097] The smelting equipment used is a 25kg pressurized induction furnace with a maximum operating pressure of 3.5MPa and a furnace loading of 20kg.

[0098] Based on formulas [1], [2], [3], [4], [5], [6] and [7], the target nitrogen content, smelting temperature, ammonia pressure during the nitrogen addition and deoxidation stage, nitriding time, bottom blowing pressure and bottom blowing flow rate are reasonably matched: The target nitrogen content of P900 high nitrogen steel is 1.00%, the smelting temperature throughout the process is about 1570℃, the nitrogen pressure for gas phase nitrogen addition on the surface of the molten steel under smelting pressure is 0.33MPa, the nitrogen addition amount in step 2 is 0.05%, the ammonia cylinder output pressure during bottom blowing is 0.64MPa, the bottom blowing flow rate is 14L / min, the nitrogen addition amount in step 3 is 0.85%, the bottom blowing time is 16min, the nitrogen addition amount in step 4 is 0.10%, the bottom blowing flow rate is 15L / min, the minimum bottom blowing time is 5min, and the bottom blowing time is 10min.

[0099] Detailed operation steps:

[0100] Raw material processing in this invention includes turning iron bars to remove the outer layer of iron oxide scale, and crushing other raw materials to the required particle size (diameter 1cm-3cm). Traditional processing methods well-known in the art can be used for raw material processing, and there are no special requirements. The prepared raw materials are then placed into the furnace in a specific order. In this invention, there are no special requirements regarding the order in which the raw materials are placed into the furnace; traditional feeding methods well-known in the art can be used.

[0101] In this invention, after the raw materials are loaded into the furnace and sealed, the furnace temperature is slowly increased while a vacuum is applied. When the furnace pressure drops from atmospheric pressure (101 kPa) to 2 Pa, a high vacuum is maintained and the power is increased until the raw materials begin to melt. After the raw materials begin to melt, argon gas is injected into the furnace to bring the furnace pressure to 20 kPa. The argon gas purity is 99.99%. The negative pressure and power are maintained until the raw materials are completely melted. After the molten steel is completely melted, the vacuum is evacuated again to 2 Pa. During this process, the power is maintained to prevent the molten steel from solidifying.

[0102] After the vacuuming is completed, nitrogen is introduced into the furnace chamber to raise the internal pressure to 0.33 MPa. Ammonia is then introduced into the furnace by opening the bottom-blowing vent plug, controlling the ammonia cylinder output pressure to 0.64 MPa, the bottom-blowing flow rate to 14 L / min, and the bottom-blowing time to 16 min.

[0103] After the bottom blowing of ammonia is completed, the bottom blowing gas is switched to nitrogen, and the output pressure of the nitrogen cylinder is controlled at 0.64 MPa and the bottom blowing flow rate is 15 L / min. Bottom blowing continues for 10 minutes.

[0104] After bottom blowing is completed, casting is performed.

[0105] After smelting, the steel ingot was removed and subjected to compositional analysis. The results showed that the nitrogen content was 1.007%, the oxygen content was 13 ppm, the sulfur content was 9 ppm, and the hydrogen content was 3.1 ppm. The test results met expectations and satisfied the required compositional content for P900.

[0106] Example 3

[0107] Example 3 uses the P900 series (20kg) as a specific example, and the raw material composition is shown in Table 1.

[0108] The smelting equipment used is a 25kg pressurized induction furnace with a maximum operating pressure of 3.5MPa and a furnace loading of 20kg.

[0109] Based on formulas [1], [2], [3], [4], [5], [6] and [7], the target nitrogen content, smelting temperature, ammonia pressure during the nitrogen addition and deoxidation stage, nitriding time, bottom blowing pressure and bottom blowing flow rate are reasonably matched: The target nitrogen content of P900 high nitrogen steel is 1.02%, the smelting temperature throughout the process is about 1590℃, the nitrogen pressure for gas phase nitrogen addition on the surface of the molten steel under smelting pressure is 0.35MPa, the nitrogen addition amount in step 2 is 0.05%, the ammonia cylinder output pressure during bottom blowing is 0.66MPa, the bottom blowing flow rate is 15L / min, the nitrogen addition amount in step 3 is 0.87%, the bottom blowing time is 17min, the nitrogen addition amount in step 4 is 0.10%, the bottom blowing flow rate is 15L / min, the minimum bottom blowing time is 6min, and the bottom blowing time is 11min.

[0110] Detailed operation steps:

[0111] Raw material processing in this invention includes turning iron bars to remove the outer layer of iron oxide scale, and crushing other raw materials to the required particle size (diameter 1cm-3cm). Traditional processing methods well-known in the art can be used for raw material processing, and there are no special requirements. The prepared raw materials are then placed into the furnace in a specific order. In this invention, there are no special requirements regarding the order in which the raw materials are placed into the furnace; traditional feeding methods well-known in the art can be used.

[0112] In this invention, after the raw materials are loaded into the furnace and sealed, the furnace temperature is slowly increased while a vacuum is applied. When the furnace pressure drops from atmospheric pressure (101 kPa) to 2 Pa, a high vacuum is maintained and the power is increased until the raw materials begin to melt. After the raw materials begin to melt, argon gas is injected into the furnace to bring the furnace pressure to 20 kPa. The argon gas purity is 99.99%. The negative pressure and power are maintained until the raw materials are completely melted. After the molten steel is completely melted, the vacuum is evacuated again to 2 Pa. During this process, the power is maintained to prevent the molten steel from solidifying.

[0113] After the vacuuming is completed, nitrogen is introduced into the furnace chamber to raise the internal pressure to 0.35 MPa. Ammonia is then introduced into the furnace by opening the bottom-blowing vent plug, controlling the ammonia cylinder output pressure to 0.66 MPa, the bottom-blowing flow rate to 15 L / min, and the bottom-blowing time to 17 min.

[0114] After the bottom blowing of ammonia is completed, the bottom blowing gas is switched to nitrogen, and the output pressure of the nitrogen cylinder is controlled at 0.66 MPa, the bottom blowing flow rate is 15 L / min, and bottom blowing continues for 11 minutes.

[0115] After bottom blowing is completed, casting is performed.

[0116] After smelting, the steel ingot was removed and subjected to compositional analysis. The results showed that the nitrogen content was 1.026%, the oxygen content was 11 ppm, the sulfur content was 6 ppm, and the hydrogen content was 2.6 ppm. The test results met expectations and satisfied the required compositional content for P900.

[0117] Example 4

[0118] Example 4 uses Mn18Cr18 high-nitrogen steel (20kg) as a specific example. The required Mn18Cr18 composition content is shown in Table 3 below. The alloy raw materials used are iron rod, electrolytic manganese and metallic chromium. The composition of the alloy raw materials is shown in Table 4 below.

[0119] Table 3. Component content of Mn18Cr18

[0120]

[0121] Table 4 Alloy Raw Material Composition

[0122]

[0123] The smelting equipment used is a 25kg pressurized induction furnace with a maximum operating pressure of 3.5MPa and a furnace loading of 20kg.

[0124] Based on Equations [1], [2], [3], [4], [5], [6] and [7], the target nitrogen content, smelting temperature, ammonia pressure during the nitrogen addition and deoxidation stage, nitriding time, bottom blowing pressure and bottom blowing flow rate are reasonably matched: The target nitrogen content of Mn18Cr18 high nitrogen steel is 1.2%, the smelting temperature throughout the process is about 1610℃, the nitrogen pressure for gas phase nitrogen addition on the surface of the molten steel under smelting pressure is 0.65MPa, the nitrogen addition amount in step 2 is 0.05%, the ammonia cylinder output pressure during bottom blowing is 1.01MPa, the bottom blowing flow rate is 18L / min, the nitrogen addition amount in step 3 is 1.00%, the bottom blowing time is 21min, the nitrogen addition amount in step 4 is 0.15%, the bottom blowing flow rate is 16L / min, the minimum bottom blowing time is 8min, and the bottom blowing time is 13min.

[0125] Detailed operation steps:

[0126] Raw material processing in this invention includes turning iron bars to remove the outer layer of iron oxide scale, and crushing other raw materials to the required particle size (diameter 1cm-3cm). Traditional processing methods well-known in the art can be used for raw material processing, and there are no special requirements. The prepared raw materials are then placed into the furnace in a specific order. In this invention, there are no special requirements regarding the order in which the raw materials are placed into the furnace; traditional feeding methods well-known in the art can be used.

[0127] In this invention, after the raw materials are loaded into the furnace and sealed, the furnace temperature is slowly increased while a vacuum is applied. When the furnace pressure drops from atmospheric pressure (101 kPa) to 2 Pa, a high vacuum is maintained and the power is increased until the raw materials begin to melt. After the raw materials begin to melt, argon gas is injected into the furnace to bring the furnace pressure to 20 kPa. The argon gas purity is 99.99%. The negative pressure and power are maintained until the raw materials are completely melted. After the molten steel is completely melted, the vacuum is evacuated again to 2 Pa. During this process, the power is maintained to prevent the molten steel from solidifying.

[0128] After the vacuuming is completed, nitrogen is introduced into the furnace chamber to raise the internal pressure to 0.65 MPa. Ammonia is then introduced into the furnace by opening the bottom-blowing vent plug, controlling the ammonia cylinder output pressure to 1.01 MPa, the bottom-blowing flow rate to 18 L / min, and the bottom-blowing time to 21 min.

[0129] After the bottom blowing of ammonia is completed, the bottom blowing gas is switched to nitrogen, and the output pressure of the nitrogen cylinder is controlled at 1.01 MPa, the bottom blowing flow rate is 16 L / min, and bottom blowing continues for 13 minutes.

[0130] After bottom blowing is completed, casting is performed.

[0131] After smelting, the steel ingot was removed and its composition was analyzed. The results showed that the nitrogen content was 1.203%, the oxygen content was 8 ppm, the sulfur content was 5 ppm, and the hydrogen content was 1.8 ppm. The test results met expectations and satisfied the required composition of Mn18Cr18 high-nitrogen steel.

[0132] Comparative Example 1

[0133] Comparative Example 1 will be compared with Example 1, except that nitrogen is used instead of ammonia during bottom blowing. All other steps are exactly the same as those in Example 1, using the same smelting steps and parameters. P900 series (20kg) is also used as a specific example, and the raw material composition is shown in Table 1.

[0134] The smelting equipment used is a 25kg pressurized induction furnace with a maximum operating pressure of 3.5MPa and a furnace loading of 20kg.

[0135] Based on Equations [1], [2], [3] and [7], the target nitrogen content, smelting temperature, nitrogen pressure, nitriding time and bottom blowing flow rate are reasonably matched: The target nitrogen content of P900 high nitrogen steel is 0.98%, the smelting temperature throughout the process is about 1550℃, the nitrogen pressure for gas phase nitriding on the surface of the molten steel under smelting pressure is 0.31MPa, the nitrogen addition amount in step 2 is 0.05%, the nitrogen cylinder output pressure during bottom blowing is 0.63MPa, the bottom blowing flow rate is 15L / min, and the bottom blowing time is 21min.

[0136] Detailed operation steps:

[0137] Raw material processing in this invention includes turning iron bars to remove the outer layer of iron oxide scale, and crushing other raw materials to the required particle size (diameter 1cm-3cm). Traditional processing methods well-known in the art can be used for raw material processing, and there are no special requirements. The prepared raw materials are then placed into the furnace in a specific order. In this invention, there are no special requirements regarding the order in which the raw materials are placed into the furnace; traditional feeding methods well-known in the art can be used.

[0138] In this invention, after the raw materials are loaded into the furnace and sealed, the furnace temperature is slowly increased while a vacuum is applied. When the furnace pressure drops from atmospheric pressure (101 kPa) to 2 Pa, a high vacuum is maintained and the power is increased until the raw materials begin to melt. After the raw materials begin to melt, argon gas is injected into the furnace to bring the furnace pressure to 20 kPa. The argon gas purity is 99.99%. The negative pressure and power are maintained until the raw materials are completely melted. After the molten steel is completely melted, the vacuum is evacuated again to 2 Pa. During this process, the power is maintained to prevent the molten steel from solidifying.

[0139] After the vacuuming is completed, nitrogen is introduced into the furnace cavity to raise the internal pressure to 0.31 MPa. The bottom-blowing vent plug is then opened to introduce nitrogen into the furnace, controlling the nitrogen cylinder output pressure to 0.63 MPa, the bottom-blowing flow rate to 15 L / min, and the bottom-blowing time to 21 min.

[0140] After the bottom blowing of ammonia is completed, casting is performed.

[0141] After smelting, the steel ingots were removed and their composition was analyzed. The results showed that the nitrogen content was 0.476%, the oxygen content was 168 ppm, the sulfur content was 69.1 ppm, and the hydrogen content was 0 ppm. The comparison shows that using ammonia for bottom blowing to increase nitrogen is indeed more effective than using nitrogen for bottom blowing, and ammonia does indeed possess deoxidation and desulfurization capabilities under high pressure.

[0142] Comparison of the results from the embodiments demonstrates that the high-nitrogen steel smelting process of the present invention can reduce the oxygen content in molten steel to below 15 ppm and the sulfur content to below 10 ppm using the coupling reaction of ammonia without adding deoxidizing and desulfurizing agents, and the nitrogen addition efficiency is higher than that of nitrogen gas; the smelting process can effectively remove hydrogen and reduce the drawbacks of using ammonia gas for nitrogen addition; the multiple calculation formulas provided by the present invention can indeed effectively help to accurately control the nitrogen content in molten steel, with a nitrogen content control accuracy error ≤ 0.005%; and the smelting process of the present invention is suitable for smelting various types of high-nitrogen austenitic stainless steel.

[0143] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, characterized in that, The process includes the following steps: Step 1: Vacuum the alloy material to 0-2 Pa, maintain the vacuum until the raw material begins to melt, then introduce argon gas to bring the furnace pressure to 20-60 kPa. After the raw material is completely melted, vacuum the material again to 0-2 Pa; Step 2: After vacuuming, stabilize the smelting temperature at 1550-1650℃, and introduce nitrogen gas into the pressure induction furnace cavity to the target nitrogen pressure. Entering the gas-phase nitrogen enrichment stage on the surface of molten steel, based on the nitrogen content of the molten steel at time t during surface nitrogen enrichment, the nitrogen enrichment in this stage is determined to reach 5% to 10% of the target nitrogen content; Step 3: Adjust the output pressure of the ammonia cylinder. The pressure of bottom-blown ammonia is controlled to conduct a synergistic nitrogen enhancement stage involving pressurized bottom-blown ammonia and pressurized nitrogen on the surface of the molten steel. Based on the nitrogen content of the molten steel at time t during bottom-blown ammonia, the nitrogen content is determined to be increased to 75% to 85% of the target nitrogen content during this stage. The formula for calculating the nitrogen content of the molten steel at time t during bottom-blown ammonia is as follows: ;in, Let t be the nitrogen content in the molten steel. For the reaction in molten steel Balanced nitrogen content; For the reaction in molten steel Balanced nitrogen content; For the reaction in molten steel Balanced nitrogen content; For the surface reaction of molten steel Balanced nitrogen content; The nitrogen content in the molten steel at time t-1; The mass transfer coefficient of nitrogen atoms in the gas-liquid boundary layer during the bottom-blown ammonia nitrogen enhancement stage; ρ is the surface area of ​​bubbles generated in the molten steel per unit time during the high-pressure bottom blowing ammonia process; ρ is the density of the molten steel. Where is the surface area of ​​the molten steel; W is the weight of the molten steel; Step 4: Switch the bottom-blown ammonia gas to the bottom-blown nitrogen gas, and enter the stage of synergistic nitrogen enhancement of the molten steel surface pressurization and bottom-blown nitrogen gas, so that the bubbles are stirred and the reaction by-products are discharged. Based on the nitrogen content of the molten steel at time t of the bottom-blown nitrogen gas, determine and enhance the nitrogen to 98% to 102% of the target nitrogen content, and determine the minimum bottom-blowing time based on the hydrogen content in the molten steel. This enables the efficient and precise preparation of high-purity, high-nitrogen steel through nitrogen enrichment; the formula for calculating the minimum bottom blowing time is: ;in, The mass transfer coefficient of hydrogen atoms in the gas-liquid boundary layer during the bottom-blown nitrogen enrichment stage; ρ represents the surface area of ​​bubbles generated in the molten steel per unit time during bottom-blowing nitrogen gas; W represents the density of the molten steel; and W represents the weight of the molten steel. The required hydrogen content in the molten steel; This refers to the hydrogen content in the molten steel after bottom blowing of ammonia; the formula for calculating the hydrogen content is: ;in, For the reaction The equilibrium constant; For the reaction The equilibrium constant; R is the ideal gas constant; T is the reaction temperature; Standard atmospheric pressure; V furnace cavity volume; is the activity coefficient of hydrogen; is the activity coefficient of nitrogen; The target nitrogen content is 75% to 85%.

2. The method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, as described in claim 1, is characterized in that... The formula for calculating the nitrogen content of the liquid steel at time t during surface nitriding is as follows: ;in, Let be the nitrogen content of the molten steel at time t; For the reaction in molten steel Balanced nitrogen content; Let be the nitrogen content of the molten steel at time t-1; is the mass transfer coefficient of nitrogen atoms in the liquid boundary layer at the surface of molten steel; ρ is the surface area of ​​the molten steel; W is the weight of the molten steel; ρ is the density of the molten steel.

3. The method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, as described in claim 1, is characterized in that... In step 2, the duration of the gas phase nitrogen enrichment stage on the surface of the molten steel is 2 to 5 minutes.

4. The method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, as described in claim 1, is characterized in that... In step 3, the flow rate of bottom-blown ammonia is 0.5–1.0 L / (min·kg), and the bottom-blowing time is 15–25 min.

5. The method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, as described in claim 1, is characterized in that... In step 4, the formula for calculating the nitrogen content of the liquid steel at time t using bottom-blown ammonia is: ;in, Let t be the nitrogen content in the molten steel. For the surface reaction of molten steel Balanced nitrogen content; The nitrogen content in the molten steel at time t-1; This refers to the mass transfer coefficient of nitrogen atoms in the gas-liquid boundary layer during the bottom-blown nitrogen enrichment stage; ρ is the surface area of ​​the molten steel; W is the density of the molten steel; and ρ is the weight of the molten steel. This refers to the surface area of ​​bubbles generated in the molten steel per unit time during bottom-blowing nitrogen gas process.

6. The method for preparing high-nitrogen steel with high efficiency and high purity through pressurized bottom-blown ammonia gas and pressurized nitrogen gas on the surface of molten steel, as described in claim 1, is characterized in that... In step 4, the rate of bottom blowing nitrogen is 0.5 to 1.0 L / (min·kg), and the bottom blowing time is 5 to 15 min.

7. A high-nitrogen steel prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The high-nitrogen steel has a nitrogen content range of 0.9% to 1.5%, an oxygen content of ≤15ppm, a sulfur content of ≤10ppm, and a hydrogen content of ≤3.5ppm.

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