High-nitrogen steel preparation method for efficiently and accurately increasing nitrogen through pressurized gas phase nitriding and nitrogen bottom blowing

Abstract

The invention relates to a high-nitrogen steel preparation method capable of efficiently and accurately increasing nitrogen through pressurized gas phase nitriding and bottom blowing nitrogen, which comprises the following steps: filling a furnace chamber of a pressurized induction furnace with first target nitrogen pressure, and entering a molten steel surface gas phase nitrogen increasing stage; and then pressurizing and bottom blowing nitrogen, controlling the pressure of the bottom blowing nitrogen by adjusting the output pressure of a nitrogen cylinder, controlling the bottom blowing flow, and entering a pressurized gas phase nitriding and bottom blowing nitrogen increasing stage. And then pressurizing bottom nitrogen blowing is stopped, second target nitrogen pressure needed by casting continues to be filled into the furnace cavity of the pressurizing induction furnace, and the molten steel surface gas phase nitrogen increasing stage under the casting nitrogen pressure enters. By combining the bottom blowing nitrogen, the nitrogen increasing efficiency is improved, the preparation period is greatly shortened, and therefore the production efficiency of the high-nitrogen steel is improved. Besides, the nitrogen pressure, the bottom blowing flow and the nitrogen increasing amount are accurately controlled in stages, dynamic prediction is carried out in combination with a calculation formula, accurate control over the liquid nitrogen content of the steel is achieved, and the requirements of different high-nitrogen steel products are met.

Description

Technical Field

[0001] The invention relates to the technical field of high nitrogen steel preparation, and in particular to a high nitrogen steel preparation method for efficient and precise nitrogen addition by pressurized gas phase nitriding and bottom blowing nitrogen. Background Art

[0002] As a low-cost and environmentally friendly alloying element, nitrogen can not only replace expensive nickel metal when added to stainless steel, but also improve the strength, hardness and corrosion resistance of steel through solid solution strengthening, fine grain strengthening and nitrogen-molybdenum synergy. As an important engineering material, high nitrogen steel has been widely used in aerospace, petrochemical, energy, marine engineering and atomic energy industries.

[0003] High nitrogen steel refers to steel whose actual nitrogen content exceeds the limit that can be achieved when preparing the material under normal pressure (0.1MPa). Adding nitriding alloys during the smelting process is an effective means of preparing high nitrogen steel, but it will lead to uneven nitrogen distribution in the molten steel, and the nitrogen content is difficult to control, and it is easy to pollute the molten steel. With the development of pressurized metallurgical equipment and preparation technology, the use of abundant and cheap nitrogen instead of nitriding alloys to nitridize molten steel not only reduces costs and increases efficiency, but also has many advantages such as uniform nitrogen distribution and easy adjustment of the nitrogen content of molten steel by nitrogen pressure. It is an effective way to produce high nitrogen steel efficiently and at low cost. High nitrogen steel is prepared under high nitrogen pressure conditions to improve the nitrogen solubility of molten steel. At the same time, the nitrogen pressure is further increased on the basis of the smelting pressure for casting, so as to inhibit the precipitation of pores during solidification and prevent the deterioration of the performance of the ingot.

[0004] Pressurized gas nitriding is a highly efficient gas nitriding process at the contact surface between nitrogen and molten steel. However, it is limited by the reasonable matching of the induction coil size and production capacity of the pressurized induction furnace equipment. The free surface to volume ratio of the molten pool generally decreases with the increase of the induction furnace capacity. Therefore, in the large-scale preparation of high nitrogen steel, there are problems such as low nitriding efficiency and long preparation cycle, which restricts the application of gas phase nitrogen alloying technology of high nitrogen steel. Therefore, pressurized gas nitriding combined with bottom blowing nitrogen can further increase nitrogen efficiently. Although the pressurized bottom blowing technology has been applied in metallurgical equipment such as AOD refining furnace, the kinetic prediction of nitrogen increase by bottom blowing nitrogen is still insufficient. The control of nitrogen content in molten steel is highly dependent on real-time nitrogen content detection and other means, and it is impossible to accurately predict and control the nitrogen content of molten steel. Therefore, it is very necessary to develop a method for preparing high nitrogen steel by pressurized gas nitriding and bottom blowing nitrogen with high efficiency and precision. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The technical problem to be solved by the present invention is how to prepare high nitrogen steel by means of pressurized gas phase nitriding and bottom blowing nitrogen to increase nitrogen efficiently and accurately.

[0007] (II) Technical solution

[0008] To this end, the present invention discloses a method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and precise nitrogen addition, comprising:

[0009] Step 1: operating in a pressurized induction furnace; stably controlling the smelting temperature, charging the furnace chamber of the pressurized induction furnace with a first target nitrogen pressure, entering the stage of gas phase nitrogen addition on the surface of the molten steel, and performing gas phase nitriding under the smelting nitrogen pressure, wherein the nitrogen addition amount in the stage of gas phase nitrogen addition on the surface of the molten steel is 5% to 10% of the target nitrogen content;

[0010] Step 2: Perform pressurized bottom blowing of nitrogen, and control the bottom blowing nitrogen pressure and the bottom blowing flow rate by adjusting the output pressure of the nitrogen bottle;

[0011] Entering the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage, the steel liquid is gas phase nitrided under the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage, and the nitrogen increase amount is 85% to 95% of the target nitrogen content.

[0012] Step 3: Stop pressurized bottom blowing nitrogen, and continue to fill the furnace chamber of the pressurized induction furnace with the second target nitrogen pressure required for casting, and enter the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure. The amount of nitrogen increase in the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure is 1.5% to 5% of the target nitrogen content.

[0013] Further, in step 1, the calculation formula of the first target nitrogen pressure in the smelting process in the pressurized induction furnace is:

[0014]

[0015] Among them, P 氮气 is the first target nitrogen pressure, P 0 is the standard atmospheric pressure, [%N] is the target nitrogen content, K N is the equilibrium constant of nitrogen dissolution reaction, T is the smelting temperature, is the first-order interaction coefficient of nitrogen with itself, is the first-order interaction coefficient of element j on N, is the second-order interaction coefficient of element j on N, and [% j] is the content of element j in steel.

[0016] Further, in step 1, in the stage of gas phase nitrogen addition on the surface of the molten steel, the calculation formula for the nitrogen content of the molten steel at time t is:

[0017]

[0018] Where, [%N] t is the nitrogen content of the molten steel at time t, k Nis the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer during the gas phase nitrogen addition stage on the surface of molten steel under high nitrogen pressure, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​the molten steel, W is the weight of the molten steel, [% N] t-1 It is the nitrogen content in the molten steel at time t-1 during the gas phase nitrogen increase stage on the surface of the molten steel under smelting nitrogen pressure.

[0019] Furthermore, in step 2, the calculation formula for the output pressure of the nitrogen cylinder is:

[0020] P 输出 =P 底吹 +P 损失 =1.05×(P 氮气 +ρ 钢液 gh)+P 损失 ;

[0021] Among them, P 输出 is the output pressure of the nitrogen cylinder, P 底吹 is the nitrogen bottle output pressure and bottom blowing pressure, P 氮气 is the first target nitrogen pressure, P 静压力 is the static pressure of molten steel, P 损失 is the nitrogen pressure lost in the bottom blowing pipeline, ρ 钢液 is the density of molten steel, g is the acceleration due to gravity, and h is the depth of molten steel.

[0022] Further, in step 2, the calculation formula for the bubble diameter generated by pressurized bottom blowing nitrogen is:

[0023]

[0024] Among them, d g is the bubble diameter generated by pressurized bottom blowing nitrogen, σ is the gas-liquid surface tension coefficient, d0 is the nozzle diameter of the bottom blowing air plug, Q g is the bottom blowing gas flow rate, ρ 钢液 is the density of molten steel, and g is the acceleration due to gravity.

[0025] Further, in step 2, the calculation formula for the rising speed of bubbles generated by pressurized bottom blowing nitrogen is:

[0026]

[0027] Where v is the rising velocity of bubbles generated by pressurized bottom blowing nitrogen, σ is the gas-liquid surface tension coefficient, and ρ 钢液 is the density of molten steel, g is the acceleration due to gravity, d g It is the bubble diameter generated by pressurized bottom blowing nitrogen.

[0028] Further, in step 2, the calculation formula for the surface area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing nitrogen process is:

[0029]

[0030] Among them, A 气泡 A is the surface area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing nitrogen process. g is the surface area of ​​a single bubble, Q g is the bottom blowing gas flow rate, V g is the volume of a single bubble, h is the depth of molten steel, r is the radius of the nitrogen bubble generated by pressurized bottom blowing nitrogen, and v is the rising speed of the bubble generated by pressurized bottom blowing nitrogen.

[0031] Further, in step 2, during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stages, the calculation formula for the nitrogen content at time t is:

[0032]

[0033] in, is the nitrogen content at time t during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen addition stages, is the mass transfer coefficient of nitrogen atoms in the liquid boundary layer during the pressurized gas phase nitriding and bottom blowing nitrogen nitriding stages, is the nitrogen content at time t-1 during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen addition stage, A 气泡 is the surface area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing nitrogen process, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​molten steel, and W is the weight of molten steel.

[0034] Further, in step 3, the calculation formula of the second target nitrogen pressure required for casting is:

[0035] P 浇铸 =[(0.1~0.15)×P 氮气 / P 0 +(0.5~0.6)];

[0036] Among them, P 浇筑 The second target nitrogen pressure required for casting, P 氮气 is the first target nitrogen pressure, P 0 is standard atmospheric pressure.

[0037] Further, in step 3, during the gas phase nitrogen addition stage on the surface of the molten steel under the casting nitrogen pressure, the calculation formula for the nitrogen content at time t is:

[0038]

[0039] in, is the nitrogen content on the surface of the molten steel at time t during the gas phase nitrogen addition stage under the casting nitrogen pressure, is the nitrogen content on the surface of the molten steel at time t-1 during the gas phase nitrogen addition stage under the casting nitrogen pressure, [%N] is the target nitrogen content, k N is the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer during the gas phase nitrogen addition stage on the surface of molten steel under high nitrogen pressure, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​molten steel, and W is the weight of molten steel.

[0040] (III) Beneficial effects

[0041] The beneficial effects of the present invention are as follows: the present invention mentions a method for preparing high nitrogen steel by pressurized gas phase nitriding and bottom blowing nitrogen for efficient and precise nitrogen addition, comprising: operating in a pressurized induction furnace; stably controlling the smelting temperature, charging the first target nitrogen pressure into the furnace chamber of the pressurized induction furnace, entering the stage of gas phase nitrogen addition on the surface of the molten steel, and performing gas phase nitriding under the smelting nitrogen pressure; then performing pressurized bottom blowing nitrogen, and controlling the bottom blowing nitrogen pressure by adjusting the output pressure of the nitrogen bottle. Then stop pressurized bottom blowing nitrogen, continue to charge the furnace chamber of the pressurized induction furnace with the second target nitrogen pressure required for casting, and enter the stage of gas phase nitrogen addition on the surface of the molten steel under the casting nitrogen pressure.

[0042] This application increases nitrogen in the pressurized gas phase, while accurately controlling the nitrogen content, ensuring the stability and uniformity of the nitrogen content in high nitrogen steel, which is beneficial to improving product quality. At the same time, a suitable nitrogen pressure is designed for the casting process, which effectively avoids the adverse effects of pores in the molten steel during casting and solidification, and improves the quality of the ingot. Combined with bottom blowing nitrogen, the nitrogen increase efficiency is improved, the preparation cycle is greatly shortened, thereby improving the production efficiency of high nitrogen steel, which is beneficial to large-scale production. In addition, by accurately controlling the nitrogen pressure, bottom blowing flow rate and nitrogen increase amount in stages, and combining the calculation formula for dynamic prediction, the precise control of the nitrogen content of the molten steel is achieved to meet the needs of different high nitrogen steel products. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic flow chart of a method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and precise nitrogen addition mentioned in the present application;

[0044] Figure 2 This is a structural diagram of a pressurized induction furnace in a high nitrogen steel preparation method for efficient and precise nitrogen addition by pressurized vapor nitriding and bottom blowing nitrogen mentioned in this application.

[0045] Description of Reference Numerals

[0046] 1. Induction furnace body; 2. Furnace cover rotating and lifting mechanism; 3. Furnace cover; 4. Crucible; 5. Induction coil; 6. Monitoring; 7. Temperature measuring mechanism; 8. Thermocouple; 9. Vent; 10. Pressure gauge; 11. Sealing flange; 12. Inflating pipe; 13. Ventilation plug; 14. Steel beam; 15. Silo; 16. Crucible tilting mechanism; 17. Ingot mold. DETAILED DESCRIPTION

[0047] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0048] When amount, concentration or other value or parameter is represented by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1-5", described range should be interpreted as including range "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0049] In these embodiments, unless otherwise specified, the parts and percentages are all by mass. "Parts by mass" refers to the basic unit of measurement representing the mass ratio of multiple components, and 1 part can represent any unit mass, such as 1g, or 3.527g. If we say that the mass of component A is a part and the mass of component B is b parts, then the ratio a:b of the mass of component A and the mass of component B is represented. Alternatively, the mass of component A is represented by a K, and the mass of component B is represented by b K (K is an arbitrary number, representing a multiple factor). It should not be misunderstood that, unlike mass parts, the sum of the mass of all components is not limited to 100 parts. "And / or" is used to represent that one or both of the situations described may occur, for example, A and / or B include (A and B) and (A or B).

[0050] refer to Figure 1 The present application discloses a method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen with high efficiency and precision, comprising:

[0051] Step 1: Operate in a pressurized induction furnace; stably control the smelting temperature, illustratively, the smelting temperature is between 1500 and 1520°C, and then fill the furnace chamber of the pressurized induction furnace with a first target nitrogen pressure, enter the gas phase nitrogen increase stage on the surface of the molten steel, and perform gas phase nitriding under the smelting nitrogen pressure. The amount of nitrogen increase in the gas phase nitrogen increase stage on the surface of the molten steel is 5% to 10% of the target nitrogen content.

[0052] The first target nitrogen pressure is filled into the furnace chamber to increase nitrogen on the surface of the molten steel in the gas phase, which serves as the basis for further pressurized bottom blowing. This can avoid serious splashing of the molten steel due to excessive bottom blowing pressure and too low pressure on the surface of the molten steel. At the same time, it can avoid denitrification on the surface of the molten steel due to low nitrogen pressure while increasing nitrogen through pressurized bottom blowing. The simultaneous occurrence of the two will result in the inability to accurately control the nitrogen content of the molten steel. The amount of nitrogen increase at this stage is 5% to 10% of the target nitrogen content, which can control the nitrogen content more accurately.

[0053] Step 2: Perform pressurized bottom blowing of nitrogen, and control the bottom blowing nitrogen pressure by adjusting the output pressure of the nitrogen bottle;

[0054] Entering the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage, the steel liquid is gas phase nitrided under the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage, and the nitrogen increase amount is 85% to 95% of the target nitrogen content.

[0055] It should be noted that pressurized bottom blowing nitrogen can make nitrogen fully contact with molten steel and improve the efficiency of nitrogen addition. By adjusting the output pressure of the nitrogen bottle to control the bottom blowing nitrogen pressure, the speed and degree of nitrogen addition can be accurately controlled according to actual needs. The nitrogen addition amount at this stage is 85% to 95% of the target nitrogen content, which can quickly and efficiently make the nitrogen content in the molten steel close to the target value, greatly improving production efficiency, while also ensuring the stability and uniformity of the nitrogen content in high-nitrogen steel, which is conducive to improving product quality.

[0056] Step 3: Stop pressurized bottom blowing nitrogen, and continue to fill the furnace chamber of the pressurized induction furnace with the second target nitrogen pressure required for casting, and enter the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure. The amount of nitrogen increase in the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure is 1.5% to 5% of the target nitrogen content.

[0057] After stopping the bottom blowing of nitrogen, continue to fill the furnace chamber with the second target nitrogen pressure required for casting to increase the gas phase nitrogen on the surface of the molten steel. The nitrogen increase amount in this stage is 1.5% to 5% of the target nitrogen content. The nitrogen content is finely adjusted, and the appropriate nitrogen pressure is provided for the casting process, which helps to inhibit the precipitation of pores during solidification and prevent deterioration of the performance of the ingot.

[0058] The present application uses gas phase nitrogen addition and bottom blowing nitrogen to enable nitrogen to contact the molten steel more efficiently for nitrogen addition, while enhancing the stirring of the molten steel, providing good kinetic conditions, and achieving efficient and uniform nitrogen addition effects, effectively avoiding the difficulties in controlling the nitrogen content and uneven distribution caused by the addition of nitrided alloys. The present application accurately controls the nitrogen pressure and nitrogen addition amount in stages, first introducing a small amount of nitrogen to lay the foundation in step 1, performing efficient nitrogen addition close to the target value in step 2, and fine-tuning the nitrogen content in step 3 to accurately reach the target value, so as to more accurately control the nitrogen content in the molten steel.

[0059] In addition, by combining the bottom blowing nitrogen method, the problem of low nitriding efficiency in large-scale preparation with simple pressurized gas phase nitriding is solved. Bottom blowing nitrogen allows nitrogen to fully contact with molten steel, improving the efficiency of nitrogen addition. The nitrogen addition amount in step 2 can reach 85% to 95% of the target nitrogen content, greatly improving production efficiency. By rationally arranging the three steps, nitrogen addition is carried out in a targeted manner at different stages, effectively shortening the preparation cycle.

[0060] refer to Figure 2 , the following is the working process of the pressurized induction furnace: in the charging stage, the furnace cover 3 is lifted from the induction furnace body 1 by the furnace cover rotating lifting mechanism 2, and the metal materials are respectively loaded into the silo 15 and the crucible 4 according to the needs. Close the silo 15, lower the furnace cover 3 by the furnace cover rotating lifting mechanism 2, ensure the sealing of the furnace body by the sealing flange 11, and provide support for the crucible 4 by the steel beam 14. In the smelting stage, control the power of the induction coil 5, induction heat the raw materials in the crucible 4, and control the appropriate smelting temperature. The first target nitrogen pressure is filled into the furnace chamber of the pressurized induction furnace through the vent 9, and the gas phase nitrogen increase stage of the molten steel surface is entered. At this time, the pressure gauge 10 monitors the pressure in the furnace in real time. The temperature of the molten steel is continuously monitored by the temperature measuring mechanism 7 and the thermocouple 8, and the monitoring 6 records the situation in the furnace in real time. In the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stages, pressurized bottom blowing nitrogen is performed, and the bottom blowing nitrogen pressure is controlled by adjusting the output pressure of the nitrogen bottle. Nitrogen is filled into the molten steel from the bottom of the crucible 4 through the gas filling pipe 12 and the air-permeable plug 13 in turn to perform full contact nitriding. In the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stages, the nitrogen increase amount is 85% to 95% of the target nitrogen content through the gas phase nitriding of the molten steel. In the stage of gas phase nitrogen increase on the surface of the molten steel under the casting nitrogen pressure, the pressurized bottom blowing nitrogen is stopped. The second target nitrogen pressure required for casting continues to be filled into the furnace chamber of the pressurized induction furnace, and the stage of gas phase nitrogen increase on the surface of the molten steel under the casting nitrogen pressure is entered to fine-tune the nitrogen content. The molten steel in the crucible 4 is poured into the ingot mold 17 through the crucible tilting mechanism 16 to complete the casting.

[0061] In step 1 of the technical solution, the calculation formula for the first target nitrogen pressure in the smelting process in the pressurized induction furnace is:

[0062]

[0063] In formula [1], P 0 is the standard atmospheric pressure (P 0 =101325Pa), [%N] is the target nitrogen content in step (1), K N is the equilibrium constant of nitrogen dissolution reaction, T is the smelting temperature (K), is the first-order interaction coefficient of nitrogen with itself, is the first-order interaction coefficient of element j on N, is the second-order interaction coefficient of element j on N, and [% j] is the content of element j in steel.

[0064] Formula [1] is used to calculate the first target nitrogen pressure in the pressurized induction furnace smelting process. Taking into account factors such as standard atmospheric pressure, target nitrogen content, nitrogen dissolution reaction equilibrium constant, smelting temperature, and the interaction coefficient of various elements in steel with nitrogen, this formula can be used to determine the appropriate nitrogen pressure to be filled into the furnace chamber in step 1, so as to achieve precise control of the initial nitrogen addition amount and lay the foundation for the subsequent nitrogen addition process.

[0065] In this technical solution, the gas phase nitriding process is controlled by the mass transfer rate of nitrogen atoms in the liquid phase boundary layer. According to Fick's first law, it is controlled by the first-order equation. During the gas phase nitrogen addition stage on the surface of the molten steel under the smelting nitrogen pressure, the nitrogen content at time t can be calculated and predicted by formula [2]:

[0066]

[0067] In formula [2], k N A is the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer during the gas phase nitrogen addition stage on the surface of molten steel under high nitrogen pressure (m / s), which is about 0.00020-0.00025 m / s. 表面 is the surface area of ​​the molten steel (m 2 ), W is the weight of molten steel (kg), [%N] t-1 It is the nitrogen content in the molten steel at time t-1 during the gas phase nitrogen increase stage on the surface of the molten steel under smelting nitrogen pressure.

[0068] Formula [2] is used to calculate and predict the nitrogen content at time t in the gas phase nitrogen addition stage of the molten steel surface under the smelting nitrogen pressure, 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, which can help determine the change in the nitrogen content of the molten steel at this stage in step 1, thereby achieving control of the nitrogen addition amount at this stage.

[0069] In step 2 of the technical solution, the nitrogen bottle output pressure and bottom blowing pressure can be calculated according to formula [3]:

[0070] P 输出 =P 底吹 +P 损失 =1.05×(P 氮气 +ρ 钢液 gh)+P 损失 [3];

[0071] In formula [3], P 氮气 is the nitrogen pressure in the furnace chamber (MPa), the static pressure of the molten steel P 静压力 =ρ 钢液 gh,ρ钢液 is the density of molten steel (kg / m 3 ), g is the acceleration of gravity (N / kg), h is the depth of molten steel (m), P 损失 The nitrogen pressure loss in the bottom blowing pipeline is 0.28~0.32MPa.

[0072] Formula [3] is used to calculate the nitrogen bottle output pressure and bottom blowing pressure. Taking into account factors such as the nitrogen pressure in the furnace chamber, the static pressure of the molten steel, the density of the molten steel, the gravity acceleration, the depth of the molten steel, and the nitrogen pressure lost in the bottom blowing pipeline, this formula can be used to determine the appropriate nitrogen bottle output pressure and bottom blowing pressure when performing pressurized bottom blowing nitrogen in step 2, so as to achieve an efficient bottom blowing nitrogen enrichment process.

[0073] In step 2 of the present technical solution, the bubble diameter generated by pressurized bottom blowing can be expressed by formula [4]:

[0074]

[0075] In formula [4], σ is the gas-liquid surface tension coefficient (N / m), d0 is the nozzle diameter of the bottom blowing air plug 13 (mm), and Q g is the bottom blowing gas flow rate (mL / min), preferably, the bottom blowing flow rate per unit mass of molten steel Q g * It is 80~120mL / (min·kg).

[0076] Formula [4] represents the diameter of bubbles generated by pressurized bottom blowing. It involves parameters such as the gas-liquid surface tension coefficient, the nozzle diameter of the bottom blowing gas plug 13, and the bottom blowing gas flow rate. This formula can help determine the size of bubbles generated during the bottom blowing process. The bubble size will affect the contact area between nitrogen and molten steel and the mass transfer efficiency.

[0077] In step 2 of the technical solution, the rising speed (m / s) of the bubbles generated by the pressurized bottom blowing nitrogen can be expressed by formula [5]:

[0078]

[0079] Formula [5] represents the rising speed of bubbles generated by pressurized bottom blowing of nitrogen. The rising speed affects the residence time of bubbles in the molten steel and the contact effect with the molten steel, thus affecting the nitrogen addition efficiency.

[0080] In step 2 of the technical solution, the area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing of nitrogen can be expressed by formula [6]:

[0081]

[0082] In formula [6], A g is the surface area of ​​a single bubble (m 2 ), Vg is the volume of a single bubble (m 3 ), r is the radius of nitrogen bubbles generated by pressurized bottom blowing nitrogen (m);

[0083] Formula [6] is used to calculate the area of ​​bubbles generated in the molten steel per unit time during the process of pressurized bottom blowing nitrogen. It involves parameters such as the surface area of ​​a single bubble, the volume of a single bubble, and the radius of nitrogen bubbles generated by pressurized bottom blowing nitrogen. The bubble area affects the contact area between nitrogen and molten steel, and thus affects the nitrogen addition efficiency.

[0084] In step 2 of the technical solution, during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stages, the nitrogen content at time t can be expressed by formula [7]:

[0085]

[0086] In formula [7], is the mass transfer coefficient of nitrogen atoms in the liquid boundary layer during the pressurized gas phase nitriding and bottom blowing nitrogen nitriding stages (m / s), which is approximately It is the nitrogen content at time t-1 during the pressurized bottom blowing and surface composite nitrogen addition stage.

[0087] Formula [7] is used to calculate the nitrogen content at time t during the pressurized gas phase nitriding and bottom blowing nitrogen 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. It can accurately predict the change in nitrogen content of the molten steel at this stage in step 2, so as to achieve accurate control of the nitrogen addition amount at this stage.

[0088] In step 3 of the technical solution, the nitrogen pressure (MPa) required for casting can be calculated according to formula [8]:

[0089] P 浇铸 =[(0.1~0.15)×P 氮气 / P 0 +(0.5~0.6)][8];

[0090] Formula [8] is used to calculate the nitrogen pressure required for casting. Determining the appropriate casting nitrogen pressure and providing a suitable nitrogen pressure for the casting process can help inhibit the formation of pores during solidification and improve the quality of the ingot.

[0091] In step 3 of the technical solution, during the gas phase nitrogen addition stage on the surface of the molten steel under the casting nitrogen pressure, the nitrogen content at time t can be expressed by formula [9]:

[0092]

[0093] In formula [9], is the nitrogen content on the surface of the molten steel at time t during the gas phase nitrogen addition stage under the casting nitrogen pressure, is the nitrogen content on the surface of the molten steel at time t-1 during the gas phase nitrogen addition stage under the casting nitrogen pressure, [%N] is the target nitrogen content, k N is the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer during the gas phase nitrogen addition stage on the surface of molten steel under high nitrogen pressure, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​molten steel, and W is the weight of molten steel.

[0094] Formula [9] is used to calculate the nitrogen content at time t during the gas phase nitrogen addition stage on the surface of the molten steel under the casting nitrogen pressure. It involves parameters such as the nitrogen content at time t-1, the target nitrogen content, the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer, the density of the molten steel, the surface area of ​​the molten steel, and the weight of the molten steel. It can help determine the change in the nitrogen content of the molten steel at this stage in step 3, achieve fine-tuning of the nitrogen content, and ensure that the nitrogen content of the final product accurately reaches the target value.

[0095] The present application provides a number of calculation formulas, which provide a kinetic prediction basis for efficient and accurate nitrogen addition by pressurized vapor nitriding and bottom blowing nitrogen, so that the nitrogen content of molten steel can be more accurately predicted and controlled without relying on real-time nitrogen content detection methods.

[0096] The present application provides a method for preparing high nitrogen steel by pressurized gas phase nitriding and bottom blowing nitrogen with high efficiency and precision. The core idea is to sequentially carry out nitrogen addition through the gas phase nitrogen addition stage on the surface of molten steel under smelting nitrogen pressure, the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen addition stage, and the gas phase nitrogen addition stage on the surface of molten steel under casting nitrogen pressure. According to the thermodynamics of nitrogen dissolution under pressure, the kinetic theory of gas phase nitrogen addition, and the influence of pressurized bottom blowing on the nitrogen dissolution surface area and mass transfer coefficient, the smelting temperature, smelting nitrogen pressure, bottom blowing nitrogen pressure, casting nitrogen pressure, and the time of each gas phase nitriding stage are designed to achieve high efficiency and precision nitrogen addition in the whole process of high nitrogen steel production.

[0097] In order to better understand the technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0098] Embodiment 1

[0099] The smelting equipment used is a 500kg pressurized induction furnace with a maximum operating pressure of 2.0MPa and a furnace load of 500kg.

[0100] According to formula [1], formula [2], formula [3], formula [7], formula [8] and formula [9], the target nitrogen content, smelting temperature, nitrogen pressure in each nitriding stage, nitriding time and bottom blowing flow rate are reasonably matched: the target nitrogen content of 30Cr15Mo1N high nitrogen stainless steel is 0.38%, and the whole process smelting temperature is about 1500℃. The nitrogen pressure in the gas phase nitrogen increase stage of the molten steel surface under the smelting nitrogen pressure is 0.34MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.0002m / s; the bottom blowing nitrogen pressure in the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stage is 0.38MPa, the bottom blowing flow rate is 40L / min, the time is 16min, and the gas phase nitriding area on the steel liquid surface is 0.1963m 2 The bottom blowing bubble nitriding area is 0.1513m 2 The total area of ​​vapor nitriding is 0.3476m 2 , the mass transfer coefficient is 0.0004m / s; and the nitrogen pressure in the gas phase nitrogenization stage on the surface of the molten steel under the casting nitrogen pressure is 0.9MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.0002m / s.

[0101] The mass fractions of the alloy raw materials are as follows: C: 0.31%, Si: 0.52%, Mn: 0.51%, Cr: 15.11%, Mo: 1.10%, Ni: 0.23% and Fe (balance);

[0102] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25-0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00-16.00%, Mo: 0.85-1.10%, Ni: ≤0.50%, N: 0.30-0.50% and Fe (balance);

[0103] (1) In a pressurized induction furnace, the smelting temperature is stably controlled at about 1500°C, and a nitrogen pressure of 0.34 MPa is filled into the furnace chamber to perform gas phase nitriding of the molten steel under nitrogen pressure (time is 2 min) in the gas phase nitrogen increase stage of the molten steel surface. The nitrogen increase amount is 0.0260%, which is 6.81% of the target nitrogen increase amount.

[0104] (2) Further pressurized bottom blowing of nitrogen was started, and the output pressure of the nitrogen bottle was adjusted (0.68 MPa, P 损失 =0.3MPa) to control the bottom blowing nitrogen pressure (0.38MPa), and carry out pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage steel liquid gas phase nitriding (bottom blowing flow rate is 40L / min, time is 16min), the nitrogen increase amount is 0.3484%, which is 91.20% of the target nitrogen increase amount.

[0105] (3) Stop the pressurized bottom blowing of nitrogen and continue to fill the furnace cavity with the nitrogen pressure required for casting (0.9 MPa) to carry out the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure (time is 2 minutes). The nitrogen increase amount is 0.0133%, which is 1.99% of the target nitrogen increase amount.

[0106] Table 1 shows the composition (%) of the 30Cr15Mo1N high nitrogen stainless steel ingot prepared in Example 1

[0107] C Si Mn Cr Mo Ni N S P Fe 0.30 0.51 0.50 15.10 1.10 0.23 0.3820 0.005 0.008 margin

[0108] It can be seen from Table 1 that Example 1 can efficiently and accurately obtain a 30Cr15Mo1N high nitrogen stainless steel ingot with a target nitrogen content.

[0109] Embodiment 2

[0110] The smelting equipment used is a 500kg pressurized induction furnace with a maximum operating pressure of 2.0MPa and a furnace load of 500kg.

[0111] According to formula [1], formula [2], formula [3], formula [7], formula [8] and formula [9], the target nitrogen content, smelting temperature, nitrogen pressure in each nitriding stage, nitriding time and bottom blowing flow rate are reasonably matched: the target nitrogen content of 30Cr15Mo1N high nitrogen stainless steel is 0.39%, and the whole process smelting temperature is about 1530℃. The nitrogen pressure in the gas phase nitrogen increase stage of the molten steel surface under the smelting nitrogen pressure is 0.38MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00022m / s; the bottom blowing nitrogen pressure in the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stage is 0.43MPa, the bottom blowing flow rate is 45L / min, the time is 15min, and the gas phase nitriding area on the steel liquid surface is 0.1963m 2 The bottom blowing bubble nitriding area is 0.1618m 2 The total area of ​​vapor nitriding is 0.3581m 2 , the mass transfer coefficient is 0.00045m / s; and the nitrogen pressure in the gas phase nitrogenization stage of the molten steel surface under the casting nitrogen pressure is 1.0MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00022m / s.

[0112] The mass fractions of the alloy raw materials are as follows: C: 0.33%, Si: 0.50%, Mn: 0.50%, Cr: 15.21%, Mo: 1.01%, Ni: 0.21% and Fe (balance);

[0113] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25-0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00-16.00%, Mo: 0.85-1.10%, Ni: ≤0.50%, N: 0.30-0.50% and Fe (balance);

[0114] (1) In a pressurized induction furnace, the smelting temperature was stably controlled at about 1530°C, and a nitrogen pressure of 0.38 MPa was filled into the furnace chamber to perform gas phase nitriding of the molten steel under nitrogen pressure (time was 2 min) in the gas phase nitrogen increase stage of the molten steel surface. The nitrogen increase amount was 0.0290%, which was 7.40% of the target nitrogen increase amount.

[0115] (2) Further pressurized bottom blowing of nitrogen was started, and the output pressure of the nitrogen bottle was adjusted (0.73 MPa, P 损失 =0.3MPa) to control the bottom blowing nitrogen pressure (0.43MPa), and carry out pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage steel liquid gas phase nitriding (bottom blowing flow rate is 45L / min, time is 15min), the nitrogen increase amount is 0.3548%, which is 90.49% of the target nitrogen increase amount.

[0116] (3) Stop the pressurized bottom blowing of nitrogen and continue to fill the furnace cavity with the nitrogen pressure required for casting (1.0 MPa) to carry out the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure (time is 2 min). The nitrogen increase amount is 0.0083%, which is 2.11% of the target nitrogen increase amount.

[0117] Table 2 shows the composition (%) of the 30Cr15Mo1N high nitrogen stainless steel ingot prepared in Example 2

[0118] C Si Mn Cr Mo Ni N S P Fe 0.31 0.49 0.48 15.20 1.00 0.21 0.3921 0.006 0.007 margin

[0119] It can be seen from Table 2 that Example 2 can efficiently and accurately obtain a 30Cr15Mo1N high nitrogen stainless steel ingot with a target nitrogen content.

[0120] Embodiment 3

[0121] The smelting equipment used is a 500kg pressurized induction furnace with a maximum operating pressure of 2.0MPa and a furnace load of 500kg.

[0122] According to formula [1], formula [2], formula [3], formula [7], formula [8] and formula [9], the target nitrogen content, smelting temperature, nitrogen pressure in each nitriding stage, nitriding time and bottom blowing flow rate are reasonably matched: the target nitrogen content of 30Cr15Mo1N high nitrogen stainless steel is 0.40%, and the whole process smelting temperature is about 1550℃. The nitrogen pressure in the gas phase nitrogen increase stage of the molten steel surface under the smelting nitrogen pressure is 0.44MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00023m / s; the bottom blowing nitrogen pressure in the pressurized vapor nitriding and bottom blowing nitrogen nitrogen increasing stages is 0.49MPa, the bottom blowing flow rate is 50L / min, the time is 14min, and the vapor nitriding area on the steel liquid surface is 0.1963m 2 The bottom blowing bubble nitriding area is 0.1718m 2 The total area of ​​vapor nitriding is 0.3681m 2 , the mass transfer coefficient is 0.00048m / s; and the nitrogen pressure in the gas phase nitrogenization stage on the surface of the molten steel under the casting nitrogen pressure is 1.1MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00023m / s.

[0123] The mass fractions of the alloy raw materials are: C: 0.32%, Si: 0.49%, Mn: 0.49%, Cr: 14.92%, Mo: 1.01%, Ni: 0.20% and Fe (balance);

[0124] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25-0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00-16.00%, Mo: 0.85-1.10%, Ni: ≤0.50%, N: 0.30-0.50% and Fe (balance);

[0125] (1) In a pressurized induction furnace, the smelting temperature was stably controlled at about 1550°C, and a nitrogen pressure of 0.44 MPa was filled into the furnace chamber to perform gas phase nitriding of the molten steel under nitrogen pressure (time was 2 min) in the gas phase nitrogen increase stage of the molten steel surface. The nitrogen increase amount was 0.0309%, which was 7.64% of the target nitrogen increase amount.

[0126] (2) Further pressurized bottom blowing of nitrogen was started, and the output pressure of the nitrogen bottle was adjusted (0.79 MPa, P 损失 =0.3MPa) to control the bottom blowing nitrogen pressure (0.49MPa), and carry out pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage steel liquid gas phase nitriding (bottom blowing flow rate is 50L / min, time is 14min), the nitrogen increase amount is 0.3654%, which is 90.38% of the target nitrogen increase amount.

[0127] (3) Stop the pressurized bottom blowing of nitrogen and continue to fill the furnace cavity with the nitrogen pressure required for casting (1.1 MPa) to carry out the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure (time is 2 minutes). The nitrogen increase amount is 0.0080%, which is 1.98% of the target nitrogen increase amount.

[0128] Table 3 shows the composition (%) of the 30Cr15Mo1N high nitrogen stainless steel ingot prepared in Example 3

[0129]

[0130]

[0131] It can be seen from Table 3 that Example 3 can efficiently and accurately obtain 30Cr15Mo1N high nitrogen stainless steel ingots with target nitrogen content.

[0132] Embodiment 4

[0133] The smelting equipment used is a 500kg pressurized induction furnace with a maximum operating pressure of 2.0MPa and a furnace load of 500kg.

[0134] According to formula [1], formula [2], formula [3], formula [7], formula [8] and formula [9], the target nitrogen content, smelting temperature, nitrogen pressure in each nitriding stage, nitriding time and bottom blowing flow rate are reasonably matched: the target nitrogen content of 30Cr15Mo1N high nitrogen stainless steel is 0.40%, and the whole process smelting temperature is about 1570℃. The nitrogen pressure in the gas phase nitrogen increase stage of the molten steel surface under the smelting nitrogen pressure is 0.43MPa, the time is 3min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00024m / s; the bottom blowing nitrogen pressure in the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stage is 0.48MPa, the bottom blowing flow rate is 55L / min, the time is 12min, and the gas phase nitriding area on the steel liquid surface is 0.1963m 2 The bottom blowing bubble nitriding area is 0.1813m 2 The total area of ​​vapor nitriding is 0.3776m 2 , the mass transfer coefficient is 0.00052m / s; and the nitrogen pressure in the gas phase nitrogenization stage on the surface of the molten steel under the casting nitrogen pressure is 1.2MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00024m / s.

[0135] The mass fractions of the alloy raw materials are as follows: C: 0.33%, Si: 0.50%, Mn: 0.53%, Cr: 15.23%, Mo: 1.00%, Ni: 0.21% and Fe (balance);

[0136] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25-0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00-16.00%, Mo: 0.85-1.10%, Ni: ≤0.50%, N: 0.30-0.50% and Fe (balance);

[0137] (1) In a pressurized induction furnace, the smelting temperature was stably controlled at about 1570°C, and a nitrogen pressure of 0.43 MPa was filled into the furnace chamber to perform gas phase nitriding of the molten steel (for 3 min) at the stage of gas phase nitrogen increase on the surface of the molten steel under the smelting nitrogen pressure. The nitrogen increase amount was 0.0319%, which was 7.94% of the target nitrogen increase amount.

[0138] (2) Further pressurized bottom blowing of nitrogen was started, and the output pressure of the nitrogen bottle was adjusted (0.78 MPa, P 损失 =0.3MPa) to control the bottom blowing nitrogen pressure (0.48MPa), and carry out pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage steel liquid gas phase nitriding (bottom blowing flow rate is 55L / min, time is 12min), the nitrogen increase amount is 0.3603%, which is 89.65% of the target nitrogen increase amount.

[0139] (3) Stop the pressurized bottom blowing of nitrogen and continue to fill the furnace cavity with the nitrogen pressure required for casting (1.2 MPa) to carry out the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure (time is 2 min). The nitrogen increase amount is 0.0097%, which is 2.41% of the target nitrogen increase amount.

[0140] Table 4 shows the composition (%) of the 30Cr15Mo1N high nitrogen stainless steel ingot prepared in Example 4

[0141] C Si Mn Cr Mo Ni N S P Fe 0.31 0.49 0.51 15.22 1.00 0.21 0.4019 0.006 0.007 margin

[0142] It can be seen from Table 4 that Example 4 can efficiently and accurately obtain 30Cr15Mo1N high nitrogen stainless steel ingots with target nitrogen content.

[0143] Embodiment 5

[0144] The smelting equipment used is a 500kg pressurized induction furnace with a maximum operating pressure of 2.0MPa and a furnace load of 500kg.

[0145] According to formula [1], formula [2], formula [3], formula [7], formula [8] and formula [9], the target nitrogen content, smelting temperature, nitrogen pressure in each nitriding stage, nitriding time and bottom blowing flow rate are reasonably matched: the target nitrogen content of 30Cr15Mo1N high nitrogen stainless steel is 0.40%, and the whole process smelting temperature is about 1600℃. The nitrogen pressure in the gas phase nitrogen increase stage of the molten steel surface under the smelting nitrogen pressure is 0.48MPa, the time is 3min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00025m / s; the bottom blowing nitrogen pressure in the pressurized vapor nitriding and bottom blowing nitrogen nitrogen increasing stages is 0.53MPa, the bottom blowing flow rate is 60L / min, the time is 10min, and the vapor nitriding area on the steel liquid surface is 0.1963m 2 The bottom blowing bubble nitriding area is 0.1905m 2 The total area of ​​vapor nitriding is 0.3868m 2 , the mass transfer coefficient is 0.00055m / s; and the nitrogen pressure in the gas phase nitrogenization stage on the surface of the molten steel under the casting nitrogen pressure is 1.2MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00025m / s.

[0146] The mass fractions of the alloy raw materials are as follows: C: 0.30%, Si: 0.50%, Mn: 0.52%, Cr: 15.01%, Mo: 1.00%, Ni: 0.23% and Fe (balance);

[0147] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25-0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00-16.00%, Mo: 0.85-1.10%, Ni: ≤0.50%, N: 0.30-0.50% and Fe (balance);

[0148] (1) In a pressurized induction furnace, the smelting temperature is stably controlled at about 1600°C, and a nitrogen pressure of 0.48 MPa is filled into the furnace chamber to perform gas phase nitriding of the molten steel under nitrogen pressure (time is 3 min) in the gas phase nitrogen increase stage of the molten steel surface. The nitrogen increase amount is 0.0333%, which is 8.27% of the target nitrogen increase amount.

[0149] (2) Further pressurized bottom blowing of nitrogen was started, and the output pressure of the nitrogen bottle was adjusted (0.83 MPa, P 损失 =0.3MPa) to control the bottom blowing nitrogen pressure (0.53MPa), and carry out pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage steel liquid gas phase nitriding (bottom blowing flow rate is 60L / min, time is 10min), the nitrogen increase amount is 0.3602%, which is 89.49% of the target nitrogen increase amount.

[0150] (3) Stop the pressurized bottom blowing of nitrogen and continue to fill the furnace cavity with the nitrogen pressure required for casting (1.2 MPa) to carry out the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure (time is 2 min). The nitrogen increase amount is 0.0090%, which is 2.24% of the target nitrogen increase amount.

[0151] Table 5 shows the composition (%) of the 30Cr15Mo1N high nitrogen stainless steel ingot prepared in Example 5

[0152] C Si Mn Cr Mo Ni N S P Fe 0.29 0.49 0.50 15.00 1.00 0.23 0.4011 0.006 0.009 margin

[0153] It can be seen from Table 5 that Example 5 can efficiently and accurately obtain a 30Cr15Mo1N high nitrogen stainless steel ingot with a target nitrogen content.

[0154] Embodiment 6

[0155] The smelting equipment used is a 500kg pressurized induction furnace with a maximum operating pressure of 2.0MPa and a furnace load of 500kg.

[0156] According to formula [1], formula [2], formula [3], formula [7], formula [8] and formula [9], the target nitrogen content, smelting temperature, nitrogen pressure in each nitriding stage, nitriding time and bottom blowing flow rate are reasonably matched: the target nitrogen content of 18Cr18Mn2Mo0.9N high nitrogen stainless steel is 0.90%, and the whole process smelting temperature is about 1550℃. The nitrogen pressure in the gas phase nitrogen increase stage of the molten steel surface under the smelting nitrogen pressure is 0.2MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00023m / s; the bottom blowing nitrogen pressure in the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stage is 0.24MPa, the bottom blowing flow rate is 47.5L / min, the time is 11min, and the gas phase nitriding area on the steel liquid surface is 0.1963m 2 The bottom blowing bubble nitriding area is 0.1669m 2 The total area of ​​vapor nitriding is 0.3632m 2 , the mass transfer coefficient is 0.00047m / s; and the nitrogen pressure in the gas phase nitrogenization stage on the surface of the molten steel under the casting nitrogen pressure is 0.8MPa, the time is 2min, and the gas phase nitriding area on the surface of the molten steel is 0.1963m 2 , the mass transfer coefficient is 0.00023m / s.

[0157] The mass fractions of the alloy raw materials are: C: 0.11%, Si: 0.51%, Mn: 18.02%, Cr: 18.01%, Mo: 1.80% and Fe (balance);

[0158] The target composition of 18Cr18Mn2Mo0.9N high nitrogen stainless steel is: C: ≤0.12%, Si: ≤0.80%, Mn: 17.50-20.00%, Cr: 17.50-20.00%, Mo: 1.50-2.50%, N: 0.75-1.00% and Fe (balance);

[0159] (1) In a pressurized induction furnace, the smelting temperature was stably controlled at about 1550°C, and a nitrogen pressure of 0.20 MPa was filled into the furnace chamber to perform gas phase nitriding of the molten steel under nitrogen pressure (time was 2 min) in the gas phase nitrogen increase stage of the molten steel surface. The nitrogen increase amount was 0.0489%, which was 5.39% of the target nitrogen increase amount.

[0160] (2) Further pressurized bottom blowing of nitrogen was started, and the output pressure of the nitrogen bottle was adjusted (0.54 MPa, P 损失 =0.3MPa) to control the bottom blowing nitrogen pressure (0.24MPa), and carry out pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage steel liquid gas phase nitriding (bottom blowing flow rate is 47.5L / min, time is 11min), the nitrogen increase amount is 0.8248%, which is 91.01% of the target nitrogen increase amount.

[0161] (3) Stop the pressurized bottom blowing of nitrogen and continue to fill the furnace cavity with the nitrogen pressure required for casting (0.8 MPa) to carry out the gas phase nitrogen increase stage on the surface of the molten steel under the casting nitrogen pressure (time is 2 minutes). The nitrogen increase amount is 0.0326%, which is 3.60% of the target nitrogen increase amount.

[0162] Table 6 shows the composition (%) of the 18Cr18Mn2Mo0.9N high nitrogen stainless steel ingot prepared in Example 6

[0163] C Si Mn Cr Mo N S P Fe 0.10 0.50 18.00 18.00 1.80 0.9063 0.007 0.009 margin

[0164] As can be seen from Table 6, Example 6 can efficiently and accurately obtain 18Cr18Mn2Mo0.9N high nitrogen stainless steel ingots with target nitrogen content. The above describes the basic principles, main features and advantages of the present invention. However, the above is only a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other implementation methods obtained by any technician in this field without departing from the technical solution of the present invention should be included in the patent scope of the present invention.

[0165] In the description of the present invention, each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0166] In the description of the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically limited. Moreover, the term "includes", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the sentence "comprising one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0167] In the present invention, unless otherwise clearly specified and limited, when a first feature is “on” or “below” a second feature, it may be that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, when a first feature is “above”, “above” or “above” a second feature, it may be that the first feature is directly above or obliquely above the second feature, or it may simply mean that the first feature is higher in level than the second feature. When a first feature is “below”, “below” or “below” a second feature, it may be that the first feature is directly below or obliquely below the second feature, or it may simply mean that the first feature is lower in level than the second feature.

[0168] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "embodiment", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0169] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen with high efficiency and precision, characterized in that: include: Step 1: operating in a pressurized induction furnace; stably controlling the smelting temperature, charging a first target nitrogen pressure into the furnace chamber of the pressurized induction furnace, entering a gas phase nitrogen increase stage on the surface of the molten steel, and performing gas phase nitriding under the smelting nitrogen pressure, wherein the nitrogen increase amount in the gas phase nitrogen increase stage on the surface of the molten steel is 5% to 10% of the target nitrogen content; Step 2: Perform pressurized bottom blowing of nitrogen, and control the bottom blowing nitrogen pressure and the bottom blowing flow rate by adjusting the output pressure of the nitrogen bottle; Entering the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stage, the steel liquid is gas phase nitrided under the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increasing stage, and the nitrogen increasing amount is 85% to 95% of the target nitrogen content; Step 3: stop pressurized bottom blowing nitrogen, continue to fill the furnace chamber of the pressurized induction furnace with the second target nitrogen pressure required for casting, and enter the stage of gas phase nitrogen increase on the surface of the molten steel under the casting nitrogen pressure. The amount of nitrogen increase in the stage of gas phase nitrogen increase on the surface of the molten steel under the casting nitrogen pressure is 1.5% to 5% of the target nitrogen content.

2. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen with high efficiency and precision according to claim 1, characterized in that: In step 1, the calculation formula for the first target nitrogen pressure in the smelting process in the pressurized induction furnace is: Among them, P 氮气 is the first target nitrogen pressure, P 0 is the standard atmospheric pressure, [%N] is the target nitrogen content, K N is the equilibrium constant of nitrogen dissolution reaction, T is the smelting temperature, is the first-order interaction coefficient of nitrogen with itself, is the first-order interaction coefficient of element j on N, is the second-order interaction coefficient of element j on N, and [% j] is the content of element j in steel.

3. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and accurate nitrogen addition according to claim 1, characterized in that: In step 1, in the stage of gas phase nitrogen addition on the surface of molten steel, the calculation formula for the nitrogen content of molten steel at time t is: Where, [%N] t is the nitrogen content of the molten steel at time t, k N is the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer during the gas phase nitrogen addition stage on the surface of molten steel under high nitrogen pressure, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​the molten steel, W is the weight of the molten steel, [% N] t-1 It is the nitrogen content in the molten steel at time t-1 during the gas phase nitrogen increase stage on the surface of the molten steel under smelting nitrogen pressure.

4. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen with high efficiency and precision according to claim 1, characterized in that: In step 2, the output pressure of the nitrogen cylinder is calculated as: P 输出 =P 底吹 +P 损失 =1.05×(P 氮气 +ρ 钢液 gh)+P 损失 ; Among them, P 输出 is the output pressure of the nitrogen cylinder, P 底吹 is the nitrogen bottle output pressure and bottom blowing pressure, P 氮气 is the first target nitrogen pressure, P 静压力 is the static pressure of molten steel, P 损失 is the nitrogen pressure lost in the bottom blowing pipeline, ρ 钢液 is the density of molten steel, g is the acceleration due to gravity, and h is the depth of molten steel.

5. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and accurate nitrogen addition according to claim 1, characterized in that: In step 2, the calculation formula for the bubble diameter generated by pressurized bottom blowing nitrogen is: Among them, d g is the bubble diameter generated by pressurized bottom blowing nitrogen, σ is the gas-liquid surface tension coefficient, d0 is the nozzle diameter of the bottom blowing air plug, Q g is the bottom blowing gas flow rate, ρ 钢液 is the density of molten steel, and g is the acceleration due to gravity.

6. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and accurate nitrogen addition according to claim 1, characterized in that: In step 2, the calculation formula for the rising speed of bubbles generated by pressurized bottom blowing nitrogen is: Where v is the rising velocity of bubbles generated by pressurized bottom blowing nitrogen, σ is the gas-liquid surface tension coefficient, and ρ 钢液 is the density of molten steel, g is the acceleration due to gravity, d g It is the bubble diameter generated by pressurized bottom blowing nitrogen.

7. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and accurate nitrogen addition according to claim 1, characterized in that: In step 2, the calculation formula for the surface area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing nitrogen process is: Among them, A 气泡 A is the surface area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing nitrogen process. g is the surface area of ​​a single bubble, Q g is the bottom blowing gas flow rate, V g is the volume of a single bubble, h is the depth of molten steel, r is the radius of the nitrogen bubble generated by pressurized bottom blowing nitrogen, and v is the rising speed of the bubble generated by pressurized bottom blowing nitrogen.

8. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and accurate nitrogen addition according to claim 1, characterized in that: In step 2, during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen increase stage, the calculation formula for the nitrogen content at time t is: in, is the nitrogen content at time t during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen addition stages, is the mass transfer coefficient of nitrogen atoms in the liquid boundary layer during the pressurized gas phase nitriding and bottom blowing nitrogen nitriding stages, is the nitrogen content at time t-1 during the pressurized gas phase nitriding and bottom blowing nitrogen nitrogen addition stage, A 气泡 is the surface area of ​​bubbles generated in the molten steel per unit time during the pressurized bottom blowing nitrogen process, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​molten steel, and W is the weight of molten steel.

9. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen with high efficiency and precision according to claim 1, characterized in that: In step 3, the calculation formula for the second target nitrogen pressure required for casting is: P 浇铸 =[(0.1~0.15)×P 氮气 / P 0 +(0.5~0.6)]; Among them, P 浇筑 The second target nitrogen pressure required for casting, P 氮气 is the first target nitrogen pressure, P 0 is standard atmospheric pressure.

10. The method for preparing high nitrogen steel by pressurized vapor nitriding and bottom blowing nitrogen for efficient and accurate nitrogen addition according to claim 1, characterized in that: In step 3, during the gas phase nitrogen addition stage on the surface of the molten steel under the casting nitrogen pressure, the calculation formula for the nitrogen content at time t is: Where, [%N] t * is the nitrogen content on the surface of the molten steel at time t during the gas phase nitrogen addition stage under the casting nitrogen pressure, is the nitrogen content on the surface of the molten steel at time t-1 during the gas phase nitrogen addition stage under the casting nitrogen pressure, [%N] is the target nitrogen content, k N is the mass transfer coefficient of nitrogen atoms in the liquid phase boundary layer during the gas phase nitrogen addition stage on the surface of molten steel under high nitrogen pressure, ρ 钢液 is the density of molten steel, A 表面 is the surface area of ​​molten steel, and W is the weight of molten steel.

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