A method for preparing a high-nitrogen steel powder with an ultra-high nitrogen content

Abstract

The application discloses a preparation method of high-nitrogen steel powder with super-high nitrogen content, and specifically comprises the following steps: adding high-nitrogen steel powder into a vacuum boiler with nitrogen gas flowing therethrough for heating, and continuously stirring the powder to uniformly heat the powder and avoid agglomeration; after proper heat preservation, opening a filter screen window under the boiler and a lower powder outlet of the boiler, and under the action of high-pressure nitrogen gas jet, the powder in the boiler is screened through the filter screen; the screened powder falls into a liquid nitrogen pool for rapid cooling and nitrogen dissolving treatment; after the powder is treated in the liquid nitrogen for a certain time, the filter screen at the bottom of the liquid nitrogen pool is opened to treat the excess liquid nitrogen and screen the powder, and finally, the high-nitrogen steel powder with super-high nitrogen content is obtained in the liquid nitrogen pool. The method can obtain the high-nitrogen steel powder with super-high nitrogen content on the basis of traditional high-nitrogen steel powder preparation, and has the advantages of simple process, low cost, high practicability, easy industrial production and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of high-nitrogen steel powder with super-high nitrogen content, and belongs to the field of preparation of high-nitrogen steel powder for additive manufacturing. BACKGROUND

[0002] High-nitrogen steel is a kind of steel developed in recent years, and is called high-nitrogen steel because the nitrogen content thereof is higher than that of ordinary nitrogen-containing stainless steel under normal pressure. At present, the nitrogen content of martensite / ferrite high-nitrogen steel is greater than 0.08%, and the nitrogen content of austenite high-nitrogen steel is higher than 0.4%. Nitrogen has the effect of stabilizing the austenite phase region, and to some extent, expands the austenite phase region and reduces the martensite formation phase region, so that the steel has good corrosion resistance. The high-nitrogen steel powder is currently mainly used in the field of additive manufacturing, especially in the process of selective laser melting forming. In additive manufacturing (AM), due to the characteristics of rapid cooling, fine grain structures will be formed in the sample, that is, obvious fine grain strengthening effect will occur in the grain, so that the strength and toughness of the high-nitrogen steel formed by traditional casting forming will be greatly improved, and the high-nitrogen steel obtained by additive manufacturing can maintain good corrosion resistance under the premise of ensuring strength and toughness. However, in the current research on additive manufacturing (especially selective laser melting forming technology), it is found that the Gaussian form of laser energy delivery in the process of additive manufacturing of high-nitrogen steel will cause loss of nitrogen content, that is, more nitrogen atoms will overflow from the sample, which will cause certain defects in the sample and weaken the advantages of high-nitrogen steel. At present, for offshore work ships, military and civilian aircraft and other fields, the existence of high-nitrogen steel materials with high strength and toughness and good corrosion resistance is particularly important. For traditional casting forming technology, the production and application of high-nitrogen steel have many shortcomings such as high cost and complex process, so it is difficult to quickly put into production. SUMMARY

[0003] The technical problem solved by the application is that the nitrogen content is obviously lost in the process of additive manufacturing of high-nitrogen steel, which finally leads to the decline of the performance of the material after additive manufacturing. A preparation method of high-nitrogen steel powder with super-high nitrogen content is provided, which provides a new idea for additive manufacturing of high-nitrogen steel.

[0004] There are two main starting points for the preparation methods of high-nitrogen stainless steel powder for additive manufacturing. On the one hand, appropriate alloy design can be used to achieve the required high nitrogen content in the steel, meeting the high nitrogen content requirements of high-nitrogen stainless steel. On the other hand, suitable preparation techniques can be employed to obtain the desired high-nitrogen steel, such as adding nitrides, or using methods like explosive methods, plasma methods, and aerosol methods. Different preparation methods are suitable for different additive manufacturing processes, but they all have some problems, such as the inability to dissolve as much nitrogen as possible in the high-nitrogen steel powder. Furthermore, they are relatively expensive and pose safety risks. Therefore, for current processes for preparing high-nitrogen steel powder, finding a method that is economical, stable, effective, safe, and environmentally friendly is of paramount importance. In addition, ensuring that the highest possible nitrogen content is stored in the steel during the production of high-nitrogen stainless steel is also a noteworthy issue.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] A method for preparing high-nitrogen steel powder with ultra-high nitrogen content is disclosed. This method is based on the traditional high-nitrogen steel powder and combines the characteristics of liquid nitrogen to achieve further nitrogen solid solution, thereby preparing high-nitrogen steel powder with ultra-high nitrogen content.

[0007] Step 1. Pour ordinary high-nitrogen steel powder into a boiler, heat and keep it at a constant temperature, create a vacuum environment, use nitrogen as a protective gas, and continuously stir the powder in the boiler with a stirring rod. The boiler temperature is the solid-liquid critical temperature of the powder, the holding time is 30 minutes, the oxygen content is less than 500 ppm, and the pressure inside the boiler is 65-70 mbar.

[0008] Step 2. The heated powder from Step 1 is screened through a 300-mesh stainless steel filter to obtain usable heat-insulated high-nitrogen steel powder.

[0009] Step 3. The powder screened in Step 2 is blown into a liquid nitrogen tank using a nitrogen jet. The powder is retained in the liquid nitrogen tank for 10-20 minutes. When the nitrogen jet device is working, the nozzle is kept 75 mm away from the surface of the powder, and the nitrogen flow rate is greater than 5 L / min and less than or equal to 20 L / min, with a preferred flow rate range of 5-10 L / min.

[0010] Step 4. After passing the excess liquid nitrogen from Step 3 through a 1000-mesh stainless steel sieve, the usable powder will be retained in the liquid nitrogen pool, and finally, high-nitrogen steel powder with ultra-high nitrogen content will be obtained.

[0011] Compared with the prior art, the present invention has the following significant advantages: 1) the process is simple and fast; 2) it is easy to prepare high-nitrogen steel powder with ultra-high nitrogen content in large quantities; 3) the cost is low; 4) the obtained powder has good sphericity and high purity, which is beneficial to the subsequent selective laser melting additive manufacturing process.

[0012] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the preparation method of high-nitrogen steel powder with ultra-high nitrogen content.

[0014] Figure 2 This is a schematic diagram of the apparatus for preparing high-nitrogen steel powder with ultra-high nitrogen content.

[0015] Figure 3 This is a morphology diagram of the ultra-high nitrogen content high-nitrogen steel powder prepared using this method in Example 1.

[0016] Figure 4 This is the XRD phase analysis diagram of the high-nitrogen steel powder prepared in Example 1.

[0017] Figure 5 This is an EBSD phase distribution diagram of the powder cross section of the high-nitrogen steel powder prepared in Example 1.

[0018] Figure 6 This is a powder average particle size distribution diagram of the high-nitrogen steel powder prepared in Example 2.

[0019] Figure 7 This is a powder morphology diagram of the high-nitrogen steel powder prepared in Example 2.

[0020] Figure 8 This is a particle size distribution diagram of the high-nitrogen steel powder prepared in Example 3.

[0021] Table 1 shows the composition of two existing high-nitrogen steel powder raw materials.

[0022] Table 2 shows the comparison results of nitrogen content of the three powders in Examples 1, 2 and 3.

[0023] Among them, 1 is the outer base of the liquid nitrogen tank, 2 is the support column of the liquid nitrogen tank, and 3 is the liquid nitrogen tank ( Figure 2 1. Liquid nitrogen (below the red line), 2. Positioning pin, 3. External base of the device, 4. Boiler, 5. Nitrogen protective gas inlet, 6. Nitrogen inlet, 7. Gas flow channel valve (red part), 8. Nitrogen jet inlet, 9. Boiler vacuum protection cover, 10. Oxygen content detector, 11. Boiler stirring rod, 12. Exhaust port for vacuuming, 13. Pressure testing element, 14. Fixing screw, 15. Stirring rod support, 16. Temperature measuring element, 17. 300-mesh stainless steel filter (blue line part), 20. Positioning pin, 21. 1000-mesh stainless steel filter (blue line part), 22. Push rod, 23. Excess liquid nitrogen container (magenta represents the left and right walls of the boiler). Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] Combination Figure 1 The present invention discloses a method for preparing high-nitrogen steel powder with ultra-high nitrogen content, comprising the following steps:

[0026] Step 1: Pour nearly spherical high-nitrogen steel powder with a particle size of 15-53 μm into the boiler, cover the boiler with a vacuum protective cover, and heat the boiler to the solid-liquid critical temperature of the added powder, followed by a heat preservation treatment of about 30 minutes. The entire process is conducted in a vacuum environment, with the oxygen content maintained below 500 ppm and the pressure inside the boiler maintained at 65-70 mbar. After covering the vacuum protective cover, open the ordinary nitrogen gas flow valve to introduce nitrogen into the environment around the boiler, using nitrogen as a protective gas. During this process, the stirring rod continuously stirs the powder in the boiler, ensuring uniform heating and preventing agglomeration.

[0027] Step 2: The heated powder from Step 1 is screened through a 300-mesh stainless steel filter to obtain a near-spherical high-nitrogen steel powder with a particle size range of 15-48μm, which can be used for additive manufacturing.

[0028] Step 3: Close the ordinary nitrogen gas flow valve, increase the gas supply pressure, and simultaneously open the nitrogen jet channel valve. Blow the powder selected in Step 2 into the liquid nitrogen pool using a nitrogen jet. The powder should remain in the liquid nitrogen pool for 10-20 minutes. During operation, the nozzle of the nitrogen jet device should be 75mm away from the surface of the powder, and the nitrogen flow rate should be greater than 5L / min and less than or equal to 20L / min, with the optimal flow rate range being 5-10L / min.

[0029] Step 4: After passing the excess liquid nitrogen from Step 3 through a 1000-mesh stainless steel sieve, the liquid nitrogen flows into an excess liquid nitrogen container for recovery. Usable ultra-high nitrogen content high-nitrogen steel powder is retained in the liquid nitrogen pool, resulting in final ultra-high nitrogen content high-nitrogen steel powder. The particle size of the final high-nitrogen steel powder is controlled within the range of 15-48 μm, and the shape is nearly spherical, making it suitable for selective laser melting forming (SLM) additive manufacturing processes.

[0030] The high-nitrogen steel powder of this invention has a higher nitrogen content than ordinary high-nitrogen steel powders currently on the market. Therefore, this high-nitrogen steel powder is more suitable for additive manufacturing fields such as selective laser melting (DED), where significant nitrogen content loss occurs during processing. Furthermore, the high nitrogen content can, to some extent, avoid phase changes caused by variations in nitrogen content during the additive manufacturing process of high-nitrogen steel, thus preventing a significant difference in the performance of the additively manufactured sample compared to the actual high-nitrogen steel material. The method for preparing high-nitrogen steel powder of this invention can be said to have improved and promoted the development of high-nitrogen steel in the additive manufacturing field to a certain extent. The two existing high-nitrogen steel powder raw materials used in this invention have good sphericity and conform to the national standard GB / T 14265–2017. One high-nitrogen steel powder has a nitrogen content of 0.81%, and the other has a nitrogen content of 0.45%, the specific compositions of which are shown in Table 1 below. The particle size of both high-nitrogen steel powders is 15–53 μm.

[0031] Table 1. Composition of two existing high-nitrogen steel powder raw materials

[0032]

[0033] In addition to the above, such as Figure 2 This device can prepare large quantities of ultra-high nitrogen steel. Since liquid nitrogen is mainly used in the nitrogen dissolution process and nitrogen protection is maintained throughout the powder heating process, it can ensure that the prepared ultra-high nitrogen steel powder will not contain any impurities other than its own elements. It can also ensure that only the nitrogen content changes, while other elements do not change significantly, thus ensuring high purity.

[0034] The device of the present invention includes a liquid nitrogen tank outer base 1, a liquid nitrogen tank support column 2, a liquid nitrogen tank 3, a positioning pin 4, a device outer base 5, a boiler 6, a nitrogen protective gas inlet 7, a nitrogen inlet 8, an airflow channel valve 9, a nitrogen jet inlet 10, a boiler vacuum protection cover 11, an oxygen content detector 12, a boiler retractable stirring rod 13, an exhaust port for vacuuming 14, a pressure testing element 15, a fixing screw 16, a stirring rod bracket 17, a temperature measuring element 18, a 300-mesh stainless steel filter screen 19, a positioning pin 20, a 1000-mesh stainless steel filter screen 21, a push rod 22, and an excess liquid nitrogen container 23.

[0035] The entire device is mounted on the outer base 5.

[0036] Boiler 6 is located beneath the boiler vacuum protection hood 11, and liquid nitrogen tank 3 is located beneath boiler 6. A 300-mesh stainless steel filter screen 19 is installed between boiler 6 and liquid nitrogen tank 3. An excess liquid nitrogen container 23 is located beneath liquid nitrogen tank 3, and a 1000-mesh stainless steel filter screen 21 is installed between liquid nitrogen tank 3 and excess liquid nitrogen container 23. The boiler 6, liquid nitrogen tank 3, and excess liquid nitrogen container 23 within the boiler vacuum protection hood 11 provide a reaction space for the preparation of high-nitrogen steel powder. A nitrogen protective gas inlet 7, a nitrogen inlet 8, an airflow channel valve 9, a nitrogen jet inlet 10, and an oxygen content meter are respectively installed on the vacuum protection hood 11 of boiler 6. The boiler 6 includes a detector 12, an exhaust port 14 for vacuuming, a pressure testing element 15, and a temperature measuring element 18. A retractable stirring rod 13 for powder mixing is fixed inside the boiler 6 via fixing screws 16 and a stirring rod bracket 17. A 300-mesh stainless steel filter screen 16 at the bottom of the boiler 6 has a positioning pin 4 and a positioning pin 20 at each end. A 1000-mesh stainless steel filter screen 18 has the same structure at both ends. A liquid nitrogen tank 3 has a liquid nitrogen tank support column 2, which is mounted on the outer base 1 of the liquid nitrogen tank. Push rods 22 are provided for the 300-mesh stainless steel filter screen 19, the 1000-mesh stainless steel filter screen 21, and the excess liquid nitrogen container 23.

[0037] The main body and boiler of the device used in this invention are made of cast iron, which is low in cost and durable. The stainless steel filter screens are all made of 316L material.

[0038] Further, the exhaust port used for vacuuming requires an external vacuuming device during the exhaust process.

[0039] Furthermore, the nozzle device used for nitrogen jetting is telescopic for more efficient powder handling.

[0040] In addition, boiler control, vacuuming and exhaust, nitrogen jetting, stirring rod stirring, filter screening, removal of final powder and residual liquid nitrogen, etc. can all be set up and operated in a unified control system. It adopts touch screen operation, which makes it convenient for users to input different parameters such as heat preservation time, oxygen content, chamber pressure, and retention time in liquid nitrogen for different high-nitrogen steel powders.

[0041] The device used in this invention has a simple principle and structure, is easy to disassemble and clean, and can be used with various types of high-nitrogen steel powders. The used liquid nitrogen can be recycled and reused, making it energy-saving and environmentally friendly.

[0042] The present invention will be further described in detail below with reference to embodiments:

[0043] Example 1

[0044] Take, for example, a high-nitrogen steel powder with a nitrogen content of 0.81% that can be used for selective laser melting additive manufacturing.

[0045] 1. Pour the high-nitrogen steel powder into the boiler, cover it with the boiler vacuum protective cover, open the ordinary nitrogen gas channel, and introduce nitrogen as a protective gas. Gradually raise the boiler temperature to the solid-liquid critical temperature of the high-nitrogen steel powder, and then perform a 30-minute heat treatment. Maintain a vacuum environment throughout the process, keeping the oxygen content below 500 ppm and the boiler pressure at 65-70 mbar. During boiler heating, continuously stir the high-nitrogen steel powder in the boiler using a stirring rod.

[0046] 2. After the high-nitrogen steel powder is heated and kept at a constant temperature, it is pushed into a 300-mesh stainless steel filter screen to screen the powder, and finally high-nitrogen steel powder with a particle size of 15-48μm is obtained.

[0047] 3. Close the normal nitrogen channel and open the nitrogen jet channel, keeping the flow rate at 5-10 L / min. Blow the powder into the liquid nitrogen tank in the direction of the filtered powder.

[0048] 4. After all the powder has entered the liquid nitrogen pool, after the powder has been retained in the liquid nitrogen pool for 10-20 minutes, it is pushed into a 1000-mesh stainless steel filter screen. The excess liquid nitrogen flows into the excess liquid nitrogen container for liquid nitrogen recovery. The final high-nitrogen steel powder with ultra-high nitrogen content is obtained in the liquid nitrogen pool. The final powder particle size is 15-48μm.

[0049] After the above steps, the high-nitrogen steel powder obtained underwent nitrogen content testing using an inductively coupled plasma optical emission spectrometer (ICAP PRO X) according to national standard GB / T 14265-2017. The final nitrogen content of the high-nitrogen steel powder was 1.3563%, classifying it as ultra-high nitrogen content high-nitrogen steel powder. The average powder particle size (D) was measured using an ultra-high-speed intelligent laser particle size analyzer (Mastersize3000, Malvern) according to national standard GB / T 19077. 50 The particle size was 35 μm. According to the national standard GB / T 1482, the Hall flow rate of the powder was 16.4 s / 50 g, indicating good powder flowability. Furthermore, the morphology of the powder was observed using electron microscopy, as shown below. Figure 3 As can be seen from the figure, the high-nitrogen steel powder with ultra-high nitrogen content prepared by this method has good sphericity. Furthermore, phase diffraction (XRD) analysis reveals that the main constituent phase of the powder is austenite, as shown below. Figure 4 As shown, and through backscatter diffraction (EBSD) analysis, based on the following... Figure 5 The phase distribution diagram shows that the austenite phase is relatively uniformly distributed. Further powder observation and testing confirm that this ultra-high nitrogen content steel meets the requirements for high-nitrogen steel, meaning that the above method can successfully prepare ultra-high nitrogen content high-nitrogen steel.

[0050] Example 2

[0051] Using the same high-nitrogen steel powder as in Example 1, but with different process parameters.

[0052] 1. Pour the high-nitrogen steel powder into the boiler, cover it with the boiler vacuum protective cover, open the ordinary nitrogen gas channel, and introduce nitrogen as a protective gas. Gradually raise the boiler temperature to the solid-liquid critical temperature of the high-nitrogen steel powder, and then perform a 60-minute heat treatment. Maintain a vacuum environment throughout the process, keeping the oxygen content below 500 ppm and the boiler pressure at 65-70 mbar. During boiler heating, continuously stir the high-nitrogen steel powder in the boiler using a stirring rod.

[0053] 2. After the high-nitrogen steel powder is heated and kept at a constant temperature, it is pushed into a 300-mesh stainless steel filter screen to screen the powder, and finally high-nitrogen steel powder with a particle size of 15-48μm is obtained.

[0054] 3. Close the normal nitrogen channel and open the nitrogen jet channel, keeping the flow rate at 30L / min. Blow the powder into the liquid nitrogen tank in the direction of the filtered powder.

[0055] 4. After all the powder has entered the liquid nitrogen pool, after the powder has been retained in the liquid nitrogen pool for 10-20 minutes, it is pushed into a 1000-mesh stainless steel filter screen. The excess liquid nitrogen flows into the excess liquid nitrogen container for liquid nitrogen recovery. The final high-nitrogen steel powder with ultra-high nitrogen content is obtained in the liquid nitrogen pool. The final powder particle size is 15-48μm.

[0056] After the above steps, the high-nitrogen steel powder obtained underwent nitrogen content testing using an inductively coupled plasma optical emission spectrometer (ICAP PRO X) according to national standard GB / T 14265-2017. The final nitrogen content of the high-nitrogen steel powder was 0.63%, classifying it as ultra-high-nitrogen steel powder. Using an ultra-high-speed intelligent laser particle size analyzer (Mastersize3000, Malvern), the average powder particle size (D50) was measured to be 39.9 μm according to national standard GB / T 19077, as follows: Figure 6 As shown. The Hall flow rate of the powder, measured according to national standard GB / T 1482, was 23 s / 50 g, indicating good powder flowability. In addition, the morphology of the powder was observed using electron microscopy, as shown below. Figure 7As shown in the figure, under these process parameters, the sphericity of the powder is poor, and powder stacking occurs on the powder surface. This phenomenon may be related to the flow rate of the nitrogen jet; an excessively high flow rate causes the powder to be impacted, resulting in physical collisions between powder particles, leading to a decrease in sphericity and an increase in average grain size, which affects its use in additive manufacturing. Furthermore, because the high-nitrogen steel powder used as raw material was kept at room temperature in the boiler for a long time, a significant amount of nitrogen content was lost from the powder, failing to achieve the desired nitrogen enrichment effect. Therefore, controlling the holding time is equally important.

[0057] Example 3

[0058] Take, for example, a high-nitrogen steel powder with a nitrogen content of 0.45% that can be used for selective laser melting.

[0059] The process is essentially the same as in Example 1, except for the different raw materials used to prepare the ultra-high nitrogen content high-nitrogen steel powder and the different retention time in the liquid nitrogen bath. In this process, the high-nitrogen steel raw material is only kept in liquid nitrogen for 2-5 minutes after being heated. The resulting high-nitrogen steel powder was then tested for nitrogen content using the same testing equipment, an inductively coupled plasma optical emission spectrometer (ICAP PRO X), according to national standard GB / T 14265-2017. The nitrogen content in the high-nitrogen steel was found to be 0.49%. Using an ultra-high-speed intelligent laser particle size analyzer (Mastersize 3000, Malvern), according to national standard GB / T 19077, the average powder particle size (D50) was measured to be 34.1 μm, as follows: Figure 8 As shown. Additionally, the Hall flow rate of this powder is 18.1 gs / 50g. The change in nitrogen content in this powder indicates that if the high-nitrogen steel powder is held in liquid nitrogen for too short a time after heat treatment, insufficient time is allowed for nitrogen to diffuse into the powder, resulting in a poor nitrogen-enhancing effect. Therefore, it is necessary to hold the powder in liquid nitrogen for an appropriate time.

[0060] The nitrogen content in the high-nitrogen steel powders of the three embodiments above is compared in Table 2 below. The comparison shows that the process parameters in this invention have a better preparation effect on high-nitrogen steel powders with ultra-high nitrogen content. Furthermore, the equipment used in the preparation process involved in this invention also plays a significant role in improvement.

[0061] Table 2. Comparison of powder nitrogen content in Examples 1, 2 and 3

[0062] Original powder nitrogen content / % Final powder nitrogen content / % Notes 0.81 1.3563 Using the process in the invention 0.81 0.63 Soaking time and jet velocity changes 0.45 0.49 Changes in time remaining in the liquid nitrogen bath

Claims

1. A method for preparing high-nitrogen steel powder with ultra-high nitrogen content, characterized in that, The method includes the following steps: Step 1. Pour the existing high-nitrogen steel powder into the boiler, heat and keep it at a constant temperature, while the stirring rod continuously stirs the powder in the boiler. In Step 1, the boiler's holding temperature is the solid-liquid critical temperature of the high-nitrogen steel powder, the holding time is 30 min, the oxygen content is less than 500 ppm, and the boiler pressure is 65-100 mbar. Step 2. The heated powder from Step 1 is sieved to obtain usable powder; Step 3. Flow the powder screened in Step 2 into the liquid nitrogen pool; In step 3, nitrogen jetting is used to propel the powder into the liquid nitrogen pool rapidly, where the powder remains for 10-20 minutes. During operation, the nozzle of the nitrogen jetting device is kept 75 mm away from the surface of the powder, and the nitrogen flow rate is greater than 5 L / min and less than or equal to 20 L / min. Step 4. The excess liquid nitrogen from Step 3 is drained through a sieve, and the usable powder remains in the liquid nitrogen pool to obtain high-nitrogen steel powder with ultra-high nitrogen content.

2. The method for preparing high-nitrogen steel powder with ultra-high nitrogen content according to claim 1, characterized in that, In step 1, the boiler environment is kept under vacuum and nitrogen is introduced as a protective gas.

3. The method for preparing high-nitrogen steel powder with ultra-high nitrogen content according to claim 1, characterized in that, In step 2, the selected sieve mesh size is 300 mesh.

4. The method for preparing high-nitrogen steel powder with ultra-high nitrogen content according to claim 1, characterized in that, The flow rate of nitrogen is controlled within the range of 5 to 10 L / min.

5. The method for preparing high-nitrogen steel powder with ultra-high nitrogen content according to claim 1, characterized in that, In step 4, the selected sieve mesh is 1000 mesh.

6. The method for preparing high-nitrogen steel powder with ultra-high nitrogen content according to claim 1, characterized in that, The selected screen material is stainless steel.

7. An apparatus for preparing high-nitrogen steel powder with ultra-high nitrogen content as described in any one of claims 1-6, characterized in that, include: Boiler, liquid nitrogen tank, stainless steel filter screen, vacuum protective cover; The boiler is located under the boiler vacuum protection cover. A liquid nitrogen tank is installed under the boiler. A 300-mesh stainless steel filter screen is installed between the boiler and the liquid nitrogen tank. An excess liquid nitrogen container is installed under the liquid nitrogen tank. A 1000-mesh stainless steel filter screen is installed between the liquid nitrogen tank and the excess liquid nitrogen container. The boiler, liquid nitrogen tank, and excess liquid nitrogen container inside the boiler vacuum protection hood provide a reaction space for the preparation of high-nitrogen steel powder. The vacuum protection cover of the boiler is equipped with a nitrogen protective gas inlet, a nitrogen inlet, an airflow channel valve, a nitrogen jet inlet, an oxygen content detector, an exhaust port for vacuuming, a pressure testing element, and a temperature measuring element. The boiler's retractable stirring rod, used for powder mixing, is fixed inside the boiler by fixing screws and a stirring rod bracket. The 300-mesh stainless steel filter screen at the bottom of the boiler is equipped with positioning pins and positioning pins at both ends, and the 1000-mesh stainless steel filter screen is also equipped with the same structure at both ends. The liquid nitrogen tank is equipped with a liquid nitrogen tank support column, which is set on the base outside the liquid nitrogen tank; The 300-mesh stainless steel filter, the 1000-mesh stainless steel filter, and the excess liquid nitrogen container are all equipped with push rods.

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