Preparation method of high-nitrogen steel powder with ultrahigh nitrogen content

Abstract

The invention discloses a preparation method of high-nitrogen steel powder with ultrahigh nitrogen content, which specifically comprises the following steps: adding the high-nitrogen steel powder into a vacuum boiler filled with nitrogen for heating, and continuously stirring to uniformly heat the powder and avoid agglomeration at the same time; after heat preservation is conducted for a proper time, a filter screen window below the boiler is opened, meanwhile, a lower powder outlet of the boiler is opened, and powder in the boiler is screened through a filter screen under the action of high-pressure nitrogen jet flow; the screened powder falls into a liquid nitrogen pool for rapid cooling and nitrogen dissolving treatment; and after the powder is treated by liquid nitrogen for a certain time, a filter screen at the bottom of the liquid nitrogen pool is opened to treat redundant liquid nitrogen and screen the powder, and finally the high-nitrogen steel powder with the ultrahigh nitrogen content is obtained in the liquid nitrogen pool. According to the method, the high-nitrogen steel powder with the ultrahigh nitrogen content can be obtained on the basis of traditional high-nitrogen steel powder preparation, and the method has the advantages of being simple in process, low in cost, high in practicability, convenient to achieve industrial production and the like.

Description

Technical Field

[0001] The invention relates to a method for preparing high nitrogen steel powder with ultra-high nitrogen content, and belongs to the field of preparation of high nitrogen steel powder for additive manufacturing. Background Art

[0002] High nitrogen steel is a type of steel introduced in recent years. Because its nitrogen content at normal pressure is higher than that of ordinary nitrogen-containing stainless steel, it is called high nitrogen steel. At present, for martensitic / ferritic high nitrogen steel, its nitrogen content is greater than 0.08%, and for austenitic high nitrogen steel, its nitrogen content is higher than 0.4%. Nitrogen has the function of stabilizing the austenite phase, expanding the austenite phase to a certain extent, and reducing the martensite formation phase, so this type of steel has good corrosion resistance. High nitrogen steel powder is currently mainly used in the field of additive manufacturing, especially the selective laser melting forming process. Under additive manufacturing (AM), due to the characteristics of rapid cooling of this process, a fine grain structure will be formed inside the sample to a large extent, that is, a significant fine grain strengthening effect will be produced inside the grain. Under this, compared with the traditional casting high nitrogen steel, its strength and toughness will be greatly improved, and through the characteristics of nitrogen stabilizing the austenite phase, the high nitrogen steel obtained under additive manufacturing can maintain excellent corrosion resistance while ensuring strength and toughness. However, in the current research on additive manufacturing (especially the selective laser melting forming technology), it is found that this Gaussian form of laser energy transfer will cause a loss of nitrogen content in the process of additive manufacturing of high nitrogen steel, that is, more nitrogen atoms will overflow from the sample, which will cause certain defects inside the sample, and on the other hand, it will weaken the advantages of the high nitrogen steel material itself. At present, for offshore vessels, military and civilian aircraft and other fields, the existence of this high nitrogen steel material 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 has many disadvantages such as high cost and complex process, so it is difficult to quickly put it into production. Summary of the invention

[0003] The technical problem solved by the present invention is: to solve the problem that the nitrogen content is obviously lacking in the additive manufacturing process of high nitrogen steel, which ultimately leads to the degradation of the performance of the material after additive manufacturing, a method for preparing high nitrogen steel powder with ultra-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 method of high nitrogen stainless steel powder for additive manufacturing. On the one hand, the nitrogen content in the steel can meet the high nitrogen content requirements of high nitrogen stainless steel through appropriate alloy design. On the other hand, the required high nitrogen steel can be obtained by adopting appropriate preparation technology, such as adding nitrides or explosion method, plasma method and aerosol method. Different preparation methods are suitable for different additive manufacturing processes, but there are some problems, such as the inability to dissolve as much nitrogen as possible in high nitrogen steel powder. In addition, the cost is relatively high and there are safety risks. In this regard, for the current process preparation method for high nitrogen steel powder, it is most important to find a method that is economically efficient, stable, effective, safe and environmentally friendly. In addition, in the production and preparation process of high nitrogen stainless steel, it is also a problem worthy of attention to store as high a nitrogen content as possible in the steel.

[0005] The technical solution to achieve the purpose of the present invention is:

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

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

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

[0009] Step 3. Blow the powder screened in step 2 into the liquid nitrogen pool by nitrogen jet, and keep the powder in the liquid nitrogen pool for 10-20 minutes. When the nitrogen jet device is working, the nozzle is kept 75mm away from the outermost layer of the powder, and the flow rate of nitrogen is greater than 5L / min and less than or equal to 20L / min, and the preferred flow rate range is controlled at 5-10L / min.

[0010] Step 4. The excess liquid nitrogen in step 3 is passed through a 1000-mesh stainless steel screen and then flows out. The usable powder will remain in the liquid nitrogen pool, and high nitrogen steel powder with ultra-high nitrogen content will eventually be obtained.

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

[0012] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a process flow chart of a method for preparing high nitrogen steel powder with ultra-high nitrogen content.

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

[0015] Figure 3 This is a morphology picture of high nitrogen steel powder with ultra-high nitrogen content prepared by 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 the EBSD phase distribution diagram of the powder cross section of the high nitrogen steel powder prepared in Example 1.

[0018] Figure 6 3 is a graph showing the average particle size distribution of the high nitrogen steel powder prepared in Example 2.

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

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

[0021] Table 1 is a table of the composition of two existing high nitrogen steel powder raw materials.

[0022] Table 2 is a comparison table of nitrogen contents of the three powders in Examples 1, 2 and 3.

[0023] Among them, 1 is the outer base of the liquid nitrogen pool, 2 is the support column of the liquid nitrogen pool, and 3 is the liquid nitrogen pool ( Figure 2 Below the red line in the middle is liquid nitrogen), 4 is a positioning pin, 5 is the outer base of the device, 6 is a boiler, 7 is the nitrogen protective gas inlet, 8 is the nitrogen vent, 9 is the air flow channel valve (red part), 10 is the nitrogen jet inlet, 11 is the boiler vacuum protection cover, 12 is the oxygen content detector, 13 is the boiler stirring rod, 14 is the exhaust port for vacuuming, 15 is the pressure test element, 16 is the fixing screw, 17 is the stirring rod bracket, 18 is the temperature measuring element, 19 is a 300-mesh stainless steel filter (blue line part), 20 is a positioning pin, 21 is a 1000-mesh stainless steel filter (blue line part), 22 is a push rod, and 23 is a pot for holding excess liquid nitrogen (the left and right walls of the boiler are represented by magenta). DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings

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

[0026] Step 1: Pour nearly spherical high nitrogen steel powder with a particle size of 15-53μm into the boiler, cover the boiler vacuum protection cover, heat the boiler to the solid-liquid critical temperature of the added powder, and then carry out insulation treatment for about 30 minutes. The whole process is in a vacuum environment, the oxygen content is kept below 500ppm, and the pressure in the boiler is maintained at 65-70mbar. After covering the vacuum protection cover, open the ordinary nitrogen gas flow valve, and introduce nitrogen into the surrounding environment of the boiler, using nitrogen as a protective gas. During this process, the stirring rod is continuously stirred in the boiler to ensure that the powder is heated evenly and avoid agglomeration.

[0027] Step 2: The powder heated in step 1 is screened through a 300-mesh stainless steel filter to obtain a metal powder that can be used for additive manufacturing, and the particle size range is 15-48 μm, and the nearly spherical high nitrogen steel powder.

[0028] Step 3: Close the valve of the ordinary nitrogen gas flow, increase the gas supply pressure, and at the same time, open the valve of the nitrogen jet channel, and blow the powder screened in step 2 into the liquid nitrogen pool by means of nitrogen jet, and keep the powder in the liquid nitrogen pool for 10-20 minutes. When the nitrogen jet device is working, the nozzle is kept 75mm away from the outermost layer of the powder, the flow rate of nitrogen is greater than 5L / min and less than or equal to 20L / min, and the best flow rate range of nitrogen is controlled at 5-10L / min.

[0029] Step 4: The excess liquid nitrogen in step 3 is passed through a 1000-mesh stainless steel screen and flows into the excess liquid nitrogen container for liquid nitrogen recovery. The available ultra-high nitrogen content high nitrogen steel powder will be retained in the liquid nitrogen pool, and the final ultra-high nitrogen content high nitrogen steel powder will be obtained, wherein the particle size range of the final high nitrogen steel powder is controlled within the range of 15-48 μm, and the shape is nearly spherical, which can be used for the additive manufacturing process of selective laser melting.

[0030] The ultra-high nitrogen content high nitrogen steel powder of the present invention has a higher nitrogen content than the general high nitrogen steel powder on the market, so the high nitrogen steel powder is more suitable for some additive manufacturing fields (such as DED) such as selective laser melting, which will cause more nitrogen content loss during the manufacturing process. And the high nitrogen content can avoid the phase change caused by the change of nitrogen content in the process of additive manufacturing of high nitrogen steel to a certain extent, which leads to the phenomenon that the performance of the sample after additive manufacturing and the performance of the high nitrogen steel material are very different. The method for preparing high nitrogen content high nitrogen steel powder of the present invention can be said to improve and promote the development of high nitrogen steel in the field of additive manufacturing to a certain extent. The two existing high nitrogen steel powder raw materials used in the present invention have good sphericity and meet the national standard GB / T 14265-2017. The nitrogen content of one high nitrogen steel powder is 0.81%, and the nitrogen content of the other high nitrogen steel powder is 0.45%. The specific composition can be seen in Table 1 below. Among them, the particle size of the two high nitrogen steel powders is 15-53μm.

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

[0032]

[0033] In addition to the above, if Figure 2 The device can prepare large quantities of high-nitrogen steel with ultra-high nitrogen content. In the nitrogen dissolving process, liquid nitrogen is mainly used, and nitrogen protection is provided throughout the powder heating process. This can ensure to the greatest extent that the prepared high-nitrogen steel powder with ultra-high nitrogen content will not contain impurities other than its own elements. It can also ensure to a certain extent that only the nitrogen content changes, and other elements will not change significantly, and the purity is well guaranteed.

[0034] The device of the present invention comprises a liquid nitrogen pool outer base 1, a liquid nitrogen pool support column 2, a liquid nitrogen pool 3, a positioning pin 4, a device outer base 5, a boiler 6, a nitrogen protective gas inlet 7, a nitrogen gas outlet 8, an air flow channel valve 9, a nitrogen jet inlet 10, a boiler vacuum protection cover 11, an oxygen content detector 12, a boiler telescopic stirring rod 13, an exhaust port 14 for vacuuming, 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 19, a positioning pin 20, a 1000-mesh stainless steel filter 21, a push rod 22, and an excess liquid nitrogen containing pot 23.

[0035] The entire device is arranged on an outer base 5 of the device.

[0036] Among them, the boiler 6 is under the boiler vacuum protection cover 11, and a liquid nitrogen pool 3 is arranged under the boiler 6. A 300-mesh stainless steel filter 19 is arranged between the boiler 6 and the liquid nitrogen pool 3. An excess liquid nitrogen storage pot 23 is arranged under the liquid nitrogen pool 3, and a 1000-mesh stainless steel filter 21 is arranged between the liquid nitrogen pool 3 and the excess liquid nitrogen storage pot 23; the boiler 6, the liquid nitrogen pool 3, and the excess liquid nitrogen storage pot 23 in the boiler vacuum protection cover 11 provide a reaction space for preparing high nitrogen steel powder; a nitrogen protective gas inlet 7, a nitrogen gas outlet 8, an air flow channel valve 9, a nitrogen jet inlet 10, an oxygen content Detector 12, exhaust port 14 for vacuuming, pressure testing element 15, temperature measuring element 18; boiler retractable stirring rod 13 for powder stirring is fixed in boiler 6 by fixing screw 16 and stirring rod bracket 17; 300 mesh stainless steel filter 16 at the bottom of boiler 6 is provided with positioning pin 4 and positioning pin 20 at both ends respectively; 1000 mesh stainless steel filter 18 is also provided with the same structure at both ends; liquid nitrogen pool 3 is provided with liquid nitrogen pool support column 2, and is arranged on the outer base 1 of liquid nitrogen pool; 300 mesh stainless steel filter 19, 1000 mesh stainless steel filter 21, and excess liquid nitrogen holding pot 23 are all provided with push rod 22.

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

[0038] It is further provided that the exhaust port used for vacuuming needs to be connected to an external vacuuming device during the exhausting process.

[0039] It is further provided that the nozzle device for nitrogen jetting is telescopic to treat the powder more effectively.

[0040] In addition, boiler control, vacuum exhaust, nitrogen jet, stirring rod stirring, filter screening, removal of final powder and residual liquid nitrogen, etc. can all be set up in a unified control system, and the touch screen operation is used, which is convenient for users to input different insulation time, oxygen content, cabin pressure, retention time in liquid nitrogen and other related parameters for different high nitrogen steel powders.

[0041] The device used in the present invention has a simple principle, a simple structure, is easy to disassemble and clean, and can be used for a variety of different types of high nitrogen steel powders. The used liquid nitrogen can be recycled and reused, which is energy-saving and environmentally friendly.

[0042] The present invention is described in further detail below in conjunction with embodiments:

[0043] Example 1

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

[0045] 1. Pour the high nitrogen steel powder into the boiler, cover the boiler vacuum protection cover, open the ordinary nitrogen channel, and introduce nitrogen as the protective gas. Gradually increase the boiler temperature to the solid-liquid critical temperature of the high nitrogen steel powder, and then carry out a 30-minute heat preservation treatment. The whole process is in a vacuum environment, the oxygen content is kept below 500ppm, and the pressure in the boiler is maintained at 65-70mbar. During the heating process of the boiler, the high nitrogen steel powder is continuously stirred in the boiler with a stirring rod;

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

[0047] 3. Close the ordinary nitrogen channel, open the nitrogen jet channel, keep the flow rate at 5-10L / min, and blow the powder flowing down the filter into the liquid nitrogen pool;

[0048] 4. After all the powders enter the liquid nitrogen pool, when the powders remain in the liquid nitrogen pool for 10-20 minutes, they are pushed into a 1000-mesh stainless steel filter, and the excess liquid nitrogen flows into the excess liquid nitrogen container for liquid nitrogen recovery, and the final high nitrogen steel powder with ultra-high nitrogen content is obtained in the liquid nitrogen pool, and the final powder particle size is 15-48μm.

[0049] The high nitrogen steel powder obtained after the above steps was tested for nitrogen content using an inductively coupled plasma emission spectrometer (ICAP PRO X) according to the national standard GB / T 14265-2017. Finally, the nitrogen content in the high nitrogen steel powder was 1.3563%, which is a high nitrogen steel powder with ultra-high nitrogen content. The average powder particle size (D 50 ) is 35μm. According to the national standard GB / T 1482, the Hall flow rate of the powder is 16.4s / 50g, and the powder has good fluidity. In addition, the morphology of the powder was observed by 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. And through phase diffraction (XRD) analysis, it can be found that the main component phase of the powder is austenite phase, as shown below Figure 4 As shown, and analyzed by backscatter diffraction (EBSD), according to the following Figure 5 From the phase distribution diagram, it can be found that the austenite phase is distributed relatively evenly. According to further powder observation and testing, it can be shown that this steel with ultra-high nitrogen content meets the requirements of high nitrogen steel, that is, the above method can successfully prepare high nitrogen steel with ultra-high nitrogen content.

[0050] Example 2

[0051] Take the same high nitrogen steel powder as in Example 1 as an example, but the process parameters are changed.

[0052] 1. Pour the high nitrogen steel powder into the boiler, cover the boiler vacuum protection cover, open the ordinary nitrogen channel, and introduce nitrogen as the protective gas. Gradually increase the boiler temperature to the solid-liquid critical temperature of the high nitrogen steel powder, and then carry out a 60-minute heat preservation treatment. The whole process is in a vacuum environment, the oxygen content is kept below 500ppm, and the pressure in the boiler is maintained at 65-70mbar. During the boiler heating process, the high nitrogen steel powder is continuously stirred in the boiler with a stirring rod;

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

[0054] 3. Close the ordinary nitrogen channel, open the nitrogen jet channel, keep the flow rate at 30L / min, and blow the powder flowing down the filter into the liquid nitrogen pool;

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

[0056] The high nitrogen steel powder obtained after the above steps was tested for nitrogen content using an inductively coupled plasma emission spectrometer (ICAP PRO X) according to the national standard GB / T 14265-2017. Finally, the nitrogen content in the high nitrogen steel powder was 0.63%, which is a high nitrogen steel powder with ultra-high nitrogen content. Using an ultra-high-speed intelligent laser particle size analyzer (Mastersize3000, Malvern), according to the national standard GB / T 19077, the average powder particle size (D50) was measured to be 39.9 μm, which can be as follows Figure 6 As shown. According to the national standard GB / T 1482, the Hall flow rate of the powder is 23s / 50g, and the powder has good fluidity. In addition, the morphology of the powder was observed by electron microscopy, as shown below Figure 7As can be seen from the figure, under this process parameter, the sphericity of the powder is poor, and the powder stacking phenomenon occurs on the powder surface. The occurrence of this phenomenon may be related to the flow rate of the nitrogen jet. The excessively large flow rate causes the powder to be impacted, and physical collisions occur between the powders, resulting in a decrease in sphericity and an increase in the average grain size, which affects the use of additive manufacturing. In addition, since the high-nitrogen steel powder as the raw material is kept warm in the boiler for a long time, this leads to a large loss of nitrogen content in the powder, and the nitrogen increase effect is not achieved. The control of the insulation time is also equally important.

[0057] Example 3

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

[0059] The specific method is basically the same as Example 1, the only difference is that the raw materials used to prepare the high nitrogen steel powder with ultra-high nitrogen content are different and the retention time in the liquid nitrogen pool is different. In this process, the high nitrogen steel raw materials after insulation are only kept in liquid nitrogen for 2-5 minutes. The high nitrogen steel powder finally obtained is tested for nitrogen content, and the same test equipment, inductively coupled plasma emission spectrometer (ICAP PRO X), is also used. According to the national standard GB / T 14265-2017, the nitrogen content of the high nitrogen steel is 0.49%. Using an ultra-high-speed intelligent laser particle size analyzer (Mastersize 3000, Malvern), the average powder particle size (D50) is measured to be 34.1 μm in accordance with the national standard GB / T 19077, which can be as follows Figure 8 In addition, the Hall flow rate of the powder is 18.1gs / 50g. From the change of nitrogen content in the powder, it can be seen that if the high nitrogen steel powder after heat preservation is kept in liquid nitrogen for too short a time, there is not enough time for nitrogen to diffuse into the high nitrogen steel powder, and the nitrogen addition effect is poor. It is necessary to keep the powder in liquid nitrogen for a proper time.

[0060] The nitrogen content of the high nitrogen steel powder in the above three embodiments can be compared as shown in Table 2. By comparison, it can be found that the process parameters in the present invention have a better preparation effect on the preparation of high nitrogen steel powder with ultra-high nitrogen content. In addition, the equipment used for preparation involved in the present invention also has an important improvement effect.

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

[0062] Nitrogen content of original powder / % Nitrogen content of final powder / % Remark 0.81 1.3563 Using the process of the present invention 0.81 0.63 Changes in holding time and jet velocity 0.45 0.49 Changes in retention time in liquid nitrogen pool

Claims

1. A method for preparing high nitrogen steel powder with ultra-high nitrogen content, characterized in that: The method comprises the following steps: Step 1. Pour the existing high nitrogen steel powder into the boiler and heat it to keep it warm. During this process, the stirring rod is constantly stirred in the boiler; Step 2. Screening the powder heated in step 1 to obtain usable powder; Step 3. Flow the powder screened in step 2 into the liquid nitrogen pool; Step 4. The excess liquid nitrogen in step 3 flows out through the 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 in 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 1, the insulation temperature of the boiler is the solid-liquid critical temperature of the high nitrogen steel powder, the insulation time is 30 minutes, the oxygen content is less than 500 ppm, and the pressure in the boiler is 65-100 mbar.

4. 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 specification is 300 mesh.

5. The method for preparing high nitrogen steel powder with ultra-high nitrogen content according to claim 1, characterized in that: In step 3, a nitrogen jet is used to force the powder to quickly enter the liquid nitrogen pool, and the powder is retained in the liquid nitrogen pool for 10-20 minutes; wherein the nozzle of the nitrogen jet device is kept 75 mm away from the outermost layer of the powder when working, and the flow rate of the nitrogen is greater than 5 L / min and less than or equal to 20 L / min.

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

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

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

9. High nitrogen steel powder with ultra-high nitrogen content prepared by the method according to any one of claims 1 to 8.

10. An apparatus for preparing high nitrogen steel powder with ultra-high nitrogen content according to any one of claims 1 to 8, characterized in that: include: Boiler, liquid nitrogen pool, stainless steel filter, vacuum protection cover; The boiler is located under the boiler vacuum protection cover, a liquid nitrogen pool is arranged under the boiler, a 300-mesh stainless steel filter is arranged between the boiler and the liquid nitrogen pool, an excess liquid nitrogen storage pot is arranged under the liquid nitrogen pool, and a 1000-mesh stainless steel filter is arranged between the liquid nitrogen pool and the excess liquid nitrogen storage pot; The boiler, liquid nitrogen pool and excess liquid nitrogen storage pot inside the boiler vacuum protection cover provide reaction space for preparing high nitrogen steel powder; A nitrogen protective gas inlet, a nitrogen gas vent, an air flow channel valve, a nitrogen jet inlet, an oxygen content detector, an exhaust port for vacuuming, a pressure test element, and a temperature measurement element are respectively arranged on the vacuum protection cover of the boiler; The boiler retractable stirring rod for powder stirring is fixed in the boiler by fixing screws and a stirring rod bracket; The 300-mesh stainless steel filter at the bottom of the boiler is equipped with a positioning pin at both ends, and the same structure is also set at both ends of the 1000-mesh stainless steel filter; The liquid nitrogen pool is provided with a liquid nitrogen pool support column, which is arranged on a base outside the liquid nitrogen pool; The 300-mesh stainless steel filter, 1000-mesh stainless steel filter and excess liquid nitrogen container are all equipped with push rods.

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