A method for preparing nitrogen-containing alloy powder in ammonia metallurgy, and a co-production method for preparing nitrogen-containing alloy powder and reducing iron oxide powder.

Abstract

This invention belongs to the fields of green metallurgy and special alloy technology, and particularly relates to a method for preparing nitrogen-containing alloy powder in powder ammonia metallurgy, and a co-production method for preparing nitrogen-containing alloy powder and reducing iron oxide powder. In this invention, raw material powder is spread evenly on the support platform of a movable device, and reacted at 400-750°C in an ammonia-containing atmosphere to obtain the nitrogen-containing alloy powder; the raw material powder includes one or more of stainless steel powder, titanium alloy powder, nickel-based alloy powder, and iron oxide powder. The preparation method provided by this invention improves the preparation efficiency of nitrogen-containing alloy powder, reduces costs, and mitigates the adverse effects of hydrogen in metallurgy.

Description

Technical Field

[0001] This invention relates to the fields of green metallurgy and special alloy technology, and in particular to a method for preparing nitrogen-containing alloy powder in powder ammonia metallurgy, and a method for the co-production of nitrogen-containing alloy powder preparation and iron oxide powder reduction. Background Technology

[0002] In traditional metallurgy, nitrogen is generally considered a harmful impurity element, and its content is strictly controlled. However, for stainless steel, titanium alloys, and high-temperature alloys, nitrogen addition can have a significant solid solution strengthening effect, significantly improving hardness and strength, while also improving biocompatibility and corrosion resistance. It has excellent application prospects in marine engineering equipment, aerospace, energy and chemical industries, and biomedicine.

[0003] For example, high-nitrogen austenitic stainless steel is non-magnetic or weakly magnetic, and its strength is 2 to 3 times that of ordinary austenitic stainless steel. It is widely used in marine engineering, medical devices, petrochemicals, nuclear power, and other fields. High-nitrogen martensitic stainless steel can be used to manufacture high-performance molds, bearings, valves, etc. Adding nitrogen to high-speed steel can refine the grain, further improve red hardness, wear resistance, and toughness. Adding nitrogen to titanium alloys can significantly improve hardness and strength, enhance biocompatibility, and has good application prospects in artificial joints, aerospace, and other fields.

[0004] Currently, the main methods for preparing nitrogen-containing alloys include conventional metallurgy, high-pressure metallurgy, and powder metallurgy. Conventional metallurgy cannot add sufficient nitrogen, making it difficult to meet the requirements for nitrogen-containing alloys.

[0005] Both domestically and internationally, high-pressure metallurgy (nitrogen pressure melting) is widely used to prepare nitrogen-containing alloys. However, nitrogen pressure melting has drawbacks such as complex equipment, hazardous high-pressure and high-temperature gases, complex technology, and high production costs. Furthermore, the amount of nitrogen added remains limited, rarely exceeding 1 wt.%.

[0006] In comparison, powder metallurgy makes it easier to incorporate large amounts of nitrogen into alloys, and the nitrogen content distribution is more uniform and easier to control. However, the preparation of nitrogen-containing alloy powders has disadvantages such as low efficiency and high cost, which limits their application.

[0007] To achieve green production, especially new metallurgical processes that use hydrogen and ammonia instead of traditional fossil fuels as reducing agents in metal smelting, have been proposed and put into practice, and are expected to become a key path for the low-carbon transformation of the metallurgical industry. Compared with hydrogen, ammonia (NH3) can be liquefied at room temperature and lower pressure (<1MPa), with obvious advantages in safety and economy. Moreover, there is already a mature ammonia production, storage, and transportation system, which can replace hydrogen as a fuel and reducing agent in the metallurgical industry, and is particularly suitable for the manufacturing of high-performance nitrogen-containing alloys.

[0008] Both hydrogen metallurgy and ammonia metallurgy require melting metals at extremely high temperatures. At these melting temperatures, both processes generate high-temperature hydrogen and high-temperature water vapor, which corrode equipment. This results in high production and maintenance costs, severely restricting the development and application of hydrogen and ammonia metallurgy technologies. Furthermore, hydrogen can enter the molten metal, leaving hydrogen residues in the alloy and easily causing hydrogen embrittlement. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a method for preparing nitrogen-containing alloy powder in powder ammonia metallurgy, and a method for the co-production of nitrogen-containing alloy powder preparation and iron oxide powder reduction. The preparation method provided by this invention reduces the reaction temperature, alleviates equipment corrosion caused by high-temperature melting, and slows down the introduction of hydrogen into the iron-nitrogen alloy powder.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing nitrogen-containing alloy powder for ammonia metallurgy, comprising the following steps: The raw material powder is spread evenly on the support platform of the movable device, and reacted at 400~750℃ in an atmosphere containing ammonia to obtain the nitrogen-containing alloy powder. The raw material powder includes one or more of stainless steel powder, titanium alloy powder, nickel-based alloy powder, and iron oxide powder.

[0011] Preferably, the movable device includes a furnace tank and a tooling located inside the furnace tank. The tooling includes a supporting shell and a plurality of supporting platforms installed on the inner wall of the supporting shell and arranged in parallel. The supporting platforms are made of built-in stainless steel mesh.

[0012] Preferably, the principle for spreading the raw material powder is as follows: When the particle size of the raw material powder is greater than 100μm, the thickness of the raw material powder spread on a single support platform shall not exceed 10mm. When the particle size of the raw material powder is greater than 50μm and less than or equal to 100μm, the thickness of the raw material powder spread on a single bearing platform shall not exceed 6mm. When the particle size of the raw material powder is greater than 10μm and less than or equal to 50μm, the thickness of the raw material powder spread on a single bearing platform shall not exceed 4mm. When the particle size of the raw material powder is greater than 1μm and less than or equal to 10μm, the raw material powder is pressed into a thin cake with a thickness of less than or equal to 3mm before being spread out, and then spread out on the support platform. When the particle size of the raw material powder is less than or equal to 1 μm, the raw material powder is pressed into a thin cake with a thickness of less than or equal to 2 mm before being spread out, and then spread out on the support platform.

[0013] Preferably, the aperture of the built-in stainless steel mesh is 1 cm, and the diameter of the steel wire used to prepare the built-in stainless steel mesh is 2-3 mm; the material of the built-in stainless steel mesh is 316 stainless steel; and an aluminum oxide film is provided on the surface of the built-in stainless steel mesh. The distance between two adjacent support surfaces is 20~30mm.

[0014] Preferably, the furnace tank is made of austenitic stainless steel; the inner wall of the furnace tank is pretreated before use, the pretreatment including hot-dip aluminizing and high-temperature oxidation treatment in sequence.

[0015] Preferably, the reaction pressure is a positive pressure of 0.01~0.05MPa.

[0016] Preferably, when the raw material powder is one or more of stainless steel powder, titanium alloy powder, and nickel-based alloy powder, the reaction is a nitriding reaction, and the nitriding reaction includes low-temperature gas nitriding, medium-temperature gas nitriding, or high-temperature gas nitriding; The nitriding temperature of the cryogenic gas is 400~500℃, the pressure is positive pressure 0.03~0.05MPa, and the time is 1~3 hours; The temperature for nitriding the medium-temperature gas is 500.1~599.9℃, the pressure is positive pressure 0.02~0.04MPa, and the time is 0.5~2 hours; The high-temperature gas nitriding temperature is 600~700℃, the pressure is positive pressure 0.01~0.02MPa, and the time is 0.1~2 hours.

[0017] Preferably, when the raw material powder is iron oxide powder, the reaction is a reduction-nitriding reaction, the temperature of the reduction-nitriding reaction is 700~750℃, the pressure is positive pressure 0.01~0.02MPa, and the time is 0.1~1 hours.

[0018] This invention also provides a method for the co-production of nitrogen-containing alloy powder preparation and iron oxide powder reduction, comprising the following steps: According to the preparation method described in the above technical solution, the raw material powder is spread out in a flat manner, and low-temperature gas nitriding is carried out in an ammonia atmosphere to obtain low-temperature nitriding alloy powder and low-temperature gas nitriding tail gas. According to the preparation method described in the above technical solution, the raw material powder is spread out in a flat manner, and medium-temperature gas nitriding is carried out in the mixed atmosphere of low-temperature gas nitriding tail gas and ammonia gas to obtain medium-temperature nitriding alloy powder and medium-temperature gas nitriding tail gas. According to the preparation method described in the above technical solution, the raw material powder is spread out in a flat manner, and high-temperature gas nitriding is carried out in the mixed atmosphere of medium-temperature gas nitriding tail gas and ammonia to obtain high-temperature nitriding alloy powder and high-temperature gas nitriding tail gas; the raw material powder independently includes one or more of stainless steel powder, titanium alloy powder and nickel-based alloy powder. According to the preparation method described in the above technical solution, iron oxide powder is spread out in a flat manner, and a reduction-nitriding reaction is carried out under the atmosphere of the high-temperature gas nitriding tail gas to obtain iron-nitrogen alloy powder.

[0019] Preferably, the volume ratio of the cryogenic gas nitriding tail gas to the ammonia gas in the mixed atmosphere is 5:1. The volume ratio of the intermediate-temperature gas nitriding tail gas and ammonia in the mixed atmosphere is 3:1.

[0020] This invention provides a method for preparing nitrogen-containing alloy powder for powder metallurgy. The method allows the raw material powder to react at a relatively low temperature, mitigating equipment corrosion caused by high-temperature melting and the introduction of hydrogen into the iron-nitrogen alloy powder. Even if a small amount of hydrogen is introduced into the iron-nitrogen alloy powder, it can be removed during the powder metallurgy process, thus completely avoiding hydrogen embrittlement. Furthermore, this invention involves spreading the raw material powder evenly on the support platform of a movable device. After the raw material powder in the movable device has reacted completely, the device can be lifted out, and the device containing unreacted raw material powder can be placed back into the furnace to continue the reaction. This achieves continuous production, high efficiency, and reduces costs while increasing efficiency.

[0021] This invention also provides a method for the co-production of nitrogen-containing alloy powder and iron oxide powder reduction. This co-production method can simultaneously obtain nitrogen-containing alloy powders with different nitrogen contents and microstructures to meet diverse application needs. Simultaneously, it can reduce and nitrid iron oxide powder to form an iron-nitrogen alloy, achieving co-production with extremely high economic benefits and reduced waste gas emissions. This co-production method, through improved mobile equipment and optimized process flow, can simultaneously achieve the batch production of multiple nitrogen-containing alloy powders with different requirements, significantly improving the production efficiency of nitrogen-containing alloy powders and substantially reducing costs. Furthermore, by utilizing the nitriding tail gas to reduce iron oxide powder followed by nitriding, iron-nitrogen alloy powder is obtained, which can be directly used in metallurgical smelting, avoiding corrosion and hydrogen embrittlement problems caused by high-temperature hydrogen and water vapor, and significantly reducing costs while achieving near-zero carbon emissions. The co-production process of this invention is green and environmentally friendly, with no harmful waste emissions; it provides technical support and reference for the mass production and industrial application of special novel nitrogen-containing alloy materials. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a movable device; Figure 2 This is a diagram of the co-production system for the preparation of nitrogen-containing alloy powder and the reduction of iron oxide powder according to the present invention; Figure 3 This is a schematic diagram of a low-temperature gas nitriding furnace. Figure 4 This is a schematic diagram of a medium-temperature gas nitriding furnace. Figure 5 This is a schematic diagram of a high-temperature gas nitriding furnace. Figure 6 This is a schematic diagram of the iron oxide powder reduction-nitriding furnace structure; Figure 7 SEM images of nitrogen-containing 316L stainless steel powder obtained at different gas nitriding temperatures in Example 1, with a scale bar of 20 μm; Figure 8 The macroscopic morphology of Fe2O3 powder before (left) and after (right) reduction-nitriding reaction in Example 1 is shown. Figure 9 The images show SEM images of the iron-nitrogen alloy powder obtained in Example 1 at different magnifications. The scale bar in the left image is 30 μm, and the scale bar in the right image is 5 μm. Figure 10 The image shows a sample (SEM) of the iron-nitrogen alloy powder obtained in Example 1 after hot pressing and sintering at 900℃. Figure 11 The above are SEM images of nitrogen-containing TC4 titanium alloy powders obtained at different gas nitriding temperatures in Example 2, with a scale bar of 20 μm. Figure 12 The macroscopic morphology of the rolled iron oxide scale powder before (left) and after (right) reduction-nitriding reaction in Example 2 is shown. Figure 13 The images show SEM images of the iron-nitrogen alloy powder obtained in Example 2 at different magnifications. The left graph shows a scale bar of 40 μm, and the right graph shows a scale bar of 5 μm. Figure 14 The image shows a sample (SEM) of the iron-nitrogen alloy powder obtained in Example 2 after hot pressing and sintering at 950℃. The scale bar is 5 μm. Figure 15 The image shows SEM images of nitrogen-containing In718 high-temperature alloy powders obtained at different gas nitriding temperatures in Example 3, with a scale bar of 50 μm. Detailed Implementation

[0023] This invention provides a method for preparing nitrogen-containing alloy powder, comprising the following steps: The raw material powder is spread evenly on the support platform of the movable device, and reacted at 400~750℃ in an atmosphere containing ammonia to obtain the nitrogen-containing alloy powder. The raw material powder includes one or more of stainless steel powder, titanium alloy powder, nickel-based alloy powder, and iron oxide powder.

[0024] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0025] First, combined Figure 1 The structure of the movable device will be described. In this invention, as... Figure 1 As shown, the movable device includes a furnace tank. In this invention, the furnace tank is preferably made of austenitic stainless steel; the inner wall of the furnace tank is preferably pretreated before use, and the pretreatment preferably includes: hot-dip aluminizing and high-temperature oxidation treatment in sequence. This invention does not specifically limit the operation of the hot-dip aluminizing and high-temperature oxidation treatments; the hot-dip aluminizing and high-temperature oxidation treatments can obtain a dense alumina film, preventing the inner wall of the furnace tank from being nitrided during gas nitriding. In this invention, the movable device preferably also includes a furnace cover that matches the furnace tank. In this invention, the furnace tank and the furnace cover are preferably sealed by a sealing ring.

[0026] In this invention, the movable device preferably further includes a stirring fan, which is installed on the inner top of the furnace and the furnace cover.

[0027] In this invention, the movable device preferably further includes a cooling water pipe, which is preferably wrapped around the top outer side of the furnace tank.

[0028] In this invention, the movable device includes a tooling located inside the furnace. Preferably, the tooling includes a supporting shell and several parallel support platforms mounted on the inner wall of the supporting shell. The support platforms preferably have a built-in stainless steel mesh; the type of stainless steel used for the built-in mesh is not limited, but is used to distinguish it from the external stainless steel mesh. The spacing between two adjacent support platforms is preferably 20-30 mm. The aperture of the built-in stainless steel mesh is preferably 1 cm, and the diameter of the steel wire used to prepare the built-in stainless steel mesh is preferably 2-3 mm. The material of the built-in stainless steel mesh is preferably 316 stainless steel; the built-in stainless steel mesh serves a supporting function. The surface of the built-in stainless steel mesh is preferably provided with an alumina film, and the thickness of the alumina film is preferably 10-20 μm. The method for preparing the alumina film preferably includes the following steps: performing vapor-phase aluminizing treatment on the surface of the stainless steel mesh, followed by oxidation treatment; the parameters for the vapor-phase aluminizing treatment and oxidation treatment are not specifically limited in this invention, and operations well known to those skilled in the art can be used. In this invention, an aluminum oxide film is applied to the surface of the built-in stainless steel mesh for passivation to prevent the mesh from being nitrided during gas nitriding, thereby increasing the number of times the stainless steel mesh can be reused and reducing costs. This invention also features multiple parallel support platforms, which improves production efficiency, enhances the gas nitriding effect, and facilitates the placement and removal of alloy powder.

[0029] In this invention, the movable device preferably further includes an inlet pipe and an outlet pipe, which are located on opposite sides of the tooling. In this invention, the inlet pipe is preferably connected to different gas sources as needed, specifically one or more of nitrogen, argon, and ammonia sources. In this invention, the outlet pipe is preferably connected to different post-treatment systems as needed, specifically including one or more of a combustion furnace, a tail gas recovery and reuse system, or a vacuum pump.

[0030] In this invention, the raw material powder is laid flat on the support platform of the movable device, which facilitates the placement and removal of the alloy powder and improves production efficiency.

[0031] In this invention, the raw material powder includes one or more of stainless steel powder, titanium alloy powder, nickel-based alloy powder, and iron oxide powder. Specifically, the stainless steel powder is preferably 316L stainless steel powder; the titanium alloy powder is preferably TC4 titanium alloy powder; and the nickel-based alloy powder is preferably In718 high-temperature alloy powder.

[0032] In this invention, the principle for spreading the raw material powder is as follows: When the particle size of the raw material powder is greater than 100μm, the thickness of the raw material powder spread on a single support platform shall not exceed 10mm. When the particle size of the raw material powder is greater than 50μm and less than or equal to 100μm, the thickness of the raw material powder spread on a single bearing platform shall not exceed 6mm. When the particle size of the raw material powder is greater than 10μm and less than or equal to 50μm, the thickness of the raw material powder spread on a single bearing platform shall not exceed 4mm. When the particle size of the raw material powder is greater than 1μm and less than or equal to 10μm, the raw material powder is pressed (referred to as the first pressing) before being spread to form a thin cake with a thickness of less than or equal to 3mm, and then spread on the support platform. When the particle size of the raw material is less than or equal to 1 μm, the raw material powder is pressed (referred to as the second pressing) before being spread to form a thin cake with a thickness of less than or equal to 2 mm, and then spread on the support platform.

[0033] In this invention, the pressure of the first pressing is preferably 10 MPa.

[0034] In this invention, the pressure of the second pressing is preferably 5 MPa.

[0035] In this invention, before the raw material powder is spread on the support platform of the movable device, it is preferably spread on an external stainless steel mesh, and then the external stainless steel mesh with the raw material powder is placed on the internal stainless steel mesh. In this invention, the aperture size of the external stainless steel mesh is preferably smaller than the particle size of the raw material powder to prevent the raw material powder from leaking out of the sieve. In this invention, the diameter of the steel wire used to prepare the external stainless steel mesh is preferably 2-3 mm; the material of the external stainless steel mesh is preferably 316 stainless steel. In this invention, the external stainless steel mesh is passivated before use; the passivation treatment is preferably the same as the passivation treatment operation of the internal stainless steel mesh described in the above technical solution, and will not be repeated here.

[0036] In this invention, the principle of spreading the raw material powder evenly ensures that the evenly spread raw material powder can achieve a high-efficiency reaction.

[0037] In this invention, the volume content of ammonia in the ammonia-containing atmosphere is preferably 10-99.99%, specifically preferably 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or 99.99%.

[0038] In this invention, the reaction pressure is preferably a positive pressure of 0.01~0.05 MPa, specifically preferably a positive pressure of 0.01 MPa, 0.015 MPa, 0.02 MPa, 0.025 MPa, 0.03 MPa, 0.035 MPa, 0.04 MPa, 0.045 MPa, or 0.05 MPa; the positive pressure of 0.01 MPa refers to adding 0.01 MPa to the atmospheric pressure.

[0039] In this invention, when the raw material powder is one or more of stainless steel powder, titanium alloy powder, and nickel-based alloy powder, the reaction is a nitriding reaction, which includes low-temperature gas nitriding, medium-temperature gas nitriding, or high-temperature gas nitriding.

[0040] In this invention, the preferred temperature for cryogenic gas nitriding is 400-500℃, specifically 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 495℃; the preferred pressure is a positive pressure of 0.03-0.05 MPa, specifically 0.03 MPa, 0.035 MPa, 0.04 MPa, 0.045 MPa, or 0.05 MPa; the preferred time is 1-3 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. In this invention, cryogenic gas nitriding can obtain nitrogen-containing alloy powder with a large amount of nitrogen solid solution, small powder deformation, and low nitrogen content; for stainless steel alloys, cryogenic gas nitriding can reduce the nitrogen content in the nitrided stainless steel alloy to ≤0.5 wt.%.

[0041] In this invention, the preferred temperature for medium-temperature gas nitriding is 500.1~599.9℃, specifically 500.1℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 595℃; the preferred pressure is a positive pressure of 0.02~0.04MPa, specifically 0.02MPa, 0.025MPa, 0.03MPa, 0.035MPa, or 0.04MPa; the preferred time is 0.5~2 hours, specifically 0.5 hours, 1 hour, 1.5 hours, or 2 hours. In this invention, medium-temperature gas nitriding can obtain nitrogen-containing alloy powder with a large amount of nitrogen solid solution and a small amount of nitride precipitation, and a high nitrogen content; for stainless steel alloys, medium-temperature gas nitriding can achieve a nitrogen content of 0.5~2wt.% in the nitrided stainless steel alloy.

[0042] In this invention, the preferred temperature for high-temperature gas nitriding is 600~700℃, specifically 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, or 700℃; the preferred pressure is a positive pressure of 0.01~0.02MPa, specifically 0.01MPa, 0.015MPa, or 0.02MPa; the preferred time is 0.1~2 hours, specifically 0.1 hours, 0.5 hours, 1 hour, 1.5 hours, or 2 hours. In this invention, high-temperature gas nitriding can obtain nitrogen-containing alloy powder with a large amount of nitrogen solid solution and a large amount of nitride precipitation, resulting in an ultra-high nitrogen content; for stainless steel alloys, high-temperature gas nitriding can make the nitrogen content in the nitrided stainless steel alloy ≥2wt.%.

[0043] In this invention, when the raw material powder is iron oxide powder, the reaction is a reduction-nitriding reaction. The temperature of the reduction-nitriding reaction is preferably 700~750℃, specifically preferably 700℃, 710℃, 720℃, 730℃, 740℃ or 750℃; the pressure is preferably positive pressure 0.01~0.02MPa, specifically preferably positive pressure 0.01MPa, positive pressure 0.015MPa or positive pressure 0.02MPa; the time is preferably 0.1~1 hour, specifically preferably 0.1 hour, 0.5 hours or 1 hour.

[0044] In this invention, during the reaction process, the rotation speed of the stirring fan is preferably 150~300 rpm, and the stirring fan can ensure the uniformity of atmosphere and temperature.

[0045] In this invention, the reaction is preferably carried out in a gas nitriding furnace, and the movable device is preferably placed in the gas nitriding furnace.

[0046] After the reaction is completed, the present invention preferably removes the movable device from the gas nitriding furnace for cooling, and at the same time removes the movable device loaded with raw material powder into the gas nitriding furnace to continue the reaction, so as to realize continuous production; during the removal and removal process, preferably, a small amount of ammonia gas is introduced into the furnace tank of the movable device for protection.

[0047] In this invention, after the movable device is lifted out of the gas nitriding furnace, it preferably further includes: when the temperature inside the furnace of the movable device drops below 300°C; replacing the ammonia gas with nitrogen, argon, or vacuum conditions; when the temperature inside each furnace cools to below 40°C; closing the atmosphere and vacuum; taking out the powder; and obtaining nitrogen-containing alloy powder.

[0048] This invention also provides a method for the co-production of nitrogen-containing alloy powder preparation and iron oxide powder reduction, comprising the following steps: According to the preparation method described in the above technical solution, the raw material powder is spread out in a flat manner, and low-temperature gas nitriding is carried out in an ammonia atmosphere to obtain low-temperature nitriding alloy powder and low-temperature gas nitriding tail gas. According to the preparation method described in the above technical solution, the raw material powder is spread out in a flat manner, and medium-temperature gas nitriding is carried out in the mixed atmosphere of low-temperature gas nitriding tail gas and ammonia gas to obtain medium-temperature nitriding alloy powder and medium-temperature gas nitriding tail gas. The raw material powder is spread out in a flat-laying manner according to the preparation method described in the above technical solution. High-temperature gas nitriding is carried out in the mixed atmosphere of medium-temperature gas nitriding tail gas and ammonia to obtain high-temperature nitriding alloy powder and high-temperature gas nitriding tail gas. The raw material powder independently includes one or more of stainless steel powder, titanium alloy powder and nickel-based alloy powder. According to the preparation method described in the above technical solution, iron oxide powder is spread out in a flat manner, and a reduction-nitriding reaction is carried out under the atmosphere of the high-temperature gas nitriding tail gas to obtain iron-nitrogen alloy powder.

[0049] In this invention, the co-production method is preferably carried out in... Figure 2 The process is carried out in the system shown below, in conjunction with... Figure 2 The co-production method of the present invention will be described.

[0050] The raw material powder is spread out in a flat manner according to the preparation method described in the above technical solution. Low-temperature gas nitriding is then performed under an ammonia atmosphere to obtain low-temperature nitrided alloy powder and low-temperature gas nitriding tail gas. In this invention, the raw material powder includes one or more of stainless steel powder, titanium alloy powder, and nickel-based alloy powder. In this invention, the purity of the ammonia gas is preferably ≥99%, more preferably ≥99.99%. In this invention, the temperature, pressure, and time of the low-temperature gas nitriding are consistent with the above technical solution and will not be repeated here. In this invention, the ammonia decomposition rate is controlled at 10~30% during the low-temperature gas nitriding process. In this invention, the low-temperature gas nitriding is preferably performed at... Figure 3 The process was carried out in the low-temperature gas nitriding furnace shown.

[0051] After obtaining the low-temperature gas nitriding tail gas, the present invention spreads the raw material powder evenly according to the preparation method described in the above technical solution. Under a mixed atmosphere of the low-temperature gas nitriding tail gas and ammonia, medium-temperature gas nitriding is performed to obtain medium-temperature nitriding alloy powder and medium-temperature gas nitriding tail gas. In the present invention, the raw material powder includes one or more of stainless steel powder, titanium alloy powder, and nickel-based alloy powder. In the present invention, the volume ratio of the low-temperature gas nitriding tail gas to ammonia at room temperature in the mixed atmosphere is preferably 5:1; the purity of the ammonia is preferably consistent with the above technical solution and will not be repeated here. In the present invention, the temperature, pressure, and time of the medium-temperature gas nitriding are preferably consistent with the above technical solution and will not be repeated here. In the present invention, the ammonia decomposition rate is controlled at 30-50% during the medium-temperature gas nitriding process. In the present invention, the medium-temperature gas nitriding is preferably performed at... Figure 4 The process was carried out in the medium-temperature gas nitriding furnace shown.

[0052] After obtaining the intermediate-temperature gas nitriding tail gas, the present invention spreads the raw material powder evenly according to the preparation method described in the above technical solution. High-temperature gas nitriding is then performed in a mixed atmosphere of the intermediate-temperature gas nitriding tail gas and ammonia to obtain high-temperature nitriding alloy powder and high-temperature gas nitriding tail gas. In this invention, the raw material powder includes one or more of stainless steel powder, titanium alloy powder, and nickel-based alloy powder. In this invention, the volume ratio of the intermediate-temperature gas nitriding tail gas to ammonia at room temperature in the mixed atmosphere is preferably 3:1, and the purity of the ammonia is preferably consistent with the above technical solution, and will not be repeated here. In this invention, the temperature, pressure, and time of the high-temperature gas nitriding are preferably consistent with the above technical solution, and will not be repeated here. In this invention, the ammonia decomposition rate is controlled at 50-90% during the high-temperature gas nitriding process. In this invention, the high-temperature gas nitriding is preferably performed at... Figure 5 The process is carried out in the high-temperature gas nitriding furnace shown.

[0053] After obtaining the high-temperature gas nitriding tail gas, the present invention spreads iron oxide powder in a flat-laying manner according to the preparation method described in the above technical solution. A reduction-nitriding reaction is then carried out under the atmosphere of the high-temperature gas nitriding tail gas to obtain iron-nitrogen alloy powder. In the present invention, the iron oxide powder preferably includes one or more of iron oxide, iron ore powder, and magnetite. In the present invention, the temperature, pressure, and time of the reduction-nitriding reaction are preferably consistent with the above technical solution and will not be repeated here. In the present invention, the reduction-nitriding reaction is preferably carried out under the atmosphere of the high-temperature gas nitriding tail gas to obtain iron-nitrogen alloy powder. Figure 6 The reduction-nitriding furnace shown is used for this process.

[0054] After the reduction-nitriding reaction is completed, the present invention preferably further includes obtaining reduction tail gas, which is directly discharged after combustion, and the combustion temperature is preferably 800~850℃; the combustion is preferably carried out in a catalytic combustion furnace; after the reduction tail gas is fully combusted, it mainly produces water vapor and nitrogen, which does not pollute the environment and can be directly discharged.

[0055] The co-production method provided by this invention can simultaneously obtain nitrogen-containing alloy powders with different nitrogen contents and microstructures to meet diverse application requirements. Furthermore, it can reduce and nitrid iron oxides, achieving the co-production of iron-nitrogen alloys, resulting in significant economic benefits. In addition, the co-production method of this invention can effectively utilize nitriding tail gas, improve the preparation efficiency of nitrogen-containing alloy powders, significantly reduce production costs, and reduce waste gas emissions.

[0056] The following detailed description, in conjunction with embodiments, illustrates the preparation method of nitrogen-containing alloy powder for powdered ammonia metallurgy, the co-production method of nitrogen-containing alloy powder preparation and iron oxide powder reduction provided by the present invention, but these should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1 exist Figure 2 The system shown undergoes co-production, and the specific process is as follows: Three equal portions of spherical 316L stainless steel powder with an average particle size of approximately 40 μm were weighed and spread evenly on three 500-mesh external stainless steel wire meshes. Three sheets of external stainless steel wire mesh with powder on them were placed on three fixtures (with internal stainless steel mesh, 316 stainless steel sieves with a 1cm aperture, and stainless steel wire with a 2mm diameter for making the sieves). They were then placed in low-temperature, medium-temperature, and high-temperature gas nitriding furnaces, respectively. Ammonia gas was introduced into the low-temperature gas nitriding furnace. The low-temperature gas nitriding tail gas produced by the low-temperature gas nitriding furnace was mixed with ammonia gas at a room temperature molar ratio of 5:1. The mixture was then directly introduced into the medium-temperature gas nitriding furnace. The medium-temperature gas nitriding tail gas produced by the medium-temperature gas nitriding furnace was mixed with ammonia gas at a room temperature molar ratio of 3:1. The mixture was then introduced into the high-temperature gas nitriding furnace. The high-temperature gas nitriding tail gas produced by the high-temperature gas nitriding furnace was directly introduced into a 700℃ furnace containing iron oxide powder. A reduction-nitriding reaction was carried out at a positive pressure of 0.01MPa for 0.5 hours to obtain iron-nitrogen alloy powder. Finally, the tail gas was introduced into an 800℃ catalytic combustion furnace for complete combustion treatment.

[0058] The low-temperature gas nitriding furnace, the medium-temperature gas nitriding furnace, and the high-temperature gas nitriding furnace were operated at temperatures of 450℃, 550℃, and 600℃, respectively, and at pressures of 0.04MPa, 0.02MPa, and 0.02MPa, respectively, for 1 hour of gas nitriding treatment.

[0059] After gas nitriding is completed, each nitriding furnace and the reduction-nitriding furnace furnace are lifted out of the furnace body for cooling. At the same time, furnaces filled with powder and ready for nitriding are lifted back into the furnace body to continue the nitriding process, achieving continuous production. During the lifting out and lifting in processes, a small amount of ammonia gas is introduced into each furnace for protection.

[0060] When the temperature inside the furnace drops below 300°C, the protective gas can be switched to nitrogen, argon, or vacuum conditions. Once the temperature inside each furnace has cooled to below 40°C, the protective atmosphere and vacuum are turned off, and the powder is removed to obtain nitrogen-containing alloy powder.

[0061] The morphologies of the obtained nitrogen-containing alloy powders are shown below. Figures 7-9 As shown, the nitrogen content is shown in Tables 1 and 2.

[0062] Table 1. Test results (wt.%) of nitrogen content in 316L stainless steel powder nitrided by different processes.

[0063] Table 2. Composition of iron-nitrogen alloy powder (wt.%)

[0064] from Figures 7-9 It can be seen that nitriding temperature has a significant impact on the morphology of 316L stainless steel powder. As the nitriding temperature increases, the infiltration of a large amount of nitrogen leads to obvious deformation or cracking of the powder. Therefore, to maintain a good spherical morphology in nitrided 316L stainless steel powder, gas nitriding treatment should be performed at a lower temperature. High-temperature nitriding tail gas can be used for the reduction-nitriding treatment of iron oxide powder, providing a new approach and method for the reduction of iron ore powder with ammonia.

[0065] Tables 1 and 2 show that nitriding temperature has a significant impact on the nitrogen content in 316L stainless steel powder; the nitrogen content increases significantly with increasing nitriding temperature. The iron-nitrogen alloy obtained by reducing iron oxide powder with high-temperature nitriding tail gas and then nitriding exhibits a very high Fe content, indicating a significant reduction effect.

[0066] Iron-nitrogen alloy powder was shaped in a graphite mold and then hot-pressed at 900℃. The resulting hot-pressed sintered sample was scanned by SEM, and the results are as follows. Figure 10 As shown. From Figure 10 It can be seen that iron-nitrogen alloy powder can be sintered to obtain pure iron material with a full ferrite structure, providing a reference for the application of the reduced powder in powder metallurgy and metallurgy.

[0067] Energy dispersive spectroscopy (EDS) was performed on the hot-pressed sintered samples. Point scanning of the selected micro-regions was conducted during the test, and the results are shown in Table 3.

[0068] Table 3 Energy Dispersive Spectroscopy (EDS) Results of Hot-Pressed Sintered Samples

[0069] As can be seen from Table 3, the hot-pressed sintered samples are mainly Fe elements and basically do not contain O elements, indicating that the reduction effect is obvious. The carbon elements in the hot-pressed sintered samples are generated by diffusion from the graphite mold. The Fe-N alloy decomposes and denitrifies at high temperature, so it does not contain nitrogen elements after high-temperature sintering.

[0070] Considering only nitriding of stainless steel powder, the cost is approximately 3000-4000 yuan / ton, equivalent to 3-4 yuan / kg. This cost is less than 5% of the selling price of 3D-printed stainless steel powder, but the addition of nitrogen can significantly improve the overall performance of stainless steel products, making it highly cost-effective. Simultaneously, the exhaust gas is used to reduce iron ore powder, with the cost of reducing iron ore powder not exceeding 1000 yuan / ton. The reduction process has near-zero carbon emissions, resulting in significant economic and social benefits.

[0071] Example 2 exist Figure 2 The system shown undergoes co-production, and the specific process is as follows: Three equal portions of spherical TC4 titanium alloy powder with an average particle size of approximately 45 μm were weighed and spread evenly on three 500-mesh external stainless steel wire meshes. The three external stainless steel wire meshes with powder were placed on three fixtures (with built-in stainless steel mesh, 316 stainless steel sieves with a 1 cm aperture, and stainless steel wires with a diameter of 2 mm used to make the sieves). Then, they were placed in low-temperature, medium-temperature, and high-temperature gas nitriding furnaces, respectively. Ammonia gas was introduced into the low-temperature gas nitriding furnace, and the tail gas from the low-temperature gas nitriding furnace was mixed with ammonia gas at a room temperature molar ratio of 5:1. After mixing, the mixture was directly introduced into the medium-temperature gas nitriding furnace. The tail gas from the medium-temperature gas nitriding furnace was mixed with ammonia gas at a room temperature molar ratio of 3:1. After mixing, the mixture was introduced into the high-temperature gas nitriding furnace. The tail gas from the high-temperature gas nitriding furnace was directly introduced into a 750°C atmosphere furnace containing rolled iron oxide scale powder. The reduction-nitriding reaction was carried out at a positive pressure of 0.02 MPa for 0.5 hours. Finally, the tail gas was introduced into an 800°C catalytic combustion furnace for complete combustion treatment.

[0072] Among them, the temperatures of the three gas nitriding furnaces—low-temperature gas nitriding furnace, medium-temperature gas nitriding furnace, and high-temperature gas nitriding furnace—are 500℃, 550℃, and 600℃, respectively, and the pressures are positive pressure 0.03MPa, positive pressure 0.04MPa, and positive pressure 0.02MPa, respectively, and each furnace is subjected to gas nitriding treatment for 1 hour.

[0073] After gas nitriding is completed, each nitriding furnace and the reduction-nitriding furnace furnace are lifted out of the furnace body for cooling. At the same time, furnaces filled with powder and ready for nitriding are lifted back into the furnace body to continue the nitriding process, achieving continuous production. During the lifting out and lifting in processes, a small amount of ammonia gas is introduced into each furnace for protection.

[0074] When the temperature inside the furnace drops below 300°C, the protective gas can be switched to nitrogen, argon, or vacuum conditions. Once the temperature inside each furnace has cooled to below 40°C, the protective atmosphere and vacuum are turned off, and the powder is removed to obtain nitrogen-containing alloy powder.

[0075] The morphology of the obtained powders is shown in the figures below. Figures 11-13 The nitrogen content is shown in Tables 4 and 5.

[0076] Table 4. Test results (wt.%) of nitrogen content in TC4 titanium alloy powder nitrided by different processes.

[0077] Table 5. Composition of iron-nitrogen alloy powder (wt.%)

[0078] from Figures 11-13 It can be seen that the microstructure of titanium alloy powder after nitriding at different temperatures shows that the powder still maintains a good spherical shape after nitriding, and no obvious deformation or cracking was found. The nitriding tail gas was used to reduce and nitrid the iron oxide scale powder of rolled steel, and achieved a good reduction and nitriding effect, basically reducing it completely. The macroscopic and microscopic morphologies are the same as those of iron-nitrogen alloy powder.

[0079] As can be seen from Tables 4 and 5, the nitrogen content in TC4 titanium alloy powder increases significantly after nitriding, and the nitrogen content increases significantly with the increase of nitriding temperature. The iron-nitrogen alloy powder obtained by reducing and nitriding rolled iron oxide scale powder with nitriding tail gas is basically free of oxygen, indicating that the reduction effect is obvious. Nitrifying tail gas can be used for the reduction treatment of rolled iron oxide scale, which significantly reduces the reduction cost and improves the secondary utilization value of rolled iron oxide scale powder.

[0080] Iron-nitrogen alloy powder was formed in a graphite mold and then hot-pressed at 950℃. The resulting hot-pressed sintered sample was scanned by SEM, and the results are as follows. Figure 14 As shown, from Figure 14 It can be seen that the microstructure of the iron-nitrogen alloy powder samples after sintering is ferrite.

[0081] Meanwhile, energy dispersive spectroscopy (EDS) tests were performed on the bulk samples obtained by hot pressing and sintering, and the results are shown in Table 6.

[0082] Table 6. Energy Dispersive Spectrum (EDS) Results of Bulk Bodies After Hot Pressing and Sintering

[0083] As can be seen from Table 6, the sintered samples basically do not contain oxygen, indicating that the method of high-temperature gas nitriding tail gas reduction-nitriding treatment of rolled iron oxide powder is feasible. The carbon element was introduced by the sintering graphite mold, and the nitrogen element was removed by the high-temperature decomposition and denitrification reaction of the Fe-N alloy. Except for Fe, the other elements in the table are the original elements in the steel and were not introduced after reduction.

[0084] For every ton of iron oxide scale generated during steel rolling (priced at approximately 800-1000 yuan / ton), a loss of about 1500 yuan is incurred. If the generated iron oxide scale is reduced by high-temperature nitriding tail gas and then reused in steel metallurgy, the loss can be reduced by 1000 yuan. If the reduced Fe-N alloy powder is used as a raw material in powder metallurgy, it can be sold for 5000 yuan / ton. The cost of reducing iron oxide scale with nitriding tail gas is approximately 1000 yuan / ton, resulting not only in no loss but also in significant additional profit. The reduction process has near-zero carbon emissions, demonstrating significant social benefits.

[0085] Example 3 exist Figure 2 The system shown undergoes co-production, and the specific process is as follows: Three equal portions of spherical In718 high-temperature alloy powder with an average particle size of approximately 55 μm were weighed and spread evenly on three 400-mesh external stainless steel wire meshes. Three sheets of external stainless steel wire mesh with powder laid on them were placed on three fixtures (with internal stainless steel mesh, 316 stainless steel sieves with a 1cm aperture, and stainless steel wire with a 2mm diameter used to make the sieves). They were then placed in low-temperature, medium-temperature, and high-temperature gas nitriding furnaces, respectively. Ammonia gas was introduced into the low-temperature gas nitriding furnace. The exhaust gas from the low-temperature gas nitriding furnace was mixed with ammonia gas at a room temperature molar ratio of 5:1. The mixture was then directly introduced into the medium-temperature gas nitriding furnace. The exhaust gas from the medium-temperature gas nitriding furnace was mixed with ammonia gas at a room temperature molar ratio of 3:1. The mixture was then introduced into the high-temperature gas nitriding furnace. The exhaust gas from the high-temperature gas nitriding furnace was directly introduced into a 700℃ atmosphere furnace containing iron oxide powder. The iron oxide powder was reduced and nitrided under a positive pressure of 0.015MPa for 1 hour. Finally, the exhaust gas was introduced into an 800℃ catalytic combustion furnace for complete combustion treatment.

[0086] Among them, the temperatures of the three gas nitriding furnaces—low-temperature gas nitriding furnace, medium-temperature gas nitriding furnace, and high-temperature gas nitriding furnace—were 450℃, 590℃, and 650℃, respectively, and the pressures were positive pressure 0.03MPa, positive pressure 0.02MPa, and positive pressure 0.01MPa, respectively, and each furnace was subjected to gas nitriding treatment for 2 hours.

[0087] After gas nitriding is completed, each nitriding furnace and the reduction-nitriding furnace furnace are lifted out of the furnace body for cooling. At the same time, furnaces filled with powder and ready for nitriding are lifted back into the furnace body to continue the nitriding process, achieving continuous production. During the lifting out and lifting in processes, a small amount of ammonia gas is introduced into each furnace for protection.

[0088] When the temperature inside the furnace drops below 300°C, the protective gas can be switched to nitrogen, argon, or vacuum conditions. Once the temperature inside each furnace has cooled to below 40°C, the protective atmosphere and vacuum are turned off, and the powder is removed to obtain nitrogen-containing alloy powder.

[0089] The morphology of the obtained powder is shown in Figure 15 The nitrogen content is shown in Tables 7 and 8.

[0090] Table 7. Test results (wt.%) of nitrogen content in In718 high-temperature alloy powder nitrided by different processes.

[0091] Table 8. Composition of iron-nitrogen alloy powder (wt.%)

[0092] from Figure 15 It can be seen that the In718 high-temperature alloy powder still maintains a good spherical shape after being nitrided with gas at different temperatures, without obvious deformation or cracking.

[0093] As can be seen from Table 7, after nitriding with gas at different temperatures, the powder contained a high nitrogen content, and the nitrogen content increased with the increase of nitriding temperature.

[0094] Regardless of whether it is iron oxide powder, ferric oxide powder, or magnetite powder, the main phase component obtained after reduction nitriding is ε-Fe. 2～3 N and a small amount of γ ’ -Fe4N.

[0095] According to the method of the present invention, the cost of nitriding each ton of In718 high-temperature alloy powder is about 4,500 to 5,000 yuan, which is equivalent to about 4.5 to 5 yuan per kilogram.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the production of a powder ammonia metallurgical nitrogen containing alloy powder, characterized in that, Includes the following steps: The raw material powder is spread evenly on the support platform of the movable device, and reacted at 400~750℃ in an atmosphere containing ammonia to obtain the nitrogen-containing alloy powder. The raw material powder includes one or more of stainless steel powder, titanium alloy powder, nickel-based alloy powder, and iron oxide powder.

2. The preparation method according to claim 1, characterized in that, The movable device includes a furnace tank and tooling located inside the furnace tank. The tooling includes a supporting shell and a plurality of support platforms installed on the inner wall of the supporting shell and arranged in parallel. The support platforms are made of built-in stainless steel mesh.

3. The preparation method according to claim 1, characterized in that, The principle for spreading the raw material powder is as follows: When the particle size of the raw material powder is greater than 100μm, the thickness of the raw material powder spread on a single support platform shall not exceed 10mm. When the particle size of the raw material powder is greater than 50μm and less than or equal to 100μm, the thickness of the raw material powder spread on a single bearing platform shall not exceed 6mm. When the particle size of the raw material powder is greater than 10μm and less than or equal to 50μm, the thickness of the raw material powder spread on a single bearing platform shall not exceed 4mm. When the particle size of the raw material powder is greater than 1 μm and less than or equal to 10 μm, the raw material powder is pressed into a thin cake with a thickness of less than or equal to 3 mm before being spread out, and then spread out on the support platform. When the particle size of the raw material powder is less than or equal to 1 μm, the raw material powder is pressed into a thin cake with a thickness of less than or equal to 2 mm before being spread out, and then spread out on the support platform.

4. The preparation method according to claim 1, characterized in that, The built-in stainless steel mesh has a mesh size of 1 cm, and the steel wire used to prepare the built-in stainless steel mesh has a diameter of 2-3 mm; the material of the built-in stainless steel mesh is 316 stainless steel; and an aluminum oxide film is provided on the surface of the built-in stainless steel mesh. The distance between two adjacent support surfaces is 20~30mm.

5. The preparation method according to claim 1, characterized in that, The furnace tank is made of austenitic stainless steel; the inner wall of the furnace tank is pretreated before use, and the pretreatment includes hot-dip aluminizing and high-temperature oxidation treatment in sequence.

6. The preparation method according to claim 1, characterized in that, The reaction is carried out at a positive pressure of 0.01~0.05 MPa.

7. The preparation method according to claim 1 or 6, characterized in that, When the raw material powder is one or more of stainless steel powder, titanium alloy powder and nickel-based alloy powder, the reaction is a nitriding reaction, and the nitriding reaction includes low-temperature gas nitriding, medium-temperature gas nitriding or high-temperature gas nitriding. The nitriding temperature of the cryogenic gas is 400~500℃, the pressure is positive pressure 0.03~0.05MPa, and the time is 1~3 hours; The temperature for nitriding the medium-temperature gas is 500.1~599.9℃, the pressure is positive pressure 0.02~0.04MPa, and the time is 0.5~2 hours; The high-temperature gas nitriding temperature is 600~700℃, the pressure is positive pressure 0.01~0.02MPa, and the time is 0.1~2 hours.

8. The preparation method according to claim 1 or 6, characterized in that, When the raw material powder is iron oxide powder, the reaction is a reduction-nitriding reaction, the temperature of the reduction-nitriding reaction is 700~750℃, the pressure is positive pressure 0.01~0.02MPa, and the time is 0.1~1 hours.

9. A method for the co-production of nitrogen-containing alloy powder preparation and iron oxide powder reduction, comprising the following steps: The raw material powder is spread out in the preparation method according to any one of claims 1 to 8, and then subjected to low-temperature gas nitriding in an ammonia atmosphere to obtain low-temperature nitriding alloy powder and low-temperature gas nitriding tail gas. The raw material powder is spread out in the preparation method according to any one of claims 1 to 8, and medium-temperature gas nitriding is carried out in the mixed atmosphere of the low-temperature gas nitriding tail gas and ammonia to obtain medium-temperature nitriding alloy powder and medium-temperature gas nitriding tail gas. The raw material powder is spread out in a flat-laying manner according to any one of claims 1 to 8, and high-temperature gas nitriding is carried out in a mixed atmosphere of medium-temperature gas nitriding tail gas and ammonia to obtain high-temperature nitriding alloy powder and high-temperature gas nitriding tail gas; the raw material powder independently includes one or more of stainless steel powder, titanium alloy powder and nickel-based alloy powder. Iron oxide powder is spread out in a flat-laying manner according to any one of claims 1 to 8, and a reduction-nitriding reaction is carried out under the atmosphere of the high-temperature gas nitriding tail gas to obtain iron-nitrogen alloy powder.

10. The co-production method according to claim 9, characterized in that, The volume ratio of the cryogenic gas nitriding tail gas to ammonia in the mixed atmosphere is 5:

1. The volume ratio of the intermediate-temperature gas nitriding tail gas and ammonia in the mixed atmosphere is 3:1.

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