A Preparation Method of High-Performance Rapidly Quenched Samarium-Iron-Nitrogen Magnetic Powder

Abstract

The present invention provides a method for preparing high-performance rapidly quenched samarium iron nitride magnetic powder, belonging to the technical field of magnetic materials, and comprising the following steps: A1. Weigh according to 2-3% excess of Sm, and smelt and rapidly solidify samarium powder and iron powder in a small-scale melting and rapid quenching device to obtain primary alloy powder; A2. After cooling the primary alloy powder, mix it evenly with metallic samarium powder, and smelt and rapidly solidify it again to obtain secondary alloy magnetic powder; A3. Perform HDDR treatment on the secondary alloy powder to obtain modified alloy powder; A4. Perform nitriding treatment on the modified alloy powder to obtain high-performance rapidly quenched samarium iron nitride magnetic powder with uniform structure. By addressing the loss of metallic samarium in the primary alloy powder stage and the alloy composition segregation caused by the difference in the density of the molten pool during melting, the present invention adds metallic samarium during the secondary melting to effectively suppress the non-uniform magnetic properties of the magnetic powder particles caused by alloy composition segregation, enabling the prepared magnetic material to have high coercivity, magnetic properties, and uniformity.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic materials, and particularly relates to a method for preparing high-performance rapidly quenched samarium iron nitride magnetic powder. Background Art

[0002] Samarium iron nitride materials have a high Curie temperature and good corrosion resistance, and can be used for a long time in a humid environment. They have a wide range of applications in the preparation of micro-motor magnetic strips and functional magnetic materials. With the lightweight and high-performance development of household appliances, instruments, aerospace, and new energy vehicles, there is an urgent need to develop high-performance and cost-effective samarium iron nitride materials.

[0003] In existing industrial production, it is usually necessary to carry out melting and rapid solidification treatment under the protection of inert gas, obtain fine powder with a specific crushing device, and slowly cool it after high-temperature nitridation to obtain samarium iron nitride magnetic powder. However, due to the active chemical properties of samarium element, during the preparation of samarium iron nitride materials, when melting and rapid solidification are carried out, due to the relatively high vapor pressure of samarium and its melting point of 1074 °C, which is significantly lower than that of iron at 1538 °C, metallic samarium is prone to loss due to preferential volatilization at the melting temperature of 1600 - 1700 °C. Moreover, insufficient vacuum degree or too long melting time during melting will lead to the loss of samarium. Although the total loss rate of samarium has been reduced from 15 - 20% to 3 - 5% after optimizing the process in the prior art, such as through liquid nitrogen crushing and dynamic argon protection, due to the density difference in the molten pool, it will further cause composition segregation in the molten alloy, resulting in samarium-poor phase and samarium-rich phase. Because the rapid quenching cooling roller requires the molten pool alloy liquid surface to be extremely stable to eject continuous strips during subsequent cooling, in order to ensure the stability of the cooling strips, mechanical or current stirring cannot be used. The composition density difference under the static and stable state of the molten pool liquid surface leads to composition segregation of the alloy strips flowing out to the cooling roller, resulting in problems such as low magnetic properties and extremely uneven properties of the finished magnetic powder, making it difficult to achieve high magnetic properties and consistency for the final magnetic powder. In current production practice, a magnetic separator is generally used to classify and screen the magnetic powder into high, medium, and low performance, causing waste of rare earth resources and energy and reducing production efficiency. Summary of the Invention

[0004] To solve the problems in the background art, the present invention provides a method for preparing high-performance rapidly quenched samarium iron nitride magnetic powder, which can effectively inhibit the problems of samarium loss and composition segregation during the preparation of samarium iron nitride materials, and effectively improve production efficiency, and prepare a samarium iron nitride magnetic powder with high coercivity and uniform magnetic properties.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing high-performance rapidly quenched samarium iron nitride magnetic powder, comprising the following steps:

[0007] A1. Sm2Fe 17 Based on the components, weigh according to the excess of 2-3% Sm, melt, quench and solidify samarium powder and iron powder in a small melting and quenching device under vacuum and argon filling conditions, and crush to a particle size of 30-400 mesh to obtain a primary alloy powder;

[0008] A2, mixing the primary alloy powder and the metal samarium powder and stirring them evenly, subjecting the mixture to a smelting, rapid quenching and rapid solidification treatment in a small smelting and rapid quenching device under vacuum and argon filling conditions, and crushing the mixture into particles of 60-200 mesh to obtain a secondary modified alloy powder;

[0009] A3, subjecting the secondary modified alloy powder to HDDR treatment, crushing it to a particle size of 100-400 mesh, and subjecting it to aging treatment to obtain modified alloy powder;

[0010] A4. Place the modified alloy powder in a high-temperature nitriding furnace for 4-12 hours, and then rapidly cool it to room temperature in vacuum within 1 hour to obtain high-performance rapidly quenched samarium iron nitrogen magnetic powder with uniform structure.

[0011] Furthermore, the small-scale smelting and quenching device comprises a continuous feeding overflow crucible and a cold cutting roller, which continuously feed materials at one end and continuously overflow materials at the other end. The cold cutting roller is placed at the overflow port of the crucible. The feeding port and the overflow port of the continuous feeding overflow crucible adopt a double-end sealing structure. An annular argon nozzle with a pressure of 0.2-0.5MPa is arranged on the periphery of the overflow port and the cooling roller interface to form an inert gas barrier. The outer diameter of the continuous feeding overflow crucible is: diameter 80-300mm, height: 100-300mm.

[0012] Furthermore, the feed port of the continuous feeding overflow crucible is located at the top of the crucible for continuously adding raw materials. Dynamic sealing is used to accommodate continuous feeding. The feed port uses a double gate valve or a rotary air lock valve to achieve synchronization of feeding and sealing. The overflow port is located at the bottom of the crucible to control the stable outflow of the melt and form a uniform liquid film to prevent gas backflow. The discharge port maintains the local atmosphere through gas protection or mechanical sealing to prevent gas disturbance in the cooling roller area, thereby realizing a double-end sealing structure for the feed port and overflow port of the continuous feeding overflow crucible. ‌‌

[0013] Furthermore, in step A1, the smelting rapid quenching and rapid solidification treatment process is as follows: under vacuum and then argon filling conditions, the mixture of samarium powder and iron powder is placed in a small smelting rapid quenching device and heated to 1600-1700°C, a uniform melt is continuously obtained by continuously feeding at one end and continuously overflowing at the other end, and the melt is placed on the surface of a cooling roller rotating at a speed of 20-30m / s for cooling for ≥10 5 The cooling rate of K / s is fast solidification. Affected by factors such as vacuum degree, the smelting, rapid quenching and rapid solidification treatment is carried out in a single material warehouse batch of ≤500 kg.

[0014] Further, in step A1, the crushing method is physical crushing by a jet mill or a vacuum crusher, the crushing temperature is 120 - 140°C, and the pressure is 0.06 - 0.1 Mpa.

[0015] Further, in step A2, the addition ratio of the samarium metal powder is recorded by calculating the input amount of raw materials and the product mass through mass balance, and the total loss rate is calculated by the difference method. The formula for the difference method is: total loss rate = (1 - mass of Sm in the finished magnetic powder / mass of Sm in the raw material) × 100%, and the precision control range is ±0.5%.

[0016] Further, in step A3, the specific process of HDDR treatment is: heating from room temperature to 750 - 850°C under vacuum conditions, disproportionating for 1.5 - 2.5 h in a hydrogen atmosphere of 0.04 - 0.6 MPa, slowly heating to 900 - 950°C, and dehydrogenating under vacuum for 1 - 2 h.

[0017] Further, in step A3, the specific process of aging treatment is: first heating to 650 - 700°C, holding for 30 - 60 min, then cooling under vacuum to 200 - 220°C, and holding for 2 - 3 h.

[0018] Further, in step A4, the nitrogen pressure for the high-temperature nitriding treatment is: heating from room temperature to 500 - 600°C under the condition of 0.1 - 1.5 MPa.

[0019] This application has the following beneficial effects:

[0020] 1. The present invention provides a method for preparing high-performance rapidly quenched samarium iron nitride magnetic powder. By compensating for the loss of samarium metal in the primary alloy powder stage and the alloy composition segregation caused by the difference in the density of the molten pool during melting, the addition of samarium metal in the secondary melting and weighing according to the excess of Sm by 2 - 3% effectively curb the non-uniform magnetic properties of the magnetic powder particles caused by alloy composition segregation, effectively suppress the non-uniform magnetic properties of the samarium iron nitride material during the preparation process, and make the prepared magnetic material have a high coercivity and magnetic property uniformity.

[0021] 2. To cooperate with the precise replenishment of samarium in secondary melting, a small-scale melting and rapid quenching device with a continuous feeding and overflow crucible is used in the preparation of rapidly quenched samarium-iron-nitrogen magnetic powder. In this device, one end of the hopper continuously feeds the crucible, and the other end overflows continuously. The overflow design can ensure the stability of the alloy liquid level relative to the cooling roll during the melting process, reduce the size fluctuation of the alloy strip, and improve the alloy uniformity. The small-sized crucible has a small molten pool volume and a short heating time, which can avoid the excessive waiting time for the alloy liquid due to the large amount of heating raw materials, reduce the loss of samarium element caused by high-temperature volatilization. The device is small in size and has a good sealing performance with a double-end sealing structure. Under the condition of 1.1 atmospheric pressure of high-purity industrial argon gas, the dynamic positive argon pressure protection can reduce the oxidation loss of samarium during the melting process. Moreover, the continuous feeding and overflow crucible small-scale melting equipment can shorten the time of fractional melting and reduce the generation of waste. The raw material cost per unit mass of magnetic powder is reduced by 15 - 20%, and it is suitable for large-scale production scenarios. The single hopper single batch is ≤ 500 kg, and combined with the peripheral segmented vacuum feeding system to replenish the hopper regularly, it can even produce continuously without stopping. Detailed implementation mode

[0022] The following further elaborates on this application in conjunction with examples.

[0023] Unless otherwise specified, the raw materials in the examples and comparative examples of this application are all commercially available. Example 1

[0024] A method for preparing high-performance rapidly quenched samarium-iron-nitrogen magnetic powder includes the following steps:

[0025] 1. Based on the composition of Sm2Fe 17 group, weigh with Sm being 2% in excess, and carry out melting, rapid quenching and rapid solidification treatment on samarium powder and iron powder in a small-scale melting and rapid quenching device under the condition of vacuum and then filling with argon. Use a hydrogen gas jet mill for crushing, with a crushing temperature of 130 °C and a pressure of 0.08 Mpa, and crush to a particle size of 200 mesh to obtain the primary alloy powder.

[0026] A2. Calculate the total loss rate of samarium by the difference method, mix and stir the primary alloy powder and the calculated loss of metallic samarium powder evenly, and then carry out melting, rapid quenching and rapid solidification treatment on the mixture again in a small-scale melting and rapid quenching device under the condition of vacuum and filling with argon. Use a hydrogen gas jet mill for crushing, with a crushing temperature of 130 °C and a pressure of 0.08 Mpa, and crush to a particle size of 100 mesh to obtain the secondary alloy powder.

[0027] A3. Subject the secondary-modified alloy powder to HDDR treatment. Under vacuum conditions, heat it from room temperature to 800 °C, disproportionate it in a hydrogen atmosphere of 0.05 MPa for 2 h, then slowly heat it to 900 °C and dehydrogenate it under vacuum for 1.5 h. Crush it to a particle size of 200 mesh, and conduct aging treatment. First, heat it to 650 °C and hold for 40 min, then cool it under vacuum to 220 °C and hold for 2 h to obtain the modified alloy powder;

[0028] A4. Place the modified alloy powder in a high-temperature nitriding furnace, conduct high-temperature nitriding treatment at 500 °C from room temperature under the condition of 0.2 MPa for 8 h, and then quickly cool it to room temperature under vacuum within 1 h to obtain high-performance rapidly quenched samarium-iron-nitrogen magnetic powder with uniform structure.

[0029] In step A1, the process of melting and rapid quenching and solidification treatment is as follows: Under the condition of vacuum and argon filling, place the mixture of samarium powder and iron powder in a continuous feeding overflow crucible with an outer diameter of 200 mm and a height of 186 mm and heat it to 1600 °C. Continuously obtain a uniform melt by continuously feeding at one end and overflowing at the other end. Place the melt on the surface of a cooling roller rotating at a speed of 25 m / s for cooling, and rapidly solidify it at a cooling rate of 10 5 K / s.

[0030] Comparative Example 2

[0031] A method for preparing high-performance rapidly quenched samarium-iron-nitrogen magnetic powder, comprising the following steps:

[0032] A1. Based on the component of Sm2Fe 17 Weigh according to 2% excess Sm. Conduct melting, rapid quenching and solidification treatment on the samarium powder and iron powder in a small melting and rapid quenching device under the condition of vacuum and argon filling. Use a hydrogen jet mill for crushing, with a crushing temperature of 130 °C and a pressure of 0.08 Mpa, and crush it to a particle size of 100 mesh to obtain alloy powder;

[0033] A2. Subject the alloy powder to HDDR treatment. Under vacuum conditions, heat it from room temperature to 800 °C, disproportionate it in a hydrogen atmosphere of 0.05 MPa for 2 h, slowly heat it to 900 °C, and dehydrogenate it under vacuum for 1.5 h. Crush it to a particle size of 200 mesh, and conduct aging treatment. First, heat it to 650 °C and hold for 40 min, then cool it under vacuum to 220 °C and hold for 2 h to obtain the modified alloy powder;

[0034] A3. Place the modified alloy powder in a high-temperature nitriding furnace, conduct high-temperature nitriding treatment at 500 °C from room temperature under the condition of 1 MPa for 8 h, and then quickly cool it to room temperature under vacuum within 1 h to obtain rapidly quenched samarium-iron-nitrogen magnetic powder.

[0035] In step A1, the smelting and rapid quenching process is as follows: Under the condition of vacuum argon filling, the mixture of samarium powder and iron powder is placed in a continuous feeding overflow crucible with an outer diameter of 148 mm and a height of 186 mm and heated to 1600 °C. A uniform melt is continuously obtained by continuously feeding at one end and continuously overflowing at the other end. The melt is cooled in a cooling roller rotating at a speed of 25 m / s and rapidly solidified at a cooling rate of 10 5 K / s.

[0036] Comparative Example 3

[0037] A method for preparing high-performance rapidly quenched samarium-iron-nitrogen magnetic powder, comprising the following steps:

[0038] A1. Based on the Sm2Fe 17 component, weighing is carried out according to the chemical formula ratio. The samarium powder and iron powder are subjected to smelting and rapid quenching treatment in a smelting device under the condition of vacuum argon filling. The smelting time is 1 h. It is crushed using a hydrogen gas stream mill. The crushing temperature is 130 °C and the pressure is 0.08 Mpa. It is crushed to a particle size of 200 mesh to obtain alloy powder;

[0039] A2. The alloy powder is subjected to HDDR treatment. Under vacuum conditions, it is heated from room temperature to 800 °C, disproportionated in a hydrogen atmosphere of 0.05 MPa for 2 h, slowly heated to 900 °C, and vacuum dehydrogenated for 1.5 h. It is crushed to a particle size of 200 mesh and subjected to aging treatment. First, it is heated to 650 °C and held for 40 min, and then vacuum cooled to 220 °C and held for 2 h to obtain modified alloy powder;

[0040] A3. The modified alloy powder is placed in a high-temperature nitriding furnace and subjected to high-temperature nitriding treatment at 500 °C under 1 MPa for 8 h, and then rapidly cooled to room temperature within 1 h under vacuum to obtain rapidly quenched samarium-iron-nitrogen magnetic powder.

[0041] Effect verification

[0042] The samarium-iron-nitrogen magnetic powders prepared in Example 1 and Comparative Examples 2 and 3 are respectively subjected to performance tests. The test steps are as follows: 1. Screening of magnetic properties of magnetic powder: 10 kg of the magnetic powders prepared in the above examples and comparative examples are respectively screened by a magnetic separator to obtain magnetic powders with high, medium, and low performance categories. The high, medium, and low performance magnetic powders screened in the examples and comparative examples are divided into 9 portions and marked and weighed respectively; 2. Preparation of test sample columns: 98 g of each of the 9 portions of samples are respectively mixed evenly according to the ratio of 98 parts of samarium-iron-nitrogen magnetic powder, 1.5 parts of binder, and 0.5 part of auxiliary agent. Then the mixture is put into a press and molded. The molding pressure is 1.0 GPA. After pressing, a magnet is obtained, and the coercivity Hcj and the corresponding magnetic property BHmax of the magnet are tested. The results are shown in Table 1:

[0043]

[0044] Result analysis

[0045] By analyzing Example 1 and Comparative Examples 2-3 and combining Table 1, it can be seen that the samarium-iron-nitrogen magnetic powder material prepared by the method for preparing a high-performance rapidly quenched samarium-iron-nitrogen magnetic powder provided by the present invention has a high coercivity. The coercivity of the magnet can reach 14.1 KOe, the magnetic properties are uniformly distributed and excellent, and it has a high preparation yield and greatly reduces the waste rate of raw material cost per unit mass. The specific analysis is as follows:

[0046] Compared with Example 1, Comparative Example 2 did not combine secondary melting + difference method to calculate the total loss rate of samarium. Although 2% excess Sm was weighed in the early stage, the total loss of samarium was not compensated by secondary melting, resulting in a relatively larger mass balance error of samarium-iron compared to Example 1. The phenomenon of non-uniform magnetic properties of magnetic powder particles caused by alloy composition segregation was serious, and the coercivity of the magnet prepared was significantly reduced.

[0047] Compared with Example 1, Comparative Example 3 used ordinary rapid quenching melting, hydrogen breaking, and nitriding methods and an ordinary melting pool, which not only increased the time of single melting but also was not conducive to the control and calculation of raw material input, resulting in a relatively high waste rate of raw material cost per unit mass. Moreover, the total loss of samarium was not compensated during melting, and the phenomenon of non-uniform magnetic properties of magnetic powder particles caused by alloy composition segregation was even more serious. The coercivity and magnetic properties of the magnet prepared were significantly reduced.

[0048] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0049] In addition, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing high-performance rapid-quenching samarium iron nitrogen magnetic powder, characterized in that: The preparation method comprises the following steps: A1. Sm2Fe 17 Based on the components, weighing is carried out according to an excess of 2-3% of Sm, and the samarium powder and iron powder are melted, quenched and solidified in a small melting and quenching device under the conditions of vacuum first and then argon filling, and then crushed to a particle size of 30-400 mesh after cooling to obtain a primary alloy powder; A2, the primary alloy powder and the samarium metal powder are mixed and stirred evenly, and the mixture is again subjected to a smelting, rapid quenching and rapid solidification treatment in a small smelting and rapid quenching device under vacuum and then argon filling conditions, and crushed to a particle size of 60-200 mesh to obtain a secondary modified alloy powder; A3, subjecting the secondary modified alloy powder to HDDR treatment, crushing it to a particle size of 100-400 mesh, and subjecting it to aging treatment to obtain modified alloy powder; A4. Place the modified alloy powder in a high-temperature nitriding furnace for 4-12 hours of high-temperature nitriding treatment, and then rapidly cool to room temperature in vacuum within 1 hour to obtain high-performance rapidly quenched samarium iron nitrogen magnetic powder with uniform structure; Among them, in step A1, the small-scale smelting and quenching device is a continuous feeding overflow crucible and a cold cutting roller with continuous feeding at one end and continuous overflow at the other end, the cold cutting roller is placed at the overflow port of the crucible, the feeding port and the overflow port of the continuous feeding overflow crucible adopt a double-end sealing structure, and an annular argon nozzle with a pressure of 0.2-0.5MPa is arranged outside the overflow port and the cooling roller interface to form an inert gas barrier; In step A1, the smelting, rapid quenching and rapid solidification treatment process is as follows: under vacuum and argon filling conditions, the mixture of samarium powder and iron powder is placed in a small smelting and rapid quenching device and heated to 1600-1700°C, a uniform melt is continuously obtained by continuously feeding the heating crucible at one end and continuously overflowing the other end, and the melt is placed on the surface of a cooling roller rotating at a speed of 20-30m / s for cooling for ≥10 5 The cooling rate of K / s is fast solidification, and the single material warehouse batch for smelting, rapid quenching and rapid solidification treatment is ≤500 kg; Among them, in step A2, the addition ratio of the metal samarium powder is calculated by mass balance to record the raw material input amount and the product mass, and the total loss rate is calculated by the difference method, wherein the difference method calculation formula is: total loss rate = (1-Sm mass in finished magnetic powder / Sm mass of raw material) × 100%, and the accuracy control range is ±0.5%.

2. The method for preparing high-performance rapid-quenching samarium iron nitrogen magnetic powder according to claim 1, characterized in that: The outer diameter of the continuous feeding overflow crucible is 80-300 mm in diameter and 100-300 mm in height.

3. The method for preparing high-performance rapid-quenching samarium iron nitrogen magnetic powder according to claim 1, characterized in that: In step A1, the crushing method is physical crushing by air jet mill or vacuum crusher, the crushing temperature is 120-140° C., and the pressure is 0.06-0.1 MPa.

4. The method for preparing high-performance rapid-quenching samarium iron nitrogen magnetic powder according to claim 1, characterized in that: In step A3, the specific process of HDDR treatment is: heating from room temperature to 750-850° C. under vacuum conditions, disproportionation in a hydrogen atmosphere of 0.04-0.6 MPa for 1.5-2.5 h, slowly heating to 900-950° C., and vacuum dehydrogenation for 1-2 h.

5. The method for preparing high-performance rapid-quenching samarium iron nitrogen magnetic powder according to claim 1, characterized in that: In step A3, the specific process of aging treatment is: first heating to 650-700°C, keeping warm for 30-60 minutes, and then vacuum cooling to 200-300°C, keeping warm for 2-3 hours.

6. The method for preparing high-performance rapid-quenching samarium iron nitrogen magnetic powder according to claim 1, characterized in that: In step A4, the nitrogen pressure of the high temperature nitridation treatment is: heating from room temperature to 500-600° C. under the condition of 0.1-1.5 MPa.

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