CN115116687A - Method for preparing sintered neodymium-iron-boron magnetic steel - Google Patents
Method for preparing sintered neodymium-iron-boron magnetic steel Download PDFInfo
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
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Abstract
The invention belongs to the field of permanent magnet materials, and particularly discloses a method for preparing sintered neodymium iron boron magnetic steel. The preparation method comprises the following steps: mixing the fine neodymium iron boron alloy powder with an additive, then placing the mixed fine neodymium iron boron alloy powder in a forming press to be pressed into a green body, conveying the green body into a vacuum sintering furnace to be subjected to heat treatment to obtain a blank, and grinding, acid pickling and phosphating the blank after being discharged out of the furnace to obtain neodymium iron boron magnetic steel; the forming press is connected with a sintering furnace, and the pressing, conveying and heat treatment are all carried out under the protection of inert gas. The preparation method of the invention does not need cold isostatic pressing, not only shortens the process flow and has low production cost, but also does not damage the orientation degree of crystal grains in the green body, the orientation degree of the blank is higher, and the prepared neodymium iron boron magnetic steel has high remanence.
Description
Technical Field
The invention belongs to the field of permanent magnet materials, and particularly relates to a method for preparing sintered neodymium iron boron magnetic steel.
Background
Since the advent of the rare earth permanent magnet material, especially neodymium iron boron rare earth permanent magnet material, it has been widely used in the fields of new energy automobiles, white home appliances, wind power generation, elevator traction machines, etc. because of its excellent magnetic properties. The traditional technology at present is to smelt various alloys in a vacuum strip casting furnace and prepare casting sheets, the casting sheets are crushed by absorbing hydrogen and then crushed into micron-sized powder in an airflow mill, the powder is pressed in a press to prepare a green body with a certain size, the green body is placed in a vacuum sintering furnace for sintering after being subjected to cold isostatic pressing, the blank is taken out of the furnace and then is machined, cut and ground into a finished product with a specification, and then the finished product is obtained after surface treatment and packaging. The neodymium iron boron magnetic steel prepared by the method has excellent performance, is popularized in a large range in the industry, and almost all sintered neodymium iron boron enterprises produce the magnetic steel in the mode.
On one hand, however, the process flow is complex, the size of a blank prepared by sintering a green body is large, and a cutting and grinding process of machining is required to be adopted to prepare a required finished product specification subsequently, so that the processing process is complex, a large amount of cutting magnetic mud is generated at the same time, and the waste of scarce rare earth resources is caused. On the other hand, cold isostatic pressing can destroy the orientation degree of the green body, thereby causing the residual magnetism of the blank to be reduced, and expensive equipment such as cold isostatic pressing is also required, so that the integral production process still has the defects of high production cost and long production period. With the continuous reduction of the production cost in the downstream industry, cost reduction and efficiency improvement are the first requirements of the neodymium iron boron industry.
Disclosure of Invention
Aiming at the defects of high production cost and long production period of neodymium iron boron rare earth permanent magnet materials in the prior art, the invention provides a method for preparing sintered neodymium iron boron magnetic steel.
In order to achieve the purpose, the method specifically comprises the following technical scheme:
a method for preparing sintered NdFeB magnetic steel comprises the following steps:
(1) cleaning and smelting alloy raw materials to obtain neodymium iron boron alloy, and performing hydrogen breaking and airflow milling on the neodymium iron boron alloy to obtain neodymium iron boron alloy fine powder;
(2) mixing the fine neodymium iron boron alloy powder with an additive, then placing the mixed fine neodymium iron boron alloy powder in a forming press to be pressed into a green body, conveying the green body into a vacuum sintering furnace to be subjected to heat treatment to obtain a blank, and carrying out polishing, acid pickling and phosphorization processes on the blank discharged out of the furnace to obtain sintered neodymium iron boron magnetic steel; the forming press is connected with a sintering furnace, and the pressing, conveying and heat treatment are all carried out under the protection of inert gas.
The invention designs a special pressing device which is a one-step forming press, the pressing pressure can reach more than 50MPa and is higher than the pressure provided by the common press, therefore, under the pressure, additives are added, the green body can not crack and deform after being sintered, the method of the invention does not need to further carry out cold isostatic pressing treatment like the traditional process, the process flow is shortened, the orientation degree of crystal grains in the green body can not be damaged, the orientation degree of the blank is higher, and the remanence of the prepared product is higher than that of the traditional process. The profiling device is connected with the vacuum sintering furnace, and profiling, conveying and heat treatment are carried out under the protection of inert gas, so that the oxidation of alloy powder is avoided, and the performance of the magnetic steel is further improved.
As a preferred embodiment of the invention, the additive in the step (2) is at least one of methyl cinnamate, oleamide, YSH-6 and YSH-1.
The additive is used as a protective agent to prevent the alloy from being oxidized in a series of preparation processes, so that the purity of the alloy is improved, and the performance of the magnetic steel is further improved.
As a preferred embodiment of the present invention, the pressure of the pressing in step (2) is 50MPa or more.
In a further preferred embodiment of the present invention, the pressure level of the pressing in the step (2) is 80 to 100 MPa.
In the invention, the pressing pressure is higher than the conventional pressure, so that the green body can not crack or deform after being sintered, thereby omitting the cold isostatic pressing treatment step in the traditional process, shortening the process step and finally keeping the good performance of the magnetic steel.
As a preferred embodiment of the present invention, before pressing, the powder is poured into a high pressure resistant mold, the high pressure resistant mold is composed of a plurality of cells, and the specification of each cell can be designed to be close to the finished specification of the magnetic steel.
The alloy fine powder is directly pressed in a pressing device to be close to the specification of a finished product, and a green body is close to the specification of the finished product after being sintered and discharged, so that the surface is only ground without the traditional grinding and cutting process, a large amount of magnetic mud is not generated, the preparation process steps are reduced, the rare earth resource is saved, and the production cost is reduced.
In a preferred embodiment of the present invention, the heat treatment in step (2) is performed by sintering at 900 to 1500 ℃ for 5 to 10 hours, and then annealing at 400 to 1000 ℃ for 2 to 10 hours.
As a further preferred embodiment of the present invention, the heat treatment in step (2) is sintering at 1070 ℃ for 8h, and then annealing at 890 ℃ for 3h and 520 ℃ for 5 h.
In a more preferred embodiment of the present invention, the degree of vacuum during the heat treatment is less than 0.01 pa.
In a preferred embodiment of the present invention, the particle size of the fine powder of neodymium iron boron alloy in step (1) is 3 to 6 μm.
In a further preferred embodiment of the present invention, the particle size of the fine powder of neodymium iron boron alloy in step (1) is 4 to 4.2 μm.
As a preferable embodiment of the invention, the content of the rare earth metal in the neodymium iron boron alloy in the step (1) is 10-35 wt%.
As a further preferable embodiment of the present invention, the content of the rare earth metal in the neodymium iron boron alloy in the step (1) is 31 wt%.
In a preferred embodiment of the present invention, the inert gas is at least one of nitrogen and argon.
As a further preferred embodiment of the present invention, the inert gas is nitrogen.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention designs special pressing equipment, the pressing pressure reaches more than 50MPa and is higher than the pressure provided by a common press, so that under the pressure, additives are added, and the green body can not crack or deform after being sintered.
(2) The preparation method of the invention does not need a cold isostatic pressing step, not only shortens the process flow, but also does not damage the orientation degree of crystal grains in the green blank, the orientation degree of the blank is higher, and the residual magnetism of the prepared product is higher than that of the traditional process.
(3) The alloy fine powder is directly pressed in a pressing device to be close to the specification of a finished product, and a green body is close to the specification of the finished product after being sintered and discharged, so that the surface is only ground without the traditional multiple grinding and cutting process, a large amount of magnetic mud is not generated, the preparation process steps are reduced, the rare earth resource is saved, and the production cost is reduced.
(4) The invention connects the compression equipment with the vacuum sintering furnace, and carries out compression, transmission and heat treatment under the protection of inert gas, thereby avoiding the oxidation of alloy powder and further improving the performance of the magnetic steel.
(5) The preparation method has the advantages of short process flow, no need of cold isostatic pressing and no generation of a large amount of magnetic mud, and is a low-cost method for preparing the sintered neodymium-iron-boron magnetic steel.
Drawings
Fig. 1 is a schematic view of a process flow for preparing a sintered ndfeb magnetic steel finished product sample according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a process flow for preparing a neodymium iron boron magnetic steel finished product sample according to comparative example 1 of the present invention.
Detailed Description
To better illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further illustrated by specific comparative examples and examples.
The conventional press performs a pressing process using oil as a driving force, the pressing pressure is low, and the conventional pressing process needs to go through a plurality of times or various types of pressing processes (e.g., isostatic pressing). The one-step forming press related in the embodiment of the invention is special pressing equipment, the electric drive is used, the pressure which can be provided is larger than that of the traditional press, the one-step forming press is special equipment developed for the invention, inert gas is protected in the equipment, the equipment is connected with a vacuum sintering furnace through a transmission pipeline which is automatically and intelligently controlled, and the whole system is in the atmosphere protected by the inert gas. The pressing pressure of the special press reaches more than 50MPa, which is higher than the pressure provided by the common press. Therefore, the problems of cracking and the like of products cannot be caused by canceling cold isostatic pressing, and meanwhile, the one-step forming press is connected with vacuum sintering equipment and is filled with inert gas for protection, so that the pressing, sintering and conveying processes are all under the protection of the inert gas, and powder in the equipment is prevented from being oxidized.
Example 1
(1) Smelting: performing shot blasting on a raw material (containing praseodymium and neodymium) for manufacturing neodymium iron boron magnetic steel, removing surface rust, charging and smelting, and obtaining an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.2 mu m and the D90/D10 of less than 4.5 by air flow milling. Adding additive methyl cinnamate into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Pressing and sintering: introducing nitrogen to protect the integral system in a one-step forming press; and then uniformly adding the fine powder into a die cavity through a butterfly valve, and opening the pressing, wherein the pressing pressure is 80Mpa, so that the fine powder is pressed into a green body, and the specification of the green body is 30 x 10 x 5 mm. Directly conveying the obtained green body into a sintering furnace through a conveyor belt on equipment, sintering and tempering in a vacuum sintering furnace, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during tempering, then the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degree is lower than 0.01 pa; and (3) polishing the surface of the magnet by the blank after the blank is discharged from the furnace through a grinding machine, and packaging after acid pickling and phosphorization to obtain a sintered neodymium iron boron magnetic steel finished product. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1.
Example 2
(1) Smelting: the raw material (containing praseodymium and neodymium) for manufacturing the neodymium iron boron magnetic steel is subjected to shot blasting to remove surface rust, and then the raw material is loaded into a furnace and smelted to obtain an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.0 mu m and the D90/D10 of less than 4.5 by air flow milling. Adding the additive methyl cinnamate into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Pressing and sintering: introducing nitrogen to protect the integral system in a one-step forming press; then the fine powder is evenly added into a die cavity through a butterfly valve, and the pressing is started, the pressing pressure is 80Mpa, so that the fine powder is pressed into a green body, and the specification of the green body is 30 x 10 x 5 mm. Directly conveying the obtained green body into a sintering furnace through a conveyor belt on equipment, sintering and tempering in a vacuum sintering furnace, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during tempering, then the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degree is lower than 0.01 pa; and (3) polishing the surface of the magnet by the blank after the blank is discharged from the furnace through a grinding machine, and packaging after acid pickling and phosphorization to obtain a sintered neodymium iron boron magnetic steel finished product. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1.
Example 3
(1) Smelting: performing shot blasting on a raw material (containing praseodymium and neodymium) for manufacturing neodymium iron boron magnetic steel, removing surface rust, charging and smelting, and obtaining an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.0 mu m and the D90/D10 of less than 4.5 by air flow milling. Adding YSH-6 (Tianjin Sheng sanden magnetoelectric technology, Ltd.) into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Pressing and sintering: introducing nitrogen to protect the integral system in a one-step forming press; and then uniformly adding the fine powder into a die cavity through a butterfly valve, and opening the pressing, wherein the pressing pressure is 80Mpa, so that the fine powder is pressed into a green body, and the specification of the green body is 30 x 10 x 5 mm. Directly conveying the obtained green body into a sintering furnace through a conveyor belt on equipment, sintering and tempering in a vacuum sintering furnace, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during tempering, then the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degree is lower than 0.01 pa; and (3) polishing the surface of the magnet by the blank after the blank is discharged from the furnace through a grinding machine, and packaging after acid pickling and phosphorization to obtain a sintered neodymium iron boron magnetic steel finished product. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1.
Example 4
(1) Smelting: the raw material (containing praseodymium and neodymium) for manufacturing the neodymium iron boron magnetic steel is subjected to shot blasting to remove surface rust, and then the raw material is loaded into a furnace and smelted to obtain an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.0 mu m and the D90/D10 of less than 4.5 by air flow milling. And adding the additive oleamide into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Pressing and sintering: introducing nitrogen to protect the integral system in a one-step forming press; and then uniformly adding the fine powder into a die cavity through a butterfly valve, and opening the pressing, wherein the pressing pressure is 80Mpa, so that the fine powder is pressed into a green body, and the specification of the green body is 30 x 10 x 5 mm. Directly conveying the obtained green body into a sintering furnace through a conveyor belt on equipment, sintering and tempering in a vacuum sintering furnace, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during tempering, then the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degree is lower than 0.01 pa; and (3) polishing the surface of the magnet by the blank after the blank is discharged from the furnace through a grinding machine, and packaging after acid pickling and phosphorization to obtain a sintered neodymium iron boron magnetic steel finished product. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1.
Example 5
(1) Smelting: performing shot blasting on a raw material (containing praseodymium and neodymium) for manufacturing neodymium iron boron magnetic steel, removing surface rust, charging and smelting, and obtaining an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.0 mu m and the D90/D10 of less than 4.5 by air flow milling. Adding YSH-1 (Tianjin Sheng sanden magnetoelectric technology, Ltd.) into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Pressing and sintering: introducing nitrogen to protect the integral system in a one-step forming press; and then uniformly adding the fine powder into a die cavity through a butterfly valve, and opening the pressing, wherein the pressing pressure is 80Mpa, so that the fine powder is pressed into a green body, and the specification of the green body is 30 x 10 x 5 mm. Directly conveying the obtained green body into a sintering furnace through a conveyor belt on equipment, sintering and tempering in a vacuum sintering furnace, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during tempering, then the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degree is lower than 0.01 pa; and (3) polishing the surface of the magnet by the blank after the blank is discharged from the furnace through a grinding machine, and packaging after acid pickling and phosphorization to obtain a sintered neodymium iron boron magnetic steel finished product. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1.
Example 6
(1) Smelting: performing shot blasting on a raw material (containing praseodymium and neodymium) for manufacturing neodymium iron boron magnetic steel, removing surface rust, charging and smelting, and obtaining an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.2 mu m and the D90/D10 of less than 4.5 by air flow milling. Adding the additive methyl cinnamate into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Pressing and sintering: introducing nitrogen to protect the integral system in a one-step forming press; and then uniformly adding the fine powder into a die cavity through a butterfly valve, and opening the pressing, wherein the pressing pressure is 100Mpa, so that the fine powder is pressed into a green body, and the specification of the green body is 30 x 10 x 5 mm. Directly conveying the obtained green body into a sintering furnace through a conveyor belt on equipment, sintering and tempering in a vacuum sintering furnace, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during tempering, then the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degree is lower than 0.01 pa; and (3) polishing the surface of the magnet by the blank after the blank is discharged from the furnace through a grinding machine, and packaging after acid pickling and phosphorization to obtain a sintered neodymium iron boron magnetic steel finished product. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1.
Comparative example 1
This comparative example is different from example 2 in the pressing and cold isostatic pressing process in step (3), and the rest of the steps and conditions are the same.
(1) Smelting: performing shot blasting on a raw material (containing praseodymium and neodymium) for manufacturing the neodymium iron boron magnetic steel, removing surface rust, then charging and smelting, and obtaining an alloy sheet with the thickness of 0.3 +/-0.1 mm in a die, wherein the content of rare earth (praseodymium and neodymium) is 31.0 wt%.
(2) Hydrogen crushing and powder preparation: the obtained alloy sheet is made into coarse powder by a hydrogen crushing process, and the coarse powder is made into fine powder with the granularity D50 (median diameter) of 4.0 mu m and the D90/D10 of less than 4.5 by air flow milling. Adding the additive methyl cinnamate into the fine powder under the protection of nitrogen, and stirring the fine powder to fully and uniformly mix the additive and the fine powder.
(3) Profiling, cold isostatic pressing and sintering: introducing nitrogen to protect the whole system in a traditional forming press; and then uniformly adding the fine powder into a die cavity through a butterfly valve, and opening the pressing, wherein the pressing pressure is 20MPa, so that the fine powder is pressed into a green body, and the specification of the green body is 60 x 50 x 45 mm. And (4) putting the green body into isostatic pressing equipment after vacuum packaging, and performing cold isostatic pressing. Transferring the green body subjected to cold isostatic pressing to a vacuum sintering furnace for sintering and tempering treatment (the sintering and tempering treatment are also carried out under the protection of nitrogen) to form a semi-finished product, wherein the sintering temperature is 1070 ℃, the time is 8 hours, the temperature is kept constant for 3 hours at 890 ℃ during the tempering treatment, the temperature is kept constant for 5 hours at 520 ℃, and the vacuum degrees are all lower than 0.01 pa; and (3) after the blank is discharged from the furnace, the surface of the magnet is polished by multiple times of cutting and multiple times of plane polishing of a grinding machine, and the finished product of the neodymium iron boron magnetic steel can be obtained by packaging after acid pickling and phosphorization. The finished product was tested for remanence (Br/KGs) and coercivity (Hcj/KOe) using NIM62000 and is summarized in Table 1. The specific process flow is shown in fig. 2.
Table 1 residual magnetism and coercive force of the finished product of ndfeb magnetic steel prepared in the examples and comparative examples 1
Fig. 1 is a flow chart of the process of the present invention, in contrast to a conventional process such as that shown in fig. 2, which shows that the conventional process requires not only cold isostatic pressing but also subsequent machining with multiple wire cutting passes.
The additive developed by the invention is used as a protective agent, can avoid the oxidation of alloy powder, and has good bonding effect, so that the powder is easy to form.
The one-step forming press is special equipment developed by the invention, the equipment is internally protected by inert gas and is connected with a vacuum sintering furnace through an automatic intelligent control transmission pipeline, and the whole system is in an inert gas atmosphere. The pressing pressure of the one-step forming press reaches more than 50MPa and is higher than the pressure which can be provided by a common press, so that under the pressure, the green body can not crack or deform after being sintered by the aid of the protective agent.
In the stage of pressing the blank by using the one-step forming press, the powder is pressed into a size close to the specification of a finished product in special press equipment, and then the powder is directly conveyed into sintering equipment through a connecting pipeline with the sintering equipment, and the blank after sintering does not need to be cut and only needs to be polished to obtain the finished product. Therefore, compared with the traditional process, the process is simple in flow and low in cost, and can save the scarce rare earth resources.
As can be seen from comparative example 1 and example 2, the remanence Br is obviously improved compared with the traditional process by adopting the one-step forming process. The one-step forming process can reach the same performance level as the traditional process, and has short process flow and low cost.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (10)
1. A method for preparing sintered NdFeB magnetic steel is characterized by comprising the following steps:
(1) cleaning and smelting alloy raw materials to obtain neodymium iron boron alloy, and performing hydrogen breaking and airflow milling on the neodymium iron boron alloy to obtain neodymium iron boron alloy fine powder;
(2) mixing the fine neodymium iron boron alloy powder with an additive, then placing the mixed fine neodymium iron boron alloy powder in a forming press to be pressed into a green body, conveying the green body into a vacuum sintering furnace to be subjected to heat treatment to obtain a blank, and carrying out polishing, acid pickling and phosphorization processes on the blank discharged out of the furnace to obtain sintered neodymium iron boron magnetic steel; the forming press is connected with a sintering furnace, and the pressing, conveying and heat treatment are all carried out under the protection of inert gas.
2. The method of claim 1, wherein the additive of step (2) is at least one of methyl cinnamate, oleamide, YSH-6, YSH-1.
3. The method of claim 1, wherein the pressing of step (2) is at a pressure of greater than or equal to 50 MPa.
4. The method according to claim 3, wherein the pressing pressure in the step (2) is 80-100 MPa.
5. The method according to any one of claims 1 to 3, wherein the heat treatment in the step (2) is sintering at 900 to 1500 ℃ for 5 to 10 hours, and then annealing at 400 to 1000 ℃ for 2 to 10 hours.
6. The method of claim 5, wherein the heat treatment in step (2) is sintering at 1070 ℃ for 8h, and then annealing at 890 ℃ for 3h and 520 ℃ for 5 h.
7. The method according to any one of claims 1 to 4, wherein the particle size of the fine powder of the NdFeB alloy in the step (1) is 3 to 6 μm.
8. The method according to any one of claims 1 to 4, wherein the content of the rare earth metal in the Nd-Fe-B alloy in the step (1) is 10 to 35 wt%.
9. The method according to any one of claims 1 to 4, wherein the inert gas is at least one of nitrogen and argon.
10. Neodymium iron boron magnetic steel prepared by the method of any one of claims 1 to 9.
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