High corrosion-resistant stainless sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The application relates to a high-corrosion-resistance stainless neodymium-iron-boron permanent magnet material and a preparation method thereof, the permanent magnet material comprises the following components in percentage by weight: RE 28-31%, B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, (Mo, W, Nb) 0-4%, Dy 0.04-0.08%, Co 0.5-1.5%, Tb 0.01-0.02%, and the rest is Fe, RE is one or more of rare earth elements Nd, Pr, Tb, Dy, La and Ce; the permanent magnet material simultaneously adds Ni and Cr elements in a smelting step, wherein the addition amount of Ni is less than that of Cr; in a use state, Ni and Cr are preferentially distributed at grain boundaries and main phases respectively, forming a microstructure of a high-corrosion-resistance Cr-containing permanent magnet main phase-high-corrosion-resistance Ni-containing grain boundary phase. The application reduces the potential difference between the grain boundary and the main phase, reduces the thermodynamic corrosion power of the magnet, and thus improves the corrosion resistance of a sintered neodymium-iron-boron permanent magnet substrate.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials technology, specifically relating to a highly corrosion-resistant, stainless sintered NdFeB magnet and its preparation method. Background Technology

[0002] With the continuous expansion and extension of new energy technologies, more and more rare earth permanent magnet materials are being used, such as in automotive motors and communication electronic products. Among them, neodymium iron boron (NdFeB), a third-generation rare earth permanent magnet material, is known as the "King of Magnets" due to its high energy density and has the most widespread applications. However, one weakness of NdFeB materials is their poor corrosion resistance. In the microstructure of NdFeB, the elements are distributed in a multiphase manner: Nd-rich grain boundary phase, Nd₂Fe₂... 14 The main phase is dominated by B, and the B-rich phase is composed of Nd2Fe. Grain boundary phases formed primarily by Nd with a relatively negative potential and Nd2Fe in the magnet are also present. 14 The high potential difference between the main phases, primarily composed of the B phase, forms a galvanic cell in a humid and hot environment. The rare-earth-rich phase acts as the anode, undergoing oxidation and corrosion, while the main phase acts as the cathode, undergoing reduction. The magnetic properties of the NdFeB permanent magnet are severely degraded after this reaction, affecting the material's lifespan. Therefore, improving the corrosion resistance of the NdFeB matrix is ​​crucial.

[0003] In the prior art, Chinese patent application No. 201310047190 discloses 'a corrosion-resistant NdFeB permanent magnet material and its preparation method'. This technical solution utilizes raw materials from praseodymium-NdFeB waste to produce alloys, and prepares corrosion-resistant NdFeB. The weight percentages of the components of this corrosion-resistant NdFeB permanent magnet material are: Nd 20-26%, Pr 5-6.5%, B 1-4%, Ir 0.05-0.065%, Os 0.05-0.065%, Sc 0.5-0.65%, Cu 0.5-0.65%, with the remainder being Fe. The permanent magnet material obtained in the embodiments has a magnetic energy product of 208-293 kJ / m. 3 The remanence is 1.2–1.25 T, and the weight loss of the magnet after 96 hours of corrosion at 120℃ and 2 atmospheres is 3.1–3.7 mg / cm³. 2 The alloy composition of this technical solution includes rare and precious metal elements Ir, Os and Sc, but the corrosion resistance of the prepared permanent magnet material is still low and the weight loss is high.

[0004] Chinese invention patent application No. 202210743535.2 discloses "a corrosion-resistant NdFeB magnet and its preparation method". This method involves incorporating alloying elements that reduce the activity of grain boundary phases to form intergranular phases Nd-M, Nd-Fe-M, Fe-MB, and MB, thereby increasing the electrode potential of the Nd-rich phase and reducing the interaction between the grain boundary phase and Nd2Fe. 14The potential difference between the B main phases reduces the corrosion kinetics of the magnet and improves its corrosion resistance. However, this method only reduces the potential difference by changing the potential of the grain boundary phase, without protecting the main phase. Therefore, the magnets prepared by this method still have poor corrosion resistance and high weight loss. Summary of the Invention

[0005] To overcome the aforementioned problems in the prior art, the present invention provides a highly corrosion-resistant stainless sintered NdFeB permanent magnet and its preparation method, which improves the corrosion resistance of the NdFeB permanent magnet matrix by simultaneously enhancing the corrosion resistance of both the grain boundary phase and the main phase.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high corrosion-resistant stainless sintered NdFeB permanent magnet material, the composition of which by weight percentage is: RE 28-31%, B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, (Mo,W,Nb) 0-4%, Dy 0.04-0.08%, Co 0.5-1.5%, Tb 0.01-0.02%, with the remainder being Fe, and RE being one or more of rare earth elements Nd, Pr, Tb, Dy, La, and Ce; Ni and Cr elements are added simultaneously during the smelting step of the permanent magnet material; in the operating state, Ni and Cr are preferentially distributed at the grain boundaries and the main phase, respectively, forming a microstructure of a high corrosion-resistant Cr-containing permanent magnet main phase and a high corrosion-resistant Ni-containing grain boundary phase.

[0008] Ni mainly enters the grain boundary phase, improving its corrosion resistance; Cr mainly enters the main phase, replacing Re₂Fe. 14 Some of the Fe atoms in B enhance the corrosion resistance of the main phase.

[0009] Due to the preferred distribution of Ni and Cr in the grain boundaries and the main phase, respectively, the potential of the grain boundary phase is increased, and the potential of the main phase is increased.

[0010] The potential difference between the grain boundary and the main phase of the permanent magnet material is less than 200mV.

[0011] At 120°C and 2 atmospheres, the magnet experiences a weight loss of 0.44 mg / cm² after 480 hours. 2 the following.

[0012] The permanent magnet material is prepared through the following steps: batching - preparation of rapidly solidified belts - hydrogen breaking - air jet milling - pressing and molding - vacuum sintering; in the vacuum sintering step, according to the desired grain boundary phase and RE2(Fe,Cr)... 14 The formation conditions of the B permanent magnet main phase are determined by setting the sintering temperature and holding time in stages.

[0013] The grain boundary phase is a Ni-containing solid solution, and contains at least a compound of Nd3Ni.

[0014] The magnet exhibits the following corrosion resistance: weight loss of less than 0.5 mg / cm³ after 500 hours at 120°C and 2 atmospheres. 2 .

[0015] A method for preparing a high corrosion-resistant, stainless sintered NdFeB permanent magnet material as described above, the method comprising the following steps:

[0016] 1) Batching: The permanent magnet material is batched according to the following weight percentages: RE 28-31%, B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, Dy 0.04-0.08%, Co 0.5-1.5%, (Mo,W,Nb) 0-4%, Tb 0.01-0.02%, with the remainder being Fe. RE is one or more of the rare earth elements Nd, Pr, Tb, Dy, La, and Ce. Ni and Cr elements are added simultaneously during the smelting step of this permanent magnet material.

[0017] 2) Preparation of rapid solidification belt: After the raw materials are batched, they are added to an induction melting furnace and heated to 1570℃~1900℃. After holding at this temperature for 30 minutes, the raw materials are poured into an ingot mold. Then, the belt is spun at a speed of 1.5-2.5m / s under an environment with a magnetic field strength of 0~0.5T to obtain a rapid solidification belt with a thickness of 0.3±0.1mm.

[0018] 3) Hydrogen-breaking: The above-mentioned NdFeB rapid solidification belt is placed in a hydrogen-breaking furnace for hydrogen-breaking;

[0019] 4) Air jet milling: The NdFeB particles after hydrogen calcification are subjected to air jet milling, and the particle size reaches 3-5 μm after air jet milling;

[0020] 5) Press molding: The magnetic powder is pressed under a magnetic field of 0.8T to 5T, and then cold isostatic pressing is performed under a heavy press to obtain a green blank;

[0021] 6) Vacuum sintering: The green body is vacuum sintered under the following process conditions: vacuum degree of 1.0*10 -3 Below Pa, depending on the desired grain boundary phase and RE2(Fe,Cr) 14 The formation conditions of the B phase are determined by setting the sintering temperature and holding time in stages. Under the condition of use, Ni and Cr are preferentially distributed in the grain boundaries and main phase, respectively, forming a stainless magnet with a high corrosion resistance of Cr-containing permanent magnet main phase and a high corrosion resistance of Ni-containing grain boundary phase.

[0022] In the ingredient preparation process, rare earth elements are lost by 3-5%.

[0023] In the vacuum sintering step, the desired grain boundary phase and RE2(Fe,Cr) are determined. 14The formation conditions of the B phase, and the sintering temperature and holding time are set in stages as follows: Based on the melting point of the grain boundary phase, the sintering temperature is 50-100℃ lower than the melting point of the grain boundary phase, and the holding time is 0.5-4 hours; then according to RE2(Fe,Cr) 14 The melting point of phase B and its sintering temperature are lower than those of RE2(Fe,Cr). 14 The B phase has a melting point of 50-150℃; hold at this temperature for 1-6 hours; maintain a vacuum level of 8*10 during the holding period. -4 the following.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The neodymium iron boron permanent magnet of this invention, after the addition of Ni and Cr elements, enters the grain boundary phase and the main phase respectively through their metallurgical behavior: forming a stainless magnet with a highly corrosion-resistant Cr-containing permanent magnet main phase and a highly corrosion-resistant Ni-containing grain boundary phase. First, the addition of Ni and Cr reduces the potential difference between the grain boundary phase and the main phase, thus reducing the thermodynamic corrosion kinetics. Second, Ni enters the grain boundary phase and forms Nd3Ni compounds with Nd, reducing the chemical activity of the grain boundary phase, stabilizing it, and thus improving its corrosion resistance. Third, Cr enters the main phase, replacing some Fe atoms. Due to the passivation properties of Cr and its ability to promote Fe passivation, a passivation film is formed, improving the corrosion resistance of the main phase. Fourth, due to the high volume fraction of the main phase, the passivation film further protects the entire magnet. Furthermore, the addition of Ni and Cr reduces the potential difference between the grain boundary phase and the main phase, reducing the thermodynamic corrosion kinetics. For all these reasons, the corrosion resistance of the neodymium iron boron permanent magnet is significantly improved after the addition of Ni and Cr elements. Furthermore, 0-4% (Mo, W, Nb) can be added to the magnet of this invention, which improves corrosion resistance compared to the prior art, and also slightly improves the magnetic properties compared to the prior art.

[0026] The potential difference between the grain boundary and the main phase obtained by atomic force microscopy within the magnet of this invention is below 200mV.

[0027] The neodymium iron boron permanent magnet obtained by this invention not only improves both the magnetic energy product and remanence, but also achieves a weight loss of 0.44 mg / cm³ after 480 hours of corrosion at 120°C, 2 atmospheres, and 100% humidity. 2 This significantly improves the corrosion resistance of the sintered NdFeB permanent magnet matrix, making it possible to use sintered NdFeB permanent magnets without coating.

[0028] The microstructure, corrosion resistance, and weight loss performance of the magnet of the present invention are superior to those of the prior art (CNNo.202210743535.2): the prior art does not use Ni and Cr elements, but only changes the grain boundary phase; the present invention adds Ni and Cr as key elements in the smelting step, and at the same time changes the composition ratio of the grain boundary phase and the main phase. Through metallurgical behavior control, Ni enters the grain boundary phase and Cr enters the main phase, thereby improving the corrosion resistance of the grain boundary phase and the main phase respectively, and a highly corrosion-resistant stainless magnet can be obtained.

[0029] The existing technology adds some corrosion-resistant elements during the powder mixing process, which only slightly improves the corrosion resistance of the magnet, resulting in a corrosion-resistant magnet. The present invention does not involve grain boundary doping, and its weight loss is significantly lower than that of the existing technology, yielding a stainless magnet.

[0030] The prior art embodiment showed a minimum weight loss of 0.45 mg / cm³ after 96 hours of corrosion at 120°C and 2 atmospheres. 2 The three embodiments of the present invention all showed a corrosion level below 0.23 mg / cm³ after 96 hours of corrosion. 2 In Embodiment 3 of the present invention, the weight loss after 480 hours of corrosion is still lower than the minimum weight loss after 96 hours of medium corrosion. Detailed implementation method:

[0031] The present invention will now be described in detail with reference to Examples 1-3.

[0032] The key to this invention lies in the following: on the one hand, it increases the potential of the grain boundary phase while decreasing the potential of the main phase, thereby achieving a potential difference between the grain boundary phase and the main phase and reducing the corrosion dynamics of the magnet; on the other hand, by adding Cr to the main phase, a passivation film is formed on the surface of the magnet, thereby protecting the entire substrate.

[0033] A high corrosion-resistant stainless sintered NdFeB permanent magnet, wherein the NdFeB permanent magnet has the following weight percentage composition: RE 28-31%, RE being rare earth elements, including one or more combinations of rare earth elements such as Nd, Pr, Tb, Dy, La, and Ce; B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, (Mo,W,Nb) 0-4%, Dy 0.04-0.08%, Co 0.5-1.5%, Tb 0.01-0.02%, with the remainder being Fe.

[0034] The process of this invention enables Ni and Cr elements to achieve a preferred distribution between the grain boundaries and the main phase, reducing the potential difference between the grain boundaries and the main phase, thereby reducing the thermodynamic corrosion kinetics of sintered NdFeB permanent magnets.

[0035] Ni and Cr elements are added simultaneously during the smelting process, with the amount of Ni added being less than that of Cr, forming a two-phase stainless magnet with a high-Cr permanent magnet main phase and a high-Ni grain boundary phase. In particular, the preferential distribution of Ni and Cr elements at the grain boundaries and in the main phase reduces the potential difference between the grain boundaries and the main phase, thereby reducing the thermodynamic corrosion kinetics of the magnet and significantly reducing the weight loss value.

[0036] A method for preparing a highly corrosion-resistant stainless neodymium iron boron permanent magnet, the method comprising the following steps:

[0037] 1) Ingredients: The raw materials are formulated according to the following weight percentages: RE 28-31%, RE is rare earth element, including one or more combinations of rare earth elements such as Nd, Pr, Tb, Dy, La, Ce, etc., B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, (Mo,W,Nb) 0-4%, Dy 0.04-0.08%, Co 0.5-1.5%, Tb 0.01-0.02%, and the remainder is Fe. The raw materials are formulated, and the loss of rare earth elements is increased by 3-5%.

[0038] 2) Belt casting: After the batching is completed, the raw materials are added to the melting furnace and heated to 1570℃~1900℃. After holding for 30 minutes, they are poured into the ingot mold. Then, in an environment of 0T≤magnetic field strength≤0.5T, the belt is cast at a speed of 1.5-2.5m / s to obtain a fast-setting belt with a thickness of about 0.3mm.

[0039] 3) The above-mentioned neodymium iron boron rapid solidification zone is subjected to hydrogen crushing in a hydrogen crushing furnace.

[0040] 4) The NdFeB particles after hydrogen calcination are subjected to air jet milling, and the particle size reaches 3-5 μm after air jet milling.

[0041] 5) Orient the magnetic powder under a magnetic field of 1T to 5T, and then perform cold isostatic pressing under a heavy press to obtain a green blank.

[0042] 6) Vacuum sinter the initial magnet, according to the desired grain boundary phase and RE2(Fe,Cr) 14 The formation conditions of the B phase are determined by segmented control of sintering temperature and holding time: based on the melting point of the grain boundary phase, the sintering temperature is 50-100℃ lower than the melting point of the grain boundary phase, and the holding time is 0.5-4 hours; then, based on RE2(Fe,Cr)... 14 The melting point of phase B and its sintering temperature are lower than those of RE2(Fe,Cr). 14 The melting point of phase B is 50-150℃, and the holding time is 1-6 hours; during the holding period, the vacuum degree is 8*10. -4 the following.

[0043] Example 1 :

[0044] High corrosion-resistant stainless neodymium iron boron permanent magnet material is prepared according to the following steps:

[0045] 1) Ingredients: The ingredients are prepared according to the following mass percentages: Nd 29.5%, Pr 0.2%, B 1.0%, Ni 0.9%, Cr 2.7%, Dy 0.05%, Co 0.9%, Tb 0.01%, and the remainder is Fe.

[0046] 2) Belt spinning: The raw material is added to the melting furnace and heated to 1780℃. After holding at this temperature for 30 minutes, it is poured into the ingot mold. Then, in an environment with a magnetic field strength > 0.5T, the belt is spun at a speed of 2m / s to obtain a fast-setting belt with a thickness of about 0.3mm.

[0047] 3) Preparation of NdFeB alloy ingots: The above-mentioned NdFeB rapid solidification zone is hydrogen-crushed in a hydrogen-crushing furnace.

[0048] 4) The NdFeB particles after hydrogen calcination were subjected to air jet milling, and the average particle size reached 3-5 μm after air jet milling.

[0049] 5) The magnetic powder is oriented and shaped under a magnetic field of 3T, and then cold isostatically pressed under a heavy press to obtain a green blank.

[0050] 6) Vacuum sinter the initial magnet at a grain boundary phase sintering temperature of 750℃ for 1 hour; RE2(Fe,Cr) 14 The B-phase sintering temperature was 1120℃, and the holding time was 1.5 hours; the vacuum degree during the holding stage was 5.0*10. -4 Pa.

[0051] Example 2 :

[0052] High corrosion-resistant stainless neodymium iron boron permanent magnet material is prepared according to the following steps:

[0053] 1) Ingredients: The ingredients are prepared according to the following mass percentages: Nd 29.5%, Pr 0.2%, B 1.0%, Ni 1.2%, Cr 3.6%, (Mo,W,Nb) 4%, Dy 0.05%, Co 0.9%, Tb 0.01%, and the remainder is Fe.

[0054] 2) Belt casting: The raw material is added to the melting furnace and heated to 1900℃. After holding at this temperature for 30 minutes, it is poured into the ingot mold and then cast at a speed of 2m / s to obtain a fast-setting belt with a thickness of about 0.3mm.

[0055] 3) Preparation of NdFeB alloy ingots: The above-mentioned NdFeB rapid solidification zone is hydrogen-crushed in a hydrogen-crushing furnace.

[0056] 4) The NdFeB particles after hydrogen calcination were subjected to air jet milling, and the average particle size reached 3-5 μm after air jet milling.

[0057] 5) The magnetic powder is oriented and shaped under a magnetic field of 2T, and then cold isostatically pressed under a heavy press to obtain a green blank.

[0058] 6) The initial magnet was vacuum sintered at a grain boundary phase sintering temperature of 800℃ for 1.5 hours; RE2(Fe,Cr) 14 The B-phase sintering temperature was 1100℃, and the holding time was 3 hours; the vacuum degree during the holding stage was 7.0*10. -4 Pa.

[0059] Example 3 :

[0060] High corrosion-resistant stainless neodymium iron boron permanent magnet material is prepared according to the following steps:

[0061] 1) Ingredients: The ingredients are prepared according to the following mass percentages: Nd 29.5%, Pr 0.2%, B 1.0%, Ni 1.5%, Cr 4.5%, Dy 0.05%, Co 0.9%, Tb 0.01%, and the remainder is Fe.

[0062] 2) Belt spinning: The raw material is added to the melting furnace and heated to 1570℃. After holding at this temperature for 30 minutes, it is poured into the ingot mold. Then, in an environment with a magnetic field strength of 0.01T≤0.5T, the belt is spun at a speed of 2m / s to obtain a fast-setting belt with a thickness of about 0.3mm.

[0063] 3) Preparation of NdFeB alloy ingots: The above-mentioned NdFeB rapid solidification zone is hydrogen-crushed in a hydrogen-crushing furnace.

[0064] 4) The NdFeB particles after hydrogen calcination were subjected to air jet milling, and the average particle size reached 3-5 μm after air jet milling.

[0065] 5) The magnetic powder is oriented and shaped under a magnetic field of 2T, and then cold isostatically pressed under a heavy press to obtain a green blank.

[0066] 6) Vacuum sinter the initial magnet at a grain boundary phase sintering temperature of 850℃ for 2 hours; RE2(Fe,Cr) 14 The B-phase sintering temperature was 1090℃, and the holding time was 4 hours; the vacuum degree during the holding stage was 1.0*10. -4 Pa.

[0067] The magnetic properties and corrosion resistance test results of the high corrosion-resistant stainless NdFeB materials obtained in various embodiments of the present invention are shown in Table 1 below.

[0068] This invention, through metallurgical behavior regulation, induces Ni to enter the grain boundary phase, forming a Nd3Ni compound; Cr enters the main phase, replacing Nd2Fe. 14Some Fe atoms in B. Elements entering the grain boundary phase are mainly selected through screening of elements that can form compounds with Nd based on the phase diagram, and those with a more positive standard electrode potential than Nd elements; elements entering the main phase are mainly selected through first-principles calculations, entering Nd₂Fe. 14 The formation energy of B is lower than that of Nd2Fe. 14 The formation energy of B. The process is consistent with the conventional preparation process of NdFeB magnets. The microscopic reaction that occurs is that Ni reacts with Nd to form Nd3Ni, and Cr enters the main phase to replace Nd2Fe. 14 Some of the Fe atoms in B.

[0069] Table 1

[0070]

Claims

1. A highly corrosion-resistant, stainless sintered NdFeB permanent magnet material, characterized in that: The permanent magnet material has the following composition by weight percentage: RE 28-31%, B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, (Mo,W,Nb) 0-4%, Dy 0.04-0.08%, Co 0.5-1.5%, Tb 0.01-0.02%, with the remainder being Fe. RE is one or more of the rare earth elements Nd, Pr, Tb, Dy, La, and Ce. Ni and Cr elements are added simultaneously during the smelting process. In the operating state, Ni and Cr are preferentially distributed at grain boundaries and in the main phase, respectively, forming a microstructure of a highly corrosion-resistant Cr-containing permanent magnet main phase and a highly corrosion-resistant Ni-containing grain boundary phase, as shown below: Ni mainly enters the grain boundary phase, improving its corrosion resistance; Cr mainly enters the main phase, replacing Re₂Fe. 14 Some of the Fe atoms in B improve the corrosion resistance of the main phase; The permanent magnet material is prepared through the following steps: batching - preparation of rapid solidification belt - hydrogen breaking - air jet milling - pressing and molding - vacuum sintering; In the step of preparing the rapid solidification belt: after the ingredients are prepared, the raw materials are added to the induction melting furnace and heated to 1570℃~1900℃. After holding at the temperature for 30 minutes, the raw materials are poured into the ingot mold. Then, under the environment of magnetic field strength of 0~0.5T, the belt is spun at a speed of 1.5-2.5m / s to obtain a rapid solidification belt with a thickness of 0.3±0.1mm. The grain boundary phase is a Ni-containing solid solution, and contains at least a compound of Nd3Ni.

2. The high corrosion-resistant, stainless sintered NdFeB permanent magnet material according to claim 1, characterized in that: Due to the preferred distribution of Ni and Cr in the grain boundaries and the main phase, respectively, the potential of the grain boundary phase is increased, and the potential of the main phase is increased.

3. The high corrosion-resistant stainless sintered NdFeB permanent magnet material according to claim 1, characterized in that: The potential difference between the grain boundary and the main phase of the permanent magnet material is less than 200mV.

4. The high corrosion-resistant stainless sintered NdFeB permanent magnet material according to claim 1, characterized in that: At 120°C and 2 atmospheres, the magnet experiences a weight loss of 0.44 mg / cm² after 480 hours. 2 the following.

5. The high corrosion-resistant stainless sintered NdFeB permanent magnet material according to claim 1, characterized in that: In the vacuum sintering step, the desired grain boundary phase and RE2(Fe,Cr) are determined. 14 The formation conditions of the B permanent magnet main phase are determined by setting the sintering temperature and holding time in stages.

6. The high corrosion-resistant stainless sintered NdFeB permanent magnet material according to claim 5, characterized in that: This permanent magnet material exhibits the following corrosion resistance: weight loss of less than 0.5 mg / cm³ after 500 hours at 120℃ and 2 atmospheres. 2 .

7. A method for preparing a high corrosion-resistant, stainless sintered NdFeB permanent magnet material as described in claim 1, characterized in that: The method includes the following steps: 1) Batching: The permanent magnet material is batched according to the following weight percentages: RE 28-31%, B 0.88-1%, Ni 0.5-4%, Cr 1.5-5%, Dy 0.04-0.08%, Co 0.5-1.5%, (Mo,W,Nb) 0-4%, Tb 0.01-0.02%, with the remainder being Fe. RE is one or more of the rare earth elements Nd, Pr, Tb, Dy, La, and Ce. Ni and Cr elements are added simultaneously during the smelting step of this permanent magnet material. 2) Preparation of rapid solidification belt: After the raw materials are batched, they are added to an induction melting furnace and heated to 1570℃~1900℃. After holding at the temperature for 30 minutes, they are poured into an ingot mold. Then, under a magnetic field strength of 0~0.5T, the belt is spun at a speed of 1.5-2.5m / s to obtain a rapid solidification belt with a thickness of 0.3±0.1mm. 3) Hydrogen-breaking: The above-mentioned NdFeB rapid solidification belt is placed in a hydrogen-breaking furnace for hydrogen-breaking; 4) Air jet milling: The NdFeB particles after hydrogen calcification are subjected to air jet milling, and the particle size reaches 3-5 μm after air jet milling; 5) Press molding: The magnetic powder is pressed into shape under a magnetic field of 0.8T~5T, and then cold isostatic pressing is performed under a heavy press to obtain a green blank; 6) Vacuum sintering: The green body is vacuum sintered under the following process conditions: vacuum degree of 1.0*10 -3 Below Pa, depending on the desired grain boundary phase and RE2(Fe,Cr) 14 The formation conditions of the B phase are determined by setting the sintering temperature and holding time in stages. Under the condition of use, Ni and Cr are preferentially distributed in the grain boundaries and main phase, respectively, forming a stainless magnet with a high corrosion resistance of Cr-containing permanent magnet main phase and a high corrosion resistance of Ni-containing grain boundary phase.

8. The preparation method according to claim 7, characterized in that: In the ingredient preparation process, rare earth elements are lost by 3-5%.

9. The preparation method according to claim 7, characterized in that: In the vacuum sintering step, the desired grain boundary phase and RE2(Fe,Cr) are determined. 14 The formation conditions of the B phase, and the sintering temperature and holding time are set in stages as follows: Based on the melting point of the grain boundary phase, the sintering temperature is 50-100℃ lower than the melting point of the grain boundary phase, and the holding time is 0.5-4 hours; then according to RE2(Fe,Cr) 14 The melting point of phase B and its sintering temperature are lower than those of RE2(Fe,Cr). 14 The B phase has a melting point of 50-150℃; hold at this temperature for 1-6 hours; maintain a vacuum level of 8*10 during the holding period. -4 the following.

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