CN111872374A - Composite binder and method for preparing soft magnetic composite material by using same - Google Patents
Composite binder and method for preparing soft magnetic composite material by using same Download PDFInfo
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Abstract
The invention relates to a composite binder and a method for preparing a soft magnetic composite material by using the same, belonging to the technical field of preparation of soft magnetic materials. The composite binder is prepared by the following method: firstly, preparing acetone solution of organic silicon resin, then adding carbon nano tubes accounting for 1-5% of the weight of the organic silicon resin, and uniformly dispersing the carbon nano tubes in the acetone solution of the organic silicon resin by ultrasonic oscillation and mechanical stirring to form the composite binder. The organic silicon resin molecules in the composite binder are adhered to the surface of the carbon nano tube to form a net-shaped structure, and after the composite binder is coated, a net-shaped coating structure can be formed on the surface of iron powder, so that the volatility of the composite binder and a lubricant adhered to the net-shaped structure during annealing can be obviously improved, a diffusion channel is provided for steam to enter the interior of the magnet, organic matters can be more effectively removed, a uniform and complete oxidation strengthening layer is formed, and the mechanical strength of the SMC magnet is greatly improved.
Description
Technical Field
The invention relates to the technical field of soft magnetic material preparation, and particularly provides a composite binder and a method for preparing a soft magnetic composite material by using the same.
Background
Soft magnetic composites (SMC materials for short) achieve high resistivity and low loss by coating the surface of each iron powder particle with an insulating coating of high resistivity, which corresponds to air gaps evenly distributed in the magnet. Different from laminated silicon steel sheets with a laminated structure, the air gaps uniformly distributed in the magnet bring good magnetocaloric three-dimensional isotropy to the SMC material, so that magnetic devices with a two-dimensional magnetic circuit structure, such as a motor stator, a reactor and the like, made of the laminated silicon steel sheets can be designed into a new three-dimensional magnetic circuit structure by adopting the SMC material to replace the silicon steel sheets, for example, successful design and production of a three-dimensional magnetic circuit hub motor and a tank type reactor are realized, and the magnetic device has great significance for development of high efficiency and light weight of the magnetic devices.
For magnetic devices, SMC materials are required to meet the requirements of magnetic properties and loss characteristics, and an important index requirement is mechanical strength. The high strength can ensure that the material cannot drop slag and crack in the assembling process, and the device cannot lose efficacy due to stress damage in the using process.
The mechanical strength of the SMC material depends mainly on the strength of the bond between the coating and the iron powder and the strength of the bond between the iron powder particles. During the preparation of the SMC material, the insulating coating, pressing and heat treatment steps all affect the strength of the SMC material. A great deal of research shows that the inorganic-organic composite coating method of passivating by phosphoric acid and bonding by organic silicon resin is more beneficial to reducing the loss of SMC materials, which is also a relatively easy industrialized SMC material coating method, but the strength of the SMC materials is reduced due to poor binding force between inorganic phosphate and organic silicon resin; when the pressing force is too large or the pressing structure is not uniform in the material pressing process, a region with weak mechanical property can be formed by local stress concentration or low density, and the region becomes a position which is easily damaged by stress; in addition, the strength of the SMC material is also reduced by a large amount of residual pores in the material after volatilization of the organic matter, weak bonding between the insulating coating layer and the iron powder, and the like during the heat treatment.
In the prior art, on one hand, the interface bonding force between the inorganic coating layer and the organic silicon resin is enhanced by adding a coupling agent between the inorganic coating layer and the organic coating layer, so that the mechanical strength of the final magnet is improved. For example, CN103666364A is coated with a coupling agent and a silicone resin; CN104368807A adopts sol-gel to coat the coupling agent and the inorganic-organic composite coating of the silicon resin after the iron powder coats the nano aluminum oxide. The coupling agent is combined with an organic interface and an inorganic interface through covalent bonds and the like, so that the effects of enhancing the adsorption force of the coupling agent and the inorganic interface in the coating process and improving the coating integrity uniformity can be achieved. But the acting force between covalent bonding is relatively small, and the strengthening effect on the mechanical strength of the magnet is not obvious.
On the other hand, an oxidation strengthening layer is formed on the surface of the powder by adopting a heat treatment process of steam annealing, and the interface bonding force between the powder is increased, so that the mechanical strength of the material is increased. However, the inventor finds in the research process that steam needs to diffuse into the whole magnet through air gaps among particles during steam annealing, and an oxidation strengthening layer is formed on the surface of all powder materials to play a better role in optimizing the mechanical properties, so that a complete dewaxing step is required to remove organic matters such as composite binders, lubricants and the like in the magnet before steam treatment, and a good channel is formed for the steam to enter. However, the practical situation is that the compression requirement of the green density is difficult to completely dewax during the heat treatment process, so that the distribution of the oxidation strengthening layer in the magnet is not uniform, and the improvement range of the mechanical strength is limited.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a composite binder and a method for preparing a soft magnetic composite material by using the same.
In order to solve the technical problems, the invention provides the following technical scheme:
in one aspect, the invention provides a composite binder, which is prepared by the following method:
firstly, preparing acetone solution of organic silicon resin, then adding carbon nano tubes accounting for 1-5% of the weight of the organic silicon resin, and uniformly dispersing the carbon nano tubes in the acetone solution of the organic silicon resin by ultrasonic oscillation and mechanical stirring to form the composite binder.
Preferably, the carbon nanotube has a length of 200nm to 1 μm and a diameter of 10 to 50 nm.
Preferably, in the acetone solution of the silicone resin, the volume ratio of the silicone resin to the acetone is 1: 8-12.
Preferably, the carbon nanotubes are used in an amount of 2 to 3% by weight based on the silicone resin.
On the other hand, the invention also provides a preparation method of the soft magnetic composite material, which comprises the following steps:
step 1: iron powder pretreatment;
step 2: insulating and coating: passivating iron powder with phosphoric acid to form an inorganic coating layer, and then performing organic coating by using the composite binder of any one of claims 1 to 3 to obtain insulating iron powder; wherein the addition amount of the composite binder is 0.2-0.4 wt% of the iron powder;
and step 3: and (3) pressing and forming: adding a lubricant into the insulating iron powder, and then performing compression molding;
and 4, step 4: annealing treatment: firstly, primary annealing is carried out in a nitrogen atmosphere, then secondary annealing is carried out in a water vapor atmosphere, and then furnace cooling is carried out to obtain the soft magnetic composite material.
Preferably, in the step 4, after the primary annealing, the material is cooled to room temperature, and then secondary annealing is performed.
Preferably, the step 4 specifically comprises: and (3) annealing twice: primary annealing: vacuumizing the annealing furnace, and then filling nitrogen to stabilize to 0.04 MPa; heating from room temperature to 350-400 ℃ at the heating rate of 10-15 ℃/min, preserving the heat for 40-60 min, and cooling to room temperature; and then carrying out secondary annealing, raising the temperature from room temperature to 450 ℃ at the temperature rise rate of 10-15 ℃/min in the nitrogen atmosphere, introducing water vapor, reducing the temperature rise rate to 3-5 ℃/min, raising the temperature to 500-540 ℃, preserving the temperature for 20-35 min, introducing nitrogen, removing the water vapor, reducing the temperature to room temperature, and discharging the furnace, wherein the annealing curve is shown in figure 1.
Preferably, in the step 3, the pressing pressure is 800-1000 MPa; the lubricant is micro wax powder; the dosage of the lubricant is 0.15-0.3 wt% of the dosage of the iron powder.
Further, in the step 1, the iron powder pretreatment specifically comprises: performing mechanical ball milling pretreatment on iron powder, wherein the rotating speed of a ball mill is 300-600 revolutions per minute in the ball milling treatment process, the ball-material ratio is 2:1-6:1, and the pretreatment time is 5-10 minutes; then ultrasonic vibration cleaning is carried out by adopting alcohol or acetone solution, and then drying is carried out at 60-80 ℃.
Further, in the step 2, the phosphoric acid passivation specifically comprises: uniformly diluting orthophosphoric acid and alcohol according to the volume ratio of 1:50-1:80, and insulating and coating iron powder by adopting an atomization method to form a phosphoric acid coating layer.
Preferably, the iron powder is water atomized iron powder, the purity requirement is more than 99.9%, and the particle size of the iron powder is 180-250 μm.
Compared with the prior art, the invention has the following beneficial effects:
the composite binder consists of the carbon nano tube and the organic silicon resin, and firstly, the mechanical property of the resin material can be effectively improved by improving the interface bonding force between the carbon nano tube and the organic silicon resin; and secondly, the composite binder structure is a reticular structure formed by adhering organic silicon resin molecules on the surface of the carbon nano tube, and after the composite binder is coated, a reticular coating structure can be formed on the surface of the iron powder, the reticular structure can provide a multidimensional reticular channel for the coming-out of organic matters and the entering of steam in the annealing process, and a uniform and complete oxidation strengthening layer is formed in the completely dewaxed magnet, so that the optimization of the mechanical strength of the magnet is facilitated. In addition, the addition of the carbon nano tube can effectively enhance the bonding strength between the composite binder and the interface of the inorganic coating material.
In addition, the temperature of the organic matter discharged in the single dewaxing process is reduced under the condition of 350-400 ℃, so that air holes and the like left after the organic matter is discharged can be effectively contracted in the process of reducing the temperature to the room temperature, and then the temperature is increased from the room temperature again to carry out steam treatment, so that the air holes cannot be enlarged due to continuous heating, the number of defects in the final magnet is reduced, and the performance of the magnet is effectively improved. Therefore, by adopting the modified composite binder provided by the invention to form a net-shaped coating structure on the surface of the iron powder, the mechanical strength of the material can be effectively improved on the basis of not influencing the magnetic property and the loss characteristic, and meanwhile, the SMC material with greatly improved mechanical strength can be obtained by matching with a sectional type heating-cooling-reheating nitrogen gas and steam annealing treatment process.
Drawings
FIG. 1 is a graph showing two annealing processes in the process of preparing a soft magnetic composite material according to the present invention;
FIG. 2 is an SEM photograph of the surface of the insulating coated powder prepared in example 1 of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following detailed description is given with reference to specific embodiments.
The reagents and materials used in the examples and comparative examples were commercially available unless otherwise specified; the carbon nanotubes are commercially available, and may be single-walled carbon nanotubes or multi-walled carbon nanotubes.
The invention provides a composite binder and a method for preparing a soft magnetic composite material by using the same, and the specific embodiment is as follows.
Example 1
A method for preparing a soft magnetic composite material, comprising:
step 1: preparing a composite binder: preparing a solution of 1:10 by using organic silicon resin and acetone, uniformly mixing the solution and the solution by using ultrasonic oscillation treatment, and then putting a carbon nano tube with 2 wt% of organic silicon resin, wherein the length of the carbon nano tube is 200nm-1 mu m; the diameter is 10-50 nm; ultrasonic vibration treatment is carried out for 1 hour, and the mixture is stirred for 2 hours at room temperature to ensure that the carbon nano tubes are uniformly dispersed in the solution, so as to obtain a composite binder;
step 2: iron powder pretreatment: the purity requirement of the water atomized iron powder is more than 99.9 percent, and the particle size of the iron powder is 180-; the iron powder is subjected to mechanical ball milling pretreatment and ultrasonic cleaning, so that the adsorbability of the surface of the iron powder to a coating agent is improved; the ball milling processing parameters are that the rotating speed of the ball mill is 300-; then ultrasonic vibration cleaning is carried out by adopting alcohol or acetone solution, and then drying is carried out at 60-80 ℃;
and step 3: insulating and coating: uniformly diluting orthophosphoric acid and alcohol according to the volume ratio of 1:50 to prepare a first layer of inorganic coating agent solution, wherein the addition amount of phosphoric acid is 0.4 wt% of iron powder; the coating agent solution is then atomized into small droplets by atomization and the droplets are brought into intimate contact with the rotating iron powder to form a coating layer having a thickness of, for example, 10-50 nm. Then mixing the composite binder solution with iron powder passivated by phosphoric acid by an atomization method to obtain insulated iron powder; wherein the addition amount of the composite binder is 0.3 wt% of iron powder; in the composite binder, the organic silicon resin is adsorbed on the surface of the carbon nano tube, so that a net-shaped coating structure shown in figure 2 is formed on the surface of the iron powder;
and 4, step 4: and (3) pressing and forming: adding a lubricant into the insulating iron powder, and performing compression molding under 900 MPa; wherein the lubricant is micro wax; the dosage of the lubricant is 0.3 wt% of that of the iron powder;
and 5: annealing treatment: placing the pressed blank block in an annealing furnace, vacuumizing the furnace chamber, filling nitrogen to stabilize to 0.04MPa, heating to 400 ℃ at the heating rate of 15 ℃/min, preserving heat for 40 min, and cooling to room temperature; and then, carrying out secondary heating, introducing nitrogen, heating to 450 ℃ at a heating rate of 15 ℃/min, introducing steam, reducing the heating rate to 5 ℃/min, heating to 530 ℃, keeping the temperature for 30 min, introducing nitrogen, starting cooling, and taking out the sample after the furnace temperature is cooled to room temperature.
Example 2
The preparation method of the soft magnetic composite material comprises the following steps of: placing the pressed blank block in an annealing furnace, vacuumizing the furnace chamber, filling nitrogen to stabilize to 0.04MPa, heating to 380 ℃ at the heating rate of 15 ℃/min, preserving the heat for 60 min, and cooling to room temperature; then, carrying out secondary heating, introducing nitrogen, heating to 450 ℃ at a heating rate of 15 ℃/min, introducing steam, reducing the heating rate to 5 ℃/min, heating to 520 ℃, keeping the temperature for 35 min, introducing nitrogen, starting cooling, and taking out a sample after the furnace temperature is cooled to room temperature; the remaining conditions were the same as in example 1.
Example 3
The preparation method of the soft magnetic composite material comprises the following steps of: placing the pressed blank block in an annealing furnace, vacuumizing the furnace chamber, filling nitrogen to stabilize to 0.04MPa, heating to 400 ℃ at the heating rate of 15 ℃/min, and preserving heat for 60 min; then, carrying out secondary heating, heating to 450 ℃ at a heating rate of 15 ℃/min, then starting to introduce water vapor, reducing the heating rate to 5 ℃/min, heating to 520 ℃, keeping the temperature for 35 min, then introducing nitrogen, starting to reduce the temperature, and taking out a sample after the furnace temperature is cooled to room temperature; the remaining conditions were the same as in example 1.
Example 4
A preparation method of a soft magnetic composite material is provided, wherein, the carbon nano tube accounts for 1% of the weight of the organic silicon resin; the remaining conditions were the same as in example 1.
Example 5
A preparation method of a soft magnetic composite material, wherein carbon nanotubes account for 5% of the weight of organic silicon resin; the remaining conditions were the same as in example 1.
Example 6
A method for preparing a soft magnetic composite material, comprising:
step 1-step 2: the same as example 1;
and step 3: insulating and coating: uniformly diluting orthophosphoric acid and alcohol according to the volume ratio of 1:80 to prepare a first layer of inorganic coating agent solution, and then preparing the coating agent solution into atomized small drops by adopting an atomization method to fully contact with rotating iron powder to form an inorganic coating layer. Then mixing the composite binder solution with iron powder passivated by phosphoric acid by an atomization method to obtain insulated iron powder; wherein the addition amount of the composite binder is 0.2 percent by weight of iron powder,
and 4, step 4: and (3) pressing and forming: adding a lubricant into the insulating iron powder, and performing compression molding under 1000 MPa; wherein the lubricant is micro wax; the amount of the lubricant is 0.15 wt% of the amount of the iron powder.
And 5: and (3) annealing twice: primary annealing: vacuumizing the annealing furnace, and then filling nitrogen to stabilize to 0.04 MPa; heating from room temperature to 350 ℃ at the heating rate of 10 ℃/min, preserving the heat for 50 min, and cooling to room temperature; and (3) annealing for the second time, heating for the second time, introducing nitrogen, heating from room temperature to 450 ℃ at the heating rate of 10 ℃/minute, introducing water vapor, reducing the heating rate to 3 ℃/minute, heating to 500 ℃, keeping the temperature for 20 minutes, introducing nitrogen, removing water vapor, cooling to room temperature, and discharging.
Example 7
A method for preparing a soft magnetic composite material, comprising:
step 1-step 2: the same as example 1;
and step 3: insulating and coating: uniformly diluting orthophosphoric acid and alcohol according to the volume ratio of 1:80 to prepare a first layer of inorganic coating agent solution, and then preparing the coating agent solution into atomized small drops by adopting an atomization method to fully contact with rotating iron powder to form an inorganic coating layer. Then mixing the composite binder solution with iron powder passivated by phosphoric acid by an atomization method to obtain insulated iron powder; wherein the addition amount of the composite binder is 0.4 percent by weight of iron powder,
and 4, step 4: and (3) pressing and forming: adding a lubricant into the insulating iron powder, and performing compression molding under 1000 MPa; wherein the lubricant is micro wax; the amount of the lubricant is 0.2 wt% of the amount of the iron powder.
And 5: and (3) annealing twice: primary annealing: vacuumizing the annealing furnace, and then filling nitrogen to stabilize to 0.04 MPa; heating from room temperature to 400 ℃ at the heating rate of 15 ℃/min, preserving the heat for 40 min, and cooling to room temperature; and (3) secondary annealing, namely heating the mixture from room temperature to 450 ℃ at the heating rate of 15 ℃/min after introducing nitrogen, introducing water vapor, reducing the heating rate to 5 ℃/min, heating to 540 ℃, preserving the heat for 20 min, introducing nitrogen, removing the water vapor, cooling to room temperature, and discharging the product.
To further illustrate the beneficial effects of the present invention, the comparative examples are designed as follows for the sake of limited space.
Comparative example 1
The carbon nanotubes were omitted and coated with a common silicone resin under the same conditions as in example 1.
Comparative example 2
Step 5 is as follows: placing the pressed blank block in an annealing furnace, vacuumizing the furnace chamber, filling nitrogen to stabilize to 0.04MPa, heating to 400 ℃ at the heating rate of 15 ℃/min, and preserving heat for 40 min; then continuing to heat to 530 ℃ and preserving the temperature for 30 minutes, then beginning to cool, and taking out the sample after the furnace temperature is cooled to room temperature; the remaining conditions were the same as in example 1.
Comparative example 3
Omitting the carbon nano tube, and using common organic silicon resin for coating, wherein the step 5 is as follows: placing the pressed blank block in an annealing furnace, vacuumizing the furnace chamber, filling nitrogen to stabilize to 0.04MPa, heating to 400 ℃ at the heating rate of 15 ℃/min, and preserving heat for 40 min; then continuing to heat to 530 ℃ and preserving the temperature for 30 minutes, then beginning to cool, and taking out the sample after the furnace temperature is cooled to room temperature; the remaining conditions were the same as in example 1.
Comparative example 4
Step 5 is as follows: placing the pressed blank block in an annealing furnace, vacuumizing the furnace chamber, filling nitrogen to stabilize to 0.04MPa, heating to 400 ℃ at the heating rate of 15 ℃/min, preserving heat for 40 min, and cooling to room temperature; and then carrying out secondary heating, introducing nitrogen, heating to 450 ℃ at a heating rate of 15 ℃/min, reducing the heating rate to 5 ℃/min, heating to 530 ℃, preserving the temperature for 30 min, cooling, taking out the sample after the furnace temperature is cooled to room temperature, and carrying out the same conditions as in example 1.
Comparative example 5
The carbon nanotubes were omitted and coated with a common silicone resin under the same conditions as in example 3.
Comparative example 6
The carbon nanotubes were replaced with carbon nanopowder having a particle size of 20nm, which was commercially available, and the rest of the conditions were the same as in example 1.
The soft magnetic composite materials prepared in examples 1 to 7 and comparative examples 1 to 6 were subjected to the performance test, and the results are shown in Table 1.
TABLE 1
As can be seen from table 1, the composite binder containing carbon nanotubes, in combination with steam annealing, can greatly improve the mechanical strength of the magnet without affecting the magnetic properties and the loss characteristics, wherein the transverse rupture strength TRS of example 1 can reach 138MPa, and the transverse rupture strength TRS of example 3 is 115 MPa; under the same process conditions, the TRS of the material prepared according to example 1, in which the material was prepared using a conventional binder, was only 105MPa (comparative example 1), and the TRS of the material prepared according to example 3 was only 92MPa (comparative example 5). In the invention, the dewaxing process at 350-400 ℃ in the first stage and the steam annealing in the second stage are carried out in two times, which is more beneficial to the improvement of the mechanical strength of the magnet, and when the nitrogen dewaxing and steam annealing process without an intermediate temperature reduction process is adopted (example 3), the mechanical property of the magnet corresponding to the annealing process carried out in two times in the temperature reduction stage is lower (examples 1-2 and examples 4-7).
The TRS of the prepared material can only reach 75MPa (comparative example 2) by adopting the composite binder to carry out secondary coating under the condition of a nitrogen annealing process instead of adopting a steam annealing process, but when the common organic silicon resin is adopted as a secondary coating agent, the TRS of the prepared material under the same process condition is far lower than that of a magnet coated by the composite binder and is only 40MPa (comparative example 3); the TRS of the material prepared by using the annealing process with the temperature reduction process of the present invention, but omitting the steam treatment step, was only 80MPa (comparative example 4).
In the initial preparation process of the composite binder, acetone is used as a solvent, organic silicon resin molecules are attached to the surface of the carbon nano tube and do not undergo a chemical reaction, but the organic silicon resin is changed from original granular state into multidimensional state attached to the surface of the carbon nano tube, so that the organic silicon resin is compositely coated on the surface of iron powder coated by phosphoric acid to form a coating structure of the reticular carbon nano tube and the organic silicon resin, organic matters are volatilized from the reticular structure more easily in the heat treatment process after the powder is pressed, and then steam enters the interior of the magnet more easily through the reticular channel to form a more uniform oxidation strengthening layer.
In addition, the TRS of the material prepared by replacing the carbon nano tube with the carbon powder is only 104MPa (comparative example 6), which is greatly different from 138MPa in the example 1, and the result proves that the mechanical property of the material cannot be greatly improved by the traditional carbon powder. The nano carbon powder is in a granular structure, and the organic coating layer cannot be changed into a net-shaped multi-dimensional structure by adding the nano carbon powder, so that the subsequent steam treatment is not greatly improved.
In conclusion, the organic silicon resin molecules are adhered to the surfaces of the carbon nanotubes to form a net-shaped structure, and after the composite binder is coated, the net-shaped coating structure can be formed on the surface of the iron powder, so that the volatility of the composite binder and a lubricant adhered to the net-shaped structure during annealing can be obviously improved, a diffusion channel is provided for steam to enter the interior of the magnet, organic matters can be more effectively removed, a uniform and complete oxidation strengthening layer is formed, and the mechanical strength of the SMC magnet is greatly improved.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. The composite binder is characterized by being prepared by the following method:
firstly, preparing acetone solution of organic silicon resin, then adding carbon nano tubes accounting for 1-5% of the weight of the organic silicon resin, and uniformly dispersing the carbon nano tubes in the acetone solution of the organic silicon resin by ultrasonic oscillation and mechanical stirring to form the composite binder.
2. The composite binder of claim 1 wherein the carbon nanotubes have a length of 200nm to 1 μm and a diameter of 10 nm to 50 nm.
3. The composite binder as claimed in claim 1, wherein in the acetone solution of the silicone resin, the volume ratio of the silicone resin to the acetone is 1: 8-12;
the amount of the carbon nano tube is 2-3% of the weight of the organic silicon resin.
4. A method for preparing a soft magnetic composite material, comprising:
step 1: iron powder pretreatment;
step 2: insulating and coating: passivating iron powder with phosphoric acid to form an inorganic coating layer, and then performing organic coating by using the composite binder of any one of claims 1 to 3 to obtain insulating iron powder; wherein the addition amount of the composite binder is 0.2-0.4 wt% of the iron powder;
and step 3: and (3) pressing and forming: adding a lubricant into the insulating iron powder, and then performing compression molding;
and 4, step 4: annealing treatment: firstly, primary annealing is carried out in a nitrogen atmosphere, then secondary annealing is carried out in a water vapor atmosphere, and then furnace cooling is carried out to obtain the soft magnetic composite material.
5. A method for preparing a soft magnetic composite material according to claim 4, characterized in that in step 4, after the primary annealing, the material is cooled to room temperature and then subjected to secondary annealing.
6. The method for preparing a soft magnetic composite material according to claim 5, wherein the step 4 is specifically: and (3) annealing twice: primary annealing: vacuumizing the annealing furnace, and then filling nitrogen to stabilize to 0.04 MPa; heating from room temperature to 350-400 ℃ at the heating rate of 10-15 ℃/min, preserving the heat for 40-60 min, and cooling to room temperature; and then carrying out secondary annealing, raising the temperature from room temperature to 450 ℃ at the temperature rise rate of 10-15 ℃/min in the nitrogen atmosphere, introducing water vapor, reducing the temperature rise rate to 3-5 ℃/min, raising the temperature to 540 ℃, preserving the temperature for 20-35 min, introducing nitrogen to remove water vapor, reducing the temperature to room temperature, and discharging the furnace.
7. The method for preparing a soft magnetic composite material according to claim 4, wherein in the step 3, the pressing pressure is 800-1000 MPa; the lubricant is micro wax powder; the dosage of the lubricant is 0.15-0.3 wt% of the dosage of the iron powder.
8. The method for preparing a soft magnetic composite material according to claim 4, wherein in the step 1, the iron powder pretreatment specifically comprises: performing mechanical ball milling pretreatment on iron powder, wherein in the ball milling treatment process, the rotating speed of a ball mill is 300-600 revolutions per minute, the ball-material ratio is 2:1-6:1, and the pretreatment time is 5-10 minutes; then ultrasonic vibration cleaning is carried out by adopting alcohol or acetone solution, and then drying is carried out at 60-80 ℃.
9. The method for preparing a soft magnetic composite material according to claim 4, wherein in the step 2, the phosphoric acid passivation is specifically: uniformly diluting orthophosphoric acid and alcohol according to the volume ratio of 1:50-1:80, and insulating and coating iron powder by adopting an atomization method to form a phosphoric acid coating layer.
10. A method for preparing a soft magnetic composite material according to any of claims 4-9, characterized in that the iron powder is water atomized iron powder with purity requirement > 99.9%, and the particle size of the iron powder is 180-250 μm.
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