JPH04217305A - Manufacture of iron-nitride-based high-density sintered body - Google Patents

Abstract

PURPOSE:To get a practical iron nitride high-density sintered body by a manufacturing process comprising a step for applying nitride treatment to iron or iron alloy powder and making Fe, N, etc., at the periphery of the powder particles, a step for sintering the powder particles, and a step for applying interparticle oxidation treatment. CONSTITUTION:Using water atomized iron powder and carbonyl iron powder, the iron powder is nitrized into nitrized powder by gas nitriding method. For nitriding treatment, using H2 gas and NH3 gas as reaction gas, the particles mainly composed of Fe4N and Fe16N2 or particles whose insides consist of Fe and the peripheries mainly consist of Fe4N or Fe16N2 are formed. As regards the one where approximately the whole has become Fe4N, the reduction treatment is performed in the mixed gas atmosphere of H2/NH3 so as to form the metal shell of Fe on the surface of nitrized powder particles. Then, it is sintered while being oxidated in an oxidative atmosphere.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an iron nitride-based high-density sintered body suitable as a soft magnetic material for high and medium frequency ranges.

0002

BACKGROUND OF THE INVENTION Iron nitride is an interstitial compound whose crystal system changes depending on the nitrogen content and whose magnetic properties also vary greatly. This iron nitride is a material with properties intermediate between metals and oxides, and metal F
It has better corrosion resistance and weather resistance than e, and is harder. In particular, Fe4N and Fe16N2 have high saturation magnetization and are expected to be used as magnetic materials with excellent corrosion resistance, weather resistance, and mechanical properties. However, as mentioned above, it is difficult to obtain a sintered body that takes into consideration the excellent properties, and the actual situation is that it has not been applied as a sintered body. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a practical method for manufacturing an iron nitride-based high-density sintered body.

0003

[Means and Effects for Solving the Problems] A method for producing a nitride-based high-density sintered body according to the present invention includes a method for producing a nitride-based high-density sintered body by subjecting iron or iron alloy powder to a nitriding treatment so that at least the outer periphery of the powder particles contains Fe.
The present invention is characterized by comprising a step of forming 4 N or Fe16N2, a step of sintering the powder particles thus formed, and a step of subjecting these particles to intergranular oxidation treatment.

[0004] By such a method, particles mainly composed of Fe4N or Fe16N2, or particles containing Fe or Fe alloy in the interior and Fe4N or Fe16 in the outer periphery can be obtained.
It is possible to obtain a nitride-based high-density sintered body consisting of a composite sintered body in which particles mainly composed of N2 are dispersed in a matrix of Fe3O4 as a spinel type magnetic oxide. Such a high-density sintered body is suitable as a soft magnetic material for high and medium frequency ranges.

Conventionally, soft magnetic materials include ferrite,
Silicon steel plates, permalloy, Fe-based and Co-based amorphous alloys, etc. are used. Such soft magnetic materials are required to have a high saturation magnetic flux density, low loss, and a certain degree of magnetic permeability. Among these, metal materials such as silicon steel sheets, permalloy, and Fe-based and Co-based amorphous alloys have relatively high saturation magnetic flux densities and are suitable as soft magnetic materials for low frequencies. In particular, Fe groups and Co
The base amorphous alloy has high magnetic permeability. However, since these are basically metals, they have low electrical resistance.
It is difficult to apply it for high and medium frequencies. That is, since the loss (tan δ) is proportional to the square of the frequency and inversely proportional to the electrical resistance, the loss of these metal magnetic materials becomes too large in the high frequency range. Additionally, metal materials have the disadvantage of poor weather resistance. On the other hand, ferrite materials such as Mn-Zn ferrite have high electrical resistance because they are basically oxides, and are widely used as soft magnetic materials that can be used from low frequency ranges to high and medium frequency ranges. However, ferrite materials basically have a low saturation magnetic flux density, and also have the drawback that loss increases rapidly in a high frequency range of 103 kHz or higher. Therefore, the present invention provides a manufacturing method capable of compensating for the drawbacks of these materials and obtaining the above-mentioned sintered body as a soft magnetic material with extremely excellent properties.

Next, a sintered body to be obtained by the present invention will be explained. FIG. 1 is a phase diagram of the iron-nitrogen system. In this phase diagram, the γ' phase is Fe4N, and the α''
The phase is Fe16N2. Fe4N is iron fcc
It has a perovskite-type crystal lattice with nitrogen atoms at the body center of the phase. This phase is stable even at room temperature, and Tc
= 488°C ferromagnetic material. Saturation magnetization at room temperature is 19
It is 5 emu/g, which is slightly lower than pure iron, and is promising as a magnetic material. On the other hand, Fe16N2 is a metastable phase and has a bct crystal lattice with a bcc lattice as its matrix. This bct structure is a type in which nitrogen atoms are regularly inserted into the body center position of iron in the bcc structure. The saturation magnetization of this phase at room temperature is 260 emu/g, which is 1.2 times that of pure iron, and is also promising as a magnetic material. In addition, since dense α-Fe2 O3 is formed on the surfaces of Fe4 N and Fe16N2 in the atmosphere, Fe3
It has better weather resistance than Fe, which forms O4. Furthermore, since they are nitrides, they are considerably harder than iron.

[0007] Such Fe4N or Fe16N2
F as a spinel-type magnetic oxide containing particles mainly composed of
The composite sintered body dispersed in a matrix such as e3 O4 uses spinel, which has high electrical resistance, as a matrix, so it can maintain high resistance, and
Since Fe4N or Fe16N2, which has a high saturation magnetic flux density, is used as the magnetic particles in the spinel magnetic oxide matrix, magnetic continuity can be maintained.
Higher saturation magnetic flux density and relatively higher magnetic permeability than ferrite can be obtained. Therefore, loss is small even at high and medium frequencies. Furthermore, since the magnetic particles in the matrix are mainly composed of Fe4N or Fe16N2, which have high weather resistance, at least their outer peripheral portions, they have better weather resistance than metal-based soft magnetic materials.

[0008] In order to manufacture such a sintered body, first, iron powder is prepared as a starting material. This iron powder preferably has a particle size of 0.1 to 200 μm, and C
Ultrafine iron powder produced by the VD method, carbonyl iron powder, water atomized powder, gas atomized powder, and reduced iron powder can be used. In addition, these iron powders include not only pure iron but also Fe.
-Co alloy can also be used.

Next, such iron powder or iron alloy powder is nitrided by an appropriate method. In this case, if the nitriding time is long enough, the particles will be completely converted to Fe4N or Fe16N.
2, and if the nitriding treatment time is short, it is possible to nitride only the outer periphery to produce particles whose interior is made of Fe or Fe alloy and the outer periphery is made of Fe4N or Fe16N2. During this process, by appropriately specifying nitriding conditions such as nitrogen supply amount and temperature, Fe
4N or Fe16N2 can be formed. Note that, as described above, since Fe16N2 is a metastable phase, it can be obtained by rapid cooling after nitriding.

[0010] As the nitriding method, gas nitriding method and ion nitriding method are suitable. In the gas nitriding method, iron powder is charged into a reaction vessel, and while the inside of the vessel is heated to about 500°C using an external heater, NH3 gas, H2 gas, etc. are fed into the vessel to remove iron. Nitrid the powder. Also,
In the ion nitriding method, the inside of a reaction vessel is maintained at a high vacuum, and N2 or the like as a reaction gas is introduced into the vessel to nitride iron powder by glow discharge.

Next, the nitrided iron powder is sintered. In this case, when the iron nitride to be formed is Fe4N, the sintering can be carried out by compacting and then firing normally. In the case of Fe16N2, since this phase is a metastable phase and requires rapid cooling, sintering is performed by explosive molding. Explosive molding utilizes the explosive power of gunpowder, and utilizes the instantaneous enormous pressure and processing speed to shape and sinter powder. Explosive molding can be performed by filling a plastic mold with powder, placing it in water, and applying explosive force, such as in isostatic pressing, or by applying explosive force to a punch using a normal pressing mold structure. You can also do this by adding. Note that this sintering is performed so as to obtain a sintered body that is capable of producing the intergranular oxidation necessary for the subsequent intergranular oxidation treatment.

[0012] Thereafter, this sintered body is subjected to intergranular oxidation treatment. This intergranular oxidation treatment is performed by maintaining the sintered body at about 590° C. and supplying an oxidizing gas. As a result, a matrix of Fe3O4 or the like is formed around the sintered particles, resulting in a high-density sintered body. Note that this intergranular oxidation may be performed after the sintering treatment as described above, but
It is also possible to perform the sintering simultaneously with sintering in the process of sintering by making the sintering atmosphere a weakly oxidizing atmosphere.

Through these steps, the above-mentioned Fe4
A composite in which particles mainly composed of N or Fe16N2, or particles whose interior is Fe or Fe alloy and whose outer periphery is mainly Fe4N or Fe16N2, are dispersed in a matrix such as Fe3O4 as a spinel magnetic oxide. A nitride-based high-density sintered body made of a sintered body is obtained.

[0014] Such Fe4N or Fe16N2
The composite sintered body of magnetic particles containing Fe4N or Fe16N2 and a spinel-type magnetic oxide matrix may have a volume ratio of 6/100 to 100/100. preferable. In addition, such a high-density sintered body has a density of 98% of the theoretical density.
It is preferable to have a density equal to or higher than that. The iron nitride-based composite sintered body produced by the above-described method has magnetic properties suitable as a soft magnetic material for high and medium frequencies, and is excellent in weather resistance.

[0015]

[Embodiments] Examples of the present invention will be described below. (Example 1)

In this example, water atomized iron powder and carbonyl iron powder with a particle size of 1 to 40 μm were used as starting materials. This iron powder was nitrided using a gas nitriding method to obtain nitrided powder. This nitriding process uses H2 as a reaction gas.
Using gas and NH3 gas, H2 /NH3 is 0/
The nitriding process was carried out at a temperature ranging from room temperature to 750°C for 5 minutes to 2 hours, varying the temperature from 100 to 90/10. As a result, F
Particles mainly composed of e4 N or Fe16N2, or particles with Fe inside and Fe4 N or Fe16N on the outer periphery
Particles mainly consisting of 2 were formed. Among these nitrided powders, H2 /NH3 was nitrided under conditions of 50/50 to 70/30 and maintained at a temperature of 500°C for 30 minutes to become almost entirely Fe4N.
30 in a mixed gas atmosphere of 40/60 to 60/40
Reduction treatment was performed at 0°C for 5 to 15 minutes. As a result, a metal shell of Fe was formed on the surface of the nitrided powder particles.

Next, this powder was molded and then sintered in an oxidizing atmosphere while oxidizing the intergranular areas. As a result, the Fe4N particles became Fe as spinel-type magnetic oxide.
A nitride-based high-density sintered body consisting of a composite sintered body dispersed in a matrix of 3 O4 was obtained. The physical properties and characteristics of this sintered body were as shown below. Density 6.53g/c
m3 Iron loss W 0.
85W/cm3 Maximum permeability μmax
800 specific resistance ρ 0.01
Ω・cm Saturation magnetization MS 171emu
/g or more, it was confirmed that a high-density sintered body having excellent magnetic properties as a soft magnetic material for high and medium frequencies was obtained. (Example 2) In this example, the starting material has a particle size of 1 to 40
Nitriding treatment was carried out under the same conditions as in Example 1 using μm water atomized iron powder.

Among these nitrided powders, H2 /NH3
300% in a mixed gas atmosphere with H2/NH3 of 40/60 to 60/40 for those that were almost entirely nitrided by nitriding under conditions of 50/50 to 70/30 and a temperature of 500°C for 30 minutes. Reduction treatment was carried out at 5°C for 5 to 15 minutes. As a result, an Fe metal shell was formed on the surface of the nitrided powder particles.

Mn powder and Zn powder were added to this powder and mixed in a V blender, and then this powder was molded and then sintered in an oxidizing atmosphere while oxidizing the particles. As a result, a nitride-based high-density sintered body consisting of a composite sintered body in which nitride particles were dispersed in a matrix of Fe3O4 or the like as a spinel-type magnetic oxide was obtained. As a result of measuring the physical properties and characteristics of this sintered body, almost the same values as in Example 1 were obtained. That is, it was confirmed that a high-density sintered body having excellent magnetic properties as a soft magnetic material for high and medium frequencies was obtained.

[0020]

According to the present invention, a practical method for producing an iron nitride-based high-density sintered body can be provided. The sintered body produced by this method has high electrical resistance and high saturation magnetization, resulting in low loss, and relatively high magnetic permeability, so it is suitable as a soft magnetic material for high and medium frequencies. In addition, it is practical because it has better weather resistance than metal-based soft magnetic materials.

[Brief explanation of the drawing]

[Fig. 1] Phase diagram of the iron-nitrogen system.

Claims (1)

[Claims] Claim 1: Iron or iron alloy powder is subjected to nitriding treatment so that Fe4 N or Fe16 is added to at least the outer periphery of the powder particles.
An iron nitride-based high-density sintered body comprising a step of forming N2, a step of sintering the powder particles thus formed, and a step of subjecting these particles to intergranular oxidation treatment. manufacturing method.