JP3027180B2 - Iron-cobalt based sintered magnetic material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an iron-cobalt-based sintered magnetic material having a high density, a low oxygen content and a low carbon content, and excellent soft magnetic properties. About the method.

[Prior art and its problems] Generally, iron-cobalt-based magnetic materials have the highest saturation magnetic flux density among magnetic materials, and thus are widely used as magnetic materials for yokes. It has the disadvantage of being difficult. Also pure,
That is, an iron-cobalt-based magnetic material substantially consisting of only iron and cobalt has a low volume resistivity, and thus has a problem that iron loss is large when an eddy current is generated as in an alternating magnetic field. In order to solve these problems, vanadium (V) has been added to the magnetic material, but it has not yet been possible to obtain sufficient workability.

For this reason, attempts have been made conventionally to use a powder metallurgy method.However, since the density of a sintered body is low in a normal powder metallurgical method, the obtained magnetic material has low magnetic properties. There's a problem.

On the other hand, JP-A-2-138443 proposes a method in which a powder having an average particle size of 15 μm or less is injection-molded by a metal powder injection molding method, further degreased, then reduced in vacuo, and then sintered in an argon atmosphere. . According to this method, a relatively high-density sintered body can be easily obtained because a powder having a small average particle size is used, but the following problems arise because an organic binder is used during molding. That is, the active V
In a system containing, oxygen and carbon which adversely affect magnetic properties due to a part of the organic binder remaining in the system are mixed. On the other hand, in the method of sintering in an argon atmosphere after vacuum reduction, it is very difficult to simultaneously reduce both oxygen and carbon elements from the material. It is necessary to increase the amount of oxygen to reduce it. As a result, the amount of oxygen contained in the sintered body increases, so that densification is hindered, and the sintering density is only about 95 to 96% in relative density at most. Regarding its magnetic properties, the magnetic flux density B ₂₀
Value is 20 kG or less, which is considerably lower than that of ingot material, and sufficient characteristics cannot be obtained.

It is also conceivable to increase the density to near the true density by performing HIP after sintering, but the cost is higher than normal pressure sintering and the amount of oxygen and carbon remaining in the sintered body Is almost determined during sintering before HIP treatment, and it is extremely difficult to reduce the amount of oxygen and carbon after HIP.

As described above, when an iron-cobalt-based sintered magnetic material is used in place of the same ingot material, the magnetic flux density of the sintered magnetic material is reduced, so that the advantage of using the iron-cobalt-based material is reduced. In addition, there is a problem in that HIP sintering loses the economic advantage of using an inexpensive sintered material.

[Means for Solving the Problems] In the iron-cobalt-based sintered magnetic material according to claim 1 of the present invention, cobalt is 40 to 60% by weight and vanadium is 1.
0 to 2.5 wt%, oxygen is 0.02 wt% or less, carbon is 0.02 wt% or less, the balance is iron and unavoidable impurities, the relative density of the sintered body is 98% or more, and the magnetic flux density [B ₂₅ ] is 21 kG The above is a means for solving the above problem.

In the method for producing an iron-cobalt-based sintered magnetic material according to claim 2, cobalt is 40 to 60% by weight, and vanadium is
In a method of manufacturing a sintered iron-cobalt-based magnetic material, a raw material powder containing 1.0 to 2.5% by weight, the balance being iron and unavoidable impurities, is formed into a desired shape and sintered to produce a sintered magnetic material. The object of the present invention is to make the sintering process into two processes, a first process of raising the temperature in a vacuum atmosphere and a second process of performing sintering in a reducing atmosphere after the first process. Was the solution.

 Hereinafter, the present invention will be described in detail.

The sintered magnetic material of the present invention has a composition of cobalt;
It is composed of 0% by weight, vanadium: 1.0 to 2.5% by weight, oxygen: 0.02% by weight or less, carbon: 0.02% by weight or less, with the balance being iron and inevitable impurities. That is, if the cobalt content is less than 40% by weight, the magnetic permeability of the magnetic material is low, while if it exceeds 60% by weight, the magnetic flux density is low, and neither is preferable. If the content of vanadium is less than 1.0% by weight, the volume resistivity of the magnetic material becomes small, which is not preferable. On the other hand, if it exceeds 2.5% by weight, the coercive force increases, and the properties of the obtained magnetic material are compared with those in the above composition range. This is because it is inferior and is still not preferred.

Further, if the oxygen content exceeds 0.02% by weight, an oxide is generated in the sintered body, thereby densifying the sintered body and lowering the density of the sintered body. As a result, the magnetic flux density is lowered, and the movement of the domain wall by the oxide is reduced. On the other hand, if the carbon content exceeds 0.02% by weight, the carbon penetrates into the crystal and the lattice is distorted, thereby lowering the magnetic permeability of the magnetic material. Because there is no.

The sintered magnetic material has a relative density of 98%.
% Or more. That is, when the magnetic material is 98% or more, the magnetic material has a magnetic flux density [B ₂₅ ] of 21 kG or more, which is equivalent to that of the smelting material, so that it can be sufficiently used as a substitute for the smelting material.

Such a magnetic material has a high magnetic permeability, a high magnetic flux density, and a large volume specific resistance due to the above composition and the relative density of the sintered body, and thus is an excellent magnetic material.

Next, a method for manufacturing such a sintered magnetic material will be described based on the manufacturing method according to claims 2 to 7 of the present invention.

First, 40-60% by weight of cobalt and 1.0-
A raw material powder which is 2.5% by weight and the balance is iron and inevitable impurities is prepared. Here, the reason for determining the weight ratio of each element in the raw material powder is as described in the composition of the sintered magnetic material. Further, the particle size of the raw material powder is not particularly limited, but as described below, 1300 ℃
When sintering as described above, the average particle size of the raw material powder is preferably 15 μm or less, more preferably 10 μm or less, in order to sufficiently reduce the void diameter of the sintered body.

Next, an appropriate binder is added to the raw material powder and kneaded, and the kneaded product is formed into a desired shape by an appropriate molding method such as injection molding. Here, as the binder, for example, polymethacrylate, wax or the like is used.

Furthermore, the obtained molded body is degreased (binder removal) by a known degreasing treatment such as heat treatment in an inert atmosphere or extraction of the binder with a solvent. In this case, the degreasing rate of the obtained degreased body should be 60% or more, and if it is less than 60%, the density of the sintered body obtained after sintering becomes low, and the magnetic properties also deteriorate, which is not preferable.

Next, the obtained degreased body is sintered. The sintering process includes a first step of raising the temperature in a vacuum atmosphere, and a second step of performing sintering in a reducing atmosphere after the first step. Here, the reason why the sintering is performed in two steps is as described below.

Vanadium contained in the iron-cobalt alloy is oxidized at a temperature of 800 to 900 ° C. or less in a hydrogen atmosphere having a purity of about 99.99%, which is a normal sintering atmosphere. For this reason,
When the temperature is increased in a hydrogen atmosphere, the amount of oxygen contained in the sintered body increases, and the densification of the sintered body is hindered. On the other hand, in a vacuum atmosphere of 1 × 10 ⁻³ Torr or less, vanadium does not oxidize even at a high temperature, and conversely, the amount of oxygen contained in the sintered body is reduced, so that sintering is promoted and the density of the sintered body is increased. Is likely to occur.

However, the carbon contained in the sintered body does not decrease in a vacuum atmosphere unless a sufficient amount of oxygen is present in the sintered body. Then, the magnetic material obtained when carbon remains has a deteriorated magnetic property, which is not preferable,
On the other hand, when oxygen sufficient to remove carbon remains in the sintered body, densification is hindered as described above, which is not preferable. However, the carbon in the sintered body is reduced by maintaining the sintered body at a high temperature in a hydrogen atmosphere. Therefore, by sintering in a reducing atmosphere after the step of raising the temperature in a vacuum atmosphere, it is possible to suppress the oxidation of the sintered body and the inhibition of densification due to the oxide, and also include the sintered body. Since the amount of oxygen and the amount of carbon can be reduced, a sintered body with high density and high purity can be obtained.

In the first step, that is, the sintering step performed in a vacuum atmosphere, the upper limit of the temperature range is preferably 800 ° C. or more and 1250 ° C. or less. This is because vanadium may still be oxidized below 800 ° C, whereas if it exceeds 1250 ° C, densification has already progressed considerably. Because it is disadvantageous.
In the first step, it is preferable to appropriately maintain the temperature while the temperature is raised in a vacuum atmosphere because the amount of oxygen in the sintered body can be reduced and the densification can be promoted.

In the second step, that is, in the sintering step performed in a reducing atmosphere, sintering is started from the vicinity of the maximum temperature in the first step following the first step, and thus at least 1300.
Sintering is performed by raising the temperature to at least ℃. Here, as the reducing atmosphere, in order to quickly remove carbon in the sintered body,
It is preferable to use an atmosphere containing hydrogen. Also, 13
Raise the temperature to 00 ° C or higher, that is, set the maximum sintering temperature to 1300
C. or higher, the volume diffusion coefficient of the obtained sintered body increases, the densification speed in the final stage of densification increases, the time required for densification decreases, and the diffusion coefficient of carbon increases. This is because the amount of carbon contained in the sintered body rapidly decreases because sintering at a temperature of less than 1300 ° C. cannot sufficiently obtain these advantages.

Further, when the sintered body is not sufficiently densified by the time the temperature reaches 1300 ° C or higher, that is, when the relative density of the sintered body is low, the diffusion coefficient increases at a temperature of 1300 ° C or higher, Aggregation and coarsening of the voids occur, and the resulting sintered body is undesirably densified. On the other hand, the driving force for shrinking the isolated void in the sintered body is the surface stress of the void, and the surface stress of the void is inversely proportional to the diameter of the void.
Therefore, the voids that have become coarse due to aggregation are less likely to shrink due to a reduction in the driving force of the shrinkage, and furthermore, the voids are isolated within the isolated voids.
Since voids do not shrink when CO gas or the like is generated, the sintered body (or a precursor thereof) having such voids is not further densified, and thus does not become a high-density sintered body.

Therefore, in order to obtain a high-density sintered body, by controlling heating conditions such as a heating rate at a temperature lower than 1300 ° C. and a holding temperature / time, the sintering is performed in the heating step in the second step. When the sintering temperature reaches 1300 ° C for the first time, the relative density of
% Or more, so that the voids are sufficiently small and dispersed to prevent aggregation. In other words, by doing so, the voids shrink when sintered at a temperature of 1300 ° C. or more, which is extremely advantageous for obtaining a dense and high-density sintered body. In this case, 1300 ℃
As a method for densifying (increasing the density) the sintered body at the following temperature, a method of maintaining the temperature isothermally at a temperature of 1300 ° C. or lower, or a method of lowering the temperature rising rate can be adopted.

After sintering is completed in this manner, the temperature is lowered to room temperature at an appropriate speed to obtain a sintered body, that is, an iron-cobalt-based sintered magnetic material.

[Operation] According to the iron-cobalt-based sintered magnetic material according to claim 1 of the present invention, the composition and the relative density of the sintered body increase the magnetic permeability, increase the magnetic flux density, and increase the volume resistivity. It has excellent soft magnetic properties.

Further, according to the method for producing an iron-cobalt based sintered magnetic material according to claim 2, after the first step of raising the temperature in a vacuum,
Since the second step of sintering in a reducing atmosphere is performed, it is possible to promote the densification of the sintered body by preventing oxidation of the sintered body in the first step, and to perform sintering in the second step. Since carbon contained in the body can be removed, an iron-cobalt-based sintered magnetic material having a high density, a small amount of oxygen and a small amount of carbon, and a high purity can be obtained.

[Example] As raw material powder, Fe-Co-V water atomized powder having an average particle size of 8.6 µm (Co; 49.2 wt%, V; 2.2 wt%, balance Fe)
Was prepared and kneaded by adding 12 parts by weight of a binder to 100 parts by weight of the raw material powder. In addition, polymethacrylic acid ester was used as a binder.

Next, the obtained kneaded material was injected at an injection temperature of 165 ° C and an injection pressure of 100
Molding was performed under the condition of 0 kg / cm ² to obtain a ring-shaped molded body. Further, the molded body was degreased under an inert atmosphere, and the degreasing rate was 92%.
~ 94% of the defatted body was obtained.

Next, the obtained degreased body was heated to 900 ° C. at a rate of 10 ° C./min in a vacuum atmosphere of 1 × 10 ⁻³ Torr or less,
It was kept isothermally at this temperature for one hour.

Thereafter, hydrogen is introduced to form a hydrogen atmosphere (reducing atmosphere), and then the temperature is raised to 1250 ° C. at a rate of 10 ° C./min.
After maintaining the temperature isothermally for 10 hours, the temperature was raised to 1400 ° C. at a rate of 10 ° C./minute, and sintering was performed for 2 hours to obtain a sintered material.

When the density of the sintered body after sintering at 1250 ° C for 4 hours was measured, the relative density of the sintered body was about 97%, and when the temperature reached 1300 ° C, the relative density of the sintered body became 96% or more. It was confirmed that. In addition, about the obtained sintered material,
After measuring the density, the amount of oxygen and the amount of carbon, and further performing a heat treatment at 850 ° C. for 3 hours to obtain a sintered magnetic material, its DC magnetic characteristics (magnetic flux density and coercive force) Was examined.

Table 1 shows the obtained results. As comparative examples, those sintered at room temperature in a hydrogen atmosphere (Comparative Example 1), those only subjected to vacuum sintering (Comparative Example 2), and those having a sintered density of 96% when reaching 1300 ° C. Those obtained by sintering at 1400 ° C. for 4 hours without holding at 1250 ° C. so as to be less than (Comparative Example 3) were also prepared, and the characteristics and the like were also examined. The results are also shown in Table 1.

From the results shown in Table 1, it was confirmed that the product of the present invention had a high density, a low content of both oxygen and carbon, and excellent magnetic properties.

Also, when the volume resistivity value of the product of the present invention was measured,
53 μΩ · cm, which was confirmed to be a sufficiently large value.

[Effects of the Invention] As described above, the iron-cobalt-based sintered magnetic material according to claim 1 of the present invention has high magnetic permeability, magnetic flux density, and volume resistivity due to its composition and sintered body relative density. It becomes a very excellent soft magnetic material, for example, its value becomes large.

The method for producing an iron-cobalt-based sintered magnetic material according to claims 2 to 7 includes performing a second step of sintering in a reducing atmosphere after the first step of raising the temperature in a vacuum. Therefore, in the first step, the densification of the sintered body can be promoted by preventing the oxidation of the sintered body, and the carbon contained in the sintered body can be removed in the second step. In addition, an iron-cobalt-based sintered soft magnetic material having a low purity and a low oxygen content and a low carbon content can be obtained, whereby an excellent soft magnetic material can be manufactured.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 1/00-38/10

Claims (7)

(57) [Claims] (1) Cobalt is 40 to 60% by weight and vanadium is 1.
0 to 2.5 wt%, oxygen is 0.02 wt% or less, carbon is 0.02 wt% or less, the balance is iron and unavoidable impurities, the relative density of the sintered body is 98% or more, and the magnetic flux density [B ₂₅ ] is 21 kG The iron-cobalt sintered magnetic material described above. 2. Cobalt is 40 to 60% by weight and vanadium is 1.
0-2.5% by weight, with the balance being iron and inevitable impurities, a raw material powder is formed into a desired shape and sintered to produce a sintered magnetic material. The step for sintering comprises a first step of raising the temperature in a vacuum atmosphere, and a second step of sintering in a reducing atmosphere after the first step. Of producing an iron-cobalt based sintered magnetic material. 3. The method for producing a sintered iron-cobalt magnetic material according to claim 2, wherein the upper limit of the temperature range in the first step of raising the temperature in a vacuum atmosphere is 800 ° C. or more and 1250 ° C. or less. A method for producing an iron-cobalt-based sintered magnetic material. 4. The method for producing a sintered iron-cobalt magnetic material according to claim 2, wherein the maximum value of the sintering temperature in the second step of sintering in a reducing atmosphere is 1300 ° C. or more. A method for producing an iron-cobalt-based sintered magnetic material. 5. The method for producing an iron-cobalt-based sintered magnetic material according to claim 2, 3 or 4, wherein the sintering temperature is the first time in the heating step in the second step.
A method for producing an iron-cobalt based sintered magnetic material having a relative density of a sintered body of 96% or more when the temperature reaches 1300 ° C. 6. The method for producing an iron-cobalt based sintered magnetic material according to claim 2, 3, 4 or 5, wherein the reducing atmosphere in the second step is an atmosphere containing hydrogen. Material manufacturing method. 7. The method for producing an iron-cobalt based sintered magnetic material according to claim 2, 3, 4, 5 or 6, wherein the raw material powder has an average particle size of 15 μm or less. Material manufacturing method.