JP2928647B2 - Method for producing iron-cobalt based sintered magnetic material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an iron-cobalt sintered magnetic material having excellent soft magnetic properties.

[0002]

2. Description of the Related Art An iron-cobalt sintered magnetic material has the highest saturation magnetic flux density among magnetic materials, and is therefore promising as a magnetic material for a yoke. In particular, vanadium-added iron
A cobalt-based sintered magnetic material is a very excellent material because it has a large volume resistivity and suppresses iron loss. However, this material is very difficult to perform normal machining (cutting or the like), and attempts have been made to produce the material using powder metallurgy. In particular, among the powder metallurgy methods, the metal powder injection molding method uses a fine raw material powder as compared with the ordinary powder metallurgy method, so that a sintered body having a high sintering density and a high saturation magnetic flux density can be obtained. Moreover, since it can be formed into a complicated shape, it is said to be more suitable as a method for producing an iron-cobalt sintered magnetic material.

[0003]

However, in such a metal powder injection molding method, since the sintering temperature is increased in order to further increase the sintering density, the crystal grains of the obtained sintered body are likely to be non-homogeneous. There is a problem that soft magnetic characteristics are deteriorated such as an increase in coercive force. In order to improve the heterogeneity of such crystal grains, conventionally, iron-
The cobalt-based sintered magnetic material has been subjected to a heat treatment at around 850 ° C., which is lower than the temperature at which a stable α phase is transformed at room temperature into a stable γ phase at high temperature. However, in such a heat treatment, the driving force for recrystallization is smaller than that of a material subjected to rolling or the like,
Since the obtained magnetic material is hard to be uniform, there is a dissatisfaction that a sufficient effect of improving the soft magnetic properties cannot be obtained as compared with the rolling treatment.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an iron-cobalt based sintered magnetic material capable of improving the soft magnetic characteristics by homogenizing the crystal grains of a sintered body. It is to provide a method for manufacturing.

[0005]

Means for Solving the Problems Claim 1 of the present invention
In the method for producing an iron-cobalt sintered magnetic material described above, 40 to 60% by weight of cobalt and 1.0 to 2.5% of vanadium are used.
% Of the raw material powder, the balance being iron and unavoidable impurities, is molded and sintered to produce an iron-cobalt sintered magnetic material. After sintering, the first powder is heated at a temperature of 950 ° C. or more and 1200 ° C. or less. Heat treatment, then 750 ° C or higher 850
Performing the second heat treatment at a temperature of not more than ° C is a means for solving the above-mentioned problem. Further, in the method for producing an iron-cobalt based sintered magnetic material according to claim 2, after the first heat treatment,
The means for solving the above-mentioned problem is to perform the operation of cooling to less than 950 ° C. at a cooling rate of 50 ° C./min or less.

Hereinafter, the present invention will be described in detail. First, 40 to 60% by weight of cobalt and 1.0 to 2.5% of vanadium.
A raw material powder is prepared by weight%, the balance being iron and unavoidable impurities. Here, the reason why the above range was selected as the composition of the raw material powder is that when the amount of cobalt is less than 40% by weight, the magnetic permeability of the obtained magnetic material becomes low, and when it exceeds 60% by weight, the saturation magnetic flux density becomes small. If the amount of vanadium is less than 1.0% by weight, the volume resistivity of the magnetic material becomes small, while if it exceeds 2.5% by weight, the coercive force becomes large. The particle size of the raw material powder is preferably fine in order to obtain a high sintering density, and more specifically, the average particle size is desirably about 5 to 15 μm.

Next, the raw material powder is formed into a predetermined shape. The molding method is not particularly limited, but a metal powder injection molding method that can use a fine powder and can obtain a high sintering density is preferable. further,
The obtained molded body is sintered to obtain a sintered body. The sintering conditions are not particularly limited. However, since the density of the sintered body greatly affects the magnetic properties, it is preferable to set the sintered body density to 98% or more. For this purpose, sintering is performed at a sintering temperature of 1300 ° C. or more. It is desirable to increase the density of the sintered body by performing HIP (hot isostatic pressing) treatment or the like.

Next, the obtained sintered body is further heat-treated. This heat treatment consists of two steps. The first heat treatment is performed at a temperature of 850 to 1200 ° C., and the second heat treatment is performed at a temperature of 750 to 850 ° C. after the first heat treatment. It is. The reason for performing the heat treatment after sintering in two steps is as follows.

The crystal phase of the iron-cobalt based sintered body is about 95
At 0 ° C. or higher, it is a γ phase, and is transformed into a stable α phase at a low temperature in the cooling process after sintering. When transforming from the γ phase to the α phase, the grain boundaries of the γ phase are the nuclei for the generation of the α phase, but since they are usually sintered at high temperatures to increase the density of the sintered body as in this example, , The crystal grains of the γ phase become coarse. Therefore, since the nuclei of the formation of the α phase are reduced and the transformation from the γ phase to the α phase is difficult to progress, it is inevitable that the α phase crystal grains become inhomogeneous even if the cooling rate is reduced. is there. The resulting heterogeneous α-phase crystal grains
Even if annealing is performed in the α-phase region, it is very difficult to erase. That is, in the composition of the iron-cobalt sintered magnetic material, the upper limit temperature of the α phase is about 850 ° C. At such a temperature, recrystallization and grain growth are unlikely to occur without a driving force such as processing strain. is there.

Therefore, in the first heat treatment step of the present invention, the sintered body is once heated to a temperature of not less than 950 ° C. and not more than 1200 ° C. in order to eliminate the inhomogeneous α phase, and the inhomogeneous α phase is converted to γ phase. It is perverted. Here, the heat treatment temperature is 950.
The reason why the temperature was set to not less than ° C was to eliminate the α phase as a single γ phase, whereas the temperature was set to be 1200 ° C or less to prevent the growth of the γ phase. The γ phase generated at this time is transformed from the α phase, so that it becomes finer and more uniform than the γ phase in the sintering step. Therefore, from this heat treatment temperature, α
When cooled to a phase, homogenous grains are obtained because there are enough nuclei for the formation of the α phase. The time of the first heat treatment is preferably about 15 minutes to 1 hour, although it varies depending on the actual heat treatment temperature and the amount of treatment.

Further, in the second heat treatment step, heat treatment is performed at a temperature of 750 ° C. or more and 850 ° C. or less in order to eliminate the residual γ phase from the sintered body and to remove the distortion caused by the transformation. Here, the temperature is set to 850 ° C. or lower in order to transform all of the γ phase into an α single phase, while the temperature is set to 750 ° C. or higher because at a temperature lower than this temperature, the transformation from the γ phase to the α phase is sufficient. It is not possible. The time for the second heat treatment varies depending on the actual heat treatment temperature and the amount of treatment as in the case of the first heat treatment, but is preferably about 1 to 3 hours.

The operation of cooling after the first heat treatment until the second heat treatment is performed, that is, cooling to 750 to 850 ° C., is performed at a cooling rate of 50 ° C./min or less in order to reduce distortion generated in the sintered body. Preferably at speed. Note that the atmosphere for the first heat treatment and the second heat treatment is preferably a reducing atmosphere, an inert atmosphere, a vacuum atmosphere, or the like.

[0013]

According to the method for producing an iron-cobalt sintered magnetic material according to the first aspect of the present invention, after the sintering, the first heat treatment is performed at a temperature of 950 ° C. or more and 1200 ° C. or less,
Then, at a temperature of 750 ° C or more and 850 ° C or less, the second
Is performed by the first heat treatment, the heterogeneous α
The phase transforms to the γ phase, and the second heat treatment eliminates the residual γ phase and removes the strain caused by the transformation, whereby the crystal grains of the sintered body become homogeneous. Claim 2
According to the iron-cobalt sintered magnetic material manufacturing method described,
The strain generated in the sintered body is reduced.

[0014]

EXAMPLES The present invention will be described more specifically with reference to the following examples. As a raw material powder, Fe-Co- with an average particle size of 8.6 μm
V water atomized powder (Co; 49.2% by weight, V; 2.2% by weight, balance Fe) is prepared, and 12 parts by weight of a binder such as polymethacrylic acid ester is added to this raw material powder and kneaded,
A kneaded product was obtained. Next, the obtained kneaded material was injected at an injection temperature of 165.
Molding was carried out under the conditions of ° C and an injection pressure of 1000 kg / cm ² to obtain a ring-shaped molded body. Further, the molded body was degreased in an inert atmosphere to obtain a degreased body. Next, the temperature of the obtained degreased body was raised to 900 ° C. in a vacuum atmosphere of 1 × 10 ⁻³ Torr or less, and hydrogen was further introduced to form a hydrogen atmosphere. Sintering was performed to obtain a sintered body.

Next, three obtained sintered bodies were prepared, and these were heated at a heating rate of 10 ° C./minute to 950 ° C. (Example 1), 1000 ° C. (Example 2), and 1200 ° C. (Example 3). ), And held in that state for 1 hour to perform a first heat treatment. Further, the second heat treatment was performed by cooling to 850 ° C. at a rate of 2 ° C./min and maintaining the state for 2 hours. Thereafter, the mixture was cooled to room temperature at a rate of 10 ° C./min to obtain three types of iron-cobalt sintered magnetic materials of the present invention. In addition, as comparative examples, one was heat-treated at 1400 ° C. after sintering and then heat-treated again at 850 ° C. (Comparative Example 1), and another was subjected to only heat treatment at 850 ° C. after sintering (Comparative Example 2). . The magnetic flux density and coercive force of the obtained magnetic material were examined, and the results are shown in Table 1.

[0016] From the results shown in Table 1, the products 1, 2, and 3 according to the present invention were obtained.
Are magnetic flux density B ₂₅ and coercive force Hc compared to comparative products 1 and 2.
It was confirmed that both were excellent.

[0017]

As described above, the method for producing an iron-cobalt based sintered material according to the present invention converts a heterogeneous α phase into a γ phase by a first heat treatment, and further transforms the heterogeneous α phase into a γ phase by a second heat treatment. Since this method eliminates the residual γ phase and removes the strain caused by the transformation, it is possible to obtain a sintered body having excellent magnetic properties by homogenizing the crystal grains of the sintered body, thereby providing an excellent soft magnetic material. Can be manufactured. Further, according to the method for producing an iron-cobalt sintered magnetic material according to the second aspect, it is possible to reduce the distortion generated in the sintered body, thereby producing a soft magnetic material having more excellent magnetic properties. it can.

Continuation of the front page (56) References JP-A-2-125835 (JP, A) JP-A-62-263617 (JP, A) JP-A-52-103699 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) B22F 3/00-3/24 C22C 33 / 02,19 / 07

Claims (2)

(57) [Claims] 1. A raw material powder comprising 40 to 60% by weight of cobalt, 1.0 to 2.5% by weight of vanadium and the balance being iron and unavoidable impurities is molded and sintered to obtain an iron-cobalt sintered magnetic material. A method of producing a material, comprising the steps of:
A method for producing an iron-cobalt sintered magnetic material, comprising: performing a first heat treatment at a temperature of not less than 1200 ° C. and then performing a second heat treatment at a temperature of not less than 750 ° C. and not more than 850 ° C. 2. The method for producing an iron-cobalt sintered magnetic material according to claim 1, wherein the first heat treatment is performed at 950 ° C.
A method for producing an iron-cobalt sintered magnetic material, wherein the operation of cooling to less than 50 ° C./min is performed at a cooling rate of 50 ° C./min or less.