JP2703939B2 - Method for producing Fe-Si soft magnetic sintered material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a Fe—Si soft magnetic sintered material having excellent AC characteristics.

<Prior Art> Fe-Si alloys are characterized by having high electrical resistivity among soft magnetic materials, and are used in a wide range for AC applications because of their low iron loss.

However, the application of the sintered material is limited due to the difficulty of forming due to the hard and brittle nature of the present alloy. This tendency is particularly strong in the case of about 3 wt% or more of Si.

<Problems to be Solved by the Invention> As a method of improving the moldability, injection molding using an organic binder is performed because the hardness of the powder is hardly a problem.
Promising. However, when molding and sintering metal powder by injection molding, there is no method for removing C originating from the organic binder without extremely oxidizing highly oxidizable elements such as Si. A sintered material having excellent characteristics could not be obtained.

The present invention has been made in view of the above circumstances, and uses an injection molding method to remove C caused by an organic binder so as not to involve extreme oxidation, thereby providing Fe-Si having excellent exchange magnetic properties. It is an object of the present invention to provide a method for producing a soft magnetic sintered material.

<Means for Solving the Problems> Regarding the production of Fe—Si-based sintered materials using injection molding, the present inventors have studied the sintering and reactivity of raw material powders under various sintering conditions and the obtained sintering. Regarding the magnetic properties of materials,
The present invention has been accomplished by conducting detailed experiments.

That is, according to the first aspect of the present invention, a raw material powder composed of an alloy powder or a mixed powder having an average particle diameter of 3 to 9 μm is prepared, and then kneaded with an organic binder,
After performing the injection molding process and the degreasing process, the first stage heat treatment is performed at 1050 to 1250 ° C. in a reducing atmosphere or a reduced pressure atmosphere of 0.1 Torr or less, and further, the first heating process is performed in an inert gas atmosphere. 1200 degrees higher than the first stage heat treatment temperature and 1200 ° C
The second stage heat treatment is performed at a temperature within a range of ~ 1350 ° C, comprising: Si: 1.5 to 6.5 wt%, O: 0.03 to 0.5 wt%, C: 0.03 wt% or less; A method for producing an Fe—Si soft magnetic sintered material having a balance of Fe and unavoidable impurities and a sintering density ratio of 95.0% or more is provided.

According to the second aspect of the present invention, the average particle diameter is 3 to
A raw material powder composed of a 25 μm alloy powder or a mixed powder is prepared, and then kneaded with an organic binder, subjected to an injection molding treatment and a degreasing treatment, and then subjected to a reducing atmosphere or a reduced pressure atmosphere of 0.1 Torr or less. 1st at 1050-1250 ° C
The first-stage heat treatment is performed, and the second-stage heat treatment is performed at a temperature higher than the first-stage heat treatment temperature by 50 ° C. or more and in a range of 1200 to 1350 ° C. in an inert gas atmosphere of 30 to 150 atm. Characterized by the following heat treatment: Si: 1.5 to 6.5 wt%, O: 0.03 to 0.5 wt%, C: 0.03 wt% or less, the balance being Fe and unavoidable impurities, and the sintered density A method for producing a Fe—Si soft magnetic sintered material having a ratio of 95.0% or more is provided.

 Hereinafter, the present invention will be described in more detail.

First, the reason for limiting the composition of the sintered material obtained by the production method of the present invention will be described.

Si: 1.5 to 6.5 wt% Si improves the electrical resistivity by adding it to Fe, but if less than 1.5 wt%, the effect of improving the electrical resistivity is small. Also, Si improves the magnetic permeability, but 6.
If it exceeds 5 wt%, it will drop sharply.
Limited to 6.5 wt%.

O: 0.03 to 0.5 wt%, C: 0.03 wt% or less C and O adversely affect the magnetic properties, particularly the coercive force (Hc) and the maximum magnetic permeability (μmax).

However, when an extremely oxidizable element such as Si is contained, the amount of O caused by the raw material powder and the amount of C caused by the organic binder added to make the injection molding material are simultaneously reduced in a crystal atmosphere. It is virtually impossible. Therefore, the main focus has been on reducing the amount of carbon, which has a particularly adverse effect on magnetic properties. In the present invention, the C amount is reduced by increasing the O amount, which has a small adverse effect on the magnetic properties, in the present invention. That is, if the C content exceeds 0.03 wt%, the magnetic properties deteriorate significantly, so the upper limit of the C content is set to 0.03 wt%.
%. Further, in order to reduce the C content to 0.03 wt% or less, the O content is set to 0.03 wt% or more. If the O content is less than 0.03 wt%, the C content cannot be reduced to 0.03 wt% or less, so the lower limit of the O content is set to 0.03 wt%.

Further, if the O content exceeds 0.5 wt%, the magnetic properties are significantly deteriorated, so the upper limit of the O content is set to 0.5 wt%.

Sintering density ratio: 95.0% or more Magnetic flux density is proportional to sintering density ratio, and sintering density ratio is 95.0%
If the ratio is less than the above, the magnetic flux density is remarkably reduced, and no advantage over the material obtained by the die compression molding as a competitive molding method can be found.

 Therefore, the lower limit of the sintered density ratio is limited to 95.0%.

Only by limiting as described above, an Fe-Si based sintered material having excellent magnetic properties can be obtained.

 Next, the manufacturing method of the present invention will be described.

The production method of the present invention comprises kneading a metal powder with an organic binder, performing an injection molding treatment, a degreasing treatment, and a sintering treatment. In particular, the present invention has a great feature in that an injection molding method is employed in place of the compression molding method which has been conventionally generally employed. In the compression molding method, the raw material powder is limited to a coarse powder having a low sinterability, whereas the injection molding method has an advantage that a fine powder having a high sinterability can be used. This has made it possible to improve the conventional low magnetic properties.

The present inventors have found that the magnetic properties of the sintered body are closely related to the particle size of the raw material powder. The average particle size of the raw material powder affects the sintering density. If it exceeds a certain upper limit particle size, the sintered material of the present invention cannot be obtained.

The particle size of the raw material powder that can be used varies depending on the sintering method, but the average particle size needs to be 3 to 25 μm. First, in the case of sintering only by ordinary heating, 3 to 9
The average particle size of μm is preferable, and when applying pressure sintering that simultaneously uses heating and pressurization by gas pressure, 10 to 25 μm
Is preferred. When sintering is performed only by heating, the sintering density ratio decreases as the average particle size increases, and is 9 μm.
Exceeds 95.0%, the sintered density ratio cannot reach 95.0%.
If it exceeds μm, the sintered density ratio cannot reach 90%. However, when the sintering density ratio exceeds 90%, since the pores of the sintered body are closed pores, the sintering density ratio can be increased to 95.0% or more by pressure sintering.

When the average particle size is 10 μm or more, the density ratio is significantly improved by pressure sintering, and a higher density ratio can be obtained than a powder having a particle size of less than 10 μm.

On the other hand, if the average particle size exceeds 25 μm, a density ratio of 95.0% or more cannot be achieved, and the sintered material of the present invention cannot be obtained. Therefore, the upper limit of the average particle size is limited to 25 μm. Powders having an average particle size of less than 3 μm are excluded because they are expensive and are not economical.

 Next, the sintering conditions will be described.

 Sintering must be performed in two stages.

This first stage needs to be performed in a hydrogen-containing gas which is a reducing atmosphere or a reduced-pressure atmosphere of 0.1 Torr or less. Otherwise, carbon on the surface of the raw material powder due to the residual oxygen or molding aid cannot be removed, and a high-purity sintered body cannot be obtained. Further, the sintering temperature needs to be 1050 to 1250 ° C. Below this lower limit, the impurity removal reaction between the atmosphere and the raw material powder does not proceed effectively. If the upper limit is exceeded, the sintering of the powders proceeds faster than the impurity removal reaction, so that impurities cannot be removed. Since these impurities are removed as water vapor or carbon dioxide gas, losing the gas flow holes is a serious adverse effect. In particular, care must be taken since the formed body is composed of fine powder and the flow hole is originally small. In addition, these temperatures are also temperatures at which the progress of sintering starts to be rapid, and also vary depending on the particle size of the raw material powder. Therefore, when the average particle size is small, when the average particle size is larger at a lower temperature side, It is preferable to select the higher temperature side from the range of the present invention.

The sintering time is the time required for the amounts of C and O to reach the equilibrium value at the sintering temperature used, and is usually in the range of 20 minutes to 4 hours, and can be easily determined by several trial experiments.

 Next, the second stage of the sintering of the present invention will be described.

Since the second stage is a process for increasing the density of the sintered body which has been purified and closed in the first stage, it is no longer necessary to use a reactive gas. Therefore, the atmosphere gas is limited to the inert gas. Further, the temperature needs to be 50 ° C. or more higher than the first-stage sintering temperature.

The reason for setting the lower limit of the temperature to be 50 ° C. or more higher than the sintering temperature of the first stage is that the sintering temperature of the first stage is set to a temperature at which the sintering speed starts to accelerate. In addition, the high density is insufficient. Further, when a reduced-pressure atmosphere is used in the first stage, a composition distribution occurs on the surface of the sintered body due to a difference in vapor pressure of the constituent elements. Further, even in a reducing gas atmosphere, a composition distribution may be generated between the surface of the sintered body or powder contacting the gas and the inside thereof. This composition distribution is established by the atomic diffusion rate control in the sintered body. In an atmosphere in which the constituent elements at atmospheric pressure or higher do not evaporate, or in an atmosphere in which no chemical reaction occurs, the composition distribution is higher than that in the first stage. This is because it is necessary to promptly advance the homogenization process at a temperature higher than or equal to ° C., that is, at a temperature region where the diffusion rate is higher.

The upper limit temperature is a temperature at which the crystal grain size becomes unnecessarily large or melting starts. A more preferred temperature range is 12
00-1350 ° C.

Also, in the case of performing pressure sintering in the second stage, the lower limit of the temperature is lower than the first stage sintering temperature.
The temperature must be higher than 50 ° C. This lower limit temperature has a correlation with the temperature set in the first stage, which is the temperature at which the sintering speed starts to accelerate, and pressure sintering becomes effective at this temperature. Further, as described above, in order to eliminate the composition distribution formed in the first-stage sintering, it is necessary to promptly advance the homogenization treatment in this step. The upper limit temperature is the same as in the case of pressure sintering and in the case of no pressure. The pressure required for pressurization is 30 to 150
Atmospheric pressure. If the pressure is less than 30 atm, there is no significant difference from the case where no pressure is applied, and if a gas medium exceeding 150 atm is used, the equipment cost rises sharply.

The sintering time in the second stage is the sintering temperature used,
This is the time required for the sintering density and chemical composition distribution to reach equilibrium, usually in the range of 20 minutes to 2 hours, and can be easily selected by several trial experiments.

As described above, only by limiting the sintering method, it is possible to economically produce a Fe—Si-based sintered material having high magnetic properties by using the injection molding method.

The starting raw material powder constituting the raw material powder of the present invention is used after adjusting the powder obtained by a high-pressure water atomizing method, a reducing method, a carbonyl method or the like to a desired particle size by classifying or pulverizing the powder. The raw material powder of the present invention can be used alone or as a mixed powder thereof. Regarding the purity of the raw material powder, impurities other than C and O that can be removed in the sintering process may be substantially negligible.
A powder having a total amount of Fe and Si of 97 to 99 wt% can be used.

The raw material powder is kneaded with an organic binder to form a compound, and is molded by a known injection molding method. In particular, in the case of a complex-shaped part, the injection molding method is effective.

As the binder used in the present invention, a known binder mainly composed of a thermoplastic resin or wax or a mixture thereof can be used, and a plasticizer, a lubricant, a degreasing accelerator and the like are added as necessary. As the thermoplastic resin, one or a mixture of two or more of acrylic, polyethylene, polypropylene, and polystyrene can be selected. As the waxes, one or more waxes may be selected from natural waxes represented by beeswax, wood wax, montan wax and the like and synthetic waxes represented by low molecular weight polyethylene, microcrystalline wax, paraffin wax and the like. You can select and use. The plasticizer is selected depending on the combination with the main resin or wax, and DOP, DEP, DHP and the like can be used. As a lubricant,
Higher fatty acids, fatty acid amides, fatty acid esters and the like can be used, and in some cases, waxes are also used as a lubricant. A sublimable substance such as camphor may be added for the purpose of accelerating degreasing.

The amount of the binder to be added is 45 to 60 vol% of the total volume (the remaining volume is the raw metal powder), and can be adjusted in consideration of the ease of molding and the degreasing property of the shape to be molded.

For the mixing and kneading of the iron powder and the binder, a batch type or continuous type kneader can be used. After kneading, granulation is performed using a pelletizer or a crusher to obtain a raw material for molding.

The molding raw material can be molded using an ordinary plastic injection molding machine.

The obtained molded body is in the air or in an atmosphere gas.
Degreasing treatment is performed.

After the degreasing treatment, sintering is performed as described above to increase the density and reduce the amounts of C and O.

Further, if necessary, the amounts of C and O of the final sintered body are adjusted. As a method of increasing and decreasing the C and O amounts, the C / O amount ratio of the degreased body is increased and decreased.
The amount can be reduced, and the O amount can be reduced by increasing the C / O amount ratio. The C / O amount ratio can be increased or decreased by adjusting the amounts of C and O in the raw material powder, adjusting the degree of removal of the binder, or performing an oxidation treatment after the removal. Furthermore, to reduce the overall level of C and O (corresponding to the product of C and O),
The first step is carried out by changing the sintering atmosphere, and this can be achieved by reducing the pressure when using a reduced pressure atmosphere and by improving the purity of the atmosphere gas when using a reducing atmosphere.

<Example> Hereinafter, the present invention will be specifically described based on examples.

The binders shown in Table 1 were added to the respective raw material powders shown in Table 1, kneaded by a pressure kneader, and then pulverized to prepare an injection molding compound. Subsequently, a ring test piece having an outer diameter of 53 × inner diameter of 41 × 5 mm in height was prepared by an injection molding machine. This is placed in nitrogen at a rate of + 5 ° C / h for 600
After the temperature was raised to 600 ° C., the temperature was maintained at 600 ° C. for 30 minutes to perform degreasing. Next, the first-stage heat treatment and the second-stage heat treatment were performed under the conditions shown in Table 1, respectively. Table 1 shows the chemical composition, density ratio, magnetic properties and electric resistivity of the obtained sintered body.

For No. 1-1 to 1-11 in Table 1, the amount of C and O was adjusted by adjusting the level of the heating temperature within a temperature range of 350 to 650 ° C. in a hydrogen atmosphere having a dew point of 0 ° C. after degreasing. After the adjustment, the first and second heat treatments were performed.

From Table 1, it can be seen that for Nos. 1-1 to 1-11, the C content and O
When the amounts exceeded 0.03 wt% and 0.5 wt%, respectively, the magnetic properties deteriorated (Comparative Examples 1 and 2). On the other hand, when the O amount was too low (Comparative Example 1), the C amount could not be reduced, and the magnetic properties were extremely deteriorated. However, when the C and O contents were within the range of the present invention, excellent magnetic properties were obtained (Examples 1 to 8 of the present invention).

When the second-stage heat treatment temperature was not higher than the first-stage heating temperature by 50 ° C. or more (Comparative Example 3), only a low density was obtained, so that excellent magnetic properties were not obtained.

Further, in the case where heat sintering is used in the second stage heat treatment, there is no effect at a pressure lower than 30 atm (Comparative Example 4). When the average particle size of the raw material exceeds 25 μm (Comparative Example 5), there is no effect.

The sintering density ratios of those sintered under pressure at 30 atm or more (Examples 9 to 14 of the present invention) are those of normal pressure sintering (Examples 1 to 8 of the present invention).
Higher results were obtained.

<Effects of the Invention> Since the present invention is configured as described above,
By using an injection molding method and removing C caused by the organic binder without causing extreme oxidation, a Fe-Si soft magnetic sintered material having excellent AC magnetic properties can be obtained.

Claims (2)

(57) [Claims] 1. A raw material powder composed of an alloy powder or a mixed powder having an average particle diameter of 3 to 9 μm is prepared, then kneaded with an organic binder, subjected to an injection molding treatment and a degreasing treatment, and then reduced. First heat treatment at 1050 to 1250 ° C in an inert atmosphere or a reduced pressure atmosphere of 0.1 Torr or less, and more than 50 ° C higher than the first heat treatment temperature in an inert gas atmosphere And at a temperature in the range of 1200-1350 ° C
It is characterized by performing the first stage heat treatment, which contains Si: 1.5 to 6.5 wt%, O: 0.03 to 0.5 wt%, and C: 0.03 wt% or less, with the balance being Fe and unavoidable impurities. A method for producing an Fe—Si soft magnetic sintered material having a consolidated density ratio of 95.0% or more. 2. A raw material powder composed of an alloy powder or a mixed powder having an average particle diameter of 3 to 25 μm is prepared, then kneaded with an organic binder, subjected to an injection molding treatment and a degreasing treatment, and then reduced. First heat treatment at 1050 to 1250 ° C. in a neutral atmosphere or a reduced pressure atmosphere of 0.1 Torr or less, and further, the first heat treatment temperature in an inert gas atmosphere of 30 to 150 atm. The second stage heat treatment is performed at a temperature higher than 50 ° C. and in the range of 1200 to 1350 ° C., Si: 1.5 to 6.5 wt%, O: 0.03 to 0.5 wt%, C: 0.03 A method for producing a Fe-Si soft magnetic sintered material containing less than wt%, the balance being Fe and unavoidable impurities, and having a sintering density ratio of 95.0% or more.