JP2002275600A - Raw material powder for sintered soft magnetic stainless steel and production method for the sintered soft magnetic stainless steel using the powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide raw material powder as the raw material for sintered soft magnetic stainless steel which has improved compressive moldability, corrosion resistance and magnetic properties, and to produce sintered soft magnetic stainless steel which is more excellent than the conventional one. SOLUTION: In the raw material powder for sintered soft magnetic stainless steel, soft magnetic stainless steel fine powder which contains, by mass, 7 to 15% Cr and 1 to 4% Si and does not contain Al is granulated into the granulated powder having the average grain size of 10 to 150 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material powder for soft magnetic stainless steel used for corrosion-resistant electromagnetic parts such as electronic fuel injection valves for automobiles and a method for producing the stainless steel.

[0002]

2. Description of the Related Art In recent years, due to the tightening of exhaust gas regulations and fuel economy of automobiles, devices such as fuel injection valves by electronic control of automobile engines have been replacing the conventional carburetors and are increasing their mounting rates. In addition, magnetic components requiring corrosion resistance, such as ABS sensors and torque sensors, are also increasing in demand.

[0003] Corrosion resistance and magnetic properties are important for electromagnetic components such as the above-described fuel injection valve.
As disclosed in No. 19 and the like, chromium-based soft magnetic stainless steel is mainly used, and is manufactured by a mechanical forming method such as plastic working or cutting. However, electromagnetic components such as electronic fuel injection valves for automobiles have a problem that the shape of the components is complicated and the precision is severe, so that it is difficult to achieve both machinability, corrosion resistance and magnetic properties, and the processing cost is high. .

[0004]

In order to solve these problems, Japanese Patent Application Laid-Open No. 6-2077 proposes a production method by powder metallurgy using stainless steel powder. However, stainless steel powder has poor compressibility and low sintering density, and thus has poor corrosion resistance and magnetic properties. Also, the sinterability of the powder is better as the particle size of the powder is smaller, but the fluidity is poor, bridging tends to occur at the time of filling the mold,
In particular, when the component shape is complicated, uniform filling is difficult, and the dimensional accuracy of the sintered product is deteriorated. Also, there is a problem that the powder enters the gaps between the molds, damages the molds, and shortens the mold life. .

[0005]

Means for Solving the Problems The present inventors have repeatedly studied how to solve the above-mentioned problems, and as a result, by performing the composition and granulation of the raw material powder for sintered soft magnetic stainless steel, It has been confirmed that the above problems can be solved and the present invention has been completed. The essence of the present invention is that, as a composition of soft magnetic stainless steel fine powder having excellent magnetic properties, the amount of Cr is reduced to the extent that corrosion resistance is maintained, the content of Al is abolished, and the amount of Si is increased to improve magnetic properties. In this case, the powder is used as granulated powder.

The inventions of claims 1 and 2 specify the basic constitution of the raw material powder for sintered soft magnetic stainless steel, and the invention of claim 5 specifies a production method using the same. That is, the raw material powder of claim 1 is, by mass ratio, Cr: 7 to 15% (preferably C:
r: 7 to 11.5% by mass), soft magnetic stainless steel fine powder containing 1 to 4% of Si and not containing Al is granulated to form a granulated powder having an average particle diameter of 10 to 150 µm. It is characterized by having. The raw material powder according to claim 2 is obtained by granulating a mixed powder of the soft magnetic stainless steel fine powder and a Si fine powder or a Fe—Si fine powder having a Si content of 10% or more by mass ratio, Is 10 to 150 μm
And the Si content of the granulated powder is more than 1% by mass and not more than 6.5% by mass.

Claims 3 and 4 specify the details of the above soft magnetic stainless steel fine powder. Claim 3
Soft magnetic stainless steel fine powder was further added at a mass ratio of Mo: 2.
0% or less, S: 0.1% or less, Ti: 0.5% or less, N
b: A structure containing at least one kind among 0.5% or less. Claim 4 is a configuration in which the Cr content of the soft magnetic stainless steel fine powder is 7.0 to 11.5% by mass ratio.

[0008] A fifth aspect of the present invention is a sintered soft magnetic material in which a molding lubricant is mixed with the raw material powder, the mixture is charged into a mold, and a green compact obtained by compacting with a vertical punch is sintered. In the method for producing stainless steel, the raw material powder is the raw material powder for sintered soft magnetic stainless steel according to any one of claims 1 to 4, and sintered in a reducing atmosphere or vacuum to have a density ratio of 90. % Or more.

(Description of Structure) Next, the structure of the raw material powder for the sintered soft magnetic stainless steel of the present invention will be described in detail, including the grounds for limiting the numerical values.

[0010] Cr (chromium) in the raw material powder is essential for imparting corrosion resistance, but it is important to specify the content. Normally, increasing the amount of Cr is effective in terms of corrosion resistance, but from the viewpoint of magnetic properties, the amount of Fe is relatively reduced to cause a reduction in magnetic flux density. Is preferred. That is, as the raw material powder for the sintered soft magnetic stainless steel, it is effective to improve the magnetic properties by limiting the amount of Cr to the minimum addition that can maintain the corrosion resistance. In the present invention, the amount of Cr is set to 7% by mass to 15% by mass. The reason for this is that the corrosion resistance is reduced when the Cr content is less than 7% by mass from the examination and examination, so the lower limit is set to at least 7% by mass or more. At the same time, the upper limit is set to 15% by mass or less, which is optimum in relation to the magnetic properties because the magnetic flux density is reduced due to the decrease in Fe content in the matrix. If the amount of Cr exceeds 15% by mass, the magnetic flux density is significantly reduced, and the deterioration of magnetic properties is inevitable. Further, the upper limit of the Cr content is particularly preferably 11.5% by mass or less from the viewpoint of magnetic properties.

[0011] Si (silicon) in the raw material powder is effective for corrosion resistance and has the effect of increasing the electrical resistance to improve the responsiveness of the solenoid valve, reducing iron loss and increasing the specific resistance and the magnetic permeability. is there. However, if a large amount of Si is provided as a solid solution in the raw material powder, the powder is hardened and the compressibility is impaired. From this, in the present invention, the soft magnetic stainless steel fine powder S
The i amount is set to be 1.0% by mass or more in order to supplement the corrosion resistance due to the reduction of Cr and increase the specific resistance and the magnetic permeability. As for the upper limit, the content is limited to 4% by mass in order to secure the compressibility of the powder. In order to further exert the above-mentioned action, it is also possible to add Si in a larger amount without impairing the compressibility of the soft magnetic stainless steel fine powder by giving Si from the outside of the soft magnetic stainless steel fine powder as Si fine powder. it can. However, if the Si content in the overall composition exceeds 6.5% by mass, the magnetic flux density is greatly reduced due to the decrease in Fe content, and the magnetic properties are deteriorated, and the toughness of the sintered product is impaired.
For this reason, the upper limit of the Si content is limited to 6.5% by mass in terms of the amount of Si in the granulated powder.

It is also possible to use Fe-Si fine powder instead of the above Si powder. Fe-Si fine powder has a lower hardness than Si powder, so that compressibility is improved. However, when Fe-Si fine powder having a Si content of less than 10% by mass is used, a necessary amount of Si is added to secure the necessary Si content. This is not preferable because the amount of Fe-Si increases to lower the corrosion resistance of the matrix and the magnetic properties. Therefore, the Fe-Si fine powder is specified to have a Si content of at least 10% by mass or more.

Al is used for the purpose of improving corrosion resistance, improving magnetic properties by increasing specific resistance, and providing cold workability by improving toughness. It is contained in. However, Al is an element that is easily oxidized, and when given as a solid solution in powder, a strong oxide film is easily formed on the powder surface, which is a factor that hinders the progress of sintering. Requires heating in a high vacuum. In the present invention, the effect of eliminating factors that hinder the progress of sintering is greater than the effect of improving the toughness required for processing because powder metallurgy is used to manufacture products in the near net shape. In addition, since the corrosion resistance is ensured by the above-mentioned Cr and the specific resistance is also ensured by the above-mentioned Si, it is necessary to omit Al content in order to avoid a decrease in magnetic flux density due to a decrease in Fe content. Mandatory from the perspective of improvement. However, in the present invention, Al is sometimes added as a deoxidizing agent in the molten metal during powder production, and the content of Al that remains in the powder as an unavoidable impurity does not affect the sinterability and is naturally acceptable. You.

In the above powder composition, soft magnetic stainless steel fine powder containing the above-mentioned components, or soft magnetic stainless steel fine powder and Si fine powder or Fe-Si fine powder are prepared, and these fine powders are produced. By granulating into a granulated powder, bridging is prevented from occurring, the sinterability is improved without damaging the mold, and a product having a sintered density ratio of 90% or more can be easily manufactured. . The sintered density ratio is 9
If it is less than 0%, the magnetic properties such as the magnetic flux density are reduced, and the corrosion resistance is also reduced due to the pitting corrosion due to the increase in pores.

More specifically, the soft magnetic stainless steel fine powder, or the soft magnetic stainless steel fine powder and Si
Fine powder or Fe-Si fine powder has a particle size (average particle size) of 4
It is preferably a fine powder smaller than 0 μm, and is used in the form of a granulated powder having an average particle size of 10 to 150 μm after granulation. Stainless steel fine powder and Si fine powder or F
When the particle size of the e-Si fine powder exceeds 40 μm, the e-Si fine powder lacks uniform dispersibility in the matrix, and the fluidity at the time of granulation becomes poor. The granulated powder has an average particle size of 10 μm.
If it is less than m, the effect of granulation is poor, and the filling property into the compacting mold becomes poor. If the average particle diameter of the granulated powder exceeds 150 μm, the packing density at the time of powder molding is reduced, so that the sintering density ratio is lower than 90%, so that the magnetic properties and corrosion resistance are reduced and the dimensional accuracy is deteriorated.

For the above granulation, a general granulation method is applied. That is, the stainless steel fine powder described above, or a mixed powder of stainless steel fine powder and Si fine powder or Fe-Si fine powder, polyvinyl alcohol as a binder,
Using an organic substance such as polyvinylpyrrolidone or wax, or a water or alcohol solution of the organic substance, granulation is performed by a granulating device such as a tumbling granulator or a mixing stirring granulator. In terms of equipment, a high-speed molding machine such as a rotary press may be used. Further, a plasticizer or a dispersant may be appropriately added to the binder.

As the raw material powder for sintered soft magnetic stainless steel, the above-mentioned granulated powder having an average particle diameter of 10 to 150 μm has a Si content of 1.0 to 6.5 mass%.
In this case, the sinterability is improved, a product having a density ratio of 90% or more can be reliably obtained, the distribution of Si is uniform, the magnetic properties can be improved, the fluidity of the raw material powder is improved, and This prevents the occurrence of bridging at the time, facilitates uniform filling, prevents the possibility that the raw material powder enters the gaps between the molds, and extends the life of the mold.

The components other than Cr, Si and Al used in the raw material powder for sintered soft magnetic stainless steel of the present invention are not particularly limited, as long as they do not hinder the progress of sintering. However, other elements may be contained within a conventionally known range. Next, as an example, the composition range recommended for the raw material powder for sintered soft magnetic stainless steel of the present invention will be outlined.

Mo is an element which improves corrosion resistance.
Addition of a large amount causes deterioration of magnetic properties. For this reason, when it is contained, the upper limit is set to 2.0% by mass or less. S lowers the corrosion resistance, but lowers the surface tension of the molten steel, is effective in atomizing the powder by the atomizing method, and is also effective in improving the machinability of the product. For this reason, when it is contained, it is preferable to keep it at most 0.1 mass% or less.

It is also useful to add Ti or Nb to suppress the influence of C harmful to magnetic properties and corrosion resistance and N harmful to magnetic properties. That is, Ti and Nb are C and N
And carbides or nitrides are formed and rendered harmless, thereby contributing to the improvement of corrosion resistance and magnetic properties. However, when the Ti content is increased, the problem of narrowing or clogging of the nozzle of the molten metal by the atomizing method occurs, and when the Nb content is increased, the hardness of the powder increases and the compressibility decreases. In addition, a large amount of Ti or Nb causes crystal grains to be refined, thereby deteriorating magnetic properties. Therefore, when it is contained, the upper limit is preferably set to 0.5% by mass.

According to the present invention, the above elements (Mo, S, Ti,
By using the soft magnetic stainless steel raw material powder containing Nb) in the composition, a sintered soft magnetic stainless steel excellent in the above-described corrosion resistance and magnetic properties can be obtained.

[0022]

EXAMPLES The characteristics of sintered soft magnetic stainless steel using the raw material powder for sintered soft magnetic stainless steel of the present invention will be clarified by examples.

Example 1 This example corresponds to claims 1, 3, and 4 of the present invention. The composition of the raw material powder for stainless steel, the granulated powder, and the performance of stainless steel using the same were examined. This is a test example. In the test, first, a stainless steel powder (stainless steel fine powder) having a composition shown in Table 1 (each component was a fine powder having an average particle diameter of 40 μm or less) was used, and polyvinylpyrrolidone 5 containing methyl alcohol as a solvent as a binder was used. % Solution was continuously supplied to a tumbling fluidized-bed granulator to obtain granulated powder having an average particle diameter shown in the left column of Table 1. Next, with respect to the mixed powder obtained by adding 0.8% by mass of zinc stearate as a molding lubricant to each of the obtained granulated powders and mixing them, a molding pressure of 5 t / cm ² and a diameter of 50 m
After forming into a ring shape of m × φ30 mm × t5 mm, sintering at 1350 ° C. for 3 hours in a hydrogen gas atmosphere, annealing at 850 ° C. × 2 hours in a vacuum, a ring shape test piece (with the present invention 1-5) Comparative Examples 1 to 4) were prepared.

[0024]

[Table 1]

The evaluation was performed on the primary side 1 for each of the above test pieces.
Winding was performed 00 times and the secondary side was wound 50 times, and the DC and AC BH curves were measured. In Table 2, as DC magnetic characteristics, the magnetic flux density at a magnetic field strength of 2000 (A / m) of each test piece is represented by B2000, the coercive force is represented by Hc, and the magnetic permeability is represented by μm. As the AC magnetic characteristics, the iron loss value at an excitation magnetic flux density of 1 T (1 Tesla) at a frequency of 50 Hz is represented by W (1 T / 50 Hz).
And an iron loss value at a frequency of 10 kHz and an excitation magnetic flux density of 50 mT is shown as W (50 mT / 10 kHz). Table 2 also shows the sintering density ratio% and the corrosion resistance. Corrosion resistance was measured by a salt spray test of 5% saline solution at 35 ° C x 3
At 0 hour, the rusting condition was visually judged. The visual result is
When no rust was observed, a circle was given, when almost all of the rust occurred, a cross was given, and when some but not all the rust occurred, a triangle was given.

[0026]

[Table 2]

Tables 1 and 2 show that the test pieces (inventions 1 to 5) using the granulated powder obtained by granulating the soft magnetic stainless steel fine powder corresponding to the present invention have good corrosion resistance and excellent magnetic properties. It turns out that there is. Among the comparative examples, in the test piece using a powder having a normal size (Comparative Example 4), the sintering density ratio did not increase, and a decrease in corrosion resistance and a decrease in magnetic flux density were observed. Similarly, in the test piece (Comparative Example 1) in which granulation was not performed even when the fine powder was used, the sintering density ratio did not increase, and a decrease in corrosion resistance and a decrease in magnetic flux density were observed. The test piece with a small Cr content (Comparative Example 2) has poor corrosion resistance and generates rust. On the other hand, the test piece with too much Si (Comparative Example 3) had poor powder compressibility,
As the sintering density ratio decreases, a decrease in magnetic flux density and a decrease in AC magnetic characteristics on the high frequency side are observed. That is, from Example 1, the granulated powder obtained by granulating the soft magnetic stainless steel fine powder of the present invention was used.
The advantage of specifying the mass% of Si and Si is apparent.

Example 2 This example corresponds to claim 2 of the present invention. In the same manner as above, the composition of the raw material powder for stainless steel, the granulated powder, and the performance of the stainless steel using the same were examined. This is a test example. That is, here, using the soft magnetic stainless steel fine powder of the test piece 4 of the present invention used in Example 1, the Si powder shown in Table 3 (Comparative Example 6 has an average particle diameter of 76
Other than that, a fine powder having an average particle size of 40 μm or less) or Fe—Si powder (a fine powder having an average particle size of 40 μm or less) was added, and a granulated powder was prepared under the same conditions as in Example 1.
Preparation and evaluation of each test piece were performed in the same manner as in Example 1. The results are shown in Table 4. Table 4 also shows the values of the test piece 4 of the present invention of Example 1 for comparison.

[0029]

[Table 3]

[0030]

[Table 4]

In Tables 3 and 4, when the test piece 4 of the present invention is compared with the test pieces 6 and 7, the addition of Si increases the magnetic flux density and magnetic permeability, and decreases the coercive force and iron loss.
The effect of improving the magnetic properties is recognized. In addition, although the test piece 8 of the present invention using Fe-10Si instead of Si powder has the same magnetic flux density, an increase in coercive force and magnetic permeability and a decrease in iron loss are recognized, and it can be seen that magnetic properties can be improved. But,
In the test piece (Comparative Example 6) using a powder having a large average particle diameter of Si of 76 μm, the sintered density ratio was not improved, corrosion resistance was reduced, rust was generated, and iron loss was reduced. In addition, Si
In the test piece using Fe-5Si (Comparative Example 5) instead of the above, a large amount of F was used in order to equalize the amount of Si in the entire composition.
e-5Si is required, and as a result, there are too many portions having poor corrosion resistance, and the corrosion resistance is deteriorated and rust is generated. Also, the sintered density ratio and the magnetic properties are all reduced. From the above, it can be confirmed that the magnetic properties can be further improved by adding the Si powder fine powder to the soft magnetic stainless steel fine powder of the present invention and granulating them together. Also, it can be confirmed that the same effect can be obtained by using Fe—Si fine powder having a Si content of 10% by mass or more instead of Si fine powder. Further, the test piece 9 of the present invention having an Si content of 6.5% in the whole composition has a maximum magnetic permeability and lower iron loss and exhibits excellent magnetic properties as compared with the test pieces 4 and 6 of the present invention. Since the magnetic flux density decreases as the amount increases, the test piece with 6.9% Si in the overall composition (Comparative Example 7) shows a remarkable decrease in magnetic flux density, and the magnetic permeability also significantly increases when the Si content exceeds 6.5%. It can be confirmed that it decreases.

[0032]

As described above, in the raw material powder for sintered soft magnetic stainless steel and the production method using the same according to the present invention, in particular, by optimizing the amounts of Cr and Si, the corrosion resistance is maintained. The powder characteristics such as fluidity of the powder are obtained by preventing a decrease in magnetic flux density and further granulating stainless steel fine powder, and granulating by adding Si which impairs compressibility as external addition as in claim 2. And good formability are improved, and a soft magnetic stainless steel with high density, high specific resistance and high magnetic flux density and low iron loss can be manufactured.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C22C 38/18 C22C 38/18 38/28 38/28 H01F 1/20 H01F 1/20 1/22 1/22 (72 ) Inventor Yoshiyuki Kato 4-44 Kawaragi Beach, Hachinohe City, Aomori Prefecture Inside Atmix Co., Ltd. 4-44 Kawaragi Kaigan, Hachinohe City, Aomori Prefecture F-term in Atmix Co., Ltd. (Reference) 4K018 AA33 BA17 BB04 BC11 CA12 DA31 5E041 AA11 AA19 BD01 CA10 HB03 HB05 HB19 NN01

Claims (5)

[Claims] 1. A mass ratio of Cr: 7 to 15%, Si: 1
Granulated soft magnetic stainless steel fine powder containing ４4% and containing no Al and having an average particle size of 10-150 μm.
A raw material powder for sintered soft magnetic stainless steel, which is a granulated powder of m. 2. The soft magnetic stainless steel fine powder according to claim 1 and a Si fine powder or a Si content of 10% by mass.
The mixed powder with the above-mentioned Fe-Si fine powder is granulated to obtain a granulated powder having an average particle size of 10 to 150 µm, and the Si content of the granulated powder is more than 1% by mass and 6.5% by mass or less. A raw material powder for sintered soft magnetic stainless steel, characterized in that: 3. The soft magnetic stainless steel fine powder further comprises Mo: 2.0% or less, S: 0.1% or less, and T:
The raw material powder for soft magnetic stainless steel according to claim 1, comprising at least one of i: 0.5% or less and Nb: 0.5% or less. 4. The raw material for a sintered soft magnetic stainless steel according to claim 1, wherein the Cr content of the soft magnetic stainless steel fine powder is 7.0 to 11.5% by mass ratio. Powder. 5. A sintered soft magnetic stainless steel obtained by mixing a molding lubricant into a raw material powder, charging the mixture into a mold, and sintering a green compact obtained by compacting with a vertical punch. In the manufacturing method, using the raw material powder for sintered soft magnetic stainless steel according to any one of claims 1 to 4 as the raw material powder, sintering in a reducing atmosphere or in a vacuum to obtain a density ratio of 90% or more. A method for producing a sintered soft magnetic stainless steel.