JP2003226945A - Soft magnetic steel having excellent cold forgeability and magnetic permeability, soft magnetic steel parts having excellent magnetic permeability and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide soft magnetic steel which can be subjected to cold forging of satisfactory dimensional precision, and can secure particularly excellent magnetic permeability. <P>SOLUTION: The soft magnetic steel contains, by mass, ≤0.05% (exclusive of 0%) C, 0.05 to 2% Si, 0.1 to 0.5% Mn, ≤0.02% (inclusive of 0%) P, ≤0.02% (inclusive of 0%) S, ≤0.1% (inclusive of 0%) Al, ≤0.005% (inclusive of 0%) N and ≤0.02% (inclusive of 0%) O, and has a metallic structure consisting of a ferrite single phase. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic steel part useful as an iron core material for solenoids, relays, solenoid valves and the like used in various electrical components for automobiles, trains, ships, etc., and raw materials therefor. The present invention relates to a soft magnetic steel material and a method for manufacturing a soft magnetic steel part, and in particular, it is possible to obtain a part with a high yield and excellent dimensional accuracy during molding (hereinafter, this characteristic is simply referred to as "cold forgeability"). ") And a soft magnetic steel material capable of ensuring excellent magnetic characteristics and excellent magnetic permeability characteristics of JIS-SUYB-0 or higher level, and excellent magnetic permeability characteristics obtained using the steel material. The present invention relates to a soft magnetic steel part and a method useful for manufacturing the soft magnetic steel part.

The "SUYB" means JIS C 2
It is a standard of magnetic characteristics defined by 503, and the electrical components are required to have magnetic characteristics of about JIS-SUYB-1 type. "SYB-2 species" rather than "S
"SUYB-1 type", "SUYB-1 type" rather than "SUYB-1 type"
"-0 type" has better magnetic properties and is effective for compactness (lightening), improvement of response speed, and power saving.
It is desired to have magnetic properties at the "YB-0 type" level or higher.

[0003]

2. Description of the Related Art Steel members that compose a magnetic circuit in electric components of automobiles are designed to save power and improve responsiveness.
As magnetic characteristics, it is required to have a characteristic that it can be easily magnetized with a low external magnetic field. Therefore, a soft magnetic steel material in which the magnetic flux density inside the steel member easily responds to the external magnetic field is usually used.

As a soft magnetic steel material having such magnetic properties, for example, a low carbon steel having a C content of about 0.01 mass% or less is used, and a soft magnetic steel part is obtained by subjecting the steel slab to hot rolling. After that, it is generally obtained by subjecting a steel wire obtained by performing a lubrication treatment and a wire drawing process to a part molding and a magnetic annealing in order.

In recent years, in the production of soft magnetic steel parts, as a means of reducing the manufacturing cost, cold forging has been promoted in place of the cutting process in the part forming process, and the steel material to be used has a complicated shape. Excellent cold forgeability capable of forming is required. On the other hand, in order to save energy in automobiles and the like, more precise control of the magnetic circuit is required for the electric component, and accompanying this, improvement of the magnetic response speed,
That is, high magnetic permeability and reduction of hysteresis loss are important issues given to steel members.

[0006] Silicon steel is a typical material that can achieve high magnetic permeability, but has the disadvantage of being inferior in cold forgeability to low carbon steel. Although the above-mentioned low-carbon steel materials are excellent in cold forgeability, their magnetic permeability characteristics are not as good as those of silicon steel, and it is necessary to realize soft magnetic materials that combine magnetic permeability characteristics and cold forgeability at a practical level. Has been done.

A technique for reducing the deformation resistance of low carbon steel in order to enhance cold forgeability is disclosed in, for example, Japanese Patent Laid-Open No. 2000-813.
No. 9 and Japanese Patent No. 2910288. The former has been shown to fix the solid solution N in steel by adjusting the alloy composition and rolling conditions, and suppress the increase in deformation resistance due to dynamic strain aging. However, the technique in the above publication is made with a focus on the material strength and cold forgeability, and the magnetic properties sensitive to the size of crystal grains and the presence of precipitates are not always satisfactory. is not. In the latter, a technique is disclosed in which alloy elements such as C and Si are reduced to the utmost limit, and C and N which are solid-solved by adding Zr and Cr are reduced to ensure cold forgeability. However, it is not intended to improve the magnetic permeability, and it is considered that further studies are needed to improve the magnetic responsiveness.

On the other hand, in order to improve the magnetic response,
Techniques such as Japanese Patent Laid-Open No. 03-90544 have been proposed. However, this technology is mainly concerned with the suppression of eddy currents that occur when an external magnetic field is applied, and realizes the improvement of magnetic permeability and the reduction of hysteresis loss, which have become important in recent soft magnetic steel parts. It's not a responsive one,
Further, since the contents of Al and Cr that hinder the improvement of magnetic permeability characteristics are in a wide range, it is considered that improvement is required to achieve high magnetic permeability.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object thereof is to ensure particularly excellent magnetic permeability as a magnetic property and to perform cold forging. In order to provide a soft magnetic steel material which can be processed with high yield with high accuracy, a soft magnetic steel part having excellent magnetic permeability characteristics obtained by using such a soft magnetic steel material, and a manufacturing method thereof.

[0010]

The soft magnetic steel material excellent in cold forgeability and magnetic permeability characteristics according to the present invention means, in mass%,
C: 0.05% or less (not including 0%), Si: 0.0
5-2%, Mn: 0.1-0.5%, P: 0.02% or less (including 0%), S: 0.02% or less (including 0%), Al: 0.1% Below (including 0%), N: 0.0
05% or less (including 0%), O: 0.02% or less (0%
(Including)
In the steel material, B is 0.000 as another chemical component.
5 to 0.005% may be contained.

Further, the present invention also defines a soft magnetic steel part obtained by using such a steel material and having excellent magnetic permeability characteristics, and C: 0.05% or less (not including 0%), S
i: 0.05 to 2%, Mn: 0.1 to 0.5%, P:
0.02% or less (including 0%), S: 0.02% or less (including 0%), Al: 0.1% or less (including 0%),
N: 0.005% or less (including 0%), O: 0.02%
The following is satisfied (including 0%), and the main point is that the metal structure is a ferrite single-phase structure. Even if B is contained in an amount of 0.0005 to 0.005% as another component. Good.

In manufacturing the soft magnetic steel part of the present invention, the soft magnetic steel material specified in the present invention is used,
It is preferable to anneal after forming into a predetermined part shape.

The term "including 0%" means that the case of 0% is not excluded, and the term "average crystal grain size of ferrite" means the average value of the minor axis and the major axis of ferrite crystal grains. I will say.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Under the circumstances as described above, the inventors of the present invention should exhibit excellent cold forgeability during molding and ensure particularly excellent magnetic permeability characteristics among magnetic characteristics. Aiming at the realization of soft magnetic steel materials that can be used, and soft magnetic steel parts with excellent magnetic permeability characteristics obtained using such steel materials,
We investigated from various angles such as the influence of chemical composition and metal structure. As a result, if the resulting steel part satisfies the composition specified by the present invention and the metal structure of the steel part has a ferrite single phase structure specified by the present invention, magnetic permeability is particularly enhanced. It was found that the cold forging with good dimensional accuracy can be performed at the time of molding, and the present invention has been made. Hereinafter, the reason for defining the metal structure and the chemical composition in the present invention will be described in detail.

The magnetic characteristics of the soft magnetic material are related to the amount of energy for fixing the magnetic flux moving inside the material, and are influenced by the size of ferrite crystal grains, the magnetic properties of precipitates, and the distribution form.

In order to reduce the grain boundaries in order to improve the magnetic properties, the present inventors need to make the metal structure of the obtained steel part a ferrite single phase structure having an average crystal grain size of 100 μm or more. Found. Average grain size is 1
If it is less than 00 μm, the effect of paramagnetic grain boundaries is large, and high magnetic permeability cannot be achieved. The average crystal grain size of the ferrite is preferably 1
It is 30 μm or more. On the other hand, heat treatment time (manufacturing cost)
If the average crystal grain size of the ferrite is increased too much by spending the time, the effect of improving the electric conductivity is only saturated, so the amount should be kept to about 250 μm or less.

In order to make the ferrite single phase,
In order to suppress the generation of pearlite, it is effective to make the carbon content in the steel material extremely small as described later.

Next, the influence of chemical composition on magnetic permeability and mechanical properties was investigated. As a result, C, P, S, etc., which deteriorate the magnetic properties, were suppressed to a necessary minimum, and by adding an appropriate amount of Si, Mn, B, excellent cold forgeability and excellent magnetic permeability properties were obtained. It has been found that soft magnetic steel parts can be realized.

FIG. 1 is a graph for investigating the influence of the Si content in steel on the maximum permeability (permeability characteristic) and the cracking limit compressibility (cold forgeability). In the experiment, the Si content was changed. Outer diameter 13 mm x inner diameter 10 using the 7 steel samples
mm ring-shaped sample was prepared and magnetically annealed in a vacuum atmosphere. Then, a magnetic field applying coil (primary coil) and a magnetic flux detecting coil (secondary coil) were wound around it to provide an automatic magnetization measuring device. The H-B curve was measured using it to determine the maximum magnetic permeability.
The cracking limit compression ratio is 13.0 mm from the rolled material.
A sample having a size of mm × height of 19.5 mm was prepared and subjected to end face restraint compression at room temperature to obtain the value.

Si acts as a deoxidizing agent during melting, has the effect of suppressing deterioration of magnetic properties due to oxygen, and improving magnetic properties (particularly magnetic permeability properties) by reducing magnetic anisotropy. As shown in FIG. 1, the magnetic permeability is increased by adding 0.05% or more, preferably 0.10% or more. However, if the Si content is too high, the cold forgeability will be impaired as shown in FIG. Further, the growth of crystal grains during magnetic annealing is suppressed, which also causes an increase in coercive force. Therefore, in the present invention, the Si content is limited to 2% or less, preferably 1% or less.

The reasons for defining the amounts of other chemical components according to the present invention will be described in detail below.

C: 0.05% or less (not including 0%) C (carbon) is a basic element that controls the balance between the strength and the ductility of the steel material. The strength decreases and the ductility decreases as the addition amount decreases. improves. Further, since C forms a solid solution in steel and causes strain age hardening, it is desirable that the content thereof be as small as possible, and it is also preferable that it is extremely low in terms of magnetic properties. Considering these facts, in order to satisfy the magnetic characteristics of JIS-SUYB-0 type or higher, the C content should be 0.0.
It is necessary to keep it below 5%. It is preferably 0.01% or less.

Mn: 0.1-0.5% Mn effectively acts as a deoxidizing agent and at the same time S in steel is
Embrittlement due to S is suppressed by forming MnS in combination with. However, when the amount of Mn is too large, Mn precipitated
Since the grain size of S becomes large and deteriorates the magnetic characteristics,
The upper limit is 0.5%. It is preferably 0.4% or less.

P: 0.02% or less (including 0%) P (phosphorus) is a harmful element that causes grain boundary segregation in steel and adversely affects cold forgeability and magnetic properties. Therefore, in the present invention, the content of P is 0.02% or less, preferably 0.
It is necessary to set the content to 01% or less. By limiting the amount of P in this way, excellent cold forgeability and magnetic properties can be guaranteed.

S: 0.02% or less (including 0%) S (sulfur) forms MnS in the steel as described above, and when the amount of S becomes too large, a large amount of MnS precipitates, causing cold working. Since forgeability and magnetic properties are significantly deteriorated, 0.02% or less,
It is preferably suppressed to 0.01% or less.

Al: 0.1% or Less (Including 0%) Al captures solid solution N and becomes AlN, which promotes miniaturization of crystal grains. As a result, the number of crystal grain boundaries is increased, resulting in deterioration of magnetic characteristics. Therefore, in the present invention, the amount of Al needs to be suppressed to 0.1% or less. In order to secure excellent magnetic properties, it is preferable to suppress the Al content to 0.005% or less.

N: 0.005% or less (including 0%) As described above, N (nitrogen) combines with Al to form AlN and impairs magnetic properties, but in addition, it is not fixed by Al or the like. N remains in the steel as solid solution N, which also deteriorates the magnetic properties. Further, solid solution N also causes an increase in deformation resistance due to strain aging. Therefore,
In any case, the amount of N should be suppressed as low as possible, but in consideration of the actual operation of steel material production, and 0.005% is set as the upper limit value, which can suppress the adverse effect to a level that can be substantially ignored. It was

O: 0.02% or less (including 0%) O (oxygen) hardly forms a solid solution in steel at room temperature, and combines with elements such as Al and Si to form a hard oxide inclusion. Magnetic properties are significantly reduced. Therefore, the O content should be reduced as much as possible, and should be suppressed to 0.02% or less.
The O content is preferably reduced to 0.01% or less, more preferably 0.005% or less.

B: 0.0005 to 0.005% B has the function of fixing the solid solution N in the form of BN, which adversely affects the magnetic properties. Furthermore, the affinity of B for N is Al
It also has a larger effect of reducing the AlN which makes the crystal grains finer, and in order to effectively exhibit such an effect, the content is 0.0005% or more, preferably 0.001% or more. However, if too much BN is present, the magnetic properties are rather deteriorated, so the upper limit of the B content is made 0.005%. It is preferably 0.003% or less.

With respect to Cu, Ni, and Cr, if precipitates of these elements occur in the steel, the magnetic properties are deteriorated. Therefore, Cu is 0.02% or less and Ni is 0.1% or less.
02 or less, and Cr is preferably 0.05% or less.

The elements specified in the present invention are as described above, and the balance component is substantially Fe. However, in addition to the ones described above, it is brought into the steel material depending on the conditions of raw materials, materials, manufacturing equipment, etc. Even when unavoidable impurities, and further, a permissible element such as As that does not adversely affect the achievement of the object of the present invention, are included in the steel material or steel part used in the present invention.

In the production of the soft magnetic steel part according to the present invention, a specified soft magnetic steel material is used, formed into a predetermined part shape, and then annealed. The annealing is preferably performed under the following conditions.

That is, if the annealing temperature is too low, the desired ferrite crystal grain size cannot be secured in a practical heat treatment time. Therefore, it is preferable to anneal at 800 ° C. or higher, more preferably 850 ° C. That is all. On the other hand, even if the annealing temperature is excessively increased, the effect of obtaining the desired ferrite crystal grain size hardly changes, so the upper limit is preferably 950 ° C.

If the annealing time is too short, the ferrite crystal grains cannot be sufficiently coarsened due to the insufficient annealing time even if the magnetic annealing temperature is set high. Therefore, annealing is performed for at least 2 hours, preferably 3 hours or more. Well,
If it is too long, the effect of securing the desired ferrite crystal grain size does not change, so it is preferable to keep it for 6 hours or less.

As a method for obtaining a soft magnetic steel part according to the present invention, a steel material containing the above-defined chemical components is melted and cast by a conventional method to obtain a steel material, which is then hot rolled into a bar material or a wire material. Then, after cold or warm forging and molding, it may be subjected to magnetic annealing under the above conditions to form a magnetic component,
For example, as a method for manufacturing a solenoid or an actuator for an automobile, there is a method in which the wire is cut into a predetermined size, molded by cold working, and then wound and magnetized inside or outside the molded product.

[0036]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately applied within a range compatible with the gist of the preceding and the following. Modifications can be made and implemented, and all of them are included in the technical scope of the present invention.

Steel samples having the chemical composition shown in Table 1 were melted,
After casting, the wire was heated to 1100 ° C. and then hot-rolled to obtain a wire rod having a diameter of 14 mm. In the hot rolling, finish rolling was performed at 875 ° C, and subsequent cooling in a temperature range of 800 to 500 ° C was performed at an average cooling rate of 1.8 ° C / sec.
The sample taken from the obtained wire rod was annealed at 850 ° C. for 3 hours, and then the metal structure of the sample was observed. In addition, a steel wire (diameter 13.3
mm) was examined for cold forgeability and magnetic properties after annealing.

The metal structure was observed by the following method. That is, the wire material was embedded in a supporting base material in a state where the cross section of the wire material was exposed, and after polishing, it was added to a 5% picric acid alcohol solution for 15 to 15 times.
After immersing for 30 seconds to corrode it, D /
The field of view of the 4 (D: diameter of the wire) portion was photographed in 100 fields at a magnification of 100 to 400, and the average grain size of ferrite was determined from the photograph.

On the other hand, the dimensional accuracy of the part after cold forging (corresponding to the cold forgeability in the present invention) has a strong correlation with the deformation resistance, so the deformation resistance value was evaluated. For the measurement of the deformation resistance, the steel wire sample having a diameter of 13.3 mm and a height of 20 mm was used, and it was determined from the load at the time of 80% compression (strain rate 10 / s) in end face constrained compression at room temperature. In the present invention, when the deformation resistance is 500 N / mm ² or less, ○, 500
The case where it exceeded N / mm ² was marked with x.

The magnetic characteristics of each sample were examined by the following method. That is, a ring-shaped sample having an outer diameter of 13 mm and an inner diameter of 10 mm was prepared using each of the above-mentioned steel wires, magnetically annealed at 850 ° C. for 3 hours, and then a magnetic field applying coil (primary coil)
And the magnetic flux detection coil (secondary coil) was wound, and the maximum magnetic permeability when the HB curve was measured using the automatic magnetization measuring device was used for the evaluation of the magnetic permeability characteristics. Evaluation of magnetic properties
This maximum magnetic permeability is 8000 or more and JIS-SUY
When the magnetic field strength defined by the B-0 class is 20 Oe (Oersted) and a magnetic flux density of 1.1 T (tesla) or more is obtained, and the maximum magnetic permeability is 8000 or more and the magnetic field strength is The case where a magnetic flux density of 1.25 T or more was obtained with 3 Oe was marked with ◯, and the case where these were not satisfied was marked with x.

Table 2 also shows the measurement results of the metal structure, deformation resistance and magnetic properties of each sample.

[0042]

[Table 1]

[0043]

[Table 2]

From Table 2, the following can be considered. In addition, the following No. Is the experiment No. in Table 2. Indicates.

No. Nos. 1 to 3 satisfy the chemical composition and the metal structure defined in the present invention, all have high magnetic permeability and have magnetic characteristics of JIS-SUYB-0 type or higher, and excellent cold forging. You can see that it also has sex.

On the other hand, No. Nos. 4 to 13 do not satisfy the component composition specified in the present invention, and the desired magnetic properties cannot be obtained, cracks occur during compression processing, and the effect of reducing deformation resistance is not sufficient. It was not very good. For details, refer to No. In No. 4, the C content exceeds the specified upper limit value, and it can be seen that both the cold forgeability and the magnetic properties are significantly deteriorated. No. 5 and No. No. 6, the amount of Si deviates from the specified requirement, and N
o. In No. 5, since the amount of Si added is less than the lower limit value, it is considered that sufficient deoxidation could not be performed, the decrease in magnetic moment due to oxygen could not be suppressed, and high magnetic permeability could not be obtained. . No. In No. 6, since the amount of Si added exceeds the specified upper limit, the cold forgeability is unfavorable,
The result is that it is difficult to mold parts without causing cracks.

No. In No. 7, since the amount of Mn exceeds the specified upper limit value, a large amount of generated MnS suppresses the growth of ferrite crystal grains, and the grain boundary area that becomes the resistance of domain wall movement increases, so that the magnetic properties are not preferable. Became.

No. In No. 8, since the amount of P exceeds the specified upper limit value, P segregates at the grain boundaries and suppresses the growth of crystal grains, resulting in deterioration of magnetic properties. No. 9 is S
Since the amount exceeds the specified upper limit value, the magnetic properties are deteriorated due to the coarsening of MnS and the increase of the precipitation density, as in the case of excessively containing Mn.

No. 10 is more than the specified amount of the present invention A
1 was added, and AlN was generated to suppress the growth of crystal grains, resulting in a marked decrease in magnetic characteristics.

No. No. 11 contained N in an amount exceeding the upper limit defined in the present invention, and therefore, in addition to an increase in deformation resistance due to strain aging, magnetic properties were deteriorated. No. In No. 12, since the oxygen content exceeds the upper limit, it is considered that hard oxide-based inclusions were precipitated and adversely affected the magnetic properties.

No. From FIG. 13, it is understood that it is desirable to add B within the range where the BN precipitation amount does not increase in order to secure good magnetic properties.

[0052]

The present invention is configured as described above,
A soft magnetic steel material that can perform cold forging with good dimensional accuracy and can secure particularly excellent magnetic permeability characteristics as magnetic characteristics, and a soft magnetic material that exhibits a high magnetic permeability using such a soft magnetic steel material. Since steel parts can be obtained, it is possible to provide various electric parts intended for automobiles, trains, ships, etc., particularly, electric parts having a good magnetic response that mainly operate in a DC mode.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of the Si content in steel on the maximum permeability and the crack initiation critical compressibility.

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Claims (5)

[Claims] 1. In mass% (hereinafter the same), C: 0.05
% Or less (not including 0%), Si: 0.05 to 2%, M
n: 0.1 to 0.5%, P: 0.02% or less (including 0%), S: 0.02% or less (including 0%), Al:
0.1% or less (including 0%), N: 0.005% or less (including 0%), O: 0.02% or less (including 0%)
The soft magnetic steel material having excellent cold forgeability and magnetic permeability characteristics, characterized in that the metal structure is a ferrite single-phase structure. 2. As another component, B is 0.0005.
The soft magnetic steel material according to claim 1, wherein the soft magnetic steel material contains 0.005% to 0.005%. 3. C: 0.05% or less (not including 0%), Si: 0.05 to 2%, Mn: 0.1 to 0.5.
%, P: 0.02% or less (including 0%), S: 0.0.
02% or less (including 0%), Al: 0.1% or less (0%
, N: 0.005% or less (including 0%), O
A soft magnetic steel part having excellent magnetic permeability characteristics, characterized by satisfying 0.02% or less (including 0%) and having a metal structure of a ferrite single phase structure having an average crystal grain size of 100 μm or more. 4. B as a further component is 0.0005.
The soft magnetic steel part according to claim 3 containing 0.005% to 0.005%. 5. The soft magnetic steel part according to claim 3 or 4, wherein the soft magnetic steel material according to claim 1 or 2 is used, formed into a predetermined part shape, and then annealed. Production method.