JP2002180215A - Composite magnetic member having excellent low temperature magnetic stability and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite magnetic member which has low temperature magnetic stability more excellent than that of the conventional member in composite magnetic members combining a ferromagnetic part and a weak magnetic part in single material, and its production method. SOLUTION: The composite magnetic member having low temperature magnetic stability has a composition containing, by mass, 0.30 to 0.80% C, 0.10 to 3.0% Si, 0.10 to 4.0% Mn, 10.0 to 25.0% Cr, 0.01 to 3.0% Al and 0.01 to 0.10% N, and containing, as selective elements, one or more kinds selected from Nb, Ti and Zr by 0.10 to 1.0% individually or in total, and the balance substantially Fe, and contains a ferromagnetic part having a structure essentially consisting of (ferrite+carbide), and in which the specific maximum permeability μr is >=400, and a feeble-magnetic part having a structure essentially consisting of austenite, and in which the specific maximum permeability μr is <=2, the average crystal grain size is <=100 μm, and the rate of the change of the specific maximum permeability in the temperature range from room temperature to -40 deg.C, (μr-40 deg.C-μrRT) /μrRT is <=1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite magnetic member having a ferromagnetic portion and a weak magnetic portion in a single material, which can be applied as a magnetic circuit component such as a motor rotor or an actuator. The present invention relates to a composite magnetic member having excellent stability and a method for producing a composite magnetic member having excellent low-temperature magnetic stability.

[0002]

2. Description of the Related Art Conventionally, in a magnetic circuit component such as a rotor or an actuator of a motor, a structure in which a nonmagnetic portion is provided in a part of a ferromagnetic material (generally, a soft magnetic material) is used. As a method of providing a non-magnetic part in a part of the ferromagnetic material, the ferromagnetic component and the non-magnetic component are fixed or joined by brazing or laser welding, or a part of the ferromagnetic material is punched out with a press and pressed. Techniques such as using the formed void as a non-magnetic portion have been performed. In contrast to the method of joining these dissimilar materials or the method of press punching, the present inventor uses a single material, and performs cold working or heat treatment on this single material by using a ferromagnetic part and a non-magnetic part (or a weak magnetic Part) is proposed. The use of such a composite magnetic member made of a single material makes it possible to secure the airtightness, prevent breakage due to vibration, etc., and to ensure reliability and mechanical strength. And it is better than a part obtained by stamping out part of a ferromagnetic material with a press.

For example, the present inventor has disclosed Japanese Patent Application Laid-Open No. 2000-364.
No. 09, C by mass%; 0.30 to 0.80%, C
r: 10.0 to 25.0%, the balance being substantially composed of Fe, a ferromagnetic part mainly composed of (ferrite + carbide) and having a specific maximum magnetic permeability of 400 or more, and a ratio substantially composed of austenite. A composite magnetic member for an actuator having a weak magnetic portion having a maximum magnetic permeability of 2 or less has been proposed. This JP 20
The composite magnetic member described in JP-A-00-36409 is a single material utilizing the phase transformation of a steel material to realize a ferromagnetic property mainly composed of (ferrite + carbide) and a weak magnetic property mainly composed of austenitic structure. It focuses on a C-based alloy. This proposal achieves both magnetic properties of ferromagnetic and weak magnetic properties which are contradictory with a single material, and furthermore, soft magnetic properties with a specific maximum magnetic permeability of 400 or more in a ferromagnetic part and a specific magnetic permeability of 2 or less in a weak magnetic part. It is excellent in finding the optimum composition range of the composite magnetic member satisfying the magnetic properties.

[0004]

The present inventor has studied the composite magnetic member described in Japanese Patent Application Laid-Open No. 2000-36409. As a result, the austenite structure of the weak magnetic portion was found to be at the Ms point (weak magnetic austenite). (The temperature at which transformation to ferromagnetic martensite begins) Ferromagnetization begins at a temperature below that of martensitic transformation, so that the relative maximum permeability of the weak magnetic portion increases as the temperature decreases, especially in the temperature range below the freezing point. There is a problem that the magnetic characteristics of the portion become unstable. In some composite magnetic members used as magnetic circuit components, quality assurance up to around −40 ° C. may be required. In this case, it is not preferable in the design of the magnetic circuit that the magnetic characteristics of the weak magnetic portion change due to a change in the operating temperature. On the other hand, Japanese Patent Laid-Open No. 2000-364 described above
In the composite magnetic member disclosed in No. 09, the stability of the characteristics of the weak magnetic portion at a low temperature was sometimes insufficient. An object of the present invention is to provide a composite magnetic member having both a ferromagnetic portion and a weak magnetic portion in a single material, among which a composite magnetic member having superior low-temperature magnetic stability and a composite magnetic member having superior low-temperature magnetic stability than conventional members. Is to provide a method of manufacturing the same.

[0005]

In order to stabilize the low-temperature characteristics of the weak magnetic part, it is necessary to lower the Ms point of the weak magnetic part and to stabilize the austenite structure. The inventor of the present invention has proposed F
In order to stabilize the low-temperature characteristics of the weak magnetic part in the e-Cr-C-based composite magnetic member, we investigated the miniaturization of the austenite grain size in the weak magnetic part. It has been found that it is effective to use pinning particles that suppress the growth of austenite crystal grains when austenitizing (weakening). And
The minimum necessary specific alloy that can suppress pinning of austenite grain size by forming pinning particles in the optimum chemical composition of the material constituting the composite magnetic member, and does not adversely affect the magnetic properties of the composite magnetic member It has been found that by adding an appropriate amount of element, it is possible to adjust to a weak magnetic part having a specific size of austenite average grain size. They have found that they can do so and have reached the present invention.

That is, according to the present invention, C: 0.30% by mass.
0.80%, Si; 0.10 to 3.0%, Mn; 0.10
4.0%, Cr; 10.0 to 25.0%, Al; 0.01
To 3.0%, N; 0.01 to 0.10%, (Nb, T
one or more selected from the group consisting of (i, Zr) alone or in a total amount of 0.10 to 1.0%, and the balance substantially consists of Fe; Ferromagnetic portion having a maximum magnetic permeability μr of 400 or more and a specific maximum magnetic permeability μr of 2 or less mainly composed of an austenite structure, an average crystal grain size of 100 μm or less, and a rate of change of the specific maximum magnetic permeability in a temperature range from room temperature to -40 ° C (μr− _{40 ° C.−} μr _RT ) / μr _RT is a composite magnetic member having a weak magnetic portion of 1 or less and excellent in low-temperature magnetic stability.

[0007] The present invention also relates to the present invention, wherein C: 0.30
0.80%, Si; 0.10 to 3.0%, Mn; 0.10
4.0%, Cr; 10.0 to 25.0%, Al; 0.01
To 3.0%, N; 0.01 to 0.10%, (Nb, T
i, Zr) is a material containing one or two or more selected from the group consisting of 0.10 to 1.0% in total or substantially the balance of Fe, with a temperature range of 550 to 900 ° C. After annealing at least once in (Ferrite + Carbide) structure to make a ferromagnetic material with a relative maximum permeability μr of 400 or more,
The ferromagnetic material is locally subjected to a heat treatment for weakening magnetism in a temperature range of 1100 to 1350 ° C., and mainly has an austenite structure, a specific maximum magnetic permeability μr of 2 or less, and an average crystal grain size of 100 μm.
m, a rate of change in specific maximum magnetic permeability in the temperature range from room temperature to _{−40 ° C.} (μr _{−40 ° C.} −μr _RT ) / μr _RT forms a weak magnetic portion of 1 or less, and is a composite excellent in low-temperature magnetic stability. This is a method for manufacturing a magnetic member.

Here, depending on the chemical composition of the material constituting the composite magnetic member, the relative magnetic permeability of the weak magnetic portion may not be as small as the gap. However, in designing a magnetic circuit using a composite magnetic member, the ratio of the relative permeability between the ferromagnetic portion and the weak magnetic portion is important, and it is often sufficient if this ratio is sufficiently large. Therefore, the weak magnetic portion of the composite magnetic member of the present invention is not dared to use the expression of non-magnetic, but is expressed as weak magnetic in the sense that soft magnetic characteristics are weaker than the ferromagnetic portion.
Of course, the weak magnetic portion of the composite magnetic member of the present invention may be nonmagnetic at the same level as the gap.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an important feature of the present invention is that the weak magnetic portion of the Fe--Cr--C composite magnetic member is made stable in order to stabilize the magnetic properties at a low temperature. The point is that the austenite particle size is reduced. Hereinafter, the reasons for defining the present invention will be described. First, of the chemical composition of the composite magnetic member,
The reason for defining the composition range of the essential elements will be described. C: 0.30 to 0.80% C is an essential element of the present invention necessary for forming a weak magnetic portion as an element forming austenite. Further, it forms a carbide with elements such as Nb, Ti, and Zr, which will be described later, and also plays an important role as pinning particles that suppress the growth of austenite grains in the weak magnetic portion. If C is less than 0.30%,
It is difficult to obtain a weak magnetic portion having a specific maximum magnetic permeability μr of 2 or less. On the other hand, if the C content exceeds 0.80%, the soft magnetic characteristics of the ferromagnetic portion deteriorate, and it becomes difficult to obtain magnetic characteristics having a specific maximum magnetic permeability of 400 or more. Therefore, in the present invention, C
Was defined as 0.30 to 0.80%. A more desirable range for C is 0.40 to 0.70%.

Si: 0.10 to 3.0% Si has an effect as a deoxidizing element of the material and is an effective element for enhancing the soft magnetic characteristics of the ferromagnetic portion. However, if it is less than 0.10%, the effect is small, and if it exceeds 3.0%, although the specific maximum magnetic permeability of the ferromagnetic portion is further increased, it is difficult to obtain a characteristic having a specific maximum magnetic permeability of 2 or less in the weak magnetic portion. Therefore, it was specified in the above range. A more desirable range of Si is 0.10 to 1.5%. Mn: 0.10 to 4.0% Mn has an effect as a deoxidizing element and is an element effective for forming a weak magnetic portion as an austenite forming element. However, the effect is small at less than 0.10%, and conversely 4.0.
%, The working of the material becomes difficult, so it is specified in the above range. A more desirable range of Mn is 0.3 to
2.5%.

Cr: 10.0 to 25.0% In the ferromagnetic portion, part of the ferromagnetic portion becomes carbide, and part of the solid solution in the matrix secures the corrosion resistance and rust resistance of the member. Further, since Cr has an effect of lowering the Ms point, it is also effective in stabilizing the low-temperature characteristics of austenite in the weak magnetic portion. The range of Cr is 10.0 to 2
When it is less than 5.0%, if it is less than 10.0%, the effect of lowering the Ms point is small.
_{-40 ° C.} -μr _RT ) / μr _RT is difficult to stabilize in the range of 1 or less. On the other hand, in the range of 25.0% or more, the low-temperature characteristics of the weak magnetic portion are improved, but the ratio of the ferromagnetic portion is improved. This is because the maximum magnetic permeability decreases. The more desirable range of Cr is 12.0.
~ 20.0%.

Al: 0.01 to 5.0% Al acts as a deoxidizing element similarly to Si and improves soft magnetic properties of the ferromagnetic portion (improvement of specific maximum magnetic permeability,
(Reduction of coercive force). The mechanism of this soft magnetic property improvement is that the addition of Al to the Fe-Cr-C-based material increases the carbide and crystal grain size of the ferromagnetic portion to facilitate domain wall movement, and that α-Fe ( This is because the degree of integration of the (200) plane, which is an easily magnetized surface of the ferrite structure, is increased. However, if it is less than 0.01%, the effect as a deoxidizing element is small. Conversely, if it exceeds 3.0%, the soft magnetic properties of the ferromagnetic portion are further improved, but the specific maximum permeability is 2 in the weak magnetic portion. Since it becomes difficult to obtain the following characteristics, it is specified in the above range. A more desirable range of Al is 0.30 to 2.5%. N: 0.01 to 0.10% N is an effective element for forming a weak magnetic portion as an austenite forming element. However, if the content is less than 0.01%, the effect is small, and if it exceeds 0.10%, material processing becomes difficult.

Next, the reason why one or more selected from Nb, Ti and Zr are used alone or in a total composition range of 0.10 to 1.0% will be described. All of these elements combine with C to form carbide XC (X = Nb, Ti, Zr). Since this carbide XC is stable up to a high temperature range of about 1350 ° C., it remains as a carbide even when the ferromagnetic material is locally demagnetized and austenitized. The carbide remaining in the austenite acts as pinning particles that suppress the growth of austenite grains, and is effective in finely controlling the austenite grain size of the weak magnetic portion. The composition range of these elements is 0.10
If it is less than 0.10%, a carbide necessary for pinning cannot be obtained, and if it exceeds 1.0%, the characteristic having a specific maximum permeability of 2 or less in the weak magnetic portion is obtained. It is difficult to obtain. Even if only one of Nb, Ti, and Zr is added, or two or more of them are added in combination, the same effect can be obtained.
It was decided to contain 10 to 1.0%. The material used as the material of the composite magnetic member of the present invention contains P, S, and O as unavoidable impurities, particularly in a range that does not degrade the magnetic characteristics of the ferromagnetic portion and the non-magnetic portion of the composite magnetic member. %
The following may be contained.

Next, the metal structure and magnetic characteristics of each of the ferromagnetic portion and the non-magnetic portion of the composite magnetic member made of the above-described material,
Further, the reason for defining the low-temperature characteristics of the weak magnetic portion will be described. First, the structure of the ferromagnetic portion is mainly composed of (ferrite + carbide) because it is a structure necessary for obtaining magnetic properties with a specific maximum permeability μr of 400 or more. In order for the specific maximum magnetic permeability of the ferromagnetic portion to be 400 or more, the matrix must have a magnetic structure and a ferrite phase with less distortion. In order to improve the specific maximum magnetic permeability, it is desirable to reduce the amount of C dissolved in the matrix as much as possible, and it is desirable that C be taken out of the matrix as a carbide. The structure mainly composed of (ferrite + carbide) described here is a structure in which ferrite and carbide occupy 80% or more of all peak areas detected when the ferromagnetic portion is analyzed by X-ray diffraction. Point to. If the peak areas of ferrite and carbide are within the above ranges, there is no problem without deviating from the range of the magnetic characteristics of the ferromagnetic portion. The structure mainly composed of (ferrite + carbide) indicates that the structure may contain a small amount of nonmetallic inclusions or internal oxides.

Next, the reason for defining the magnetic characteristics of the ferromagnetic portion will be described. The magnetic property of the ferromagnetic part is determined by the relative maximum permeability μr being 40.
The reason why it is set to 0 or more is that a member having the magnetic characteristics in this range is particularly easy to use as a magnetic circuit component. When the specific maximum magnetic permeability of the ferromagnetic portion is 400 or more, a sufficient ratio with the relative magnetic permeability of the weak magnetic portion can be obtained. A more desirable range of the magnetic characteristics of the ferromagnetic portion is that the specific maximum permeability μr is 7
00 or more.

Next, the reason for defining the metal structure of the weak magnetic portion will be described. The reason why the metal structure of the weak magnetic portion is a structure mainly composed of austenite is that it is a structure necessary for obtaining magnetic properties with a specific maximum magnetic permeability of 2 or less. The structure mainly composed of austenite described herein means that the total area of the austenite peak area accounts for 80% or more of all peak areas detected when the weak magnetic portion is analyzed by X-ray diffraction. Organization. Within this range, the range of the magnetic characteristics of the weak magnetic portion does not deviate. The structure mainly composed of austenite indicates that the structure may contain undissolved carbides and nonmetallic inclusions as pinning particles.

Next, the reason for defining the magnetic characteristics of the weak magnetic portion will be described. As described above, in designing the magnetic circuit, the weak magnetic portion does not necessarily have to be strictly non-magnetic (relative permeability of 1.01 or less), and the ratio of the relative permeability of the ferromagnetic portion is sufficiently low. In many cases, a weak magnetic property having a magnetic permeability is sufficient. In the present invention, the reason why the relative maximum magnetic permeability μr is set to 2 or less in the magnetic characteristics of the weak magnetic portion is that this range is a characteristic range allowable as a weak magnetic portion when designing a magnetic circuit. A more desirable range of the specific maximum magnetic permeability of the weak magnetic portion is 1.1 or less.

The reason for defining the average crystal grain size of austenite in the weak magnetic portion will be described. The reason why the average crystal grain size of austenite of the weak magnetic portion was set to 100 μm or less is that the room temperature to -4
In the temperature range of 0 ° C., the rate of change of the specific maximum magnetic permeability μr (μr− _{40 ° C.−} μr _RT ) / μr _RT of the weak magnetic part is set to 1 or less, and the low-temperature characteristics of the weak magnetic part are stabilized. If the average crystal grain size of austenite in the weak magnetic portion is in the above-mentioned range, the low-temperature characteristics defined in the present invention will not be deviated.

The reason for defining the low-temperature magnetic stability of the weak magnetic portion will be described. Low temperature magnetic stability of weak magnetic part from room temperature to -40 ° C
Rate of change of relative maximum magnetic permeability μr (μr _{-40 ° C} -μr
_RT ) / μr _RT is set to 1 or less because if the rate of change of μr exceeds the above range, there is a problem when the member is used in a low-temperature environment. In the design of the magnetic circuit, the above range is defined as an allowable range.

The reason for defining the method for manufacturing the member of the present invention will be described. The material for the composite magnetic member of the present invention is 550 to 900
The reason why the annealing is performed once or more in the temperature range of ° C. is because it is a necessary step for obtaining the metal structure and magnetic properties of the ferromagnetic portion of the member of the present invention. In order to express the best soft magnetic properties of the material of the present invention, it is desirable that the final annealing performed before the weak magnetic treatment be performed in the range of 600 to 750 ° C. If the final annealing is performed in this temperature range, , Can be ferromagnetic with a specific maximum magnetic permeability μr of 700 or more.

As a method of providing a local weak magnetic portion in a ferromagnetic material, it is preferable to perform a local weak magnetic heat treatment on the ferromagnetic material in a temperature range of 1100 to 1350 ° C. The temperature range of the local heat treatment for weak magnetic weakening is set to 1100 to 1350 ° C. It is difficult to obtain a weak magnetic property having a relative maximum permeability μr of 2 or less at a temperature lower than 1100 ° C. and to austenite at a temperature exceeding 1350 ° C. Since the carbide XC (X = Nb, Ti, Zr) that pins the grain growth becomes a solid solution in the austenite matrix and no longer functions as pinning grains, it is difficult to obtain austenite grains having an average crystal grain size of 100 μm or less. And eventually room temperature-
Rate of change of relative maximum magnetic permeability in the temperature range of 40 ° C (μr _{-40 °} C-
This is because it is difficult to obtain low-temperature magnetic stability of μr _RT ) / μr _RT of 1 or less. A desirable local temperature range for the weak magnetic weakening heat treatment is 1150 to 1300 ° C. Although the method of the local heat treatment for weakening the magnetism is not particularly defined, for example, a high-frequency heating device may be used.

[0022]

(Embodiment 1) In the present invention, the chemical composition of the material of the composite magnetic member and the metal structures and magnetic properties of the ferromagnetic portion and the weak magnetic portion of the composite magnetic member manufactured using the material are important. is there. Further, the austenite grain size and low-temperature magnetic stability of the weak magnetic portion are important. In order to clarify the chemical composition of the material of the composite magnetic member and the relationship between the characteristics of the ferromagnetic part and the weak magnetic part of the composite magnetic member manufactured using the material, metal materials of various compositions were vacuum- It was produced by dissolution.
These materials were heated to 1100 ° C. and subjected to hot forging and hot rolling to obtain a plate having a thickness of 5 mm and a width of 80 mm. This was mainly annealed at 860 ° C. for 4 hours for the purpose of softening the material, and then cooled at a cooling rate of 20 ° C./h. After removing the oxide scale during hot forging and annealing, cold rolling was performed to obtain a sheet material having a thickness of 1 mm. After annealing this plate at 860 ° C. for 4 hours in a vacuum for the purpose of softening and ferromagnetic (softening) the material,
After cooling at a cooling rate of 20 ° C./h, annealing was performed at 650 ° C. for 1 hour in a vacuum as final annealing to further soften the material. Table 1 shows the chemical composition of the material.

[0023]

[Table 1]

Each material shown in Table 1 will be described. In this example, the contents of C, Si, Mn, P, S, Cr, N, and O were all constant. No. Reference numerals 1 to 16 are materials of the composite magnetic member of the present invention. No. 1-5 are Fe-17% Cr-
It is a material having a basic composition of 0.5% C-0.2% Si-0.5% Mn and Nb alone added in a range of 0.1-1.0%. Similarly, No. For 6 to 10, Ti is 0.1 to 1.0.
% Alone. 11-15
Is a single addition of Zr in the range of 0.1 to 1.0%. No. 16 is Nb; 0.3% and Ti; 0.2%
Are added in combination. No. Reference numerals 17 and 18 denote materials of the comparative member of the present invention. No. 17 is Nb, Ti, Z
r is no addition, and JP-A-2000-36409
The material of the composite magnetic member disclosed in the above publication. No. 1
In No. 8, the Nb content of the material exceeds the specified range of the present invention.

A part of the ferromagnetic material produced in the above steps is
After heating to 1200 ° C. using a high-frequency heating device and holding for 5 minutes, it was air-cooled. In each material, the locally heated portion becomes a local weak magnetic portion formed in the ferromagnetic material,
Through the above steps, a composite magnetic member having a local weak magnetic portion in the ferromagnetic material was obtained.

The metal structure and magnetic properties of the ferromagnetic portion were examined by the following methods. First, the metal structure was analyzed by X-ray diffraction for the part of each part that was not affected by high-frequency heating.
The phase is identified by scanning in the range of θ = 30 ° to 120 °,
It was confirmed that the ferromagnetic portion of all parts had a (ferrite + carbide) -based structure. Next, the magnetic properties
A ring having an outer diameter of 45 mm, an inner diameter of 33 mm, and a plate thickness of 1 mm was sampled from a part of each part that was not affected by high-frequency heating, and 150 primary windings and 30 secondary windings were performed.
A DC magnetic field of 000 Am- ¹ was applied to measure the BH characteristics, and the specific maximum magnetic permeability μr was measured from the initial magnetization curve.

On the other hand, the metal structure, magnetic properties, austenite grain size, and low-temperature properties of the weak magnetic portion were examined by the following methods. First, for the metal structure, the high-frequency heating part of each part
Phase identification was performed by scanning in the range of 2θ = 40 ° to 130 ° by line diffraction, and it was confirmed that the austenitic structure was mainly formed in the weak magnetic portions of all parts. Next, the high-frequency heating part of each part was sampled by cutting, and the relative maximum magnetic permeability μr _RT of the weak magnetic part was measured by a magnetic permeability meter. Further, after embedding this sample in a resin and polishing it to a mirror surface, it was corroded by aqua regia so that the microstructure could be observed, and the average particle size of austenite was measured.

The low-temperature magnetic stability of each part is determined by cutting a high-frequency heating part of each part to obtain a test piece, and then storing the specimen in a refrigerant maintained at -40 ° C. with (ethanol + dry ice). Immerse and measure the weak magnetic part with a permeability meter.
The specific maximum magnetic permeability μr− _{40 ° C.} after immersion in the refrigerant at 40 ° _C. was measured. From this measurement result, the rate of change of the specific maximum magnetic permeability μr in the temperature range from room temperature (20 ° C.) to _{−40 ° C.} (μr _{−40 ° C.} −μr _RT )
/ μr _RT was determined. Specific maximum permeability μ of the ferromagnetic part of each part
r, specific maximum magnetic permeability μr of the weak magnetic part, austenite average particle size (μm), change rate of specific maximum magnetic permeability μr in the temperature range from room temperature to _{−40 ° C.} (μr _{-40 ° C.} -μr _RT ) / μr _RT Are summarized in Table 2.

[0029]

[Table 2]

From Table 2, in the case of Nos. 1 to 16 of the member of the present invention, the relative maximum magnetic permeability μr in the ferromagnetic portion is 400 or more,
In the weak magnetic portion, the specific maximum magnetic permeability μr satisfies the magnetic properties of 2 or less, and the austenite average particle diameter of the weak magnetic portion is 100 μm or less, and the specific maximum magnetic permeability in the temperature range from room temperature to −40 ° C. μr change rate (μr _{-40 ℃} -μr
_RT ) / μr _RT satisfies the characteristic of 1 or less. On the other hand, the comparative member of the present invention, No. 1 In No. 17, the average austenite particle size exceeds 100 μm, and the rate of change of the specific maximum permeability μr in the temperature range from room temperature to _{−40 ° C.} (μr− _{40 ° C.} −μr _RT )
/ μr _RT also exceeds 1. In the case of the member No. where the Nb content of the raw material exceeds the specified range of the present invention. In No. 18, it can be seen that the relative maximum magnetic permeability of the weak magnetic portion exceeds 2. From this, Nb, Ti, Zr and the like are added in a predetermined range to the Fe—Cr—C system as a material of the composite magnetic member, and the austenite grain growth of the weak magnetic portion of the composite magnetic member manufactured using this material is performed. It can be seen that by pinning with carbide XC (X = Nb, Ti, Zr) and finely controlling the austenite grain size, the low-temperature characteristics of the weak magnetic portion are stabilized.

(Embodiment 2) In the present invention, the heating temperature during the local heat treatment for weak magnetic weakening is also important. Therefore, the part number of the part of the present invention. With respect to No. 2, the relative maximum magnetic permeability and low-temperature characteristics of the weak magnetic portion when the temperature of the weak magnetic heat treatment was changed variously were investigated. Weak magnetizing heat treatment conditions and specific maximum magnetic permeability μr of the weak magnetic part, austenite average crystal grain size, change rate of specific maximum magnetic permeability μr in the temperature range from room temperature to _{−40 ° C.} (μr _{-40 ° C.} -μr _R
T ) / μr _RT is summarized in Table 3.

[0032]

[Table 3]

From Table 3, it can be seen that the temperature of the heat treatment for weak magnetic
It can be seen that by setting the temperature to 0 ° C. or higher, weak magnetism having a specific maximum magnetic permeability of 2 or less can be obtained. However, if the temperature of the weak magnetic heat treatment exceeds 1350 ° C., the austenite average particle size of the weak magnetic portion exceeds 100 μm, and the rate of change of the specific maximum permeability μr in the temperature range from room temperature to −40 ° C. (μr _{−40) ℃} -μr _RT ) / μr
It can be seen that _RT exceeds 1. From this, it can be seen that in order to obtain the characteristics of the weak magnetic portion of the present invention, the temperature of the weak magnetic heat treatment is preferably set to 1100 to 1350 ° C.

According to this embodiment, the range of the average austenite particle size for obtaining excellent low-temperature magnetic stability in the weak magnetic portion of the composite magnetic member, the optimum range of the material composition satisfying these characteristics, and the weak range The optimum range of the magnetizing heat treatment temperature was found. Since the composite magnetic member of the present invention exhibits better low-temperature magnetic stability than conventional members, it is a particularly easy-to-use member for component applications that require stability of characteristics below freezing.

[0035]

According to the present invention, in a composite magnetic member having a ferromagnetic portion and a weak magnetic portion with a single chemical composition, a composite magnetic member having low-temperature magnetic stability superior to conventional members can be obtained. INDUSTRIAL APPLICABILITY The present invention is an indispensable technique when a composite magnetic member is applied as a component requiring characteristic stability at a low temperature.

Claims (2)

[Claims] 1. C. by mass%; 0.30 to 0.80%, S
i; 0.10 to 3.0%, Mn; 0.10 to 4.0%, C
r: 10.0 to 25.0%, Al: 0.01 to 3.0%,
N: 0.01 to 0.10% and one or two or more selected from the group of (Nb, Ti, Zr) alone or in a total amount of 0.10 to 1.0%, with the balance substantially being A ferromagnetic portion composed mainly of (Ferrite + carbide) and having a specific maximum magnetic permeability μr of 400 or more, an austenitic structure mainly having a specific maximum magnetic permeability μr of 2 or less, and an average crystal grain size of 100
Low temperature magnetic stability characterized by having a weak magnetic portion with a relative maximum permeability change rate (μr _{-40 ° C.} -μr _RT ) / μr _RT of 1 or less in a temperature range from room temperature to _{−40 ° C.} Excellent composite magnetic member. 2. C: 0.30 to 0.80% by mass%, S
i; 0.10 to 3.0%, Mn; 0.10 to 4.0%, C
r: 10.0 to 25.0%, Al: 0.01 to 3.0%,
N: 0.01 to 0.10% and one or two or more selected from the group of (Nb, Ti, Zr) alone or in a total amount of 0.10 to 1.0%, with the balance substantially being A material having a composition of Fe is annealed at least once in a temperature range of 550 to 900 ° C. to obtain a ferromagnetic material mainly composed of (ferrite + carbide) and having a specific maximum magnetic permeability μr of 400 or more. To a local weakening heat treatment in a temperature range of 1100 to 1350 ° C., with an austenite structure as a main component, a specific maximum magnetic permeability μr of 2 or less, an average crystal grain size of 100 μm or less, and a room temperature to −40 ° C. Rate of change of the maximum magnetic permeability (μr _{-4
0 ° C.} -μr _RT ) / μr _RT : A method for producing a composite magnetic member having excellent low-temperature magnetic stability, characterized by forming a weak magnetic portion of 1 or less.