JPH108222A - Composite magnetic member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite magnetic member particularly improved in the magnetic properties in the ferromagnetic part of a composite magnetic member having ferromagnetic part and non-magnetic part in one member. SOLUTION: A material having ferromagnetism, having a composition consisting of 0.35-0.75% C, 10-16% Cr, <=7% Mn, <=4% Cu, <=0.05% N, <=2% of either or both of Si and Al, and the balance essentially Fe, is partially heated to a temp. not lower than the austenitic transformation temp. and cooled, by which austenite is allowed to remain, and ferromagnetic part and non-magnetic part are formed. The ferromagnetic part has >=200 maximum magnetic permeability μm and the non-magnetic part is composed essentially of austenitic structure, and further, magnetic permeability and Ms point are regulated to <=2 and <=-10 deg.C, respectively. As alloying element, Ni can be incorporated by <=4% within the range satisfying Cu+Ni=6%.

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 provided with a ferromagnetic portion and a non-magnetic portion on one member used for a magnetic scale or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art For example, a material for detecting a relative position of an article by detecting a non-magnetic portion and a ferromagnetic portion is called a magnetic scale or a magnetic scale and has been partially put into practical use. As a method for obtaining this magnetic scale, as described in JP-A-62-83620, an austenitic structure is usually formed, but a so-called metastable austenitic steel which is turned into martensite by working is subjected to strong working. Transformation into a work-induced martensite structure exhibiting magnetism was performed, and then a scale portion was heated with a laser or the like to form a non-magnetic portion as an austenitic structure.

[0003] The present applicant has disclosed in Japanese Patent Application Laid-Open No. 7-1139.
In No. 7, a new composite magnetic material that presents the optimum nickel equivalent, chromium equivalent, and Hirayama equivalent as a metastable austenitic steel that becomes ferromagnetic by applying strong machining and that can obtain favorable magnetic properties for solenoid valves of automobiles Proposed.
When a composite magnetic material using such a metastable austenitic steel is used, a ferromagnetic portion and a non-magnetic portion can be formed in one member, thereby ensuring airtightness, ensuring reliability such as preventing damage due to vibration, and the like. In this respect, it is superior to a component in which a ferromagnetic material and a non-magnetic material are joined.

[0004] However, in the metastable austenitic steel as described above, it is necessary to apply a high working rate in order to enhance the characteristics of the ferromagnetic portion. Performing such strong working increases the load on the manufacturing process and may cause problems such as cracking due to strong working. Further, there is a problem that even if the above-mentioned strong working is performed, only magnetic properties with a maximum magnetic permeability of about μm 160 can be obtained.
This is a problem when the magnetic characteristics of the ferromagnetic portion where m is 200 or more are particularly important.

SUMMARY OF THE INVENTION An object of the present invention is to provide a composite magnetic member in which the magnetic properties of a ferromagnetic portion in a composite magnetic member having a ferromagnetic portion and a non-magnetic portion are particularly improved, and a method of manufacturing the same. And

[0006]

The present inventors have found that the metastable austenitic steel as described above has a limit in the properties of the ferromagnetic portion, and have studied a new composite magnetic member. Then, a new composite magnetic material was studied from the knowledge that even in an alloy that normally becomes martensite, the austenite structure, which is a nonmagnetic structure, can be left by cooling treatment from the austenite transformation temperature or higher.

As a result, Cu is selected as an effective element for stabilizing austenite with respect to a C-Cr-Fe alloy which usually becomes martensite and ferromagnetic is obtained, and Cu is added in an amount of 4% or less. As a result, it has been found that the retained austenite obtained by partially heating and cooling can be stabilized, and thereby a non-magnetic portion can be partially obtained.

That is, in the present invention, C: 0.35 by mass% is used.
~ 0.75%, Cr: 10 ~ 16%, Mn: 7% or less,
Cu: 4% or less, N: 0.05% or less, Si and Al
1% or 2% or less, and the balance is substantially F
e, a ferromagnetic portion having a maximum magnetic permeability of 200 μm or more, a magnetic permeability of 2 or less mainly composed of an austenite structure, and an Ms point (the temperature at which the austenite structure turns into martensite. The more austenite becomes unstable, the more the composite magnetic member has a non-magnetic portion at -10 ° C or lower. Further, in the present invention, up to 4% of Ni, 6% or less of Cu + Ni can be added.

In the above-described composite magnetic member of the present invention, after a material having the above-described composition is annealed to obtain a ferromagnetic structure having a maximum magnetic permeability μm of 200 or more, a part of the ferromagnetic structure is reduced to an austenite transformation start temperature. After heating as described above, it can be manufactured by cooling to leave an austenite structure to obtain a non-magnetic portion. In addition, as a method of heating to a temperature equal to or higher than the austenite transformation start temperature and then cooling to leave the austenite structure, a means of partially melting and solidifying may be used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention aims to obtain a ferromagnetic portion having particularly excellent ferromagnetic properties as a composite magnetic material. Therefore, in the present invention, a C-Cr-Fe-based alloy that normally exhibits ferromagnetism is selected, and Cu is added as an austenite stabilizing element. Hereinafter, the reasons for defining the elements specified in the present invention will be described. Cu stabilizes the austenite structure and is an important element in the present invention. The reason why the range of Cu is set to 4% or less is that Cu exceeding 4% precipitates in the cooling treatment from the austenite transformation point or higher and does not show an effective effect on demagnetization.

In the present invention, Ni can be added as an element for stabilizing the austenite structure.
Ni is an element effective for stabilizing the austenite structure, but is more expensive than Cu. Further, it increases the 0.2% proof stress after annealing and makes working in the cold more difficult than in Cu. In addition, since it is an element that lowers the magnetic properties of the ferromagnetic portion, it is necessary to limit the amount of addition. In the present invention, in consideration of the above, the upper limit of Ni when added is 4%, and in order not to deteriorate workability in cold and the magnetic characteristics of the ferromagnetic portion, Ni + Cu is used when Ni is added. 6%
It was as follows.

C forms a carbide and is important as an element for securing the basic strength of the C—Cr—Fe alloy based on which the present invention is based. Further, C is an element that also contributes to stabilization of austenite. If C is less than 0.35%, it is difficult to obtain a stable nonmagnetic structure having a magnetic permeability of 2 or less and an Ms point of -10 ° C or less when heated and cooled to a temperature higher than the austenite transformation start temperature. On the other hand, when it exceeds 0.75%, it is difficult to perform cold working. Therefore, in the present invention, the range of C is set to 0.35 to 0.75%. A more desirable range for C is 0.45 to 0.65%.

Mn is added as a deoxidizing element for refining and also acts as an element for stabilizing the austenite structure. The reason why the range of Mn is set to 7% or less is that if it exceeds 7%, the magnetic properties of the ferromagnetic portion rapidly decrease and the hot workability deteriorates.

The reason why N is set to 0.05% or less is that 0.05% or less is used.
If the ratio exceeds the above, the degree of work hardening increases, and the moldability deteriorates. N is an austenite stabilizing element, and preferably by adding 0.01% or more, the nonmagnetic portion can be further stabilized.

Cr is an element that forms a solid solution with the matrix and partially becomes a carbide, thereby ensuring the mechanical strength and corrosion resistance of the present invention. In the present invention, the range of Cr is 10-1.
The reason why 6% is set is that if it is less than 10%, the corrosion resistance is inferior and 16%.
In the above, the ferrite structure is stabilized, so that it is difficult to form a non-magnetic portion. In the present invention, one or more of Si and Al may be contained in a total of 2% or less. These elements can be added for refining as deoxidizing elements.
Note that these elements are removed during the refining process, but some remain. In the present invention, the range is particularly limited to 2% or less as long as the magnetic characteristics are not deteriorated.

A feature of the method for manufacturing a composite magnetic member of the present invention described above is that a material having the above-described composition is annealed to obtain a maximum magnetic permeability μ.
After obtaining a ferromagnetic structure of m200 or more, a part of the ferromagnetic structure is heated to an austenite transformation start temperature or higher, and then cooled to leave an austenite structure to obtain a nonmagnetic portion. According to this method, the maximum permeability μm2 which cannot be obtained when using the conventional metastable austenitic steel is used.
It is possible to obtain a composite magnetic member having both a ferromagnetic portion of at least 00 and a non-magnetic portion mainly composed of an austenite structure having a magnetic permeability of 2 or less and an Ms point of −10 ° C. or less.

The above-described annealing of the material for obtaining the ferromagnetic portion releases the residual strain in the process of manufacturing the ferromagnetic portion. Must be performed in advance. The maximum magnetic permeability of 200 μm or more of the ferromagnetic portion in the present invention cannot be obtained with a metastable austenitic steel which needs to obtain ferromagnetism by strong working. The present invention secures the characteristics of the non-magnetic portion by austenite remaining after heating and cooling. This austenite can be retained more by increasing the cooling rate, and it is desirable to rapidly cool from a temperature range where austenite is stably present. In practice, it is desirable to apply a cooling method capable of securing a cooling rate higher than air cooling, and it is desirable to apply a water cooling method or an oil cooling method.

Further, as a method of leaving austenite, a method of partially dissolving and solidifying by a laser beam or plasma heating can be adopted. In the method of melting and solidifying, austenite becomes extremely stable and is effective as a method for securing the magnetic properties of the non-magnetic portion. As described above, in the present invention, since the steel which originally has a ferromagnetic martensite structure is used, it is important to secure the characteristics of the non-magnetic portion. The characteristics of the non-magnetic portion greatly change due to the above-described alloy composition and heating / cooling treatment for retaining austenite. In the present invention, the maximum magnetic permeability is set to 2 or less, and the Ms point is set to -10 ° C. or less as an index of the magnetic properties and stability of the nonmagnetic portion effective as a composite magnetic member.

[0019]

EXAMPLE A material having the composition shown in Table 1 was melted in a vacuum for 10 minutes.
After obtaining a steel ingot of kg, forging and hot rolling are performed to obtain a plate thickness of 4.
0 mm. After annealing this material below the A3 transformation point, the oxide scale is removed and the sheet thickness is reduced to 1.5 by cold rolling.
mm.

[0020]

[Table 1]

A part of this material is A3
After holding at 1150 ° C. for 1 minute above the transformation point, the mixture was cooled with water to form a nonmagnetic portion mainly composed of an austenite structure on a ferromagnetic material. Magnetic properties and M of the obtained composite magnetic material
The measurement at the s point was performed. Table 2 shows the results. here,
For the ferromagnetic portion, the maximum permeability μm
And the magnetic flux density B4000 (magnetic flux density at a magnetization intensity of 4000 (A / m)) were evaluated. For the non-magnetic portion, the magnetic permeability μ measured by a magnetic permeability meter and Ms measured by a minute scanning calorie The point was evaluated. Further, in order to evaluate the workability, a sample was taken from the material after hot rolling in the process of obtaining the above-mentioned material, and a tensile test was performed to measure a 0.2% proof stress. The results are shown in Table 2.

[0022]

[Table 2]

As shown in Table 2, Cu content of 4% or less or C
The samples of the present invention in which the u + Ni content was 6% or less all had a maximum magnetic permeability of more than 200 and 4000 in the ferromagnetic portion.
An excellent ferromagnetism having a magnetic flux density at (A / m) exceeding 1 (T) was obtained, the magnetic permeability was also 2 or less even in the non-magnetic portion, and the Ms point was stable at -10 ° C or less. I was able to confirm that. Further, Sample 1 of the present invention and C
Compared with Comparative Example 11 having the same composition as Sample 1 except that a large amount of Ni was added to stabilize the austenite structure instead of Cu without adding u, the magnetic properties in the ferromagnetic state and the non-magnetic state were compared. Although the characteristics are almost the same, Comparative Example 11 has a higher proof stress value than the present invention. From this, it can be seen that Cu is more preferable than Ni as the austenite stabilizing element in terms of enhancing workability and obtaining equivalent magnetic characteristics.

[0024]

According to the present invention, not the metastable austenitic steel but the C-Cr-Fe alloy to which Cu is added in an appropriate amount is used. A composite magnetic material can be obtained. Therefore, it is no longer necessary to apply extremely strict processing conditions as in the related art, which is extremely effective in improving the efficiency in manufacturing.
In the present invention, since the ferromagnetic portion has excellent magnetic properties, it is also effective as a magnetic path forming material such as a pole piece in a magnetic circuit.

Claims (4)

[Claims] 1. A mass% of C: 0.35 to 0.75%, C
r: 10 to 16%, Mn: 7% or less, Cu: 4% or less,
N: a ferromagnetic portion containing 0.05% or less, a total of 2% or less of one or two types of Si and Al, a balance substantially consisting of Fe, and a maximum magnetic permeability of 200 μm or more; Permeability of 2 or less mainly composed of austenite structure, M
A composite magnetic member comprising a nonmagnetic portion having an s point of −10 ° C. or lower. 2. An alloy containing 4% or less of Ni by mass% and Cu
The composite magnetic member according to claim 1, wherein + Ni is 6% or less. 3. A mass% of C: 0.35 to 0.75%, C
r: 10 to 16%, Mn: 7% or less, Cu: 4% or less,
N: 0.05% or less, a material containing one or two kinds of Si and Al in a total of 2% or less, and a material having a composition substantially composed of Fe and the balance is annealed, and a ferromagnetic part having a maximum magnetic permeability of 200 μm or more A method for producing a composite magnetic member, comprising: heating a part of the ferromagnetic structure to a temperature equal to or higher than the austenite transformation point after cooling, and then cooling to leave the austenitic structure to obtain a nonmagnetic portion. 4. The method for producing a composite magnetic member according to claim 3, wherein the material contains 4% or less of Ni in mass% and Cu + Ni: 6% or less.