JPH1070021A - Composite magnetic member and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite magnetic member having a ferromagnetic part having improved magnetic characteristics and nonmagnetic part in one member. SOLUTION: The composite magnetic member has a compsn. contg. C: 0.35 to 0.75wt.%, Cr: 10 to 16wt.%, Ni: 2.5wt.% or less, N: 0.04 to 0.1wt.%, one or two of Si, Al, Mn: 2wt.% or less, and Fe, the rest. and is composed of a ferromagnetic part having a max. permeability of 300μm or more and nonmagnetic part having an austenitic structure as a main and a permeability of 2 or less. A material having this compsn. is annealed to provide a ferromagnetic structure and part thereof is heated over the austenitic transform start temp. and cooled to remain a nonmagnetic austenitic structure, thereby obtaining the composite magnetic component.

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 nonmagnetic portion and a ferromagnetic portion is called a magnetic scale or a magnetic scale and is often used. As a method for obtaining this magnetic scale, as described in JP-A-62-83620, an austenite structure is usually formed.
The so-called metastable austenitic steel, which becomes martensitic by processing, is subjected to strong working, transformed into a work-induced martensitic structure showing ferromagnetism, and then the scale is heated by a laser or the like to form a non-magnetic part as an austenitic structure. Was obtained by forming

[0003] The present applicant has disclosed in Japanese Patent Application Laid-Open No. Hei 7-11397.
No. 2 proposes a new composite magnetic member as a component of an automotive solenoid valve, and then presents the optimal nickel equivalent, chromium equivalent, and Hirayama equivalent as a metastable austenitic steel to which strong machining is applied. The optimal composition range that can obtain the characteristics was proposed. When a composite magnetic material using metastable austenitic steel is used as a component of such a solenoid valve, a ferromagnetic portion and a non-magnetic portion can be formed in one member, thereby ensuring airtightness, preventing damage due to vibration, etc. In terms of securing the reliability of the ferromagnetic material and the non-magnetic material, it is superior to a component in which it is joined.

[0004]

However, since the metastable austenitic steel as described above originally has a nonmagnetic austenitic structure, it is necessary to apply a high working ratio in order to enhance the characteristics of the ferromagnetic portion. is there. Performing such strong working increases the load due to the manufacturing process, and also causes problems such as generation of cracks due to strong working. Even if such a strong working is performed, the maximum magnetic permeability μm is 1
There is a problem that only about 60 magnetic properties can be obtained,
A problem arises when importance is placed on the magnetic properties of the strong magnetic portion where the maximum magnetic permeability μm is 300 or more.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a composite magnetic member having improved magnetic properties of a ferromagnetic portion in a composite magnetic member having a ferromagnetic portion and a non-magnetic portion, and a method of manufacturing the same. I do.

[0006]

The inventor of the present invention has found that the metastable austenitic steel as described above has a limit in the properties of the ferromagnetic portion, and has studied a new composite magnetic member. The optimum composition as a composite magnetic material was investigated 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, N is added in an amount of 0.04 to 0.1% and Ni is limited to 2.5% or less with respect to a C-Cr-Fe alloy which usually becomes martensite and has ferromagnetic properties. As a result, it is possible to stabilize the retained austenite obtained by partially heating and cooling without greatly deteriorating the characteristics of the ferromagnetic portion, thereby obtaining a partial non-magnetic portion. Reached.

That is, in the present invention, C: 0.35 by mass% is used.
-0.75%, Cr: 10-16%, Ni: 2.5% or less, N: 0.04-0.1%, containing 2% or less of one or two of Si, Al, and Mn; The remainder is a composite magnetic member having a ferromagnetic part having a composition substantially composed of Fe and having a maximum magnetic permeability μm of 300 or more and a nonmagnetic part mainly composed of an austenite structure and having a magnetic permeability of 2 or less.

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 300 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 obtain a non-magnetic portion in which an austenite structure remains. 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 ferromagnetism as a composite magnetic material. For this purpose, in the present invention, a C-Cr-Fe-based alloy which usually exhibits ferromagnetism is selected, and a large amount of N is added as an austenite stabilizing element, and Ni is added.
Is limited. Hereinafter, the reasons for defining the elements specified in the present invention will be described. Ni stabilizes the austenite structure and is an important element indispensable in the present invention. However, an increase in Ni lowers the magnetic properties of the ferromagnetic portion after annealing. In addition, with the increase in the amount of Ni added, the yield strength after annealing increases, which causes a problem that workability is reduced. Therefore, in the present invention, the amount of addition needs to be 2.5% or less.

However, when the Ni content is 2.5% or less,
Although the magnetic properties of the ferromagnetic portion can be ensured, the stability of the non-magnetic portion in a low temperature range is poor, and the use environment is limited.
That is, when the temperature is lowered to 0 ° C. or less, the austenite structure showing non-magnetism is transformed into α ′ structure and becomes magnetic, so that it cannot be used in a low temperature range.
Therefore, an element for stabilizing austenite is required instead of Ni. As a result, the inventor has set N to 0.
It has been found that the addition of 04% or more effectively works to stabilize austenite and secure the characteristics of the ferromagnetic portion. If the N content is 0.1% or more, the corrosion resistance deteriorates, so the range of N in the present invention is set to 0.04 to 0.1%.

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 magnetic permeability of 2 or less when cooled after heating above the austenite transformation point, and if it exceeds 0.75%, it becomes 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%.

[0013] Cr is a solid solution in the matrix and partly becomes a carbide, and is an element for 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, Al and Mn may be contained in a total of 2% or less. These elements can be added for refining as deoxidizing elements. Although these elements are removed during the refining process, 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 of manufacturing a composite magnetic member according to the present invention is that a material having the above-described composition is annealed to obtain a maximum magnetic permeability μ.
After obtaining a ferromagnetic structure of m300 or more, after heating a part of the ferromagnetic structure to a temperature at or above the austenite transformation start temperature, it is possible to leave the austenite structure by cooling.
According to this method, a ferromagnetic part having a maximum magnetic permeability of 300 μm or more, which cannot be obtained when a conventional metastable austenitic steel is used, and a magnetic permeability of 2 mainly composed of an austenitic structure.
A composite magnetic member having the following non-magnetic portion can be obtained.

The annealing performed to obtain the above ferromagnetic portion is as follows:
This is to release the residual strain in the manufacturing process of the ferromagnetic portion. In order to enhance the ferromagnetic characteristics, it is necessary to perform the process before obtaining the non-magnetic portion. The maximum permeability μm 300 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 quenching. 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.

As a method of leaving austenite, a method of partially melting and solidifying by a laser beam or plasma heating can be used. In the melt solidification method, austenite becomes extremely stable,
This is effective as a method for securing the magnetic characteristics of the non-magnetic portion. As described above, in the present invention, since a steel that originally has a ferromagnetic martensite structure is used, it is important to secure a nonmagnetic 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 magnetic permeability is specified as 2 or less as an index of the magnetic properties and stability of the non-magnetic portion effective as a composite magnetic member.

(Embodiment) A material having the composition shown in Table 1 was vacuum-melted to obtain a 10 kg steel ingot, and then forged and hot-rolled to a sheet pressure of 4.0 mm. After annealing this material, the oxide scale was removed, and a sheet thickness of 1.5 mm was obtained by cold rolling.

[0018]

[Table 1]

The cold-rolled material is annealed to be ferromagnetic,
A part of the obtained sample was kept at 1150 ° C. above the A3 transformation point for 1 minute by high-frequency heating and then water-cooled to form a nonmagnetic part mainly composed of austenite structure in a ferromagnetic material. The magnetic properties of the obtained composite magnetic material were measured. The characteristic of the ferromagnetic portion is the maximum permeability μm from the BH loop.
And the magnetic flux density B4000 (magnetic flux density at a magnetization strength of 4000 A / m), and the non-magnetic portion was immersed in a liquid at -20 ° C for 24 hours before and after cooling, including the stability in the low temperature range. Was measured and evaluated. In order to evaluate the workability, a test piece was taken from the material after hot rolling in the process of obtaining the above-mentioned material, and the 0.2% proof stress was measured. The results are shown in Table 2.

[0020]

[Table 2]

As shown in Table 2, Ni content is not more than 2.5%,
All the samples of the present invention in which N was set to 0.04 to 0.1% had a maximum magnetic permeability exceeding 300 and 4000 in the ferromagnetic portion.
An excellent ferromagnetism with a magnetic flux density of (A / m) exceeding 1 (T) can be obtained, and the magnetic permeability in the non-magnetic portion slightly increases by cooling at -20 ° C. It was confirmed that the function as a composite magnetic material was obtained up to a low temperature range. In Sample 9 of Comparative Example in which N was less than 0.04%, the magnetic permeability at −20 ° C. greatly exceeded 2, indicating that the operating temperature range was limited. Sample 10 of the comparative example to which Ni was added in excess of 2.5% had a maximum magnetic permeability μm of the ferromagnetic portion after annealing of less than 300 and a very high proof stress value of 610 (N / mm ² ). It turns out that processing becomes difficult.

[0022]

According to the present invention, by using a C-Cr-Fe alloy to which Ni and N are added in an appropriate amount without using a metastable austenitic steel, the characteristics of a ferromagnetic part can be particularly improved without performing strong working. Thus, a composite magnetic material excellent in the above 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 (2)

[Claims] 1. A mass% of C: 0.35 to 0.75%, C
r: 10 to 16%, Ni: 2.5% or less, N: 0.04 to
0.1%, 2% of one or two of Si, Al and Mn
A composite comprising: a ferromagnetic part having a composition substantially consisting of Fe and the balance being substantially Fe and having a maximum magnetic permeability of 300 or more and a nonmagnetic part mainly composed of an austenitic structure and having a magnetic permeability of 2 or less. Magnetic material 2. C: 0.35 to 0.75% by mass%, C
r: 10 to 16%, Ni: 2.5% or less, N: 0.04 to
0.1%, 2% of one or two of Si, Al and Mn
After containing and annealing the material having a composition substantially consisting of Fe to obtain a ferromagnetic portion having a maximum magnetic permeability of 300 μm or more, after heating a part of the ferromagnetic structure to the austenite transformation point or more, A method for producing a composite magnetic member, comprising cooling to leave an austenitic structure to obtain a nonmagnetic portion.