JPH09143635A - Composite magnetic member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the magnetic properties of a composite magnetic member having a martensitic part and an austenitic part and to produce a new composite magnetic member improved also in the stability of a non-magnetic part. SOLUTION: This member is a composite magnetic member having a ferromagnetic body part, containing Fe, Ni, and Cr as essential components and composed of martensitic structure, and a non-magnetic body part, composed of recrystallized austenitic structure of grains finer than grain size number 8, and also having 20-500ppm nitrogen content. Further, it is preferable that this member has a composition in which Hirayama's equivalent, represented by Heq=[Ni%]+1.05[Mn%]+-0.65[Cr%]+0.35[Si%]+-12.6[C%], is regulated to 20-23% and also nickel equivalent, represented by Nieq=[Ni%]+30[C %]+-0.5[Mn%]+30[N%], and chromium equivalent, represented by Creq=[Cr%]+[Mo%]+-1.5[Si%]+0.5[Nb%], are regulated to 9-12% and 16-19%, respectively.

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 non-magnetic austenite structure part and a ferromagnetic martensite structure part used in, for example, a magnetic scale or a solenoid valve, and a method for manufacturing the same. is there.

[0002]

2. Description of the Related Art For example, a composite magnetic member in which a nonmagnetic material portion is formed in a ferromagnetic material at equal intervals is used, and a sensor close to the composite magnetic material detects a nonmagnetic portion or a ferromagnetic material portion, For positioning magnetic scales, etc.,
As described in Japanese Patent Laid-Open No. 62-161146, after the material is plastically worked into a work-induced martensite to be a ferromagnetic material, a local heating means such as laser heating is used.
A composite magnetic member in which a predetermined position is made non-magnetic by using a part of martensite as a non-magnetic austenite structure is used. Austenitic stainless steels and high manganese steels are known as materials suitable for partially austenitizing after such work-induced martensite.

[0003]

As described above, when an attempt is made to obtain a composite magnetic member, the material is
It is necessary to convert it to martensite, and then heat a part of it to austenite it. And as a composite magnetic member,
It is required that the austenite portion and martensite portion to be formed exist stably. The stability of martensite and the stability of austenite are contradictory properties and greatly depend on the composition. Conventionally, a composite magnetic material composed of a composite phase of martensite and austenite was known, but the structural conditions and the optimum composition for stabilizing both phases were not known.

That is, if a composition that easily forms martensite is selected, it does not become austenite even if it is heated after plastic working, or it easily returns to martensite even if it once undergoes a phase transformation to austenite, so that a nonmagnetic portion is obtained. The problem of difficulty arises. On the other hand, if a composition that easily transforms into austenite is selected, there arises a problem that martensite transformation does not occur even if plastic working is performed, or an extremely high working rate is required. With respect to such a problem, the inventors of the present invention set the equivalent of Hirayama, which is an index of stability of austenite, as shown below to 20 to 23 and set the nickel equivalent to 9 as proposed in JP-A-6-140216. ~ 1
2 and chromium equivalents are set to 16 to 19 to obtain tentative characteristics. Heq (Hirayama equivalent) = [Ni%] + 1.05 [Mn
%] + 0.65 [Cr%] + 0.35 [Si%] + 1
2.6 [C%] Nieq (equivalent of nickel) = [Ni%] + 30 [C
%] + 0.5 [Mn%] Creq (chromium equivalent) = [Cr%] + [Mo%] +
1.5 [Si%] + 0.5 [Nb%]

However, under the present circumstances, further improvement in magnetic characteristics and stability of the non-magnetic portion are required for both the austenite portion requiring non-magnetism and the martensite portion requiring ferromagnetism. . An object of the present invention is to provide a novel composite magnetic member having further improved magnetic characteristics of a composite magnetic member having a martensite part and an austenite part and improved stability of a non-magnetic part, and a method for producing the same. More specifically, in a magnetic material composed of a composite phase of martensite and austenite that has not been known hitherto, a structural condition and an optimal composition for stabilizing both phases, and a specific production for achieving it. Is to provide a method.

[0006]

In the composite magnetic member of the present invention, the ferromagnetic portion is required to have a high magnetic flux density, and the nonmagnetic portion is required to have a relative magnetic permeability as close to 1 as possible. The present inventors have added nitrogen [N] as an austenitizing element. Nickel equivalent Nieq = [Ni%] + 30 [C%]
An attempt was made to optimize the magnetic characteristics of the composite magnetic member by +0.5 [Mn%] + 30 [N%]. However, it has been found that increasing the nitrogen content significantly deteriorates the magnetic properties of the ferromagnetic part formed as the composite magnetic member, although it does not significantly affect the Ni equivalent. Therefore, the amount of nitrogen must be limited in the composite magnetic member.

On the other hand, in the above-mentioned austenite structure constituting the non-magnetic part, if the Ms point is high, the possibility of transformation into a martensite structure increases. Therefore, a material having a low Ms point in the non-magnetic portion is effective for the stability of the non-magnetic portion. When the present inventor investigated the relationship between the Ms point of the non-magnetic part and the nitrogen content, there was almost no change in the nitrogen content even by heating for austenitization, and nitrogen remained in the austenite structure, lowering the Ms point, It was found that it is effective to stabilize the austenite structure in the low temperature range.

Nitrogen is an effective element for reducing the magnetic permeability of the non-magnetic portion of the composite magnetic member, and is an element necessary for ensuring the non-magnetic characteristics. It was also confirmed that the addition of nitrogen significantly lowered the Ms point (the temperature at which martensite starts to be generated) in the non-magnetic portion, and the austenite structure, which is a non-magnetic structure, could be further stabilized. That is, if nitrogen is extremely reduced, it is not possible to satisfy both the characteristics of the ferromagnetic portion and the non-magnetic portion of the composite magnetic member, so it is necessary to control the nitrogen amount within the optimum range that satisfies both characteristics.

Further, the present inventor has examined the relationship between the Ms point and the austenite structure. In the structure obtained by heating for austenitization, if recrystallization is incomplete, the magnetic permeability increases, On the other hand, it was found that when heated to a high temperature, the crystal grains coarsened and the magnetic permeability was low, but the Ms point increased, impairing the stabilization of the austenite structure. Then, it was found that the Ms point can be kept low by making the grain size finer than the austenite grain size number 8. The present invention has been found based on the above findings. That is, the present invention has a ferromagnetic portion mainly composed of Fe, Ni and Cr and having a martensite structure, and a non-magnetic portion having a recrystallized austenite structure finer than austenite grain size number 8. And the amount of nitrogen contained is 20-
It is a composite magnetic member characterized by being 500 ppm.

The composite magnetic member of the present invention described above is F
e, Ni and Cr as main components, and nitrogen 20 to 5
Manufacture of a composite magnetic member of the present invention in which a material containing 00 ppm is made into a martensite structure by plastic working, and then a part of the martensite structure is heated and recrystallized to form an austenite structure having a finer grain than austenite grain size number 8. It can be obtained by the method. The composite magnetic member of the present invention includes C 0.6% or less by weight% and Cr 12 to
19%, Ni 6-12%, Mn 2% or less, Si 1%
Hereinafter, it is desirable that the composition of nitrogen is 20 to 500 ppm and the balance is substantially Fe.

In order to enhance the ferromagnetic properties of the ferromagnetic part and the nonmagnetic properties of the nonmagnetic part, the Hirayama equivalent H
eq = [Ni%] + 1.05 [Mn%] + 0.65 [C
r%] + 0.35 [Si%] + 12.6 [C%] is 20
˜23%, and nickel equivalent Nieq =
[Ni%] + 30 [C%] + 0.5 [Mn%] + 30
[N%] is 9 to 12%, chromium equivalent Creq = [Cr
%] + [Mo%] + 1.5 [Si%] + 0.5 [Nb
%] Is preferably 16 to 19%.

One of the features of the present invention is that the composite magnetic material contains 20 to 500 ppm of nitrogen. As described above, the ferromagnetic portion obtained by martensite conversion from a material having a high nitrogen composition has a large amount of nitrogen, and the ferromagnetic properties are significantly deteriorated beyond the expected Ni equivalent. Especially 50
If it exceeds 0 ppm, the deterioration of the ferromagnetic properties becomes remarkable. On the other hand, in the non-magnetic portion which is the austenite portion, the amount of nitrogen hardly changes even by heating, and nitrogen is essential for lowering the Ms point in the austenite structure and stabilizing the austenite structure. The limit amount is 20
It is above ppm. The present invention provides a composite magnetic member in which a ferromagnetic material portion and a non-magnetic material portion are integrally formed, so that the nitrogen range is specified to 20 to 500 ppm in order to satisfy both characteristics.

Nitrogen is an element that enhances cracking susceptibility, and must be regulated when a martensite structure is obtained by performing a large reduction of 50% or more or a drawing ratio of 2 or more. In the present invention, the preferable nitrogen content is 100 to 250 ppm. Another feature of the present invention is that the austenite structure is a fine-grained recrystallized structure from austenite grain size number 8. As described above, in the austenite structure, it is necessary to lower the Ms point and stabilize it.

The inventor of the present invention is not sufficient to lower the Ms point just by introducing the above-mentioned nitrogen, and by making finer grains than the austenite grain size number 8,
This is a further reduction of the Ms point. The size of the above-mentioned austenite crystal grains can be adjusted by the austenitizing temperature and time. If the austenitizing temperature is low and recrystallization is incomplete, the magnetic permeability becomes high and it cannot be used as a non-magnetic portion. On the other hand, if the austenitizing temperature is too high, the crystal grains become coarse and Ms
The point rises and the stability of the austenite structure deteriorates. That is, in the present invention, by the introduction of nitrogen and optimization of the crystal grains of the recrystallized austenite structure,
One of the major characteristics is that the Ms point of the austenite structure is low.

In the present invention, the martensite structure exhibits ferromagnetism and the austenite structure exhibits nonmagnetism, which constitutes a composite magnetic material such as a magnetic scale or a solenoid valve. Further, it is effective to heat a part of the martensite structure to obtain austenite after the martensite structure is obtained by plastic working, as a method of allowing the ferromagnetic part and the non-magnetic part to exist in an integrated molded product. As a preferable composition of the composite magnetic member of the present invention, C is set to 0.6% or less because it shows ferromagnetism even if it exceeds 0.6%, but the workability is deteriorated due to the increase in the amount of carbide. is there. Cr amount is 1
The reason why the content is set to 2 to 19% is that if it is less than 12%, the amount of Cr in martensite generated by the plastic working is reduced, so that the strength is reduced. On the other hand, if it exceeds 19%, ferrite is generated in austenite which is a non-magnetic part and the non-magnetic part is reduced.

The Ni content of 6 to 12% means that the Ni content is 6%.
If it is less than%, austenite is not very stable and ferrite is generated, so that it is difficult to obtain a non-magnetic portion. On the other hand, if it exceeds 12%, the stability of austenite becomes too high and the formation of work-induced martensite is hindered. The Mn content is set to 2% or less because if it exceeds 2%, the ductility of martensite generated by plastic working decreases and the workability also decreases. Further, Mn is an element that suppresses the formation of martensite, and it is necessary to suppress it to a low range in order to secure ferromagnetism. The preferred range is 1.0%
It is as follows. Si is set to 1% or less because if it exceeds 1%, the ductility of martensite decreases. Note that addition of 1% or less is effective in increasing the height of the member, so it is preferable to add it by aiming at about 0.3 to 0.8%.

Hirayama equivalent Heq = [Ni%] +
1.05 [Mn%] + 0.65 [Cr%] + 0.35
[Si%] + 12.6 [C%] is 20 to 23%, and the nickel equivalent is Nieq = [Ni%] + 30.
[C%] + 0.5 [Mn%] + 30 [N%] is 9 to 12
%, Chromium equivalent Creq = [Cr%] + [Mo%] +
1.5 If [Si%] + 0.5 [Nb%] satisfies the composition is from 16 to 19%, the applied magnetic field 4000A / flux density of the ferromagnetic part of the time m B _{40 00} 0.3 (T) or higher And the magnetic permeability μ in the non-magnetic portion can be easily adjusted to around 1.

Further, although Mo and Nb are not necessarily added, Mo has the effect of lowering the Ms point, and N
b has the effect of increasing the material strength, and can be added alone or in combination depending on the purpose. Here, if Mo exceeds 2% or Nb exceeds 1%, the workability decreases, so the upper limits of the amounts of addition of Mo and Nb are preferably set to 2% and 1%, respectively.

[0019]

EXAMPLE An alloy having the composition shown in Table 1 was hot-rolled into a plate having a thickness of 2.5 mm, which was then subjected to solution treatment at 1000 ° C. for 5 minutes in an inert gas, and then at 900 ° C. in a nitrogen atmosphere. The mixture was heated to 1, the nitrogen content was adjusted, and a composite magnetic member material having an austenite structure was obtained at different nitrogen contents. As shown in Table 1, although the nitrogen content was different, a material that substantially showed an austenite structure was obtained by the solution treatment. The γ amount (%) is the amount of austenite after the solution treatment, the unit is%, μ is the magnetic permeability, and [N] is the nitrogen content after the solution treatment, the unit is ppm. Also, He
q is Hirayama equivalent, Nieq is Ni equivalent, Creq is Cr
Is equivalent.

[0020]

[Table 1]

Samples 1 to 5 shown in Table 1 were cold-rolled to reduce the plate thickness from 2.5 mm to 1.2 mm,
The results of evaluation of the ferromagnetic part are shown in Table 2. The amount of α '(%) shown in Table 2 is the amount of martensite after cold rolling, the unit is%, B _{4 00} (T) is the magnetic flux density when the applied magnetic field is 4000 A / m, and the unit is T (Tesla). is there. No change in alloy composition in the test piece due to cold rolling was observed.
Also, in order to evaluate the crackability, φ6 annealed after cold rolling.
A disk-shaped material having a size of 0 mm × 0.7 tmm was drawn into a cylindrical shape having an inner diameter of 30 mm. The aperture ratio at this time is φ60 /
φ30 = 2. The presence or absence of cracks is shown in Table 2. As shown in Table 2, in the comparative examples having a high nitrogen content, cracking occurs, which is not preferable. Further, it can be seen that in the martensite part requiring ferromagnetic properties, B ₄₀₀₀ decreases with an increase in the nitrogen content, and the magnetic characteristics deteriorate.

[0022]

[Table 2]

With respect to the samples shown in Table 1, a part of the material surface was subjected to 10 ^-3 to 10 s for 3 seconds under the two conditions of 880 ° C and 1080 ° C.
Table 3 shows the characteristics of the non-magnetic portion obtained by high frequency heating in a vacuum of rr and recrystallization. As is clear from Table 3,
By partially heating, an austenitic structure that is substantially non-magnetic is obtained. As shown in Table 3, by adding nitrogen, the magnetic permeability of the austenite portion, which is required to be non-magnetic, approaches 1, and the Ms point decreases, so addition of 20 ppm or more of nitrogen is effective for securing non-magnetic characteristics. It can be seen that it is. The heating condition was as high as 1080 ° C., and the sample having coarse crystal grains with an austenite grain size number 8 or less was 20 times larger than the one having the same composition but having the crystal grains refined at 880 ° C. The Ms point is high even at temperatures above ℃. Therefore, it is understood that introduction of nitrogen and refinement of crystal grains are essential in the austenite structure that constitutes the non-magnetic portion.

As a typical austenite structure of the present invention, FIG. 1 shows the microstructure of Sample No. 3 when heat-treated at 880 ° C. As shown in FIG. 1, the austenite structure of the present invention is a fine recrystallized structure. It should be noted that γ _rev shown in Table 3 is the amount of austenite in the non-magnetic material portion after partial heating and the unit is%. GS No. is austenite grain size number, Ms
Is the temperature at which martensite formation begins.

[0025]

[Table 3]

Example 2 The same operation as in Example 1 except that the condition for forming the non-magnetic portion was set to 880 ° C. for each of the test pieces having the chemical compositions shown in sample numbers 6 to 12 in Table 4. The results obtained are shown in Tables 4 and 5. No change in the amount of nitrogen was observed during cold rolling. As is clear from Tables 4 and 5, the samples having a nitrogen content within the specified range of the present invention have a high magnetic flux density in the martensite part obtained in the cold working and are non-magnetic due to the subsequent partial heating. In the transformed austenite structure, finer grains than austenite grain size number 8
Moreover, it can be seen that a non-magnetic portion close to 1 was obtained.

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

As described above, according to the present invention, a composite magnetic member having characteristics of both a ferromagnetic portion and a non-magnetic portion is obtained by optimal inclusion of nitrogen and refinement of recrystallized grains of austenite structure. For the first time, it is possible to achieve both improvement in the ferromagnetic properties of the martensite structure and improvement and stabilization of the non-magnetic properties of the austenite structure, which could not be achieved with conventional composite magnetic materials. Therefore, a ferromagnetic material having a high magnetic flux density and a non-magnetic portion having a relative magnetic permeability close to 1 are stably formed, which is suitable for use in a magnetic scale or a solenoid valve.

[Brief description of the drawings]

FIG. 1 is a metal microstructure photograph showing a recrystallized structure of an austenite portion of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01F 1/00 H01F 1/00 Z (72) Inventor Keihiro Tanimura 1-chome, Showa-cho, Kariya city, Aichi prefecture Address: Nippon Denso Co., Ltd.

Claims (6)

[Claims] 1. A ferromagnetic material portion containing Fe, Ni and Cr as main components and having a martensite structure, and a non-magnetic material portion having a recrystallized austenite structure with finer grains than austenite grain size number 8. And the amount of nitrogen contained is 20 to 500 ppm. 2. The composite magnetic member, in% by weight, is C 0.6% or less, Cr 12 to 19%, Ni 6 to 12%, Mn 2%.
The composite magnetic member according to claim 1, wherein Si is 1% or less, nitrogen is contained in an amount of 20 to 500 ppm, and the balance is substantially Fe. 3. Hirayama equivalent Heq = [Ni%] + 1.
05 [Mn%] + 0.65 [Cr%] + 0.35 [Si
%] + 12.6 [C%] is 20 to 23%, and nickel equivalent Nieq = [Ni%] + 30 [C
%] + 0.5 [Mn%] + 30 [N%] is 9 to 12%,
Chromium equivalent Creq = [Cr%] + [Mo%] + 1.
3. The composite magnetic member according to claim 1, wherein the composition of 5 [Si%] + 0.5 [Nb%] is 16 to 19%. 4. A material containing Fe, Ni and Cr as main components and containing nitrogen in an amount of 20 to 500 ppm to have a martensite structure by plastic working, and then part of the martensite structure is heated to recrystallize to form austenite crystals. A method for producing a composite magnetic member, characterized by having an austenite structure finer than grain size No. 8. 5. The material is C 0.6% or less by weight%, C
r 12 to 19%, Ni 6 to 12%, Mn 2% or less,
The method for producing a composite magnetic member according to claim 4, wherein Si is 1% or less, nitrogen is contained in an amount of 20 to 500 ppm, and the balance is substantially Fe. 6. The material is Hirayama equivalent Heq = [Ni
%] + 1.05 [Mn%] + 0.65 [Cr%] + 0.
35 [Si%] + 12.6 [C%] is 20 to 23%, and the nickel equivalent is Nieq = [Ni%] + 3.
0 [C%] + 0.5 [Mn%] + 30 [N%] is 9 to 1
2%, chromium equivalent Creq = [Cr%] + [Mo%]
+1.5 [Si%] + 0.5 [Nb%] is 16 to 19%
6. The method for producing a composite magnetic member according to claim 4, wherein the composition satisfies