KR900001099B1 - Making process of permanent magnet - Google Patents

Abstract

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Description

Manufacturing Method by Stress Aging of Iron-Chromium-Cobalt-X Permanent Magnets Used in Speakers

1 is a test piece of the test carried out in the present invention.

Figure 2a is a state diagram of the sample of the test carried out in the present invention, Figure 2b is a heat treatment process diagram of the test carried out in the present invention.

3 is a principle diagram of the test carried out in the present invention.

4 is a magnetic characteristic according to the stress aging temperature of the test carried out in the present invention.

The fifth magnetic properties according to the stress intensity of the test carried out in the present invention.

6 is a magnetic characteristic according to the stress aging time of the test carried out in the present invention.

The present invention relates to a method for producing a permanent magnet made of iron-chromium-cobalt-X (added element) alloy used in high-quality speakers and the like.

Alnico (alnico), which is used in a conventional high-end speaker, is a strategic element and contains an expensive cobalt content of about 25wt%, and has a disadvantage in that it is not workability such as cold working with a cast magnet.

However, an alloy of iron-chromium-cobalt-X-, which has a cobalt content of about 15 wt% and magnetism similar or higher than that of alnico, has been developed.

The specific characteristics of this magnetic alloy are as follows.

1) Good cooling processing and plastic deformation.

2) Good workability can make magnet of required shape.

3) Has magnetism similar to or better than alnico.

4) The squareness of the demagnetization curve of the B-H curve is good.

5) Cobalt content, which is a strategic element and expensive, is 10-17wt% lower than that of Alnico.

6) Compared to alnico, manufacturing costs are similar or even lower.

In this Fe-Cr-Co-X-based magnetic alloy system, the value of the permanent magnet alloy has to have a form in which a ₁ (iron, cobalt, rich phase) is elongated in a certain direction. Therefore, the elongation of alpha particles has become a key to the development of this alloy.

In the present invention, a stress aging method was used to increase the spinodal decomposition particles (a ₁ ) by ageing heat treatment while applying an external stress in the Fe—Cr—Co—X alloy.

The detailed manufacturing process of the Fe-Cr-Co-X alloy is as follows.

[Alloy design]

A state diagram of Fe-Cr-Co having a content of 15 wt% Co is the same as FIG. 2a. The spinodal decomposition temperature of Fe-Cr is about 475 ℃, so the decomposition rate is too slow and it is not valuable as a magnetic material. give. But cobalt expands r-loop as an element that promotes the formation of r (nonmagnetic) phases. In this case, since the solution treatment temperature increases, the X-phase forming element (where X is α-forming element Al, V, Ti, Zr, Si, Mow, etc.) of the iron-chromium-cobalt alloy is selected from one of them, Alternatively, the mixture should be added to reduce the r-loop to allow solution treatment at low temperature and to suppress the precipitation of r-phase. If the r phase is formed, the r phase is a nonmagnetic material that impairs its magnetic properties and it is difficult to control all conditions of the heat treatment. However, it should be noted that the addition of 5% or more of X elements lowers magnetic characteristics such as saturation magnetization.

[Dissolution and solution treatment]

Melting is carried out in a high frequency induction furnace and in a vacuum or Ar atmosphere. After dissolution, it is made into ingot state and then manufactured as a rod-like sample by forging and groove-rolling. This rod-shaped sample is subjected to a solution treatment at a temperature in the range of 1000 ° C-1250 ° C for about 30 minutes to 2 hours.

Solvent-treated samples set the solution and processing temperature by confirming the precipitation of the phase by X-ray, metal, and optical microscope. When the α-phase accelerating element (Co, N) increases, the solution-processing temperature increases and the α-phase accelerating element If the amount is large, the solution treatment temperature is low.

[Stress Aging]

Stress aging is a manufacturing method developed in the present invention, which causes spinoidal decomposition while applying stress from the outside so that the α phase (iron, cobalt, floating phase) is elongated parallel to the tensile stress direction and perpendicular to the compressive stress. to be.

Existing manufacturing process uses magnetic field heat treatment (aging) method to induce morphological anisotropy of α ₁ particles. The magnetic field aging method should apply a strong magnetic field (about 2KOe) from the outside, but to apply magnetic field to solenoid It uses a magnetic field from the DC current through it. Therefore, the electrical energy loss is considerable, which acts as a factor to increase the cost of the Fe-Cr-Co-X alloy. On the other hand, if the stress aging method using gravity is adopted, there is no energy consumption required to apply the magnetic field in the magnetic field aging method, and thus the manufacturing cost is reduced, which is advantageous in terms of price.

The principle of this stress aging is as follows.

When spinodal decomposition occurs, an internal strain occurs due to a difference in composition of the α ₁ phase and the α ₂ phase, and an internal stress is generated by the deformation.

When the tensile stress is externally applied during spinodal decomposition, the internal stress is relaxed when the decomposed particles are formed parallel to the tensile stress direction by the reaction with the internal stress generated by the spinodal decomposition, resulting in lower free energy of the system. do.

Therefore, when the aging heat treatment of spinodal decomposition is applied while applying tensile stress from the outside, the decomposed spinodal particles can obtain a form in which the α ₁ particles elongate in the tensile stress direction, that is, form anisotropy.

In addition, applying compressive stress has a shape anisotropy which is elongated perpendicularly to the stress direction. After this treatment, elongated anisotropic particles are obtained, followed by secondary aging after increasing the stability of the particles by slow cooling.

[Secondary Aging Heat Treatment]

The sample subjected to stress aging is subjected to secondary aging in order to increase the composition difference between the decomposed phase, that is, α ₁ (Fe, Co floating phase) and α ₂ (Cr floating phase).

2nd aging is to the decomposition phase by slow cooling to 4-10 ℃ / hr from a temperature completing the stress aging up to 500 ℃ a composition nearly close to the equilibrium composition of the ferromagnetic particles of the α ₁ so as to give a concentration of Fe and Co high In addition, by increasing the concentration of Cr in the non-magnetic particles of α ₂ to increase the difference in the saturation magnetic density (Ms) of the magnetic α ₁ and non-magnetic or weak magnetic particles to improve the overall magnetic properties. Aging completed up to the secondary aging treatment is cooled to form the desired shape by external processing.

The magnetization of aging made in this way has similar or slightly lower magnetism to that of the magnetic field aging sample instead of stress aging. The detailed results are as follows.

Example 1

In Example 1, 20-30 wt% of chromium, 10-17 wt% of cobalt, and 1-5 wt% of an α-phase forming element are considered to be usable as an iron-chromium-cobalt-X-based alloy. Representative alloy components of the alloys were selected and performed as shown in Table 1.

Samples of the chemical compositions shown in Table 1 were carried out by changing To from 710 ° C to 620 ° C in the same process as in FIG. 2B.

At this time, the external stress was subjected to external stress aging at 6.5 Kg / mm 2 for 30 minutes, and cooled to 600 ° C. at 60 ° C./hr for 30 minutes and then subjected to secondary aging.

The resulting magnetic properties are shown in FIG. 4.

TABLE 1

Chemical composition of the used sample (wt%)

In FIG. 4, the reason for the sharp drop in magnetism between 690 ° C. and 700 ° C. is because the spinodal decomposition temperature of the sample used in the experiment is around 690 ° C., so no spinodal decomposition occurs at 700 ° C., which has the effect of heat treatment without stress. will be.

This was confirmed by electron microscopy. If the Co content of the sample is lower than 15.7wt%, the spinodal decomposition temperature is lowered and the decomposition rate is slowed down, and the adjustment difference between a ₁ and a ₂ is decreased so that the magnetic property is gradually lowered. The magnetic property becomes low as max is 2.8MGOe.

As a result, the samples used for stress aging are advantageous as the cobalt content is as high as possible. In addition, the magnetization increases considerably compared to the case of heat treatment without stress ((BH) max = 0.3MGOe), which becomes larger when the stress is large.

Example 2

When the samples of the chemical composition shown in Table 1 were subjected to stress aging at 660 ° C. for 30 minutes, the magnetic properties according to the magnitude of the external stress are shown in FIG. 5. As can be seen in FIG. 5, when aging without stress, the magnetic property has a magnetic property as low as (BH) max of about 0.3 MGOe, whereas the magnetic property is improved as the external stress increases.

This occurs because the form anisotropy induced by external stress becomes large, and the highest magnetic property is almost the same as that of the sample subjected to the magnetic field aging treatment.

However, when the external stress is less than 9.5Kg / mm2, the magnetism decreases because the external stress is so large that greep cavity and intergranular crack are generated, and the stress that is actually received by the decomposition phase is low due to the occurrence of internal defects. This is due to the occurrence of stress relaxation mechanisms in the material as well as having an effect.

Example 3

When the aging time of the sample shown in Table 1 was changed to 15 minutes, 30 minutes, and 45 minutes under a stress of 6.5 Kg / mm2 at 660 ° C, the magnetic property change is shown in FIG.

In FIG. 6, the stress aging time of 15 minutes is not enough to induce form anisotropy, so that the magnetism is relatively low, the best magnetism is obtained in about 30 minutes, and the magnetism decreases when stress aging for 45 minutes. It can be seen that.

This reason can be considered to occur because the morphological anisotropy is rather reduced by the growth of decomposition particles when the aging time is longer. In general, it is known that the magnetic field has the highest magnetic value when the magnitude of the width direction of α is about 400 mW. After all, about 30 minutes is most appropriate. The lower the temperature, the longer the time for maximum magnetism.

In the above three examples, magnetisms such as Br: 14500G, He: 595Oe, and (BH) max: 5.3 MGOe were obtained, which resulted in a magnetic magnet almost similar to that of a magnetic field aged sample, especially in terms of price. Could get a favorable magnet.

It is possible to replace Alnico-V with magnetic properties similar to that of Alnico-V magnets, and to replace the magnetic field aging process with stress aging.

Claims (1)

The alloy is 20-30wt% Cr, Co 12.5-15.7, X (X is α forming element: Ti, V, Al, Zr, Si, W, etc.) 1-5wt% range and the rest is Fe In the method of manufacturing permanent magnets made of alloys, stress aging under stress of 1 kg / mm2 -9.5 kg / mm2 for 15-45 minutes at 600 ° C-710 ° C temperature range results in a (BH) max range of 2-6MGOe. Method for producing by the stress aging of iron-chromium-cobalt-X permanent magnets, characterized in that the.

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