KR810000626B1 - Anisotropic permanent magnet alloy - Google Patents

Abstract

A thermo-magnetic-trended anisotropic permanent magnet alloy having a residual magnetic flux density of 7,000 Gauss or more and a coercive force of 300 oersted or more, said anisotropic permanent magnet alloy prepared by subjecting an alloy consisting of 17 to 45 % by weight of Cr, 3 to 14.5 by weight of Co, 0.2 to 5 % by weight of Si and a balance of substantially iron to a sol. treatment at 600 to 1300≰C, heating the alloy in a magnetic field at 570 to 670≰C for 10 min to 5 hrs, and then aging it within 200≰C below the thermomagnetic treatment temp. for 30 min. to 50 hrs.

Description

Anisotropic Permanent Magnet Alloy

1A is a diagram showing the relationship between the alloy component and the coercive force of the present invention.

1b is a diagram showing a relationship between an alloy component and residual magnetic flux density of the present invention.

2 is a graph showing the relationship of the coercive force to the thermal magnetic treatment temperature according to the present invention.

3 is a graph showing the relationship of coercive force to thermomagnetic processing time.

4 is a graph showing the relationship of the coercive force to the cooling rate of the secondary aging treatment.

The present invention relates to a thermomagnetically-treated anisotropic permanent magnet alloy containing iron, chromium, cobalt and silicon as main components, and particularly a permanent magnet alloy having excellent processability and easy heat treatment in its product process. It is about.

Permanent magnets are currently used in motors, various instruments and electrical devices, but the required magnetism varies widely depending on the intended use.

Thus, there are various permanent magnet alloys having such magnetism, and the actual representative alloy is selected according to the magnitude of the coercive force required. For example, suitable alloys are selected from among Fe—Mn—Ti alloys, Fe—Co—V alloys, Fe—Ni—Cu alloys, and Alnico to achieve a given coercive force.

Fe-Mn-Ti alloy is excellent in workability. It has a relatively low coercive force of 50 ~ 160 Orersted.

Alnico alloys are known to have not only a wide range of magnetisms but also are generally the most useful when their component content changes, but they are too hard and brittle to process and therefore poor in workability. Fe-Co-V alloys, or "Vicalloy", are known as good workability magnets, but because they contain more than 50% cobalt and more than 10% vanadium, their high price is the only major drawback.

Fe-Ni-Cu alloys, that is, "Cunife", have excellent workability and can easily have high coercive force, but have a relatively low residual magnetic flux density. Therefore, the use of this alloy is limited.

It is an object of the present invention to provide a thermomagnetically treated anisotropic permanent magnet which is free from the above mentioned drawbacks, i.e., is inexpensive and has superior magnetic properties and better processability compared to alnico alloys.

These alloys are basically thermomagnetically treated with a weight ratio of 17% to 45% chromium, 3% to 14.5% cobalt, 0.2% to 5% silicon and residual iron, especially 23% to 35% chromium, Alloys composed of 6% to 14.5% cobalt, 0.3% to 3% silicon and residual iron have better magnetic properties.

In view of such alloy construction, these alloys exhibit excellent workability, for example, in forging, rolling, drilling or bending under high cold and hot brewing conditions.

In order to give excellent magnetism to the above-mentioned alloys, it is necessary to perform thermomagnetic treatment and then heat-aging.

The alloy before the thermomagnetic treatment needs to be metallurgically single phase.

So sometimes solution treatment is taken for this purpose. The temperature required for the solution treatment of the alloy containing the above-described components is usually in the range of 650 ~ 1,300 ° C., preferably 850 ~ 1,085 ° C. However, processing may be performed at high temperature instead of solution treatment.

According to the present invention, thermomagnetic treatment is essential for obtaining excellent magnetism.

After solution treatment or thermal processing, the alloy is aged for the first 10 minutes to 5 hours at a temperature of 570 to 670 ° C in the magnetic field. The temperature of the thermomagnetic treatment is preferably within the range of 590 to 650 ° C. . Separation into the tow phase occurs by this aging treatment. In addition, it is necessary to perform secondary aging treatment on the thermomagnetically treated alloy in order to obtain high quality magnetism.

Secondary aging is performed by heating the thermomagnetically treated alloy at a temperature within 200 ° C. below the thermomagnetic treatment temperature and then cooling to a controlled cooling rate or maintaining the alloy above at a given time for a given time. .

In any case, the secondary aging treatment is carried out for 30 minutes to 50 hours. Instead of heating to the secondary aging temperature, the alloy may be gradually cooled from the thermomagnetic treatment temperature to the secondary aging temperature at the end of the thermomagnetic treatment.

Preferred aging treatment is to gradually reduce the temperature within 200 ° C. below the thermomagnetic treatment temperature. More preferred aging treatment is obtained by continuously cooling 10 ° C or more within 200 ° C lower than the thermomagnetic treatment temperature. Cooling is performed at a rate of 5 minutes to 50 hours for a 10 ° C section. Preferred cooling rates are 15 minutes to 10 hours for a 10 ° C drop. More preferable cooling rate is 30 minutes-5 hours with respect to 10 degreeC fall. The most representative secondary aging treatment takes 10 to 20 hours to cool from 600 ° C to 500 ° C.

Next, the present invention will be described in detail.

The alloy of the present invention is basically a Fe-Cr-Co base alloy in which silicon is mixed therein.

Fe—Cr—Co based alloys are well known as spinodal alloys.

Recently, it has been found that Fe-Cr-Co based alloys containing molybdenum or tungsten are useful as permanent magnets. Such alloys are described in US Pat. No. 3,806,336. However, this alloy has excellent magnetic properties, but in terms of microstructure, solution treatment has to be performed at high temperature. The reason is that nonmagnetic austenite phae is only stable at these high temperatures because it tends to remain at room temperature. Usually, the above-mentioned solution treatment temperature is required to be 1,300 ° C., but due to the high chromium content, it is very difficult in the industrial technology to perform the solution treatment in a vacuum or an oxygen-free atmosphere, and also the fluidity of the melt is small.

In order to solve the above-mentioned drawbacks in the alloy, the inventors invented a heat-treated alloy consisting of 17 to 45% chromium, 3 to 14% cobalt, 0.2 to 5% silicon and residual iron in weight ratio. The application was filed in the United States on March 21 with application number 560,941. The heat treatment alloys described in the application show relatively low magnetic properties that are insufficient for use as permanent magnets.

An object of the present invention is to provide an anisotropic permanent magnet having excellent magnetic properties, particularly high coercive force.

It has been found that the magnetism is improved according to the invention by selecting the prescribed component ratios of the main alloy components and adding the desired silicon to this alloy.

In the alloy of the present invention, chromium is one of the most essential components. If the chromium content is less than 17%, the two-phase decomposition required to obtain permanent magnetism does not occur.

If the chromium content exceeds 45%, a phase is developed which clearly adversely affects the workability.

Therefore, alloys containing chromium content in the range of 17 to 45% are suitable for permanent magnets. In terms of magnetism, a chromium content of 23-35% gives the best results.

Cobalt plays an important role in the separation of two phases with respect to chromium, but from a microstructural point of view it is closely related to the gamma phase.

With regard to the separation of the two phases, the minimum of cobalt content is 3%. If the cobalt content is less than 3%, a coercive force of 300 Hersted or less is obtained.

The coercive force increases markedly with the increase of cobalt content, but when the cobalt content exceeds 14.5%, solution treatment becomes very difficult, and as a result, it is difficult to obtain excellent magnetism at the solution treatment temperature of less than 1300 ° C, which is technically possible.

The heat treatment is easily performed in the technical field, and the cobalt content of which excellent magnetism can be obtained is 7 to 14.5%.

On the other hand, silicon should be contained in the alloy of the present invention in an amount of 0.2% or more. However, when the silicon content exceeds 5%, workability is degraded under high cold and hot temperatures.

Considering magnetic and processability, the optimum silicon content is in the range of 0.3 ~ 3%.

The range of 0.3% -3% increases the fluidity of the alloy and prevents sedimentation.

For carbon, magnesium, calcium in the furnace and raw materials, and manganese in the deoxidizer, up to 0.1 carbon and up to 5% of calcium, magnesium, and manganese are allowed to be mixed in the alloy as impurities. This mixing adversely affects magnetism and processability.

Small amounts of molybdenum and vanadium also have no adverse effect. Manganese, molybdenum, calcium and vanadium are allowed in total by 5% by weight.

Dissolution treatment is important for homogenizing the microstructure of the alloy to achieve a constant magnetism. As mentioned above, silicon is added to relax the conditions of solution treatment.

That is, Fe-Cr-Co alloys containing no silicon usually require cooling, such as water cooled from a temperature of 1,300 ° C. or more. However, when a small amount (more than 0.2%) of silicon is applied, the high temperature region at which the austenite becomes stable becomes very narrow.

It was experimentally confirmed that the alloy of Fe-Cr-Co with 0.5% to 1% of silicon can be treated in a wide range of high temperature areas.

This is very meaningful industrially.

So the addition of silicone is very beneficial.

However, if the silicon content exceeds 5%, it certainly deteriorates the workability and adversely affects the magnetism as described above.

In order for the alloy according to the present invention to exhibit optimum magnetism, solution treatment must be followed by aging treatment in the magnetic field. Secondary aging is more necessary.

The combination of prescribed alloying components and heat treatment conditions yields optimum magnetism.

According to the present invention, the aging treatment in the magnetic field may be performed at a holding temperature of about 620 ° C., but may be performed at a holding temperature raised to 700 ° C.

The optimum aging treatment condition to have the best magnetic properties for the alloy of the present invention is a temperature range of 570 ~ 670 ° C for a time of more than 10 minutes.

Thermomagnetic treatment is carried out in the temperature range of 590 ~ 650 ° C as possible, but the thermomagnetic treatment temperature to obtain the optimum magnetism varies depending on the components.

A time of 5 hours or less is suitable, and more than that, it is uneconomical. The secondary aging treatment is performed after the thermomagnetic treatment. The thermomagnetically treated alloy is heated at a temperature within 200 ° C. below the thermomagnetic treatment temperature and then gradually cooled below at least 10 ° C. at the initial temperature.

Secondary aging is performed for 30 minutes to 50 hours.

1 (a) and 1 (b) show the relationship between the component and the magnetic, in particular coercive force (Hc) and residual magnetic flux density (Br), respectively, under constant melt heating and aging treatment conditions.

1 (a) and 1 (b) show the contours of Hc and Br for alloys containing 1.5% silicon and a large amount of chromium and cobalt, respectively. After solution treatment, the solution was aged at 600 ° C. for 1 hour in a 4,000 Oe magnetic field and subsequently aged at 580 ° C. to 480 ° C. at a cooling rate of 6.25 ° C. per hour.

The following shows an embodiment of the present invention.

Example 1

A few samples were prepared consisting of 30% chromium, 10% volts, 1.5% silicon and residual iron.

They are solution treated for 20 minutes at 1,000 ° C and then aged at various temperatures for 1 hour in a magnetic field of 4,000Oe. Thermomagnetically treated samples were cooled aging for 16 hours with a 100 ° C drop from 580 ° C to 480 ° C.

The curve partitioned by the zero mark in FIG. 2 shows the relationship between the thermomagnetic treatment temperature and the coercive force shown in the above sample. Another sample was prepared consisting of 30% chromium, 14% cobalt, 1.5% silicon and residual iron.

They are solution treated and aged at various temperatures for 1 hour in a magnetic field of 4000Oe.

They are secondary aged by dropping 100 ° C from 600 ° C to 500 ° C for 16 hours.

Their coercive force is shown by the curve partitioned by the △ mark in FIG. There is another sample consisting of 35% chromium, 8% cobalt, 2.5% silicon and residual iron.

They are solution treated and aged at various temperatures for 1 hour in a magnetic field of 4000Oe.

They are also aged through 100 ° C cooling from 560 ° C to 460 ° C for a second 16 hours.

Their coercive force is shown in FIG.

There is another sample consisting of 24% chromium, 12% cobalt, 0.5% silicon and residual iron.

They are heat treated at 1,300 ° C for 10 minutes and then aged at various temperatures for 1 hour in a magnetic field of 4000Oe.

They are then secondary aged by cooling from 620 ° C to 500 ° C at a rate of 100 ° C drop in 16 hours.

Their coercive force is shown by the curve partitioned in the table of FIG. According to Figure 2 it can be seen that the thermal magnetic treatment of 570 ° C ~ 670 ° C gives a coercive force for the alloy described above, the thermal magnetic treatment of 590 ° C ~ 650 ° C gives a better coercive force.

Example 2

There is a sample consisting of 30% chromium, 10% cobalt, 1.5% silicon and residual iron.

After solution treatment they are aged at 600 ° C for several hours in a magnetic field of 4000Oe.

They are second aged by cooling from 580 ° C to 480 ° C at rates falling 100 ° C in 16 hours.

The coercive force of the heat treated sample is shown in FIG.

3 shows that the thermal magnetic treatment for 10 minutes or more gives a coercive force of 300Oe or more, and the thermal magnetic treatment for 30 minutes gives a coercive force close to the maximum.

Example 3

There is a sample consisting of 30% chromium, 10% cobalt, 1.5% silicon and residual iron.

They are solution treated and then thermomagnetically treated for 1 hour similarly to Example 2.

Thermomagnetically treated samples are cooled and aged from 580 ° C to 480 ° C at various cooling rates.

4 shows the coercivity of these samples for the time it takes for the secondary aging temperature to drop by 10 ° C. It can be seen that it takes at least 30 minutes for 10 ° C drop to obtain a coercive force of more than 300Oe.

Example 4

Alloys containing 30% chromium, 10% cobalt, 1.5% silicon and residual iron are solution treated at 1,000 ° C for 20 minutes in air and then aged at 600 ° C for 1 hour in a magnetic field of 4000Oe. Thermomagnetically treated alloys are secondarily cooled and aged from 580 ° C to 480 ° C with a cooling rate of 100 ° C for 16 hours.

This results in an anisotropic permanent magnet with a magnetic flux density of 11,700 gauss (Br), a 520 Hersted magnetic force (HC) and a maximum energy of 4.4 × 10 ⁶ Gaussian Ersted (multiplied by magnetic flux density and coercive force). Lose.

Example 5

Alloy containing 25% chromium, 8% cogant, 1.5% silicon and residual iron, solution treated at 900 ° C for 30 minutes, then aged at 620 ° C for 1 hour in a magnetic field of 4,000Oe, and subsequently Secondary aging is performed by cooling from 600 ° C to 500 ° C with a cooling rate of 100 ° C for 16 hours.

Thus, an anisotropic permanent magnet having a magnetic flux density (Br) of 12,300 gauss, a coercive force (Hc) of 410 Hersted, and an energy of up to 3.5 x 10 ⁶ Gaussian Erstedt is obtained.

Example 6

Alloys containing the components listed in the following table exhibit excellent magnetic properties, which are subjected to the heat treatment according to the present invention. They were solution treated at 1,000 ° C for 20 minutes, then aged at 600 ° C for 1 hour in 4,000Oe and in a magnetic field, again from 580 ° C to 480 ° C with a second cooling rate of 16 hours per 100 ° C. It is cooled and aged.

As shown in the results table, impurities such as manganese, molybdenum, calcium and vanadium are added in small amounts that do not adversely affect magnetism.

[table]

Claims (1)

Alloys containing 17 to 45% chromium by weight, 3 to 14.5% cobalt, 0.2 to 5% silicon and residual iron are solution treated at a temperature of 600 to 1300 ° C, and then 570 for 10 minutes to 5 hours. Thermomagnetic treatment by heating in a magnetic field under a temperature of 670 ° C, and aged at a temperature within 200 ° C lower than the thermal magnetic treatment temperature for 30 minutes to 50 hours, the residual magnetic flux density of more than 7,000 gauss and 300 ersted Anisotropic permanent magnet alloy with the above coercive force.

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