JPH01219142A - Rare earth magnetic material excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a permanent magnet excellent in corrosion resistance without deteriorating magnetic properties by specifying respective contents of Nd, Pr, and Dy as rare earth elements and also incorporating specific amounts of Cr or further Co at the time of manufacturing an Fe-B-rare earth-type permanent magnet. CONSTITUTION:At the time of manufacturing an Fe-B-rare earth-type permanent magnet, 1-15% by atom., in total, of Nd and Pr and 0.2-3.0% Dy are incorporated as rare earth elements in the composition and also the total content of the above rare earth elements Nd, Pr, and Dy is regulated to 12-17atom.%, and further, the above composition consists of, besides the above rare earth elements, 5-14%, by atom., of B, 0.2-2.0% Cr, and the balance Fe or further contains 0.5-20% Co. As to the structure, the main phase is composed of R2Fe14B tetragonal magnetic compound (where R means rare earth elements) and a part of Fe in the above is substituted by Cr or further Co, by which the permanent magnetic excellent in corrosion resistance without deteriorating the characteristics as a magnet can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application The present invention relates to a Fe-B-R rare earth permanent magnet having high magnetic properties, and a rare earth, boron, Regarding iron-based permanent magnets.

BACKGROUND TECHNOLOGY The applicant has previously proposed that the applicant does not necessarily require expensive Sm or Co, but uses resource-rich light rare earths such as Nd and Pr as rt+-C-, and uses B and Fe as the main components, instead of conventional rare earths. We proposed a Fe-B-R permanent magnet as a new high-performance permanent magnet that greatly exceeds the best characteristics of cobalt magnets (Special Publication No. 61-3
4242, JP-A-59-89401).

The Curie point of the magnetic alloy is generally 300°C to 37°C.
0°C, but by substituting a part of Fe with Co, a Fe-B-R permanent magnet with a higher Curie point can be obtained (Japanese Patent Laid-Open No. 59-64733, Japanese Patent Laid-open No. 59-6473) 1
No. 32104), and has a Curie point equal to or higher than each of the above Fe-B-R rare earth permanent magnets, as well as a higher Curie point (
BH) max, and in order to improve its temperature characteristics, especially iHc, a part of R of Fe-B-R rare earth permanent magnets mainly containing light rare earths such as Nd and Pr as rare earth elements (R). By containing at least one type of heavy rare earth elements such as Dy and Tb in the Fe-BR rare earth permanent magnet, the iHc is further improved while maintaining an extremely high (BH)max of 25 MGOe or more. proposed (JP-A-60-32306, JP-A-60-34005).

However, Fe-
Permanent magnets made of B-R magnetic anisotropic sintered bodies contain large amounts of rare earth elements and iron, which tend to oxidize in humid air and gradually produce stable oxides, so
When incorporated into a magnetic circuit and used for a long period of time, oxides generated on the surface of the magnet can cause a decrease in the output of the magnetic circuit and variations between magnetic circuits, and there is also the problem of contamination of peripheral equipment due to the falling off of the surface oxide. was there.

Therefore, in order to improve the moisture resistance of the above-mentioned Fe-B-R permanent magnet, the applicant has developed a permanent magnet (patent application) whose surface is coated with a corrosion-resistant metal plating layer by electroless plating or electrolytic plating. 58-162350), and proposed a permanent magnet whose surface was coated with a corrosion-resistant resin layer by spraying or dipping (Japanese Patent Application No. 58-171907).
No.).

Furthermore, we proposed a permanent magnet in which a corrosion-resistant vapor phase plating layer made of various metals or alloys was provided on the surface of a Fe-B-R permanent magnet (Japanese Patent Application No. 59-278489, Japanese Patent Application No. 60-794).
No. 9, Special Application No. 1983-7950, Special Application No. 1983-7951
No.).

However, although the corrosion-resistant vapor phase plating layer is extremely effective in improving corrosion resistance, there is a problem in that the processing equipment and productivity are low and the processing requires a large amount of cost.

Purpose of the Invention The purpose of the present invention is to improve the corrosion resistance of Fe-B-R permanent magnet materials, which exhibit excellent corrosion resistance by specifying the composition without applying any special surface treatment to improve corrosion resistance. The purpose of the present invention is to provide a Fe-B-R permanent magnet.

Summary of the Invention This invention aims to produce a Fe-B-R permanent magnet that exhibits excellent corrosion resistance without the need for surface treatment to improve corrosion resistance. As a result of investigation, rare earth elements (R) include Nd, Pr, and D.
By specifying y and containing specific amounts of B and Cr, it is possible to avoid deteriorating the magnetic properties of the permanent magnet material.
It has been discovered that an effect of improving corrosion resistance that cannot be obtained with conventional methods can be obtained.

That is, in this invention, the total of Nd and Pr is 11 at% to 15 at%, Dy 0
．． 2 at% to 3.0 at%, and the total amount of Nd and Pr and the total amount of Dy is 12 at% to 17
at%, contains 5 at% to 14 at% of B, 0.2 at% to 2.0 at% of Cr, or further contains 0.5 at% to 20 at% of Co, and the balance consists of Fe and unavoidable impurities. Phase is tetragonal 414
A rare earth magnet material with excellent corrosion resistance.

Structure and Effect of the Invention By having the above composition, this rare earth permanent magnet material has a (BH)max of 25 MGOe or more and an i
Hc 10kOe or more, 125℃, relative humidity 8
P-C-T test (Pressu) at 2 atm in 5% atmosphere.
re Cooker test), and 80°C, relative humidity 9
In a long-term holding test in a 5% atmosphere, conventional Fe
-B-R permanent magnets are coated with aluminum and exhibit significantly superior corrosion resistance compared to materials treated with chromate.

The microstructure of the Fe-BR-based sintered permanent magnet material has a main phase of R2Fe14B compound with a tetragonal structure, and the grain boundary phase contains almost no B, which is nonmagnetic at room temperature, and contains a few percent of Fe. It is composed of an R-rich phase, most of which is composed of rare earth elements, and an R1+ and Fe4B4 phase containing a large amount of B.

This eternity? The magnetic properties of ifλ stone material are dominated by the R2Fe14B tetragonal magnetic compound, which forms the main part, and this compound occupies a considerable part in terms of volume ratio.

In the case of the Fe:B-R permanent magnet alloy according to the present invention,
It is thought that the contained Cr mainly enters the R2Fe14B tetragonal magnetic compound forming the main phase by replacing a part of Fe, thereby greatly contributing to the corrosion resistance of the main phase without deteriorating the magnetic properties. .

Furthermore, when Co is added to the above composition, Co replaces iron and enters the tetragonal main phase, further increasing the moisture resistance improvement effect, and at the same time, a part of Co also exists at grain boundaries, improving its corrosion resistance. It also shows good results in the P-C-T test.

In addition, in the permanent magnet of the present invention, C is contained as an impurity in the raw materials used, and as an impurity in the manufacturing process due to the use of binders and lubricants in the raw material powder, but it has a large effect on the corrosion resistance of the permanent magnet. Conventionally, when the content exceeds 1000 ppm, the corrosion resistance decreases rapidly and a practical permanent stone cannot be obtained.
Even if about 0.00 ppm remains, a permanent magnet A material with excellent corrosion resistance can be obtained.

Reason for limiting the components In this invention, the total amount of Nd and Pr is 11at
%, the R (Nd, P
r) The rich phase is insufficient, and α-iron with a small coercive force appears, resulting in a sharp decline in magnetic properties.Also, when it exceeds 15 at%, the coercive force slightly increases, but the Br decreases, In addition, as (BI-I)max decreases as Br decreases, Nd + is preferably set to 11 at% to 15 at%.
Prff1 is in the range of 12 at% to 14 at%.

In addition, in water-based permanent magnets, Nd and Pr have almost the same functions as elements, and either one can be contained alone, but due to the raw material, when Nd is added, it is usually a few percent.
Pr is contained to a certain extent, and whether or not to actively add Pr may be appropriately selected depending on the raw material.

Dy is less than 0.2 at%, iHc and (BH)m
There is no effect of increasing ax, and if it exceeds 3.0 at%, it is effective in improving iHc, but Dy is scarce and expensive in terms of resources, and it also causes a decrease in Br, which is undesirable. It is limited to 2 at% to 3.0 at%. Moreover, a preferable range is 0.2 at% to 2.0 at%.

Furthermore, if the total amount of Nd+Pr and Dy, that is, the total amount of rare earth elements, is less than 12 at%, Fe will precipitate in the main phase metal compound, and iHc will decrease rapidly.
If it exceeds %, iHc increases to more than 10 kOe, but
The residual magnetic flux density Br decreases and BH) max25MGOe
Nd+
The total amount of Pr and Dy is limited to 12 at% to 17 at%. Furthermore, the total amount is preferably 12.2 at% to 15 at%.

If B is less than 5 at%, the iHc will be 10 koe or less, which is not preferable, and if it exceeds 14 at%,
iHc increases, but Br decreases and (BH)max
Since 20MGOe or more cannot be obtained, 5at%~14a
limited to t%.

Cr is effective in increasing iHc and improving moisture resistance,
! 1! When i contains Co, it also has the effect of improving iHc, which decreases as the amount of Co added increases, but 0.
If it is less than 2 at%, the effect of increasing iHc and improving corrosion resistance is small, and if it exceeds 2.0 at%, iH
Although it is effective in improving c, Br and (BH) max decrease rapidly, so it is limited to 0.2 at% to 2.0 at%. More preferable content is 0.5 at% to 1.5
It is at%.

Co is effective in raising the Curie point, corrosion resistance of products, oxidation resistance of raw material powder, and saturation magnetization Is.
If it is less than 5 at%, the effect of raising the Curie point and improving corrosion resistance will be small, and if it exceeds 20 at%, Co will be present at the grain boundaries.
is condensed at a high concentration, and a ferromagnetic R(Nd, Dy)-Co compound containing 30 at% or more of Co is precipitated, which facilitates magnetization reversal of the present magnet and lowers iHc. The content is 0.5 at% to 20 at%.

Moreover, if only corrosion resistance is considered, the addition of Co shows a remarkable effect even in a small amount, and the preferable range of Co is lat% to 8at%, more preferably 2at% to 6at%.

In the rare earth permanent magnet alloy according to the present invention, the remainder after containing the above elements is Fe and inevitable impurities, and the impurities are P, S, which are inevitably mixed in during industrial production.
Cu, Mn, Ni, etc. are acceptable.

Further, the content of 02 is preferably 8000 ppm or less, more preferably 6000 ppm or less.

In this invention, the total of Nd and Pr is 12 at% to 14 at%, Dy 0
．． 2 at% - 2,0 at%, and the total amount of Nd and Dy is 12.2 at% to 15 at%, B 5 at% to 8 at%, Cr 0.2 at% to 2.0 at%, or further Co 0.5 at% to A permanent magnet containing 20 at%, the balance consisting of Fe and unavoidable impurities, and whose main phase has a tetragonal structure, when a magnetic field is applied perpendicular to the pressing direction during pressing,
(BH) max30MGOe or more, iHc 13kOe
It has the above excellent magnetic properties and extremely high corrosion resistance.

Further, the permanent magnet material according to the present invention has a crystal grain size of lp
The main phase is a compound R2(Fe-Cr) type 14B having a tetragonal crystal structure in the range of m to 50 pm, and exhibits superior corrosion resistance.

Furthermore, when Co is added, the compound R2 (Fe-CoCr) type 14B is used as the main phase, and when the grain boundary phase structure contains Co, the corrosion resistance is the worst.

In this invention, Nb, Ti, V, Nb, Mo, W, AI, Zr, I-I within fat%
Even if f, Zn, Ca, and Si are contained, the effects of the present invention will not be impaired.

Examples Example 1 Electrolytic iron with a purity of 99.9%, ferroboron alloy, Nd, Dy, Co, and ferrochroma were used as starting materials, and the atomic ratio was Nd14.5D)'0.5Fe7B-x-y.
cOxB7cry, (x = 0.y = OXX = 0.y
=2Xx=6. After blending to a composition of y=2), high frequency melting was performed, and then casting was performed in a water-cooled copper mold to obtain ingots of various compositions. Although the ingot contains a very small amount of Pr, it is shown together with Nd here.

Thereafter, this ingot was coarsely pulverized with a stamp mill and further finely pulverized with a jet mill to obtain finely pulverized powder with an average particle size of 3.5 pm.

This finely pulverized powder was charged into a mold of a press machine, and 12 kOe was produced.
Oriented in a magnetic field of 1.5t/cm in a direction perpendicular to the magnetic field.
The molded product obtained by molding at a pressure of 1060°C ~
Sintered at 1120°C for 2 hours in an Ar atmosphere, and then allowed to cool, then sintered at 550°C for 1 hour in an Ar atmosphere.
A permanent magnet material with dimensions of 20 mm x 10 mm x 8 mm was obtained by aging treatment.

The results of measuring the magnetic properties of the obtained permanent magnet material were
Shown in the table.

In addition, the weight change per unit length area due to corrosion over time after being left in a constant temperature and humidity atmosphere of 80° C. and 95% relative humidity was measured, and the results are shown in FIG.

It can be seen that the permanent magnet material according to the present invention containing Cr exhibits remarkable effects in corrosion resistance and moisture resistance.

Furthermore, after the sample was subjected to specular ωF polishing, the fine structure was observed using an electron probe microanalyzer (EPMA). As a result, most of the added Cr was present in the crystals forming the main phase, and they were R2(FeCr).
It was found that 14B or R2 (FeCoCr) 14B, as a tetragonal compound, contributes to improving corrosion resistance.

The following margin Example 2 Nd13.5Pr0.5Dy0.5Fe78 in atomic ratio by the same manufacturing method as Example 1
．． 5-x-ycOxB7cry, (x=o, y=OXx
=0. y=2) (x=6.y=2).

Paraffin 115F was added and mixed to the finely pulverized ka during the manufacturing process, and the residual CM of the sintered body was adjusted to 300 ppm to 4200 ppm.

The change in coercive force iHc as the amount of C increased was measured and is shown in FIG.

In addition, the weight change per unit surface area due to corrosion after being left in a constant temperature and humidity atmosphere of 80° C. and 95% phase j = 1 humidity for 240 hours was measured, and the results are shown in FIG.

In the case of the permanent magnet material according to the present invention containing Cr, the negative effects of C that cause a decrease in corrosion resistance and a decrease in coercive force
It can be seen that %Q can be reduced.

[Brief explanation of the drawing]

Figure 1 is a graph showing the weight change of permanent r, 1'i stone 4"i over time in a constant temperature and humidity atmosphere. Figure 2 is a graph showing the change in coercive force iHc as the amount of C increases. Fig. 3 is a graph showing the weight change of the permanent magnet material in a constant temperature and humidity atmosphere as a function of the increase in the amount of C.

Claims (1)

[Claims] The total of Nd and Pr is 11 at% to 15 at%, Dy0.
2 at% to 3.0 at%, and the total amount of Nd and Pr and the total amount of Dy is 12 at% to 17
At%, it contains B5 at% to 14 at%, Cr0.2 at% to 2.0 at%, the balance is Fe and unavoidable impurities, and the main phase has a tetragonal structure.It has excellent corrosion resistance. Rare earth magnet material. 2 The total of Nd and Pr is 11 at% to 15 at%, Dy0.
2 at% to 3.0 at%, and the total amount of Nd and Pr and the total amount of Dy is 12 at% to 17
at%, contains B5 at% to 14 at%, CO 0.5 at% to 20 at%, Cr 0.2 at% to 2.0 at%, the balance consists of Fe and inevitable impurities, and the main phase has a tetragonal structure. A rare earth magnet material with excellent corrosion resistance.