JPH02250920A - Production of rare earth element-transition element -b magnet by forging - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Field of application of soil collection a] The present invention relates to a method for producing a rare earth element-transition element-B magnet having an alloy structure with little orientation, and in particular, relates to a method for manufacturing a rare earth element-transition element-B magnet. A permanent magnet with excellent magnetic properties that ensures good lubricity between the capsule material and the alloy material and reliably imparts high orientation when encapsulated in a metal capsule and hot-processed. This relates to the manufacturing method. Although the following explanation will be based on hot forging, which is a typical example of hot working means, the scope of the present invention is not limited thereby.

[Prior Art] Rare earth magnets are attracting attention as the third type of permanent magnet after ferrite magnets and alnico magnets. This rare earth magnet is expected to have excellent magnetic performance that can contribute to the miniaturization and higher precision of electrical products and precision instruments.
Active progress is being made on both the research and production sides.

Among them, the ones that have been particularly promising in recent years are rare earth element-transition element-B permanent magnets such as Nd-Fe-B and Pr-Fe-B, and recently Cu and Ag have been used as the fourth constituent element. The permanent magnet composition targeted by the present invention includes all of these cases, and the details will be described later. Rare earth elements in
For the sake of convenience, we will discuss a ternary element-B system (hereinafter abbreviated as RE-TM-B system magnet) as a representative example.

Initially, two methods were considered for producing RE-TM-B magnets.

The first method is the sintering method, but this method requires the following: (1) It is necessary to pulverize the alloy prior to the sintering process; Oxygen carried into the body has a negative effect on magnetic performance; ■ Magnetic performance is reduced due to the inclusion of carbon from forming aids added during sintering; ■ The formed body before sintering has a low Because of several drawbacks such as strength and poor handling, the characteristics expected of RE-TM-B magnets have not been fully demonstrated.

The second method is to make a bonded magnet using a thermoplastic resin etc. after making a quenched flake, which does not have the above drawbacks, but has the following disadvantages: 1. Low productivity; 2. In principle, only isotropic magnets can be obtained. Therefore, the maximum energy product [hereinafter expressed as (BH) + s], which is the product of residual magnetic flux density and coercive force, is low.
There are drawbacks such as poor squareness. Therefore, as a means to actively make the material anisotropic, it has been considered to subject the rapidly cooled flakes to a two-step hot press treatment (mechanical orientation treatment). However, this is not a realistic method considering the need for mass production, since the productivity is even lower.

Therefore, as a third method, hot rolling is applied to the cast alloy to achieve finer grain size and increase coercive force, as well as aligning the crystal axes in a specific direction to create magnetic anisotropy. The present applicant and others are conducting separate research on various operating conditions for carrying out hot rolling.

[Problems to be Solved by the Invention] As stated above, the main point of the development approach for rare earth magnets is to improve (BH) and □. However, the improvement of (B The cast structure obtained in the process is refined through hot working, and further refined into RE2-T, which becomes the main phase in the permanent magnet.
It is necessary to form and arrange M14-B (see below) with higher precision, and for this purpose, it is desirable to lower the strain rate during hot working. However, in the case of hot rolling according to the third method, if the strain rate is attempted to be reduced, the temperature of the workpiece will decrease during the rolling process, and as will be described later, improvements in coercive force and residual magnetic flux density cannot be expected. The problem arises that it disappears. Therefore, in the hot rolling method, it is necessary to conduct studies to prevent the above-mentioned drawbacks from occurring.

Therefore, the present inventors have been researching a fourth method for producing rare earth magnets, in which a cast alloy or a rolled material obtained by hot rolling the alloy is subjected to hot forging. The alloy ingot commonly used for forging is a rod-shaped piece (rectangular parallelepiped) with a rectangular cross section from the viewpoint of forming a columnar crystal structure in alloy casting, and the columnar crystals extend in a direction perpendicular to the axis of the rod. There is. Moreover, the same shape and crystal composition are obtained by hot-rolling the same. During forging, press pressure is applied in a direction perpendicular to the growth direction of the columnar crystals, that is, in a direction that compresses and densifies adjacent columnar crystals. It also spreads in the direction of elongation (corresponding to the width direction of the alloy ingot). However, the above-mentioned expansion in the sheet width direction has a problem in that the density of the forged piece, which is formed at both ends in the sheet width direction, is insufficiently increased. Therefore, if a forging method is used haphazardly, it is not possible to obtain magnetic anisotropy over the entire width direction of the plate.Moreover, if a desired degree of crystal axis orientation is to be formed by forging, a considerable amount of magnetic anisotropy cannot be obtained. There is also a problem in that the alloy composition of rare earth magnets is largely restricted because strong working is required and a material with workability that can handle this is required.

Therefore, when forging the alloy material, we considered restraining the alloy material from the left and right sides in the sheet width direction to prevent the alloy material from spreading in the sheet width direction when receiving external forging force. In this way, the alloy material that is rolled down in the thickness direction under forging external force will release almost all of the volume reduction due to the reduction in the form of being expanded in the longitudinal direction, and the released alloy material will be rolled out in the longitudinal direction. is strongly consolidated between the upper and lower forging dies, and the orientation of the crystal axis in a specific direction is completed over the entire length of the forged product. Comparing the state after forging is completed with the alloy material before forging, it is found that the plate thickness direction is reduced in accordance with the external forging force, but in the plate width direction, restraining force is applied from both sides, so it is extremely There is only a slight extension in the cross section, resulting in a decrease in area in the form of a decrease in thickness, and this decrease is almost entirely balanced by elongation in the longitudinal direction.

The long plate material obtained by such forging has good crystal axis orientation not only in the width direction but also in the longitudinal direction, and has magnetic anisotropy throughout the width and length directions. shows.

However, even if metal capsules are forged based on the above concept, it is necessary to improve the coercive force by making the crystal grains finer by pressing the alloy material, and to improve the magnetic anisotropy by mechanical orientation. , it is necessary to carry out hot forging under such high heat conditions as to form a liquid phase in the alloy material. However, if an attempt is made to perform hot forging by applying such high heat to bring the alloy material into a semi-molten state, the alloy material will fuse to the surfaces of the upper and lower molds, making operation impossible.

Therefore, it was considered to separate the alloy material by encapsulating it in a metal capsule made of a material with a higher melting point. However, this time, a problem arises in that the melt of the alloy material is fused to the inner surface of the metal capsule, and further diffusion of the alloy components occurs, causing the alloy material and the metal capsule to become integrated. If this kind of integration occurs, ■ it is impossible to separate the two after forging is completed, and it becomes necessary to separate them by cutting by machining, resulting in a decrease in yield due to cutting loss, and ■ physical properties change due to the above-mentioned diffusion. This may cause the metal capsule to crack and some of the semi-molten alloy material inside may come out, or the alloy ingot may undergo surface cracking due to dilution of the alloy composition, and cracks may adhere to the metal capsule side. Furthermore, cutting the rare earth magnet to remove the cracked parts leads to a decrease in yield, and furthermore, when the cracks become noticeable, the product must be treated as a defective product and sent for remelting. Many drawbacks arise.

The present invention has been made in view of these circumstances, and has been developed to meet the technical requirements of not causing the above-mentioned disadvantages in hot forging using metal capsules, especially the lubrication state between the capsule and the alloy ingot. It was completed by searching for requirements that could be maintained in good condition.

[Means for Solving the Problems] The method of the present invention completed as a result of the above research contains at least a rare earth element, a transition element, and B as core components, and has a thickness of three times or more relative to the plate thickness in the processing direction. A long alloy material is encapsulated in a metal capsule via a lubricant, and the metal capsule is constrained from the width direction while the processing temperature is set to 750 to 1100°C so that the alloy material contains a liquid phase. Hot working is performed as a state, and at this time, the hot working is performed so that the total working rate is 50% or more, and a lubricant holding material is interposed in the lubricant layer between the metal capsule material and the alloy material. is an essential configuration requirement. As a result, a highly oriented alloy structure was successfully formed without causing the above-mentioned disadvantages, and the RE-
TM-B magnets exhibit excellent magnetic properties.

[Function] The alloy composition constituting the RE-TM-B magnet of the present invention will be explained.

First, as rare earth elements, in addition to Y, there is La.

Ce, Pr, Nd, Pm, Sm, Eu, Gd.

Lanthanide rare earth elements such as Tb, Dy, Ho, Er, Tm, Yb and Lu are commonly used, but actide elements can also be used if necessary, and one or two selected from these elements. Use a combination of the above. Among these, particularly preferred are Pr, Ca, Nd, etc.

As the transition element, particularly iron group elements such as Fe, Co, and Ni are used.

When the ternary alloy of RE-TM-B is used as the target alloy of the present invention, there are no particular limitations on the composition ratio of each element, but it is recommended that the composition ratio of each element be selected in accordance with the following criteria. Ru.

The appropriate amount of rare earth elements is 8 to 25 at%, and if it is less than 8 at%, the main phase RE2-7M1 in the above ternary permanent magnet
4- B (atomic ratio, e.g. Pr2re14n) cannot be formed, resulting in a cubic crystal structure with the same structure as α iron, and good magnetic properties cannot be obtained. Cracks tend to occur during rolling. On the other hand, at the upper limit, 25 magnetic properties cannot be exhibited.

Transition elements are essential elements for magnetic phase formation, and 6
A suitable amount is 5 to 90 atomic %, and if it is less than 65 atomic %, the amount of non-magnetic phase is insufficient. On the other hand, if it exceeds 90 atomic %, the amount of rare earth elements decreases, and the drawbacks mentioned in the explanation of rare earth elements become apparent.

The most typical transition element is Fe, but C
When O is used in combination, the effect of improving the Curie point can be obtained.

B is preferably 2 to 10 atomic %, and if it is less than 2 atomic %, it becomes a rhombohedral RE-TM system, making it impossible to obtain a high coercive force.

On the other hand, the upper limit may be set at 10% in order to exhibit good workability in the casting-hot rolling process and, as a result, to exhibit good magnetic properties.

The rare earth magnet of the present invention is typically a ternary alloy in which one element is selected from each of the above ternary elements; a combination of two elements, a combination of three elements of Ce, Pr, and Nd, etc.), or a combination of two or more elements selected from the group of transition elements (for example, a combination of Fe and C).
The scope of the present invention also includes multi-component permanent magnets such as quaternary, quinary, etc., in which magnets are appropriately combined.

Furthermore, when a fourth element such as Cu or Ag is added to the RE-TM-B system, the coercive force and squareness are further improved, and an improvement in (BH)□8 is observed. Furthermore, since the plastic workability is improved, even better magnetic anisotropy can be obtained, and therefore RE-TM-B-Cu series and RE-TM
-B-Ag type magnets and the like also provide excellent anisotropic magnets by application of the present invention, so such magnets are also included within the scope of the present invention.

In addition to the above, it is also possible to contain A1, Sl, etc., and it is also good to try to improve the coercive force by adding a small amount within the limit that does not reduce the residual magnetic flux density.

The alloy ingot having the above-mentioned composition is housed in a metal capsule, but in view of the fact that the hot rolling of the present invention is carried out at a high enough temperature to generate a liquid phase in the alloy ingot, the metal capsule is is a material with a higher melting point than the alloy ingot, e.g. melting point 6
Mild steel with a temperature of 00°C or higher, structural steel, stainless steel, etc. are used.

When the alloy ingot is encapsulated in the metal capsule, a lubricant is interposed at the contact interface between the alloy ingot and the metal capsule. As lubricants, it is desirable to use various glass-based lubricants, boron nitride, alumina, sialon, and zirconia that stably exhibit their effects even under high heat. Any material that can protect the lump and the metal capsule from being integrated under hot forging conditions is applicable to the present invention.

In the hot forging of the present invention, the alloy material-filled metal capsule 3 configured as described above is placed in the groove 2 of the lower mold 1 as shown in FIG. The metal capsule 3 is rolled down in the thickness direction while being expanded in the longitudinal direction within the groove 2. By using such a forging method, metal capsule 3
Since the metal capsule 3 and, therefore, the alloy material sealed therein are rolled down in a manner that is constrained from the sheet width direction by the grooves 2a, the metal capsule 3, and therefore the alloy material sealed therein, is consolidated while being prevented from spreading in the direction of columnar crystal growth. , excellent directionality of crystal axis orientation can be obtained. Note that the method of restraint does not limit the present invention.

By the way, in the lubrication at the contact interface between the metal capsule and the alloy ingot, lubrication of the principal stress surface during machining plays an important role. Therefore, it is necessary to apply a sufficient amount of lubricant to the surface of the upper mold protrusion on which surface pressure is applied (the surface facing the protrusion of the alloy material), but even if sufficient lubricant is applied (for example, boron nitride etc. Even if the coating is applied to the above-mentioned principal stress surface of the alloy material to a thickness of 1.0%), when the processing rate reaches 80% or more, a large amount of spreading occurs, and the spreading of the lubricant cannot cope with this and the lubricant runs out. This causes seizure of the alloy material and metal capsule, and cracks occur in the alloy material.

Therefore, in the present invention, a lubricant retaining material is interposed in the lubricant layer between the metal capsule material and the alloy material, thereby increasing the amount of lubricant retained and ensuring that the lubricant spreads evenly under heavy working conditions. Prevents lubricant from running out. The lubricant retaining material is not particularly limited, but examples thereof include thin metal plates, porous plate metal members, wire mesh metal members, etc. These lubricant retaining materials may be made of the same material as the metal capsule. It is desirable that the structure be made of the same material. To further explain the case where a thin metal plate is used as an example, as shown in FIG. 2 (cross-sectional view in the width direction), a lubricant layer is formed between the four circumferences of the alloy material A and the metal capsule. Metal thin plates Bl and B2 are placed on the lid at positions corresponding to the upper and lower surfaces (upper and lower surfaces in the drawing) of the alloy ingot A in the lubricant layer.
are attached to each, and then enclosed in a metal capsule C. As a result, alloy material A and metal thin plate B1. A lubricant is present at the interface of Ba, the thin metal plate B+, and the interface of Ba and metal capsule C, respectively. That is, a lubricant layer is formed twice between the alloy material A and the metal capsule C,
A relationship is formed in which the lubrication functions are mutually supplemented. Therefore, even if the alloy material A and the thin metal plates Bl and B2 were to seize, the lubricating function would be maintained between the thin metal plates B+ and B2 and the metal capsule C, and as shown in the example below, the cracking limit of the alloy material A would be Improve dramatically. The alloy material A and the thin metal plates B1 and B2, which are stuck together due to seizure, may be separated separately by machining such as cutting. In the case of metal thin plates, the table/
By retaining the lubricant on the back surface, the lubricant layer formation effect is exhibited.
(see figure), the lubricant penetrates into the interior of these metal members and supplies the lubricant to the upper and lower surfaces of the metal members, that is, the interface on the alloy ingot side and the interface on the metal capsule side, so the upper mold Even if surface pressure from the protrusions is applied, the lubricant is less likely to run out (see Examples below).

Basically, it is sufficient to interpose one such lubricant holding member on the upper and lower surfaces of alloy material A, but of course two lubricant holding members are required.
More than one sheet may be provided, or the number of sheets may be different on the upper and lower surfaces.

When carrying out hot forging, the forging temperature can be set as appropriate by considering the forging schedule, but the lower limit temperature is determined by the need to generate a liquid phase in the alloy ingot for the reasons mentioned above. , 750° C. or higher, that is, even if the rolling temperature is lower than 750° C., both the coercive force and the residual magnetic flux density are insufficient, and there remains dissatisfaction with using rare earth magnets as permanent magnets. Further, if the temperature is less than 750°C, the deformation resistance becomes large and cracks are likely to occur.

On the other hand, it is preferable to set the upper limit based on the forging schedule as mentioned above.If the desired reduction rate is to be reached at once by one forging, it is sufficient to set the upper limit to about 1000℃, while forging is divided into two or more times. If this is the case, it is desirable to heat the product to a high temperature in advance, as heat dissipation occurs during the pause between each forging process and the deformation resistance in the subsequent forging becomes excessive, but the upper limit in this case is also around 1100°C. Just think about it.

The appropriate temperature range for hot forging was determined as described above, but despite forging within the above temperature range, cracks may be observed in the forged product depending on the relationship between the dimensions of the alloy material and the reduction rate. was there.

Figure 4.5 summarizes these relationships; Figure 4 shows the strain rate when the strain rate is 10-''/sec, and Figure 5 shows the strain rate when the strain rate is 10-''/sec. Although the former is preferable in terms of productivity and formation of crystal axis orientation in the permanent magnet, the former is preferable in terms of the risk of cracking during forging, as will be described later based on Figure 4.5, and is not practical. During operation, these points should be comprehensively judged to determine operating conditions.In other words, in Figure 4.5, the horizontal axis is the length ratio of the alloy material before forging, and ho is the thickness of the alloy material before forging. Therefore, the larger 10/h O is, the longer it is compared to the thickness. On the other hand, the vertical axis is the rolling reduction ratio, and hl indicates the thickness of the alloy material after forging. Therefore, ho/h s is The larger the value, the greater the reduction.

In these graphs, the * mark means there is a crack, the 0 mark means no crack, and the upward-sloping curve passes through the boundary between the * mark and the 0 mark, indicating the crack limit, and the numbers attached to each mark are obtained. (BH) □ of a permanent magnet manufactured from a forged product,
As seen in Figure 4.5, it can be seen that the longer the alloy material before forging is, the less cracks occur and the more it can withstand a larger rolling reduction.

The cracks before forging are thought to be caused by the formation of a rigid region inside the alloy material directly under the upper die, and the maximum shearing occurring along the boundary with the non-rigid region. Looking at Figure 4.5 from this perspective, in Figure 4 where the strain rate is slow, if the length ratio of the alloy material is 3 or more, no cracks will occur even if the reduction ratio per press is up to 50%. I understand.

In FIG. 5, where the strain rate is fast, if the length ratio of the alloy material is 4 or more, no cracking occurs even if the reduction ratio per press is up to 50%. Therefore, if an alloy material with a length ratio like the one above is forged in two or more presses, the reduction will occur with each press, and the length ratio of the alloy material may actually increase when purchased. This works advantageously and allows the desired reduction ratio to be reached without cracking. If the length ratio of the alloy material is set to 4 or 5 or more in the case of Fig. 4, and 5 or 6 or more in the case of Fig. 5, a large rolling reduction ratio that does not cause cracking is allowed, so it is possible to reduce the thickness at once with one press. It becomes possible to reach a desired rolling reduction ratio.

It goes without saying that a mold lubricant may be used in combination with each press, and all known lubricants such as glass-based lubricants can be used.

The explanation so far has been about the case where one alloy material is enclosed in a metal capsule and forged, but next we will discuss an embodiment where multiple alloy materials are enclosed in one capsule and forged at once. state

That is, it is a method in which a plurality of alloy materials are lined up in the width direction and/or length direction, enclosed in a metal capsule, and forged, and the interface between adjacent alloy materials in the width direction and/or length direction is
There are two cases: a case where a lubricant as mentioned above is used to prevent them from being integrated due to external forging force, and a case where each alloy material is actively joined and integrated without the use of a lubricant. There is a street. In the former case, it is used when manufacturing multiple pieces of forged material at once under the same forging conditions, which can equalize the quality of rolled products and contribute to improving productivity, while in the latter case, multiple pieces of alloy It is used when manufacturing large permanent magnets by integrating materials.

The reason why the alloy materials were not arranged in the height direction in any of these cases was because we wanted to orient the plates so that the width of the plates was larger than the thickness of the plates to improve magnetic energy and prevent cracking during rolling. This is due to a reason. In addition, in each of the above explanations, two methods were described: whether or not to mix a lubricant between adjacent alloy materials, but at the interface where the outer surface of the alloy ingot and the inner surface of the metal capsule contact, In order to avoid the various disadvantages mentioned above, it is desirable to have a lubricant present.

Among the above-mentioned embodiments, the method of forging a plurality of alloy materials by arranging them in the longitudinal direction without using a lubricant is useful as a means for producing long forged materials. The method of forging them side by side is useful as a means of producing wide forged materials. Furthermore, when forging a plurality of alloy materials side by side with a lubricant in the sheet width direction, separation of the alloy materials can be facilitated by interposing a lubricant retaining material such as the wire mesh member. .

[Examples] Example 1 Capsules with the following dimensions were manufactured using the composition shown in Table 1. The ingot dimensions are shown in parentheses.

30 haze ■' x 30mm" x 120mm' (
lo/Ho・4) (24) (24) (11
G) Table 1 After applying boron nitride to the outer surface of this ingot, 5IOC thin plates (1 am thick) were attached to the upper and lower surfaces of the ingot, respectively.
Further, boron nitride was applied to the exposed surface of the thin plate and sealed in a metal capsule 5 made of 510C to form a forging material. The thickness t of the upper and lower plates of the metal capsule 5 was 3 mm. This metal capsule was divided into two groups, and the first group was heated to 950°C.
Lower forging die (1-500mm) via glass-based lubricant.
) and press once (strain rate 10””/sec)
) was forged to the following dimensions.

40 haze ■' x 7. Smmh x 480mm'
The second group was forged in the same manner as the first group except that the strain rate was 10-'/sec.

The presence or absence of cracks and the (Bl()+, □) of the forged product were measured and the results were as shown in Figure 4.5.

Example 2 In order to confirm the anti-seize effect of the lubricant retaining member, a thin metal plate or a mesh plate was interposed in the lubricant layer between the alloy ingot and the metal capsule (Examples I and II). ,
When the internal crack occurrence rate was compared in the case where no intervening material was placed (comparative example) by hot forging according to the method of Example 1, the results shown in FIG. 6 were obtained.

As the metal thin plate, a 5toc thin plate with a thickness of 1 inch was used. The mesh plate used was made by weaving 5US 0.1 mm wires at a pitch of 0.3 mm.

As shown in FIG. 6, in Examples t and U, compared to the comparative example,
It was possible to significantly suppress the occurrence of internal cracks in areas where the plate thickness reduction rate is high.

[Effects of the Invention] Since the present invention is configured as described above, it has become possible to stably produce rare earth element magnets with excellent magnetic properties.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the concept of forging, Fig. 2 is a cross-sectional view in the width direction showing the internal structure of the metal capsule in the method of the present invention, and Fig. 3 is a perspective view showing the concept of forging.
Figure 4.5 is a graph showing the presence or absence of forging cracks in relation to the length ratio of alloy material and reduction ratio. Figure 6 is a graph showing the effect of using a lubricant retention agent. be.

Claims (3)

[Claims] (1) An alloy material containing at least rare earth elements, transition elements, and B as essential components and having a length at least three times the thickness of the plate in the processing direction is sealed in a metal capsule via a lubricant. , Hot working is performed at a working temperature of 750 to 1100°C while constraining the metal capsule from the width direction in a state where the alloy material contains a liquid phase, and at this time, the total working rate is 50% or more. A magnetic material characterized by hot working so as to form a highly oriented alloy structure by interposing a lubricant retaining material in the lubricant layer between the metal encapsulant and the alloy ingot. A method for manufacturing a rare earth element-transition element-B magnet with excellent properties by forging. (2) The manufacturing method according to claim (1), wherein the lubricant holding material is a thin metal plate. (3) The manufacturing method according to claim (1), wherein the lubricant holding material is a perforated plate-like or wire mesh-like metal member.