JPS62124255A - Production of permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a permanent magnet having stable coercive force, stable residual magnetic flux density and uniform characteristics by sintering alloy powder contg. a rare earth element, Fe and B as the principal components, heat treating the sintering body at a specified temp. and cooling it an a prescribed cooling rate. CONSTITUTION:Alloy powder consisting of 25-44wt% one or more kinds of rare earth elements including Y, 0.5-5wt% B and the balance Fe with impuri ties is sintered at 900-1,200 deg.C. The sintered body is heated treated at 500-700 deg.C and cooled at 4-<50 deg..C/min cooling rate to obtain the desired magnet. The alloy powder may further contain 0.02-15wt% one or more among Al, Nb, Mn, Ni, Ta, Mo, W, Ge, V, Cr, Co and Bi.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a rare earth (R)-iron-based sintered permanent magnet. In more detail, an alloy with a desired composition is created by a melting method or a reduction diffusion method, processed into a fine powder, and then compression molded.
Rare earths obtained by sintering at temperatures between 00°C and 1200°C.
The present invention relates to an improvement in a method for producing a permanent magnet containing iron-melon as a main component.

[Conventional technology]

Permanent magnets made of rare earth elements mainly composed of Nd, iron, and B have higher saturation magnetization than SmCo-based permanent magnets.
In terms of resources, Nd and iron are more advantageous than Sm and Co, so they are attracting attention as high-performance magnets that can replace SmCo-based permanent magnets.

JP-A-59-46008 Publication - 30 atoms of R (wherein R is at least one rare earth element), 2 to 2
A magnetically anisotropic sintered body consisting of 8 atoms of B1 and the remainder Fe has been proposed. One of the intentions of the invention disclosed in this publication is to make it possible to manufacture a permanent magnet body of any shape by a sintering method rather than by a liquid quenching method. Also,
Regarding R in the sintered body components, Nd alone, Pr alone, N
A combination of d and Pr, a combination of Nd and Ce, and a combination of Sm and Pr.

The magnetic properties of the sintered body are shown for combinations, combinations of Pr and Y, Nd, combinations of Pr and La, Tb alone, Dy alone, Ho alone, Er and Tb combinations, etc.

According to JP-A No. 59-64733, R8 to 30 at%
(However, R is at least one rare earth element including Y),
It has been shown that in a sintered permanent magnet containing 2 to 28 at% B, 50% or less Co, and the balance F, Co increases the Curie point and reduces the temperature dependence of the magnetic properties (Br).

[Problem that the invention seeks to solve]

In sintered permanent magnets, a certain degree of coercive force IH after sintering
c is obtained, but in order to bring out the maximum coercive force IHc that is determined by the composition of the permanent magnet and that the permanent magnet can have,
It is necessary to perform heat treatment after sintering. Among the temperatures of this heat treatment, the temperature that increases the coercive force iHc the most is 500 to 7
It is 00℃. Since there is a large difference between the heat treatment temperature and the sintering temperature, usually after sintering, the material is cooled to around room temperature, then heated again to the heat treatment temperature, and held for 30 minutes to 5 hours. Alternatively, after sintering, lower the temperature to the heat treatment temperature, then keep it at that temperature for 30 minutes ~
The same effect can be obtained even if the temperature is maintained for 5 hours, but in any case, it is necessary to maintain the temperature at the heat treatment temperature or to slowly cool it near the heat treatment temperature. Particularly in the method of cooling to the post-sintering heat treatment temperature and then holding, it is necessary to avoid slow cooling in a temperature range between the sintering temperature and the heat treatment temperature that is detrimental to the coercive force IHc characteristics.

The heat treatment temperature that maximizes the coercive force 1Hc varies within the above temperature range depending on the composition, the types and amounts of various additive elements, and the types and amounts of impurity elements introduced during the process. Furthermore, for individual magnets with different compositions, additive elements, and impurity elements, the range of heat treatment temperatures at which the maximum value of the coercive force IHc is obtained is narrow. Therefore, in order to manufacture large quantities of magnets with little variation in coercive force IHc, it is necessary to keep the above factors that cause changes in the heat treatment temperature strictly constant, or to vary the heat treatment temperature according to the above factors. maximum coercive force I
It is necessary to select a temperature that will obtain Hc.

The heat treatment temperature that maximizes the coercive force IHc also differs depending on the cooling rate after sintering and after the heat treatment, so the soaking conditions in the furnace or the difference in cooling speed between the inside and the surface of the magnet may cause variations in the coercive force IHc. Causes uniformity.

[Means for solving problems]

In the present invention, an alloy having a desired composition is prepared by a melting method or a reduction diffusion method, processed into fine powder, compression molded, and then sintered at a temperature of 900 to 1200°C. In the steps up to this point, the residual magnetic flux density Br value is determined by factors such as the composition, impurities, and the degree of orientation of the powder during molding. Thereafter, heat treatment is performed at a temperature of 500 to 700°C to improve only the coercive force IHc value. The present invention allows cooling from the heat treatment temperature to less than 50°C/min4.
Rare earth (R) -Fe obtains a stable coercive force IHc by performing it at a low speed of 4 °C/n + i n or higher.
- This relates to a method of manufacturing a B-based magnet. When performing rapid cooling, the heat treatment temperature is within the above range of 500 to 700°C, and the absolute value of the temperature at which the highest coercive force IHc is obtained varies depending on the composition value, amount of impurities, and the cooling rate after sintering. However, as the cooling rate after aging becomes faster,
The temperature range narrows. As a result, when quenching is performed in liquid N2 or oil, the temperature range in which a high coercive force lHc can be obtained is very narrow, and the coercive force iHc% is unstable. Therefore, in the present invention, a stable coercive force iHc is obtained by performing slow cooling at less than 50° C./mtn. 5
Even if it is less than 0'C/min, a cooling rate as slow as 40C/min is not preferable because the absolute value of the coercive force IHc is low.

In the permanent magnet composition, if R is less than 25 wt%, the coercive force IHc is less than 5 koe, and if it exceeds 44 wt%, the residual magnetic flux density Br is less than 9 kG). , in the present invention, the leaves of R are 2
It was set to 5 to 44vrt. Also, if B is less than 0.5 wt%, the coercive force IHe is less than 5 koe and the coercive force IHe is less than 5 wt%.
If the amount exceeds 9 kG, Br becomes less than 9 kG, so in the present invention, the amount of B is set to 0.5 to 5 wt%.

Furthermore, in the present invention, as M, A#, Nb
.

Mn+Ni +Ta+MopW+Ge, V, Ni +C
r r One or more components of CotBi from 0.02 to
It can be contained in an amount of 15%. These components are effective in increasing the coercive force iHc and improving the squareness of the demagnetization curve, but if their content exceeds 15%, the Br value becomes too low to be practical. Therefore, the upper limit was set at 15%. If the content is less than 0.02%, the effect of M is small, so the lower limit was set at 0.02%. Although the coercive force fHe of the permanent magnet is increased by these components, the coercive force iHc is further increased by performing the rapid cooling according to the present invention.

If the sintering temperature is less than 900°C, sufficient density cannot be obtained, and if it exceeds 1200°C, deformation and fusion of the sintered body will become noticeable. did. After sintering, it is cooled in the usual manner. The cooling end temperature of the sintered body may be around room temperature or around the heat treatment temperature. Further, after sintering, the effect of the next heat treatment may be enhanced by slowly cooling or maintaining the temperature in a temperature range of 700° C. or higher and lower than the sintering temperature. Heat treatment temperature range of 500
~700℃ is the coercive force IH of the R-Fe-B alloy with the above composition.
This is the temperature normally employed to increase c.

After sintering less than 50℃/mtn 4-Q□℃/mi
Cooling is performed at a cooling rate of n or more. In the present invention, the cooling rate is the average cooling rate from the heat treatment temperature to 250°C. When the cooling rate is 50°C/min or more, the dependence of the coercive force iHc on the cooling rate becomes extremely high;
If it is less than GC/min, the absolute value of the coercive force tHe will be low.

When trying to obtain 98% or more of the maximum coercive force (iHc) obtained by composition, the permissible variation in heat treatment temperature is ±15-20℃ with respect to the set value, and the permissible variation in heat treatment time is with respect to the set value. The total time is ±2 hours. This range of variation is significantly expanded compared to conventional permanent magnets.

[Effect]

According to the present invention, the coercive force iHc of the permanent magnet is significantly stabilized by slow cooling after heat treatment. Further, the residual magnetic flux density (Br) obtained in the steps up to sintering does not decrease due to slow cooling and remains stable.

〔Example〕

The present invention will be explained in detail below.

Example 1 31%Nd-1,2%D7-66%Fe-1,0%B
An alloy of -0,6% Nb -0,2 Chi Al was created using a high frequency melting furnace, and after pulverization to an average size of 10 μm, 10 ko
Compression molding was carried out at a pressure of 4 tons/2 in a magnetic field.

Next, it was sintered at 1100°C and held at each temperature of 575 to 675°C for 3 hours. Thereafter, the mixture was cooled to room temperature at cooling rates of 4, 20, and 50% i.

FIG. 1 shows the relationship among magnetic properties, heat treatment temperature, and cooling rate after heat treatment. From Figure 1, 50℃/min after heat treatment
It can be seen that when cooling at a cooling rate above, the optimum heat treatment range becomes significantly narrower. In contrast, 20°C/ml
n N When the cooling rate is 40° C./min, the coercive force iHe changes little with respect to the change in heat treatment temperature.

20°C/min s 44) For a cooling rate of -°C/min, the coercive force iHc is at the peak of 50°C/min (i
Although the Hc) value and Hc are low, other magnetic properties are similar.

Example 2 An alloy having a composition of 25 to 43% Nd - 1,0% T3 - balance Fe was prepared using a high frequency melting furnace, pulverized to an average size of 12 μm in an organic solvent with a ball mill, and after drying.
It was compression molded in a kOe magnetic field at a pressure of 4 tons/1 ytr". It was then sintered at 1040°C to 1180°C, and
After holding at 80℃ for 1 hour, 4,10.50℃,/mi
It was cooled to room temperature at each cooling rate of n. Among the samples cooled at each cooling rate, the heat treatment temperature at which the coercive force iHc value was the highest was selected and shown in the graph of FIG.

The heat treatment temperature for each plot was as follows.

13at% to 9wt%) Nd-655°C; l 5 a
t% (≦, 3, wt%) Nd-665°C: 17 at
% (37wt%) Nd-670℃: 20at% (43
wt%) Nd -670°C.

As shown in Figure 2, the amount of Nd is 29 wt% (13 at%)
If it is above, the coercive force IH is almost the same regardless of the amount of Nd.
It can be seen that c is increased. Maximum energy product (BH)
It can be seen that max and residual magnetic flux density Br do not depend on the cooling rate but depend on the composition.

Example 3 32-35% Nd, 1.1-1.3% B M (M=Al
, Nb.

Ta, Mo, W, Go, V, Ni, Cr, Co, Bi
+Mn) balance iron alloy is created using arc melting,
average lo μm in organic solvent using a Loutou Gehr mill
After drying, pulverize into 4 pieces in a 10 kOe magnetic field.
/crr? Compression molded at a pressure of Then 2 at 1080℃
After sintering for ~5 hours and holding at each temperature of 500 to 700°C for 1 hour, it was cooled to room temperature at two cooling speeds of 3, 5 and 20°C/min. At each cooling rate, the highest coercive force lH
Select one that has been heat treated once and has a high e value, and calculate its coercive force lHe.
The values are shown in the table below.

From Table 4, which shows a temperature range with a variation of lHe

〔Effect of the invention〕

Soaking requirements for heat treatment furnaces are relaxed. The product shape, dimensions, etc. of permanent magnets vary, but on the other hand, if the Co content is 0, R-F
・In order to obtain the highest coercive force iHe determined by the -B composition, the product must be soaked to maintain a temperature difference of 5°C or less, so in order to give the desired heat treatment to all products in industrial production, heat treatment is necessary. The design and structure of the furnace will become complicated, the number of patching slots will be reduced, the furnace conditions will be constantly monitored by experienced heat treatment workers, or some special heat equalization measures will be required. According to the present invention, such measures are unnecessary or relaxed.

Since differences in local temperature and cooling rate when looking at individual magnets do not appear as differences in lHe, it is possible to obtain permanent magnets with uniform characteristics.

[Brief explanation of drawings]

Figure 1 shows 31%Nd-1, 2%D7-66%Fe
-1,0T B-0,6%Nb -0,2%AJ A graph showing the relationship between heat treatment temperature, magnetic properties, and cooling rate of a permanent magnet having a composition of 25 to 43%Nd, i, o%B-balance-Fe
This is a graph showing the relationship between the amount of Nd and the magnetic properties of a permanent magnet having the following composition.

Claims (1)

[Claims] 1. 25 to 44% R (wherein R is one or more rare earth elements including Y), 0.5 to 44% by weight
Alloy powder 900 consisting of 5% B, balance Fe and impurities
After sintering at ~1200°C, heat treatment at a temperature within the range of 500-700°C, then sintering at a temperature within the range of 50°C/min to 4°C/min.
A method for manufacturing a permanent magnet, characterized by cooling at a cooling rate of n or more. 2. Weight percentage: 25 to 44% R (where R is one or more rare earth elements including Y), 0.5 to 44%
5% B, 0.02-15% M (However, M is Al, N
b, Mn, Ni, Ta, Mo, W, Ge, V, Ni, C
One or two selected from the group consisting of r, Co, and Bi
90% of alloy powder consisting of
After sintering at 0~1200℃, heat treatment at a temperature within the range of 500~700℃, and then sintering at a temperature within the range of 50℃/min to 4℃/m
A method for producing a permanent magnet, characterized by cooling at a cooling rate of in or more.