R-Fe-B sintered magnet

Abstract

SOLUTION: To provide a R-Fe-B sintered magnet that includes R (R is one or more elements selected from rare earth elements, and Nd is essential), B, X (X is one or more types of elements selected from Ti, Zr, Hf, Nb, V, Ta), and C, and in which the remainder is Fe, O, other arbitrary elements and unavoidable impurities, and the following relational expression (1) of 0.86×([B]+[C]-2×[X])-4.9<[O]<0.86×([B]+[C]-2×[X])-4.6 is satisfied when the atomic percentages of the above B, C, X, and O are [B], [C], [X], and [O], respectively.EFFECT: In an R-Fe-B sintered magnet according to the present invention, it is possible to achieve both high Br and high HcJ, which are conventionally antinomic properties by adjusting and optimizing the quantitative ratio of B, C, O, and X (one or more of Ti, Zr, Hf, Nb, V, and Ta) among constituent elements of a magnet composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an R—Fe—B based rare earth sintered magnet that has improved residual magnetic flux density while suppressing a decrease in coercive force. [Background technology]

[0002] R-Fe-B sintered magnets (hereinafter sometimes referred to as Nd magnets) are functional materials essential for energy conservation and high performance, and their range of applications and production volume are expanding year by year. For example, they are used in drive motors and electric power steering motors in hybrid and electric vehicles, air conditioner compressor motors, and voice coil motors (VCMs) in hard disk drives. In these various applications, the high remanence (hereinafter referred to as Br) of R-Fe-B sintered magnets is a major advantage, but further improvements in Br are required, for example to further reduce the size of motors.

[0003] One way to increase the Br of R-Fe-B sintered magnets is to 14 The method of reducing the R content to increase the proportion of B phase, or R2Fe 14 A method of reducing the amount of added elements that dissolve in the B phase to lower Br has been known.

[0004] However, by reducing the amount of R and other added elements, the coercive force (hereinafter referred to as H cJ It is known that the R content decreases. In particular, when the R content decreases, there is a risk that the sinterability will decrease and abnormal grain growth will occur during the sintering process of R-Fe-B sintered magnets, where densification occurs with the formation of a liquid phase. Therefore, in order to obtain R-Fe-B sintered magnets with better properties, it is necessary to reduce the amount of R and other added elements to improve H. cJ It is necessary to achieve high Br while suppressing the decrease in H cJIt is generally known that adding heavy rare earth elements such as Dy and Tb can suppress or increase the decrease in Br. However, because the addition of these elements leads to a decrease in Br and they are rare and expensive resources, methods have been proposed to reduce the amount of heavy rare earth elements such as Dy and Tb used.

[0005] For example, in International Publication No. 2013 / 191276 (Patent Document 1), the content of B is reduced below the stoichiometric composition, 0.1 to 1.0 mass% of Ga is added, and the ratios of B, Nd, Pr, C, and Ga are adjusted so that the values ​​of [B] / ([Nd]+[Pr]) and ([Ga]+[C]) / [B] satisfy specific relationships. This results in a high H content even in a composition with reduced amounts of heavy rare earth elements such as Dy and Tb. cJ A sintered magnet that can achieve the above has been proposed.

[0006] In addition, WO 2004 / 081954 (Patent Document 2) discloses that by adjusting the B content to the stoichiometric composition, R 1.1 It has been proposed that the formation of the Fe4B4 phase is suppressed, thereby obtaining a sintered magnet with a high Br content. Furthermore, by adding 0.01 to 0.08 mass % of Ga, when the B content is below the stoichiometric composition, H cJ This will lead to a decrease in R2Fe 17 By suppressing the precipitation of the phase, high Br and high H cJ It is described that both of these can be achieved. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2013 / 191276 [Patent Document 2] International Publication No. 2004 / 081954 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the magnet described in Patent Document 1, the addition of 0.1 mass % or more of Ga relatively reduces the amount of heavy rare earth elements such as Dy and Tb used, resulting in a low R2Fe 14 The saturation magnetization of the B phase is increased, while the addition of Ga results in the R2Fe 14 Since the saturation magnetization of the B phase decreases, the Br is not necessarily improved sufficiently.

[0009] Furthermore, in the technology described in Patent Document 2, good magnetic properties can be obtained in the case of R-Fe-B sintered magnets with an oxygen concentration of about 0.4 mass%, but the description of the relationship between the oxygen concentration in the sintered magnet and the magnetic properties is insufficient. At oxygen concentrations below that level, particularly below 0.2 mass%, the behavior of the properties changes significantly, and high Br and high H are not necessarily related. cJ It is not possible to achieve a balance between

[0010] The present invention has been made in view of the above-mentioned problems, and aims to achieve high Br and stable H by adjusting and optimizing the ratio of the constituent elements of an R-Fe-B based sintered magnet. cJ The object of the present invention is to provide an R—Fe—B based sintered magnet having the above-mentioned properties. [Means for solving the problem]

[0011] In order to achieve the above object, the present inventors have conducted extensive research into the composition of R-Fe-B based sintered magnets containing B, C, O, and X (one or more of Ti, Zr, Hf, Nb, V, and Ta), including C and O, which are generally considered to be impurities. As a result, they have found that by adjusting the contents of B, C, O, and X within a predetermined range, a high Br can be obtained, and within that range, a stable H cJ The present invention has been completed based on the discovery that the above can be obtained.

[0012] Accordingly, the present invention provides the following rare earth sintered magnet. [1] A method for producing an R-Fe-B based sintered magnet, comprising: a melting step of melting raw materials to obtain a raw material alloy; a pulverization step of pulverizing the raw material alloy to prepare a fine alloy powder; a compacting step of compacting the fine alloy powder in an applied magnetic field to obtain a molded body; a heat treatment step of heat treating the molded body to obtain a sintered body; and a low-temperature heat treatment step of heat treating the sintered body at a temperature lower than the sintering temperature. The pulverization step includes a coarse pulverization step and a fine pulverization step, and in the fine pulverization step, a mixture of the coarse powder and a lubricant is pulverized using a jet mill, and the oxygen concentration in the jet mill system is set to 0 ppm during the pulverization. , % of B, 0.02 to 0.5 atomic % of X (X is one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta), 0.1 to 1.6 atomic % of C, 0.2 to 0.5 atomic % of Cu, and the balance being Fe, O, other optional elements, and unavoidable impurities, and the composition satisfies the following relational formula (1): 0.86×([B]+[C]-2×[X])-4.9<[O]<0.86×([B]+[C]-2×[X])-4.6 …(1) Satisfy Obtaining R-Fe-B sintered magnets 1. A method for producing an R—Fe—B based sintered magnet. [2] The content of O is 0.1 to 0.8 atomic percent [1] Manufacturing method for R-Fe-B sintered magnets . [3] As the optional element, 0.1 to 3.5 atomic % of Co 、0 [1] or [2] containing more than 1.0 atomic percent of Al Manufacturing method for R-Fe-B sintered magnets . [4] Any one of [1] to [3] containing Zr as X Manufacturing method for R-Fe-B sintered magnets . [5] Any of [1] to [4] containing Ga in an amount of more than 0 and not more than 0.1 atomic % as the optional element. Manufacturing method for R-Fe-B sintered magnets . [Effects of the Invention]

[0013] According to the R-Fe-B based sintered magnet of the present invention, by adjusting and optimizing the ratios of B, C, O, and X (one or more of Ti, Zr, Hf, Nb, V, and Ta) among the constituent elements of the magnet composition, it is possible to achieve high Br and high H, which were previously trade-off properties. cJ It is possible to achieve both. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a graph showing the relationship between [B]+[C]-2×[X] and [O] for the magnets of Examples 1 to 5 and Comparative Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0015] As described above, the R-Fe-B based sintered magnet of the present invention has a composition containing 12.5 to 14.5 atomic % R (R is one or more elements selected from rare earth elements, essential for which is Nd), 5.0 to 6.5 atomic % B, 0.02 to 0.5 atomic % X (X is one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta), 0.1 to 1.6 atomic % C, and the remainder being Fe, O, other optional elements, and unavoidable impurities.

[0016] As described above, the element R constituting the sintered magnet of the present invention is one or more elements selected from rare earth elements, with Nd being essential. As rare earth elements other than Nd, Pr, La, Ce, Gd, Dy, Tb, and Ho are preferred, with Pr, Dy, and Tb being particularly preferred, and Pr being especially preferred. The proportion of Nd, an essential component, in R is preferably 60 atomic % or more, and particularly 70 atomic % or more, of the total R.

[0017] As mentioned above, the R content is 12.5 to 14.5 atomic %, and preferably 12.8 to 14.0 atomic %. If the R content is less than 12.5 atomic %, α-Fe crystallizes in the raw material alloy, and it is difficult to eliminate the α-Fe even after homogenization, resulting in the H of the R-Fe-B based sintered magnet. cJ Furthermore, even when the raw alloy is produced by strip casting, which is a method in which α-Fe crystallization is unlikely to occur, α-Fe crystallization occurs, which leads to a significant decrease in the H of the R-Fe-B sintered magnet. cJ In addition, the amount of liquid phase, which is mainly composed of R components and plays a role in promoting densification during the sintering process, decreases, resulting in a decrease in sinterability and insufficient densification of the R-Fe-B sintered magnet. On the other hand, if the R content exceeds 14.5 atomic %, there will be no problem in manufacturing, but the R2Fe14 The proportion of B phase decreases, and Br decreases.

[0018] As described above, the sintered magnet of the present invention contains 5.0 to 6.5 atomic percent of boron (B). A more preferred content is 5.1 to 6.1 atomic percent, and even more preferred is 5.2 to 5.9 atomic percent. In the present invention, the B content, in combination with the C and X contents described below, provides stable H cJ This is a factor that determines the range of oxygen concentration required to obtain R2Fe. 14 The proportion of B phase is reduced, Br is significantly reduced, and R2Fe 17 H phase is formed cJ On the other hand, if the B content exceeds 6.5 atomic percent, a B-rich phase is formed, and the R2Fe 14 A decrease in the ratio of B phase causes a decrease in Br.

[0019] As described above, the element X constituting the sintered magnet of the present invention is one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta. By including these elements, the XB phase formed can suppress abnormal grain growth during sintering. Although not particularly limited, it is preferable that at least one element of X contains Zr.

[0020] As described above, the content of X is 0.02 to 0.5 atomic %, preferably 0.05 to 0.3 atomic %, and more preferably 0.07 to 0.2 atomic %. If the content of X is less than 0.02 atomic %, the effect of suppressing abnormal grain growth during the sintering process cannot be obtained. On the other hand, if the content of X exceeds 0.5 atomic %, the XB phase is formed, resulting in the formation of R2Fe 14 The amount of B required to form the B phase is reduced, and the R2Fe 14 The decrease in the B phase ratio leads to a decrease in Br, and consequently to the decrease in R2Fe 17 The formation of the phase significantly cJ This could lead to a decrease.

[0021] As mentioned above, the carbon (C) content of the sintered magnet of the present invention is 0.1 to 1.6 atomic %, preferably 0.2 to 1.0 atomic %. Since C originates from the raw materials and lubricants added to improve the orientation of the powder during compaction in a magnetic field, it is difficult to obtain an R-Fe-B sintered magnet with a C content of less than 0.1 atomic %. On the other hand, if the C content exceeds 1.6 atomic %, the presence of a large amount of RC phase in the sintered magnet will significantly increase H. cJ will decrease.

[0022] The sintered magnet of the present invention contains the above-mentioned predetermined amounts of R, B, and C, with the remainder containing Fe, O, other optional elements, and inevitable impurities. In this case, the content of O in the present invention is within a range that satisfies the following relational expression (1), where the atomic percentages of B, C, X, and O are [B], [C], [X], and [O], respectively. 0.86×([B]+[C]-2×[X])-4.9<[O]<0.86×([B]+[C]-2×[X])-4.6 …(1)

[0023] In other words, in the composition of the sintered magnet of the present invention, the range of the O content varies depending on the contents of the above [B], [C], and [X]. However, considering that it may be difficult to reduce the oxygen content to less than 0.1 atomic % in the production of Nd magnets, the O content is preferably in the range of 0.1 to 0.8 atomic %, more preferably in the range of 0.2 to 0.7 atomic %, and is a content that satisfies the above relational formula (1). In the present invention, the O content is an important factor, and when the O content is less than or equal to [0.86 × ([B] + [C] - 2 × [X]) - 4.9] atomic % on the left side of the above relational formula (1), H cJ In addition, when the O content is equal to or greater than the right side of the above relational expression (1) [0.86 × ([B] + [C] - 2 × [X]) - 4.6] atomic %, H cJ decreases.

[0024] Furthermore, as described above, the sintered magnet of the present invention may contain any element other than the above-mentioned R, B, X, C, Fe, and O, such as Co, Cu, Al, Ga, or N.

[0025] The Co content is preferably 0.1 atomic % or more, and more preferably 0.5 atomic % or more, from the viewpoint of obtaining the effect of improving the Curie temperature and corrosion resistance due to the inclusion of Co. cj From the viewpoint of stably obtaining the above, the Co content is preferably 3.5 atomic % or less, and more preferably 2.0 atomic % or less.

[0026] The Cu content is preferably 0.05 atomic % or more, more preferably 0.1 atomic % or more, from the viewpoint of obtaining an optimum temperature range in the low-temperature heat treatment after sintering, which is preferably carried out to ensure good mass productivity. In addition, in order to obtain good sinterability and high magnetic properties (Br, H cJ ), the content is preferably 0.5 atomic % or less, and more preferably 0.3 atomic % or less.

[0027] The above Al content is sufficient for H cJ From the viewpoint of obtaining a high Br content, the Ga content is preferably more than 0 atomic %, more preferably 0.05 atomic % or more. From the viewpoint of obtaining a high Br content, the Ga content is preferably 1.0 atomic % or less, more preferably 0.5 atomic % or less. From the same viewpoint, the Ga content is preferably more than 0 atomic % and 0.1 atomic % or less, more preferably 0.05 to 0.1 atomic %. Furthermore, the N content is preferably from the viewpoint of obtaining a good H content. cJ From the viewpoint of obtaining the above, the content is preferably 0.7 atomic % or less.

[0028] In addition to these elements, the sintered magnet of the present invention can contain unavoidable impurities such as H, F, Mg, P, S, Cl, Ca, Mn, and Ni in an amount up to 0.1% by mass of the total of the constituent elements of the magnet and the unavoidable impurities, but the lower the content of these unavoidable impurities, the better.

[0029] As described above, the sintered magnet of the present invention has a composition adjusted so that the O content satisfies the above relational expression (1). That is, when the atomic percentages of B, C, X, and O are [B], [C], [X], and [O], respectively, the sintered magnet satisfies the following relational expression (1): 0.86×([B]+[C]-2×[X])-4.9<[O]<0.86×([B]+[C]-2×[X])-4.6 …(1) By satisfying this relationship, high Br and stable H cJ The reason for this is not entirely clear, but it can be speculated as follows. 14 It is known that a portion of B in B compounds can be substituted with C, but C usually forms an ROC phase, which is an impurity phase, at the grain boundary triple junction and hardly contributes to the formation of the main phase. On the other hand, when attempting to obtain a high Br by reducing the R content as in the present invention, it is necessary to reduce the content of O, which is an impurity, to promote liquid phase sintering. Under such low oxygen content conditions, the amount of ROC phase formed decreases and a portion of C easily becomes R2Fe. 14 Furthermore, X in sintered magnets mainly forms XB2 compounds, which suppresses abnormal grain growth during the sintering process, and also contributes to the formation of R2Fe2 by B and C. 14 It also has the effect of reducing the amount of B phase formed. 14 The amounts of B and C atoms contributing to the formation of the B phase can be expressed by ([B] + [C] - 2 × [X]). 14 The formation of B phase is thought to be related to the content of B, C, X, and O atoms. By optimizing the relationship between ([B] + [C] - 2 × [X]) and [O], high Br and high H cJ The content of O atoms can be adjusted in the pulverization step in which the raw alloy is pulverized to obtain a fine alloy powder, as in the examples described below.

[0030] Next, a method for producing the R—Fe—B based sintered magnet of the present invention will be described below. The steps involved in producing the R-Fe-B based sintered magnet of the present invention are basically the same as those in ordinary powder metallurgy processes and are not particularly limited, but typically include a melting step in which raw materials are melted to obtain a raw material alloy, a crushing step in which a raw material alloy having a predetermined composition is crushed to prepare a fine alloy powder, a compacting step in which the fine alloy powder is compressed in an applied magnetic field to obtain a green body, and a heat treatment step in which the green body is heat treated to obtain a sintered body.

[0031] First, in the melting step, metals or alloys serving as raw materials for each element are weighed to obtain the predetermined composition of the present invention, and the raw materials are melted by, for example, high-frequency melting, and cooled to produce a raw alloy. The raw alloy is generally cast by a melting casting method in which the alloy is poured into a flat mold or a book mold, or a strip casting method. In addition, the R2Fe, which is the main phase of the R-Fe-B alloy, is melted by, for example, high-frequency melting, and cooled to produce a raw alloy. 14 The present invention can also be applied to the so-called two-alloy method, in which an alloy close to the B compound composition and an R-rich alloy that becomes a liquid phase additive at the sintering temperature are separately prepared, coarsely crushed, and then weighed and mixed. However, since the α-Fe phase is likely to crystallize in an alloy close to the main phase composition depending on the cooling rate and alloy composition during casting, it is preferable to perform a homogenization treatment in a vacuum or Ar atmosphere at 700 to 1200°C for at least one hour in order to homogenize the structure and eliminate the α-Fe phase. Note that if an alloy close to the main phase composition is prepared by strip casting, homogenization can be omitted. In addition to the above-mentioned casting method, a so-called liquid quenching method can also be used for the R-rich alloy that becomes a liquid phase additive.

[0032] The pulverization process can be a multi-stage process including, for example, a coarse pulverization process and a fine pulverization process. In the coarse pulverization process, for example, a jaw crusher, a Braun mill, a pin mill, or hydrogen pulverization is used. In the case of alloys produced by strip casting, hydrogen pulverization is usually used to obtain coarse powder of, for example, 0.05 to 3 mm, particularly 0.05 to 1.5 mm. In the fine pulverization process, the coarse powder obtained in the coarse pulverization process is finely pulverized to, for example, 0.2 to 30 μm, particularly 0.5 to 20 μm, using a method such as jet mill pulverization. In one or both of the coarse pulverization and fine pulverization processes of the raw alloy, additives such as lubricants can be added as needed to adjust the C content to a predetermined range. Furthermore, the coarse pulverization and fine pulverization processes of the raw alloy are preferably carried out in a gas atmosphere such as nitrogen gas or Ar gas. However, the O content may be adjusted to a predetermined range by controlling the oxygen concentration in the gas atmosphere.

[0033] In the compacting step, a magnetic field of 400 to 1600 kA / m is applied to the alloy powder to orient it in the direction of the axis of easy magnetization, and the powder is compacted in a compression molding machine. 3 From the viewpoint of ensuring the strength of the molded body and obtaining good handling properties, the density of the molded body is preferably 2.8 g / cm 3 On the other hand, from the viewpoint of obtaining a suitable Br by ensuring good particle orientation during pressure application while obtaining sufficient compact strength, the compact density is preferably 4.2 g / cm. 3 It is preferable that the molding is carried out in a gas atmosphere such as nitrogen gas or Ar gas in order to prevent oxidation of the alloy fine powder.

[0034] In the heat treatment step, the compact obtained in the compacting step is sintered in a high vacuum or a non-oxidizing atmosphere such as Ar gas. Generally, the sintering is preferably carried out by holding the compact at a temperature in the range of 950°C to 1200°C for 0.5 to 5 hours. Cooling after sintering can be carried out by gas quenching (cooling rate: 20°C / min or more), controlled cooling (cooling rate: 1 to 20°C / min), or furnace cooling, and the resulting R-Fe-B based sintered magnets will have similar magnetic properties.

[0035] Following the above heat treatment for sintering, the sintered product may be subjected to, but is not limited to, H cJ To increase the sintering temperature, heat treatment may be performed at a temperature lower than the sintering temperature. This post-sintering heat treatment may be a two-stage heat treatment consisting of a high-temperature heat treatment and a low-temperature heat treatment, or only a low-temperature heat treatment may be performed. In the high-temperature heat treatment of the post-sintering heat treatment, the sintered body is preferably heat-treated at a temperature of 600 to 950°C, and in the low-temperature heat treatment, it is preferably heat-treated at a temperature of 400 to 600°C. Cooling during this process may be performed by any of gas quenching (cooling rate: 20°C / min or more), controlled cooling (cooling rate: 1 to 20°C / min), and furnace cooling. Regardless of the cooling method, an R-Fe-B based sintered magnet with similar magnetic properties can be obtained.

[0036] The obtained R-Fe-B sintered magnet was ground into a predetermined shape, and the R 1 oxide of R 2 Fluoride, R 3 Acid fluoride, R 4 hydroxide, R 5 carbonate, R 6 One or more basic carbonates (R 1 ~R 6A slurry containing a powder of (R is one or more elements selected from rare earth elements, which may be the same or different) can be applied or coated onto the sintered magnet surface, and then the sintered magnet surface can be heat-treated with the powder still present. This treatment is a so-called grain boundary diffusion method, and the temperature of the grain boundary diffusion heat treatment is lower than the sintering temperature and preferably 350°C or higher. The time is not particularly limited, but is preferably 5 minutes to 80 hours, more preferably 10 minutes to 50 hours, from the viewpoint of obtaining good sintered magnet structure and magnetic properties. The grain boundary diffusion treatment can be used to remove the R contained in the powder. 1 ~R 6 is diffused into the magnet, and H cJ For the sake of convenience, the rare earth elements introduced by this grain boundary diffusion are referred to as R 1 ~R 6 However, after grain boundary diffusion, both are included in the above R component of the magnet of the present invention. [Example]

[0037] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0038] [Example 1, Comparative Example 1] An alloy ribbon was produced by strip casting in an Ar gas atmosphere to obtain a mixture of 30.0 wt% Nd, 1.0 wt% Co, 0.9 wt% B, 0.2 wt% Al, 0.2 wt% Cu, 0.1 wt% Zr, 0.1 wt% Ga, and the remainder Fe. The alloy ribbon was then coarsely pulverized by hydrogenation to obtain a coarse powder. 0.1 wt% stearic acid was then added as a lubricant to the resulting coarse powder and mixed. The mixture of coarse powder and lubricant was then finely pulverized in a jet mill in a nitrogen stream to an average particle size of approximately 3.5 μm. The oxygen concentration in the jet mill system was adjusted to 0 ppm (Example 1) and 50 ppm (Comparative Example 1), thereby adjusting the O content. The fine powder was then loaded into a mold of a molding machine equipped with an electromagnet in a nitrogen atmosphere and pressure-molded perpendicular to the magnetic field of 15 kOe (1.19 MA / m) while oriented in the magnetic field. The resulting compact was then sintered in vacuum at 1050°C for 3 hours, cooled to below 200°C, and then subjected to a high-temperature heat treatment at 900°C for 2 hours and a low-temperature heat treatment at 500°C for 3 hours to obtain a sintered compact. The composition of each sintered compact was Nd: 13.5 at%, Co: 1.1 at%, B: 5.5 at%, Al: 0.5 at%, Cu: 0.2 at%, Zr: 0.07 at%, Ga: 0.1 at%, C: 0.4 at%, O: see Table 1, and Fe: balance. Metal elements were measured by ICP analysis, C by combustion infrared absorption spectroscopy, and O by inert gas fusion infrared absorption spectroscopy.

[0039] The center of each of the obtained sintered bodies was cut into a rectangular parallelepiped shape of 18 mm x 15 mm x 12 mm to obtain a sintered magnet. The magnetic properties (Br, H) of each of the sintered magnets were measured using a BH tracer. cJ ) were measured. Table 1 shows the at% of B, Zr, C and O ([B], [Zr], [C], [O]) and magnetic properties (Br, H cJ ) values. In the table, "effective [O] range in Example 1 and Comparative Example 1" refers to the range of [O] values ​​that satisfies the following relational expression (1') for [B], [C], [Zr], and [O]. 0.86×([B]+[C]-2×[Zr])-4.9<[O]<0.86×([B]+[C]-2×[Zr])-4.6 …(1')

[0040] [Table 1]

[0041] As shown in Table 1, the sintered magnet of Example 1, which satisfies the conditions of the present invention (the above relational expression (1')), has a higher H cJ It has clearly superior properties in

[0042] [Examples 2 to 5, Comparative Examples 2 to 6] The alloy ribbons were prepared, hydrogenated, and mixed with the coarse powders in the same manner as in Example 1, except that the amounts of the raw metals used were adjusted to obtain the desired composition. Next, each coarse powder and lubricant mixture was pulverized in a jet mill in a nitrogen stream to produce fine powders with an average particle size of approximately 3.5 μm. The oxygen concentration in the jet mill system was adjusted appropriately to adjust the O content. The fine powders were then molded and heat-treated in the same manner as in Example 1 to obtain sintered bodies. The composition of the resulting sintered bodies was analyzed in the same manner as in Example 1, and found to be Nd: 13.5 at%, Co: 1.1 at%, B: see Table 2, Al: 0.5 at%, Cu: 0.2 at%, Zr: 0.07 at%, Ga: 0.1 at%, C: 0.4 at%, O: see Table 2, and Fe: the balance.

[0043] The central portion of each of the sintered bodies obtained in Examples 2 to 5 and Comparative Examples 2 to 6 was cut into a rectangular parallelepiped shape measuring 18 mm x 15 mm x 12 mm to obtain a sintered magnet. The magnetic properties (Br, H) of each sintered magnet were measured using a BH tracer. cJ Table 2 shows the at% of B, Zr, C, and O ([B], [Zr], [C], [O]) and magnetic properties (Br, H cJ ) values. The "effective [O] range" in the table refers to the range of [O] values ​​that satisfy the above relational expression (1') for [B], [C], [Zr], and [O] in each magnet.

[0044] [Table 2]

[0045] As shown in Table 2, the sintered magnets of Examples 2 to 5, which satisfy the conditions of the present invention (the above-mentioned relational expression (1')), have higher H cJ It was confirmed that it has the following properties.

[0046] Based on the results of Tables 1 and 2, the relationship between ([B] + [C] - 2 × [Zr]) and [O] for Examples 1 to 5 and Comparative Examples 1 to 6 is shown in the graph of Figure 1. From Tables 1 and 2 and Figure 1, it can be seen that the O content satisfies the following relational formula (1'): 0.86×([B]+[C]-2×[Zr])-4.9<[O]<0.86×([B]+[C]-2×[Zr])-4.6 …(1') Within the range that satisfies the above, high Br and high H of 1000kA / m or more cJ It can be seen that H cJ On the other hand, when the O atom content is greater than [0.86 × ([B] + [C] - 2 × [Zr]) - 4.6], the R2Fe 14 For the basic composition represented by B, R2Fe 14 The abundance of B and C, which contribute to the formation of the B phase, is insufficient, resulting in the formation of R2Fe 17 The formation of the H cJ On the other hand, when the O atom content is less than [0.86 × ([B] + [C] - 2 × [Zr]) - 4.9], R2Fe 14 For the basic composition represented by B, R2Fe 14 The amounts of B and C that contribute to the formation of the B phase become excessive, and a heterogeneous phase consisting of R, Fe, and B is formed, resulting in H cJ It is presumed that the content of O atoms can be adjusted in the pulverization step in which the raw alloy is pulverized to obtain the fine alloy powder, as in Examples 1 to 5 above.

[0047] [Examples 6 to 9] An alloy ribbon was produced in the same manner as in Example 1, except that the amounts of the raw metals used were adjusted to Nd: 30.0 wt%, Co: 1.0 wt%, B: 0.9 wt%, Al: 0.2 wt%, Cu: 0.2 wt%, Zr: 0.1 wt%, Ga: 0-0.3 wt%, and Fe: the balance. Next, the produced alloy ribbon was coarsely pulverized by hydrogenation to obtain a coarse powder. Subsequently, 0.1 mass% of stearic acid was added as a lubricant to the obtained coarse powder and mixed. Next, the mixture of the coarse powder and the lubricant was finely pulverized in a jet mill in a nitrogen gas flow to an average particle size of approximately 3.5 μm. At this time, the oxygen concentration in the jet mill system was set to 0 ppm. Next, the produced fine powder was molded and heat-treated in the same manner as in Example 1 to obtain sintered bodies of Examples 6 to 9. The composition of the obtained sintered body was analyzed in the same manner as in Example 1, and was found to be Nd: 13.5 at%, Co: 1.1 at%, B: 5.5 at%, Al: 0.5 at%, Cu: 0.2 at%, Zr: 0.07 at%, Ga: see Table 3, C: 0.4 at%, O: see Table 3, Fe: balance.

[0048] The center of each of the sintered bodies of Examples 6 to 9 was cut into a rectangular parallelepiped shape measuring 18 mm x 15 mm x 12 mm to obtain a sintered magnet. The magnetic properties (Br, H) of each sintered magnet were measured using a BH tracer. cJ Table 3 shows the at% of Ga, B, Zr, C, and O ([Ga], [B], [Zr], [C], [O]) and magnetic properties (Br, H cJ ) are shown, and similar measured values ​​are also shown for the sintered magnet of Example 1. Note that the "effective [O] range" in the table refers to the range of [O] values ​​for [B], [C], [Zr], and [O] that satisfies the above relational expression (1') for each magnet.

[0049] [Table 3]

[0050] As shown in Table 3, the sintered magnets of Example 1 and Examples 6 to 9, which satisfy the conditions of the present invention (the above relational expression (1')), all have good Br and H cJHowever, Example 7, which does not contain Ga, has a slightly higher H content than Examples 1 and 6. cJ Furthermore, Examples 8 and 9, in which the Ga content exceeded 0.1 at %, were slightly inferior to Examples 1 and 6 in terms of Br.

Claims

1. A method for producing an R-Fe-B based sintered magnet, comprising: a melting step of melting raw materials to obtain a raw material alloy; a crushing step of crushing the raw material alloy to prepare an alloy fine powder; a compacting step of compacting the alloy fine powder under an applied magnetic field to obtain a green body; a heat treatment step of heat treating the green body to obtain a sintered body; and a low-temperature heat treatment step of heat treating the sintered body at a temperature lower than the sintering temperature, The pulverization step includes a coarse pulverization step and a fine pulverization step, and in the fine pulverization step, a mixture of the coarse powder and a lubricant is pulverized using a jet mill, while the oxygen concentration in the jet mill system is set to 0 ppm, % of B, 0.02 to 0.5 atomic % of X (X is one or more elements selected from Ti, Zr, Hf, Nb, V, and Ta), 0.1 to 1.6 atomic % of C, 0.2 to 0.5 atomic % of Cu, and the balance being Fe, O, other optional elements, and unavoidable impurities, and the composition satisfies the following relational formula (1): 0.86×([B]+[C]-2×[X])-4.9<[O]<0.86×([B]+[C]-2×[X])-4.6...(1) The present invention provides a method for producing an R—Fe—B based sintered magnet that satisfies the above requirements.

2. 2. The method for producing an R—Fe—B based sintered magnet according to claim 1, wherein the O content is 0.1 to 0.8 atomic %.

3. 3. The method for producing an R—Fe—B based sintered magnet according to claim 1, wherein the optional elements include 0.1 to 3.5 atomic % of Co and more than 0 atomic % but not more than 1.0 atomic % of Al.

4. The method for producing an R—Fe—B based sintered magnet according to any one of claims 1 to 3, wherein said X contains Zr.

5. 5. The method for producing an R—Fe—B based sintered magnet according to claim 1, wherein the optional element contains more than 0 and 0.1 atomic % or less of Ga.

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