R-T-B based sintered magnet and method for producing R-T-B based sintered magnet

1. An R-T-B based sintered magnet represented by the following formula (1):

u R w B x Ga y Cu z Al q M(100- u - w - x - y - z - q )T  (1)

where

R is composed of light rare-earth element(s) RL and optionally heavy rare-earth element(s) RH, RL is Nd and/or Pr, RH is at least one of Dy, Tb, Gd and Ho, T is Fe, and 10% by mass or less of Fe being replaced with Co, M is Nb and/or Zr, and u, w, x, y, z, q and 100-u-w-x-y-z-q are expressed in terms of % by mass;

said RH accounts for 5% by mass or less of the R-T-B based sintered magnet, the following inequality expressions (2) to (5) being satisfied:

0.20≤x≤0.70  (2)

0.07≤y≤0.2  (3)

0.05≤z≤0.5  (4)

0≤q≤0.1  (5)

v=u−(6α+10β+8γ), where the amount of oxygen (% by mass) of the R-T-B based sintered magnet is α, the amount of nitrogen (% by mass) is β, and the amount of carbon (% by mass) is γ;

0.84≤w≤0.93;

when 0.40≤x≤0.70, v and w satisfy the following inequality expressions (6) and (7):

50 w− 18.5 ≤v ≤50 w −14  (6)

−12.5 w+ 38.75 ≤v≤− 62.5 w+ 86.125  (7)

and, when 0.20≤x <0.40, v and w satisfy the following inequality expressions (8) and (9), and x satisfies the following inequality expression (10):

50 w −18.5 ≤v ≤50 w −15.5  (8)

−12.5 w +39.125 ≤v ≤−62.5 w +86.125  (9)

−(62.5 w+v −81.625)/15+0.5 ≤x≤− (62.5 w+v− 81.625)/15+0.8  (10);

wherein H cJ of the R-T-B based sintered magnet satisfies the following expression:

H cJ (kA/m)≥1,300+160[Dy]+240[Tb], where the amount of Dy (% by mass) is [Dy] and the amount of Tb (% by mass) is [Tb].

2. The R-T-B based sintered magnet according to claim 1 , wherein, when 0.40≤x≤0.70, v and w satisfy the following inequality expressions (11) and (7):

50 w −18.5 ≤v≤ 50 w −16.25  (11)

−12.5 w +38.75 ≤v≤− 62.5 w +86.125  (7)

and, when 0.20≤x<0.40, v and w satisfy the following inequality expressions (12) and (9), and x satisfies the following inequality expression (10):

50 w −18.5 ≤v≤ 50 w −17.0  (12)

−12.5 w +39.125 ≤v≤− 62.5 w +86.125  (9)

−(62.5 w+v− 81.625)/15+0.5 ≤x≤− (62.5 w+v− 81.625)/15+0.8  (10).

3. The R-T-B based sintered magnet according to claim 1 , wherein the amount of oxygen is 0.15% by mass or less.

4. A method for producing an R-T-B based sintered magnet represented by the following formula (1):

u R w B x Ga y Cu z Al q M(100- u - w - x - y - z - q )T  (1)

where

R is composed of light rare-earth element(s) RL and heavy rare-earth element(s) RH, RL is Nd and/or Pr, RH is at least one of Dy, Tb, Gd and Ho, T is Fe, and 10% by mass or less of Fe is capable of being replaced with Co, M is Nb and/or Zr, and u, w, x, y, z, q, and 100-u-w-x-y-z-q are expressed in terms of % by mass;

said RH accounts for 5% by mass or less of the R-T-B based sintered magnet, the following inequality expressions (2) to (5) being satisfied:

0.20≤x≤0.70  (2)

0.07≤y≤0.2  (3)

0.05≤z≤0.5  (4)

0≤q≤0.1  (5)

v=u−(6α+10β+8γ), where the amount of oxygen (% by mass) of the R-T-B based sintered magnet is α, the amount of nitrogen (% by mass) is β, and the amount of carbon (% by mass) is γ; and

when 0.40≤x≤0.70, v and w satisfy the following inequality expressions (6) and (7):

50 w− 18.5 ≤v≤ 50 w− 14  (6)

−12.5 w +38.75 ≤v≤− 62.5 w +86.125  (7)

and, when 0.20≤x≤0.40, v and w satisfy the following inequality expressions (8) and (9), and x satisfies the following inequality expression (10):

50 w− 18.5 ≤v≤ 50 w− 15.5  (8)

−12.5 w +39.125 ≤v≤− 62.5 w +86.125  (9)

−(62.5 w+v− 81.625)/15+0.5 ≤x ≤−(62.5 w+v− 81.625)/15+0.8(10)

the method comprising:

a step of preparing one or more kinds of additional alloy powders and one or more kinds of main alloy powders;

a step of mixing the one or more additional alloy powders with 0.5% by mass or more and 40% by mass or less among 100% by mass of the mixed alloy powder after mixing to obtain a mixed alloy powder of one or more kinds of additional alloy powders and one or more kinds of main alloy powders;

a compacting step of compacting the mixed alloy powder to obtain a compact;

a sintering step of sintering the compact to obtain a sintered body; and

a heat treatment step of subjecting the sintered body to a heat treatment;

wherein one or more kinds of additional alloy powders are respectively represented by the following inequality expression (13), each having the composition satisfying the following inequality expressions (14) to (20):

a R b B c Ga d Cu e Al f M(100- a - b - c - d - e - f )T  (13)

where

R is composed of light rare-earth element(s) RL and heavy rare-earth element(s) RH, RL is Nd and/or Pr, RH is at least one of Dy, Tb, Gd and Ho, T as balance is Fe, and 10% by mass or less of Fe is capable of being replaced with Co, M is Nb and/or Zr, and a, b, c, d, e, f and 100-a-b-c-d-e-f are expressed in terms of % by mass:

32%≤a≤66%  (14)

0.2%≤b  (15)

0.7%≤c≤12%  (16)

0%≤d≤4%  (17)

0%≤e≤10%  (18)

0%≤f≤2%  (19)

100 −a−b−c−d−e−f≤ 72.4 b   (20)

and the Ga content of one or more main alloy powders is 0.4% by mass or less.

5. The method for producing an R-T-B based sintered magnet according to claim 4 , wherein, when 0.40≤x≤0.70, v and w satisfy the following inequality expressions (11) and (7):

50 w− 18.5 ≤v≤ 50 w− 16.25  (11)

−12.5 w+ 38.75 ≤v≤− 62.5 w+ 86.125  (7)

and, when 0.20≤x≤0.40, v and w satisfy the following inequality expressions (12) and (9), and x satisfies the following inequality expression (10):

50 w− 18.5 ≤v≤ 50 w− 17.0  (12)

−12.5 w+ 39.125 ≤v≤− 62.5 w+ 86.125  (9)

−(62.5 w+v− 81.625)/15+0.5≤ x ≤−(62.5 w+v− 81.625)/15+0.8  (10).

6. The method for producing an R-T-B based sintered magnet according to claim 4 , wherein the amount of oxygen of the R-T-B based sintered magnet is 0.15% by mass or less.

7. The R-T-B based sintered magnet according to claim 1 , wherein B r of the R-T-B based sintered magnet satisfies the following expression:

B r ( T )≥1.340−0.024[Dy]−0.024[Tb].

8. An R-T-B based sintered magnet represented by the following formula (1):

u R w B x Ga y Cu z Al q M(100- u - w - x - y - z - q )T  (1)

where

R is composed of light rare-earth element(s) RL and optionally heavy rare-earth element(s) RH, RL is Nd and/or Pr, RH is at least one of Dy, Tb, Gd and Ho, T is Fe, and 10% by mass or less of Fe being replaced with Co, M is Nb and/or Zr, and u, w, x, y, z, q and 100-u-w-x-y-z-q are expressed in terms of % by mass;

said RH accounts for 5% by mass or less of the R-T-B based sintered magnet, the following inequality expressions (2) to (5) being satisfied:

0.20≤x≤0.70  (2)

0.07≤y≤0.2  (3)

0.05≤z≤0.5  (4)

0≤q≤0.1  (5)

v=u−(6α+10β+8γ), where the amount of oxygen (% by mass) of the R-T-B based sintered magnet is α, the amount of nitrogen (% by mass) is β, and the amount of carbon (% by mass) is γ;

0.84≤w≤0.910;

when 0.40≤x≤0.70, v and w satisfy the following inequality expressions (6) and (7):

50 w −18.5 ≤v≤ 50 w −14  (6)

−12.5 w + 38.75 ≤v≤− 62.5 w+ 86.125  (7)

and, when 0.20≤x≤0.40, v and w satisfy the following inequality expressions (8) and (9), and x satisfies the following inequality expression (10):

50 w− 18.5 ≤v≤ 50 w− 15.5  (8)

−12.5 w+ 39.125 ≤v≤− 62.5 w+ 86.125  (9)

−(62.5 w+v− 81.625)/15+0.5≤x≤−(62.5 w+v− 81.625)/15+0.8  (10).

9. The R-T-B based sintered magnet according to claim 8 , wherein H cJ and B r of the R-T-B based sintered magnet satisfy the following expressions:

H cJ (kA/m)≥1,300+160[Dy]+240[Tb], and

B r (T)≥1.340−0.024[Dy]−0.024[Tb],

where the amount of Dy (% by mass) is [Dy] and the amount of Tb (% by mass) is [Tb].