Method for producing R-T-B based sintered magnet

1. A method for producing an R-T-B based sintered magnet comprising:

a step of preparing an R-T-B based sintered magnet material, which is represented by the following formula (1):

uRwBxGayCuzAlqM(100-u-w-x-y-z-q)T  (1)

where

R is composed of light rare-earth element(s) RL and a 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 a transition metal element and includes Fe, 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;

the RH accounts for 5% by mass or less of the R-T-B based sintered magnet, the following inequality expressions (2) to (5) and (12) 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)

0.844≤w ≤0.93  (13)

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;

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 ≤x −(62.5 w+v− 81.625)/15+0.8  (10).

wherein in the step of preparing the R-T-B based sintered magnet material , R-T-B based sintered magnet material is obtained by sintering;

a high-temperature heat treatment step of heating the R-T-B based sintered magnet material to a temperature of 730° C. or higher and 1,020° C. or lower, and then cooling to 300° C. at a cooling rate of 25° C./min or more; and

a low-temperature heat treatment step of heating the R-T-B based sintered magnet material, after the high-temperature heat treatment step, to a temperature of 440° C. or higher and 550° C. or lower;

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

H cj (kA/m) ≥1,360 +160 [Dy]+240[Tb], where the amount of Dy (% by mass) is [Dy]) and the amount of Tb (% by mass) is [Tb]).

2. The method for producing an R-T-B based sintered magnet according to claim 1 , wherein the low-temperature heat treatment step is a step of heating to a temperature of 480° C. or higher and 550° C. or lower.

3. The method for producing an R-T-B based sintered magnet according to claim 2 , wherein the amount of oxygen of the R-T-B based sintered magnet obtained is 0.15% by mass or less.

4. The method for producing an R-T-B based sintered magnet according to claim 1 , wherein the amount of oxygen of the R-T-B based sintered magnet obtained is 0.15% by mass or less.

5. The method for producing an 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).

6. The method for producing an R-T-B based sintered magnet according to claim 5 , wherein the low-temperature heat treatment step is a step of heating to a temperature of 480° C. or higher and 550° C. or lower.

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

8. The method for producing an R-T-B based sintered magnet according to claim 5 , wherein the amount of oxygen of the R-T-B based sintered magnet obtained is 0.15% by mass or less.

9. The method for producing an 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].

10. A method for producing an R-T-B based sintered magnet comprising:

a step of preparing an R-T-B based sintered magnet material, which is represented by the following formula (1):

uRwBxGayCuzAlqM(100-u-w-x-y-z-q)T  (1)

where

R is composed of light rare-earth element(s) RL and a 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 a transition metal element and includes Fe, 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;

the RH accounts for 5% by mass or less of the R-T-B based sintered magnet, the following inequality expressions (2) to (5) and (13) 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)

0.844≤w ≤0.910  (13)

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;

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 ≤x −(62.5 w+v− 81.625)/15+0.8  (10).

wherein in the step of preparing the R-T-B based sintered magnet material , R-T-B based sintered magnet material is obtained by sintering; p 1 a high-temperature heat treatment step of heating the R-T-B based sintered magnet material to a temperature of 730° C. or higher and 1,020° C. or lower, and then cooling to 300° C. at a cooling rate of 25° C./min or more; and

a low-temperature heat treatment step of heating the R-T-B based sintered magnet material, after the high-temperature heat treatment step, to a temperature of 440° C. or higher and 550° C. or lower.

11. The method for producing an R-T-B based sintered magnet according to claim 10 , wherein H cj and B r of the R-T-B based sintered magnet satisfy the following expressions:

H cj (kA/m) ≥1,360 +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].

12. A method for producing an R-T-B based sintered magnet comprising:

a step of preparing an R-T-B based sintered magnet material, which is represented by the following formula (1):

uRwBxGayCuzAlqM(100-u-w-x-y-z-q)T  (1)

where

R is composed of light rare-earth element(s) RL and a 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 a transition metal element and includes Fe, 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;

the RH accounts for 5% by mass or less of the R-T-B based sintered magnet, the following inequality expressions (2) to (5) and (13) being satisfied:

0.40≤x≤0.70  (2)

0.07≤y≤0.2  (3)

0.05≤z≤0.5  (4)

0≤q≤ 0 . 1   (5)

0.844≤w ≤0.93  (13)

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;

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)

wherein in the step of preparing the R-T-B based sintered magnet material , R-T-B based sintered magnet material is obtained by sintering;

a high-temperature heat treatment step of heating the R-T-B based sintered magnet material to a temperature of 730° C. or higher and 1,020° C. or lower, and then cooling to 300° C. at a cooling rate of 25° C./min or more; and

a low-temperature heat treatment step of heating the R-T-B based sintered magnet material, after the high-temperature heat treatment step, to a temperature of 440° C. or higher and 550° C. or lower.