Method for manufacturing R-T-B based sintered magnet

1. A method for manufacturing an R-T-B based sintered magnet, which comprises the steps of:

preparing an R-T-B based sintered magnet material by molding and sintering alloy powder; and

performing a heat treatment by heating the R-T-B based sintered magnet material at a temperature of 450° C. or higher and 470° C. or lower for 4 hours or more and 12 hours or less, wherein

the R-T-B based sintered magnet material is represented by the formula of:

uRwBxGayCuzAlqM (100−u−w−x−y−z−q) T, where R is composed of a light rare-earth element RL and a heavy rare-earth element RH, in which RL is Nd and/or Pr, and RH is at least one element of Dy, Tb, Gd, and Ho; T is a transition metal element, indispensably containing Fe; and M is Nb and/or Zr, u, w, x, y, z, q, and 100−u−w−x−y−z−q are expressed in percent by mass,

the content of RH is 5% or less by mass in the R-T-B based sintered magnet,

29.5≤ u≤ 32.0,

0.86≤ w≤ 0.93,

0.2≤ x≤ 1.0,

0.3≤ y≤ 1.0,

0.05≤ z≤ 0.5,

0≤ q≤ 0.1, and

a relationship of p<0 is satisfied when p=[B]/10.811×14−[Fe]/55.847−[Co]/58.933, where [B], [Fe], and [Co] are contents of B, Fe, and Co in percent by mass, respectively,

wherein a fluctuation range of H cJ is 60 kA/m or less, wherein in the range of the heat treatment temperature and the heat treatment time, an optimal temperature and time at which H cJ is the highest are defined as the standard, and in the range of the heat treatment time at the optimal temperature, a difference between the H cJ defined as the standard and the lowest H cJ is determined, and the difference is defined as the fluctuation range of H cJ .

2. The method for manufacturing an R-T-B based sintered magnet according to claim 1 , wherein x and y satisfy relationships below:

0.3≤ x≤ 0.7, and

0.5≤ y≤ 0.7.

3. The method for manufacturing an R-T-B based sintered magnet according to claim 1 , wherein the heat treatment step is performed by heating the R-T-B based sintered magnet material at a temperature of 450° C. or higher and 470° C. or lower for 4 hours or more and 8 hours or less.

4. The method for manufacturing an R-T-B based sintered magnet according to claim 2 , wherein the heat treatment step is performed by heating the R-T-B based sintered magnet material at a temperature of 450° C. or higher and 470° C. or lower for 4 hours or more and 8 hours or less.

5. The method for manufacturing an R-T-B based sintered magnet according to claim 1 , wherein the heat treatment is performed in a vacuum.

6. The method for manufacturing an R-T-B based sintered magnet according to claim 1 , wherein the R-T-B based sintered magnet material does not contain any heavy rare-earth elements.