| 摘要 |
PURPOSE:To obtain a large type RM5 rare-earth permanent magnet having high magnetic characteristics without generation of cracks by a method wherein the rare-earth permanent magnet is re-heated to the temperature lower by 300 deg.C than the sintering temperature, and after the magnet has been maintained for ten minutes or longer, it is cooled down in the furnace to the low temperature which is lower by 500 deg.C than the sintering temperature at the cooling rate of 0.03 to 3 deg.C/min., and after the magnet has been maintained in that state for one hour, it is cooled down to 400 deg.C or lower at the average cooling rate of 5 to 50 deg.C/min. CONSTITUTION:In the manufacture of a rare-earth magnet having 90% or more of the degree of orientation of magnetic crystal grains in the direction of easy magnetization after sintering or heat treatment, a re-heating operation is conducted to the temperature which is lower by 300 deg.C than the sintering temperature, and after the magnet has been maintained at the above-mentioned temperature for 10 minutes or longer, it is cooled down in the furnace to the low temperature which is lower by 500 deg.C than the sintering temperature at the cooling rate of 0.03 to 3 deg.C/min., the magnet is maintained at the above-mentioned temperature for one hour, and then it is gradually cooled down to about 400 deg.C or lower at the average cooling rate of 5 to 50 deg.C/min. |
