1996 Volume 82 Issue 11 Pages 953-958
In order to produce the high quality rare-earth magnet, macrostructure control of Pr-Fe-B alloy ingot was carried out. Production method of this allov consists of melting, casting, hot rolling and heat treatment. The columnar structure of ingot is necessary to obtain the high magnetic properties. The columnar structure was produced by two kinds of method. One is thin plate casting and the other is directional solidification. By the thin plate casting sound and columnar structure ingot was produced. This alloy is cooled rapidly from the liquidus temperature to the peritectic temperoture and then cooled slowly below the peritectic temperature because this alloy is brittle. By this method the columnar structure was produced and the crack of this thin plate was protected.
In order to decrease the production cost of ingot, 400kg large size ingot was produced by the directional solidification using the hot top heating. The temperature gradient in ingot was so increased by the hot top heating that the large part of ingot showed the columnar structure. The magnetic properties such as (BH) max and iHc were improved by the hot top heating.
