| 简介 |
PROBLEM TO BE SOLVED : To obtain a raw material powder for magnet excellent in a magnetic property by forming a low heat conduction layer on a roll surface so as to suppress the generation of a fine chill crystal structure in a solidified raw material for magnet when producing a raw material for a R-T-B magnet by a rapid solidifying method by using a cooling roll. SOLUTION : When producing a raw material for a R-T-B magnet, a molten metal of the alloy is rapidly cooled/solidified in an inert gas atmosphere of Ar, etc., or a vacuum with a twin roll method, etc., to be pulverized. In this case, a surface layer of 0.1-10 mm thickness, which is made of a material having a low coefficient of heat conduction of Ni, Cr, alumina, etc., is formed on a surface of a rapid cooling roll, which is made of a material having a good coefficient of heat conduction of Cu, etc. Due to presence of the surface layer, the generation of a fine chill crystal is suppressed to a structure of the R-T-B alloy to be cooled/solidified. By setting its generation rate to <=5%, a magnetic property of the R-T-B magnet, which is obtained by crushing the alloy and forming/sintering, is improved. |
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