Patent ID: 8128758

Claim:
A method for producing an R—Fe—B based microcrystalline high-density magnet, the method comprising the steps of: (A) providing an R—Fe—B based rare-earth alloy powder, where R is at least one element selected from the group consisting of the rare-earth elements including Y and Sc, with a mean particle size of less than about 20 μm; (B) compacting the R—Fe—B based rare-earth alloy powder to make a powder compact; (C) subjecting the powder compact to a heat treatment at a temperature of about 550° C. to less than 900° C. within hydrogen gas, thereby producing hydrogenation and disproportionation reactions; (D) subjecting the powder compact to another heat treatment at a temperature of about 550° C. to less than 900° C. within either a vacuum or an inert atmosphere, thereby producing desorption and recombination reactions and obtaining a porous material including fine crystal grains, of which a density is about 50% to about 90% of a true density thereof and which have an average crystal grain size of about 0.01 μm to about 2 μm; and (E) subjecting the porous material to yet another heat treatment at a temperature of about 750° C. to less than 900° C. within either the vacuum or the inert atmosphere so that rare-earth-rich phases with areas of 1 μm 2 to 10 μm 2 are formed at a number density of at least 1.6×10 4 phases per square millimeter on a cross section that passes through a center portion of the R—Fe—B based microcrystalline high-density magnet, thereby further increasing the density thereof to about 93% or more of the true density thereof without performing any hot pressing process.