Patent ID: 8361242

Claim:
A method to produce powders for use in R—Fe—B—M type permanent magnets comprising: melting an alloy consisting of, by weight, 28.00≦R≦32.00%, where R is at least one rare earth element including Y and the sum of Dy+Tb>0.5, 0.50≦B≦2.00%, 0.50≦Co≦3.50%, 0.050≦M≦0.5%, where M is one or more of the elements Ga, Cu and Al, 0.25 wt %<O≦0.5%, 0.15% or less of C, 0.15% or less of N, balance Fe; casting said alloy to form at least one ingot, wherein the solidified ingot comprises finely dispersed α-Fe phase, and R 2 Fe 14 B and R-rich constituents; annealing said ingot at a temperature in the range of 800° C. to 1200° C. under an inert atmosphere of Ar or under vacuum to form an ingot which is free of said α-Fe phase; hydrogenating said ingots in hydrogen gas in order to hydrogenate the R-rich constituents; coarsely pulverising said ingot to form a coarsely pulverised powder; performing a fine pulverisation of said coarsely pulverised powder in an atmosphere comprising oxygen, thereby forming an oxidized, finely pulverised powder; wherein said finely pulverised powder comprises an oxygen content of 0.25 wt %<O≦0.5 wt %.