Investigated here is the dependence of the coercive force Hc of permanent powder magnets (PM) of Nd-Fe-B alloys, on the composition and microstructure of the powder used in their preparation, and the sintering and annealing temperatures. It is shown that the differences observed in the Hc of PM similar in chemical composition but produced from different melts of those alloys, are due to differences of phase composition and microstructure resulting from the 'loss' of neodymium and boron by evaporation and formation of refractory oxides.