Studies on heat treatment for Nd-Fe-B magnets

The various heat treatments of Nd15.5Fe76B8.5magnets were conducted. To botain the optimum intrinsic coercivity, iHc, it is only needed to do post-sintering annealing at 650°C for 0.5-1 hour followed by oil quench, regardless of the other heat-treatment details. The same optimum iHc value can be obtained by five different heat-treatment patterns. More than two steps heat-treatment improves little in intrinsic coercivity. The intrinsic coercivity is composition dependent and maximum iHc value increases with the increasing of Nd-content. The intrinsic coercivity drops to some lower value when the magnet was slowly cooled to room temperature after heat-treatment instead of rapid cooling. The reduction of coercivity is dependent upon the comosition and can be recovered by redoing low temperature heat-treatment followed by rapid cooling.