The Fe-6.5 wt%Si alloy powders were prepared by high-pressure gas atomization in which the nucleation ability of the melt varied with the different purities of the raw materials and experimental conditions. The results indicated that the number of heterogeneous cores has a substantial effect on the grain size of the larger atomized powder particles, i.e. the more heterogeneous cores that are contained in the melt, the smaller the grain size of the atomized powder particles will be. However, the above effect became less significant when the powder particle size decreased. When the particle size was less than a certain critical value, single-crystal particles were formed. In addition to this, it was seen that the effect of the heterogeneous core number on the secondary dendrite arm spacing was fairly insignificant. (C) 2014 Elsevier B.V. All rights reserved.