The characteristic of crystal growth of Nd–Fe–B cast strips during the rapid solidification process

•The cooling rate decreased with increasing thickness of the cast strips.•α-Fe precipitated in the free side of the strips with thickness more than 0.5 mm.•Fine equiaxed grains formed in the strips with thickness more than 0.5 mm.•The volume fraction of columnar grain increased to 91% at 0.3 mm and then decreased.•A schematic diagram of the characteristic of the crystal growth was proposed.

The microstructure of Nd–Fe–B cast strips with different thickness was investigated intensively. The cooling rate decreased with increasing thickness of the cast strips. When the thickness was more than 0.5 mm, α-Fe precipitated in the free side of the strips because the cooling rate was too low. However, the nucleation rate increased with increasing thickness. When the thickness was more than 0.5 mm, a layer of fine equiaxed grains formed near the wheel side. With the increased thickness, the volume fraction of columnar grain increased to maximum (91%) at 0.3 mm and then decreased. The characteristic of crystal growth of Nd–Fe–B cast strips with different thickness during solidification was discussed.