Very hard and very spherical ferromagnetic particles are prepared using a rapid quenching technique on a rotating disk. Glossy spherical particles with 10-300 μm diameter and Vickers hardness of 970-1100 are produced by ejecting melts of Fe_81-xCr_xB₁₇Si₂ (1≤x≤10) in a quarts tube through a 0.35 mm diameter nozzle onto a point of a rotating disk surface, the surface speed at which is 10-13 m/sec. The saturation flux density and the coercive force are 14.5 kG and 34 Oe for x=1, and 10 kG and 100 Oe for x=10. Temperature characteristics of B_s for 1≤x≤10 show three phases of microcrystalline ferromagnetic materials. Grain sizes in particles are estimated as less than 0.1 μm using SEM observations and X-ray diffraction patterns.