With the growing demand for new energy vehicles, high-strength and lightweight hot-stamping steel production has become increasingly important. The present study investigated a fast dip tester featuring a sub-rapid solidification process to refine the as-cast microstructures and adjust the mechanical properties of the 22MnB5 hot-stamping steel. It was found that the main microstructure of the studied steel evolved from ferrite and pearlite to bainite and martensite as the cooling rate increased. Moreover, the grain size of the sub-rapid solidification sample was significantly refined with high-density dislocations in the substructure. Still, the sub-rapid solidification process had little effect on grain orientation and texture. In addition, compared with the slow-cooled sample, the tensile strength of the sub-rapid solidification sample increased, but the elongation decreased.