The development in the fastener industry raises the need for steel wire coils. The wire usually has to be annealed to improve its cold formability. The quality of a spheroidized annealed wire affects the forming quality of screws. In the fastener industry, most companies use a subcritical process for spheroidized annealing. Various parameters affect the quality of spheroidized annealing such as preheating time, spheroidized annealing temperature, prolonged heating time, furnace cooling temperature, and furnace cooling time. The effects of spheroidized annealing parameters affect the quality characteristics of wires, such as tensile strength and ductility. A series of experimental tests on AISI 10B21 steel wires is carried out in a vacuum drying oven and the Taguchi method of robust design is used to obtain optimal spheroidized annealing conditions to improve the mechanical properties of steel wires for cold forming. The experimental results show that the tensile strength is the main quality characteristic of spheroidized annealed steel wires, and that the spheroidized annealing temperature and prolonged heating time have the greatest effect on the mechanical properties of AISI 10B21 steel wires. A comparison between the results obtained using the optimal spheroidizing conditions and the measures determined using the original settings shows that the new spheroidizing parameter settings effectively improve the performance measures over their values at the original settings. The formability of AISI 10B21 steel wires is effectively improved.