For the miniature races and balls in spindle motors of hard disc drives, there have been required the clean bearing steel with infinitesimal oxides, Ti inclusions and sulfides which originate acoustic noises. Chita Plant, Daido Steel, has established the new process, MRAC-SSS (Multi-function Refining and Advanced Casting - Special Solution and Soaking), to manufacture the ultra clean bearing steel. Its features are as follows.
(1) The tailored multi-functional refining process employing both LF and RH realizes the extremely low [O] and [Ti] levels in the molten steel.
(2) The tight sealing of the tundish prevents completely the secondary oxidation of the molten steel during continuous casting.
(3) The optimized reheating schedule for the cast bloom contributes to the siginificant reduction of Ti inclusions in number and size in the rolled wire or rod.
The ultra clean bearing steel manufactured through the new process proves to possess the remarkably prolonged contact rolling fatigue life.
