Patent ID: 8142576

Claim:
A process for manufacturing a clutch hub of a dry type single plate clutch, in which a degree of flatness F is defined to be 0.15% or less which is obtained by a formula “F=d/D*100”, wherein d is a camber of a flat portion (a distance from a horizontal plane to an edge portion of the flat portion) and D is a diameter of a circumscribed circle of the clutch hub, the process comprising: annealing a steel sheet composed of 0.32 to 0.38% of C (carbon), 0.15% or less of Si (silicon), 0.3 to 0.5% of Mn (manganese), 0.16 to 0.60% of Cr (chromium) and 0.0010 to 0.0050% of B (boron) by mass ratio, the balance being Fe (iron) and inevitable impurities; punching the annealed steel sheet to form a sheet-shaped material with a predetermined configuration; and applying a heat treatment to the formed sheet-shaped material to obtain a heat treated material, wherein the applying the heat treatment includes hardening the formed sheet-shaped material by putting in oil of 60 to 70° C. after heating for 1 to 2 hours at 840 to 880° C., and tempering for 1 to 2 hours at 260 to 320° C. after the hardening.