Hardness for low carbon steel balls, as measured on the balls surface is Rockwell "C" 55 (minimum) and subject to correction factors. See chart for minimum case depth. Case depth reported is the effective case measured to the HRC 50 position (ref. ABMA Std. 10-83). Minimum thickness considerations apply to case depth.
Chemical Analysis AISI 1008-1018
C=0.10-0.20%, Mn=0.60-0.90%, Si=0.10-0.20%, S=max 0.50%, P=max 0.040%