... HRC50-64 and so on! Harden steel with HRC50-67, Cutting speed, 50-150 m/min; Feed, 0.05-0.12 ... mm/rev; Cutting deepth, about 0.2mm General gray cast iron with HB ... about 200, Cutting speed, 500-1000 m/min; Feed, 0.1-0.5 ... HRC50-64, Cutting speed, 50-100 m/min; Feed, 0.1-0.3 mm/rev, Cutting deepth, about 2.5mm CBN inserts for cutting tool