... surface finish. 3. Reduces machine down time. Solid CBN insert TNMA160408, Machining harden steel with HRC50-67, general gray cast ... -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 3.0mm High hardness cast iron with HRC50-64, Cutting speed, 50-100 m/min; Feed, 0.1-0. ...