cubic boron nitride
tungsten carbide
carbon steel
diamond
Carbon is a cheap material
Carbon is easily available
Carbon enables heat treatment of steel
None
Mild steel
Cast iron
Hardened steel
Brass
Longitudinal, cross and vertical traverse
Power available
Spindle nose taper
All the above
18 % tungsten and 8 % chromium
18 % chromium and 8 % nickel
18 % nickel and 8 % chromium
18 % chromium and 8 % cobalt