As the carbon content of steel rises the metal becomes harder and stronger but less ductile and more difficult to weld. Cast irons are hard and brittle; they cannot be easily machined.

Typical composition of carbon steels
Type of steel% Carbon
Mild Steelup to 0.25
Medium Carbon Steel0.25-0.45
High Carbon Steel0.45-1.50
Cast Iron2.50-4.50

Carbon is the most cost-effective alloying material for iron, but various other alloying elements such as manganese, chromium, vanadium, and tungsten are also used.