Alloy steels have a specified composition, containing certain percentages of other elements. They have been specially processed, however, to have much more strength than carbon steels of the same weight. Stainless steels contain chromium, nickel, and other alloying elements that keep them bright and rust resistant. Tool steels are fabricated into many types of tools, or into the cutting and shaping parts of power-driven machinery for manufacturing. They contain alloying elements that give them extra strength, hardness, and resistance to wear.
Tempering decreases hardness and strength, but increases ductility and toughness.