Alloy steels are plain carbon steel with metals such as Boron (B), manganese (Mn), chromium (Cr), nickel (Ni), molybdenum (Mo), tungsten (W), and cobalt (Co) added. These give other properties than plain carbon steel. Alloy steels are made for specialized purposes. For example, chromium can be added to make stainless steel, which does not rust easily, or boron can be added to make very hard steel that is also not brittle.