Specialty alloys , and are often sold only by the kilogram and by their individual trade names.
They are generally very hard, wear-resistant, tough, nonreactive to local overheating, and frequently engineered to particular service requirements. They must be dimensionally stable during hardening and tempering. They contain strong {{link=carbide">carbide formers such as tungsten, molybdenum, vanadium, and chromium in different combinations, and often cobalt or nickel to improve high-temperature performance. See also high-speed steel .