(also called heat resistance), the ability of steel, upon heating to red heat, to retain the great hardness and durability obtained through heat treatment. A high level of red-hardness is characteristic of tool steel. Red-hardness is achieved by alloying steel with tungsten, molybdenum, vanadium, and chromium, as well as by high-temperature hardening. Red-hardness is defined as the maximum temperature at which steel retains a given hardness. For example, high-speed steel retains Rockwell C hardness of up to 60 at 620°-650°C. Hard alloys have the highest level of red-hardness (up to 900°C).