High-Speed Steel

a high-alloyed steel used chiefly to fabricate cutting tools that operate at speeds approximately three to five times higher than tools made from carbon tool steel. The feasibility of achieving such cutting speeds is due to the red hardness of this steel. A tool of high-speed steel becomes soft when heated above 550°-600° C, whereas one made of carbon tool steel softens at 200° C. The steel’s red hardness is provided by alloying elements such as tungsten (W), chromium (Cr), and vanadium (V), which form highly stable carbides. In order to obtain the needed structure and properties, a tool made from high-speed steel is given special heat treatment that consists of cooling after being heated to a temperature of 1240°-1300° C and after repeated (usually three times) tempering at a temperature of 560°-620° C. The wear resistance is increased by means of cyaniding, cold treatment, broken hardening, and other methods. The popular brands of high-speed steel in the USSR include R18 (0.7-0.8 percent C, 17.5-19 percent W, 3.8-4.6 percent Cr, 1.0-1.4 percent V, and the rest iron) and R6MZ (0.85-0.95 percent C, 3.0-3.5 percent Cr, 5.5. 6.5 percent W, 3.0-3.6 percent Mo, 2.0-2.5 percent V, and the rest iron). Highspeed steels with a higher vanadium content or the addition of cobalt to provide even better cutting properties are also used.

High-speed steel is sometimes used in machine building for parts that are heated to 500°-650° C, especially for so-called heat-resistant ball bearings. In addition to hardness and hardenability, the purity of high-speed steel is important (the reduction of nonmetallic inclusions and carbide segregation to a minimum and the elimination of defects of metallurgical origin).