Abstract AISI Type M1 is a general-purpose high-molybdenum, low-tungsten type of high-speed tool steel. It has an excellent combination of cutting ability, toughness and finishing properties. Its cutting ability is good except for heavy-duty, continuous cutting operations where the ultimate in red-hardness is required. Its toughness is as great as that of any other high-speed steel. This datasheet provides information on composition, physical properties, hardness, and elasticity as well as fracture toughness. It also includes information on forming, heat treating, and machining. Filing Code: TS-314. Producer or source: Tool steel mills.