Basic carbon steel contains relatively pure iron with less than 1% carbon. The ductile mild steels, containing about 0.25% carbon, are used to make sheets, pipe or wire. Medium steels, containing about 0.45% carbon and therefore harder, are primarily structural steels. Tools and cutting instruments are made from the hard and brittle high-carbon steels, which contain up to 2% carbon. Alloy steels, broadly defined, are steels containing significant amounts of elements other than iron and carbon. They exhibit a wide range of special properties, such as hardness, toughness, corrosion resistance, magnetizability, and ductility. The principal alloying elements for steel are chromium, nickel, manganese, molybdenum, silicon, tungsten, vanadium, and boron. Manganese is added to virtually all grades of steel. Manganese steel, which contains 11% to 14% manganese and 1% to 1.5% carbon, is non-magnetic, tough, durable and shockproof. The addition of copper improves corrosion-resistance. Sulfur improves machinability. Small amounts of born increase steel's hardness. Small additions of silicon, titanium, vanadium or niobium produce low-alloy, high-strength steels. Even stronger steels result from the addition of greater amounts of nickel, chromium, molybdenum and vanadium. Molybdenum and tungsten are used for expensive high-alloy tool steels. Stainless steels, in addition to iron and carbon, usually contain chromium and nickel, producing ductile, corrosion-resistant, high-strength steels. High-speed steels, used for cutting tools, are commonly a steel-tungsten-chromium-vanadium-molybdenum alloy. The addition of misch metal—50% cerium, 25% lanthanum, 15% neodymium and 10% other rare-earth metals and iron—to some steels makes them less brittle.