Ferrous metals and alloys are iron-based materials that are used in a wide variety of industrial applications. Examples include carbon steels, alloy steels, stainless steels, tool steels, cast iron, cast steel, maraging steel, and specialty or proprietary iron-based alloys. Many materials meet the compositional standards of the Unified Numbering System (UNS), a specification established by the American Society for Testing and Materials (ASTM), the Society of Automotive Engineers (SAE), and metal trade associations such as the American Iron and Steel Institute (AISI) and the Aluminum Association (AA). The UNS assigns metals and alloys a lettered prefix and a five-digit number. For example, carbon steels and alloy steels belong to the UNS G category and have designations such as UNS G10950. AISI-SAE is another common specification for ferrous metals and alloys. Other standards include casting grades, European Norm (EN), and U.S. military specifications (MIL-SPEC). QQ and QQS prefixes are used to designate specific MIL-SPEC metals.
There are many types of ferrous metals and alloys. Carbon steels are ferrous alloys that contain carbon and small levels of other alloying elements such as manganese or aluminum. Alloy steels contain low to high levels of elements such as chromium, molybdenum, vanadium and nickel. Stainless steels are highly corrosion resistant, ferrous alloys that contain chromium and/or nickel additions. There are three basic types of products: austenitic stainless steels, ferritic and martensitic stainless steels, and specialty stainless steels and iron superalloys. Tool steels are wear resistant, but difficult to fabricate in their hardened form. Specific grades are available for cold-working, hot-working, and high speed applications. Cast iron is a ferrous alloy with high amounts of carbon. This category includes ductile iron, gray iron and white cast iron grades. Cast steel alloy grades are made by pouring molten iron into a mold. AISI-SAE H-steels are produced to specified hardenability bands. UNS D steels have specified mechanical properties. High strength low alloy (HSLA) steels, iron-based superalloys, metal matrix composites, pure alloys, and clad or bimetal materials are also available.
Nonferrous metals and nonferrous alloys are not based on iron and include alloys of aluminum, copper, titanium, zinc, nickel, cobalt, tungsten, precious metals, and refractory metals. They are used in a variety of applications from construction to medical devices. A specialty nonferrous alloy consists of two or more materials, one of which must be a nonferrous metal. Many specialty nonferrous metals can be used in alloys and are chosen for specific characteristics such as strength, magnetic and electrical properties, and corrosion resistance. Some of these are transition metals, meaning they belong to the d-block in the periodic table and are elements which form an ion with a partially filled d-shell of electrons. Transition metals include zirconium, a silvery white metal; hafnium, a grayish metal; osmium, a blue-black metal; and tantalum, a rare, blue-gray metal. These nonferrous metals are used to create compounds such as aluminum zirconium, a common ingredient in antiperspirants, and osmium tetroxide, a volatile catalyst used to hasten chemical reactions. Other nonferrous metals and nonferrous alloys include copper beryllium, which is used for electronic components, and beryllium oxide, which is used for its electrical insulating properties.
Specialty nonferrous metals and nonferrous alloys are useful in many applications because of their versatility, high density, and tensile strength. For example, tantalum sheet metal is used frequently to create surgical instruments because it does not react with bodily fluids and is corrosion resistant. Some specialty nonferrous metals and nonferrous alloys are highly combustible and volatile, including powder zirconium, which may be stored under water for safety, and beryllium oxide, which is highly toxic if inhaled. Welding zirconium is also available. Specialty nonferrous metals and nonferrous alloys are useful for applications requiring nonmagnetic, lightweight, high strength compounds. Since specialty nonferrous metals and nonferrous alloys have high melting points, they are also often used in electrical and electronic applications.