Although stainless steel is an alloy itself, comprised of iron, carbon, chromium, additional materials such as molybdenum, nickel, nitrogen and copper can be added to create a number of stainless steel alloys. While regular steel often contains smaller amounts of chromium to enhance properties of strength and hardness, stainless steel alloys offers higher corrosion resistance due to their ability to develop a passivation layer of chromium oxide on their outer surface, effectively coating the steel and protecting it from the harmful oxidation that occurs between exposed iron and oxygen molecules in the air.
The most common stainless steel alloys include austenitic stainless steels, duplex stainless steels, ferrite stainless steels, martensitic stainless steels and precipitation-hardened stainless steels. The different stainless steel alloys work best for varying application: such as, austenitic stainless steels work best in applications such as chemical equipment and food equipment; duplex stainless steels work best for pipelines and pressure shafting; ferrite stainless steel works best for decorative trim, vehicle mufflers and cooking utensils; martensitic stainless steels work best for turbine blades, pump shafts and industrial fasteners; and precipitation-hardened stainless steels work best for petrochemical equipment, valves and gears. As a result, the different types of stainless steel alloys are utilized in a diverse range of industries including food handling, manufacturing, automotive, aerospace, chemical processing, petrochemical, architecture and telecommunications.
Stainless steel alloys are defined based on their distinct material compositions, which results in different crystalline structures. Accounting for 70% of the stainless steel family, austenitic stainless steels are non-magnetic and are composed of a maximum of .15% carbon, a minimum of 16% chromium and a high enough amount of either nickel or manganese in order to retain the austenitic structure of the stainless steel at all temperatures, including extremely hot and extremely cold. Duplex stainless steels magnetic and are composed of high levels of chromium (19-28%) as well as molybdenum and nickel, although in lower amounts than austenitic stainless steels. Duplex stainless steels are a combination of the austenite and ferrite microstructures and typically have a 40/60 mix although 50/50 is the ideal. Ferrite stainless steels are magnetic and are composed of iron and chromium, but may include minute amounts of nickel, molybdenum, aluminum and titanium. Although ferrite stainless steels cannot be hardened, they typically offer better engineering capabilities than austenitic stainless steels. Martensitic stainless steels are magnetic and are composed of chromium, molybdenum, nickel and carbon. Unlike most other stainless steel alloys, martensitic stainless steels can be hardened through heat treatment. Precipitation-hardening stainless steels are ultra-high-strength stainless steel alloys that are composed of iron, chromium and nickel. Precipitation-hardening stainless steels can have an austenitic or martensitic crystalline structure.
Stainless Steel Alloy - Metalmark Inc.