Stainless steel is an alloy of iron, chromium, and, in some cases, nickel and other metals. The other common additives are carbon, manganese, molybdenum, nitrogen, sulfur, copper, and silicon. Stainless steel is known for its corrosion resistance in varied environments in which carbon and other low alloy steels would easily corrode. The presence of chromium in stainless steel leads to the formation of a tough, adherent, invisible, corrosion-resisting chromium oxide film on the steel surface. More than 60 grades of stainless steel are available today.
Special grades of stainless steel can resist scaling and retain high strength at extremely high temperatures. The easy cleaning ability of stainless steel makes it ideal for maintaining hygiene. Stainless steel can be cut welded, bent, formed, machined, assembled, and fabricated easily. It also has a long life expectancy and is recyclable. Because of its versatile nature, stainless steel is used widely. The global stainless steel market was worth USD 111.4 billion in 2019 and is projected to reach USD 181 billion by 2027 with a growth rate of 6.3% over 2020-2027. Arch City Steel is a top distributor of commonly specified grades and sizes of stainless steel for commercial purposes.
There are mainly five types of stainless steel.
Austenitic Stainless Steel
It has austenite as the primary microstructure. When nickel is added to stainless steel in adequate quantity, its crystal structure changes to “austenite”. Austenitic stainless steel consists of 18% chromium and 8% nickel. It is the most commonly used stainless steel and is known for its high toughness and impressive resistance to elevated temperatures. It has excellent formability, fabricability, and ductility. It is used in computer keyboard key springs, kitchen sinks, food processing equipment, architectural applications, chemical plant, and equipment.
Ferritic Stainless Steel
Ferritic steel is plain chromium stainless steel. It has varying chromium content between 12% and 18%. As the chromium content increases, its corrosion resistance also increases. It has poor weldability, and its formability is not as good as austenitic. Ferritic Stainless Steels generally have better engineering abilities than austenitic grades. It is used in automotive trim, automotive exhausts, colliery equipment, and hot water tanks.
Duplex Stainless Steel
Duplex stainless steels have relatively higher chromium content (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). Hence, it is a mixture of austenitic and ferritic stainless steel. Most duplex steels contain molybdenum in a range of 2.5 – 4%. It shows high resistance to stress corrosion cracking, and has good weldability and formability. It has higher tensile and yield strength than austenitic or ferritic steels. It is used in marine equipment, desalination plants, heat exchangers, and petrochemical plants.
Martensitic Stainless Steel
It has high carbon (0.1 – 1.2%) content. These are plain chromium steels containing between 12 and 18% chromium. Martensitic Stainless Steel has moderate corrosion resistance and can be hardened by heat treatment. It shows poor weldability. Like ferritic grades, it is magnetic. It is used in knife blades, surgical instruments, shafts, spindles, and pins
Precipitation Hardening Stainless Steels
It provides a combination of austenitic and martensitic properties. It can be hardened after fabrication in a single low temperature “aging” process. It shows moderate to good corrosion resistance and has very high strength. It can be welded easily and has magnetic properties like the ferritic grades.