Stainless steel is one of the most widely used alloys of iron that is known for its extensive range of benefits such as enhanced robustness and resistance to corrosion and rust.
The alloy consists of a combination of iron and chromium. It is the presence of chromium that prevents the iron components to remain protected from rust and corrosion. The resistance to corrosion increases with enhanced amounts of chromium. Stainless steel also includes varying amounts of Silicon, Carbon, and Manganese. Certain other elements like Molybdenum and Nickel can also be added for imparting various useful characteristics and properties like enhanced corrosion resistance and increased formability.
Here is a look at the various types of stainless steel compositions and types that are mostly used across the world.
Ferritic Stainless Steel
Ferritic stainless steel is made by combining iron with chromium anywhere between 11.2% and 19% without any or very small traces of nickel. Since nickel is definitely a very expensive alloying element that is also known to go through a lot of price volatility, keeping the amount of nickel low makes it possible to maintain a stable price compared to the steel components having high amounts of nickel. Sometimes molybdenum is combined with certain grades of ferritic stainless steel so that their corrosion resistance can be improved. The welding feature of this type of stainless steel can be enhanced by adding titanium and/or niobium. Ferritic stainless steel is known for its superior toughness, durability, corrosion resistance and strong magnetic properties. The magnetism is caused by the ferritic microstructure of this type of stainless steel. They are typically resistant to very high temperatures of around 800°C to 1150°C. Compared to the standard versions of ferritic grades, they are commonly alloyed with a greater amount of carbon for enhancing their creep strength. Additionally more amounts of aluminum and silicon can be added for improving oxidation resistance.
Austenitic Stainless Steel
The austenitic stainless steel grades are notable for their enhanced corrosion resistance, better weldability and heightened formability. They are known to deliver high impact strength even at low temperatures and this feature makes them useful in various cryogenic applications. These stainless steel components are non-magnetic when in solution-annealed condition. Their strength can be increased by cold working. Sometimes the presence of small amounts of martensite gives rise to magnetic properties. They also have good creep resistance. They are mainly divided into five different subgroups, namely Cr-Mn grades, Cr-Ni grades, Cr-Ni-Mo grades, High-performance grades, and high-temperature grades.
Duplex Stainless Steel
Duplex stainless steel is known for its ferritic-austenitic microstructure which effectively combines numerous benefits of austenitic and ferritic stainless steel. This type of steel offers enhanced resistance and strength to withstand stress corrosion cracking. This form of steel has a rather high chromium content, i.e. almost 20.1% to 25.4% along with a low nickel content ranging between 1.4% to 7%. This means that like ferritic stainless steel, the duplex variant also has a stable price range. They are valued greatly for their high good corrosion resistance, great weldability, superior toughness, magnetic property and lightweight structure.
Martensitic Stainless Steel
The martensitic grades of stainless steel are by far the smallest category of stainless steel. They have got improved robustness and strength due to their higher carbon content. Sometimes nitrogen is added for further improving their strength. They have poor weldability which can be improved by adding nickel and lowering the amounts of carbon. Although they have high wear resistance and high strength, they offer very limited corrosion resistance.
Precipitation Hardening Stainless Steel
Precipitation hardening stainless steel is a type of stainless steel that is hardened with a special mechanism that makes use precipitates formed within the microstructure. This stainless steel also has magnetic properties.