Stainless steel is defined as a steel alloy that contains at least 10.5% chromium. Many other elements may be added to imbue different properties or characteristics which means there are many types of stainless steels out there.
When organizing the different types, stainless steel categories are broken down by the kind of microstructure the stainless steel has. This typically leaves stainless steel classified within one of four groups: austenitic, ferritic, martensitic, and duplex.
Austenitic steel is characterized by its face-centered cubic structure that is derived from additions of nickel, manganese, and nitrogen. This microstructure gives austenitic steel good formability and weldability.
Due to its toughness, weldability, and formability, austenitic steel is far and away the most popular stainless steel as it comprises around 70% of stainless steel production.
Austenitic steel is technically classified as non-magnetic, but it usually will have some form of magnetic response depending on the specific composition of the steel.
Ferritic stainless steels have chromium content ranging from 10%-18% and low carbon content (typically less than 0.1%).
Whereas austenitic stainless steel has a face-centered cubic structure, ferritic steel has a body-centered cubic structure.
Ferritic stainless steels are not as tough, durable, nor formidable as austenitic stainless steels, but they actually tend to have better resistance to stress corrosion cracking and are typically cheaper than austenitic steels.
Martensitic stainless steel has high chromium content and relatively high carbon content (as high as 1%) compared to the other types of stainless steel. This means that they can be hardened and tempered the same way that carbon and low-alloy steels are.
This high levels of toughness and hardness associated with tempered martensitic stainless steels are why it is commonly chosen for the production of medical tools.
The first commercially developed stainless steels were martensitic.
Duplex stainless steels are those which have equal amounts austenitic and ferritic crystalline structures.
This is achieved by combining austenitic levels of chromium with lower amounts of nickel needed to maintain a completely austenitic structure.
Duplex steels tend to have around twice the strength of austenitic steel while also maintaining relatively high resistance to pitting and stress corrosion cracking.
Duplex stainless steels are a very cost-effective choice when high strength, durability, and resistance to corrosion is needed.
We can also answer any questions you have regarding stainless steel. Superior Steel Fabrication and Superior Machining are your go-to fab and machine shops in the Pacific Northwest.