The Four Major Classifications Of Stainless Steel

Austenitic Steel

Austenitic phase stainless steel is comprised of nickel and molybdenum as its main alloying elements, and has a face-centered cubic crystal structure. The addition of nickel increases its corrosion resistance and ductility, while molybdenum improves corrosion resistance to acidic conditions. Common grades of austenitic stainless steel are 304 and 316. 

Common uses

This type of stainless steel is considered heat resistant and is commonly utilized to produce heat exchangers, boilers, and furnaces. Other common applications of austenitic stainless steel are aerospace components, electronics, locomotive parts, and chemical tanks. 200 series stainless steels are also in the austenitic family, but have manganese as an additional alloying element.  

Martensitic Steel

The martensitephase stainless steel family uses carbon and chromium as its main alloying elements. At higher carbon concentrations, the material has a body-centered tetragonal crystal structure; lower carbon concentrations form a body-centered crystal structure. Martensite is formed when austenite is quenched rapidly at room temperature. Martensitic stainless steel is commonly known as 400 series of stainless steel, such as grades 410, 420, and 440. 

Common Uses

Martensitic stainless steel is commonly utilized in applications where hardness and durability are desired, such as cutlery, tooling, turbine blades, fasteners, and gears.

Ferritic Steel

Ferrite phase stainless steel is non-magnetic and has a body-centered cubic crystal structure. Its main alloying constituents are chromium, iron (hence the name ferritic), and a low concentration of carbon. Ferritic stainless steel is therefore softer, but also has increased ductility and improved formability — but they cannot be heat treated. Examples of ferritic stainless steel are other 400 series grades, such as 409, 430, and 446.

Common Uses

Ferritic stainless steels are a common choice for kitchenware, automotive components, and industrial machinery.

Duplex Steel

Duplex stainless steel is a mixture of austenite and ferrite steel.

Common Use

Duplex steels are often used in the oil and gas, paper, and chemical industries.