Austenitic Stainless Steel
Austenitic Stainless Steel, which is known as the 300 series, has a primary phase of austenite. These are all alloys which contain nickel, chromium and in some cases molybdenum and nitrogen and are constructed around the iron composition Type 302 which is 8% nickel and 18% chromium.
To reduce the costs, the nickel content gets replaced with manganese which is the 200 series. Austenitic steel cannot be hardened by heat treatment. The most common austenitic stainless steel used is the Type 304 which is used for surgical equipment which is composed of 8-10% nickel and 18-20% chromium.
Austenitic stainless steel is the primary material used in aviation construction.