Stainless Steel Family Descriptions

Austenitic Stainless Steels

Austenitic stainless steels have a face-centered cubic (fcc) structure. This structure is attained through the liberal use of austenitizing elements such as nickel, manganese, and nitrogen. These steels are essentially nonmagnetic in the annealed condition and can be hardened only by cold working. They usually possess excellent cryogenic properties and good high-temperature strength. Chromium content generally varies from 16 to 26%; nickel, up to about 35%; and manganese, up to 15%. The 2xx series steels contain nitrogen, 4 to 15.5% Mn, and up to 7% Ni. The 3xx types contain larger amounts of nickel and up to 2% Mn. Molybdenum, copper, silicon, aluminum, titanium, and niobium may be added to confer certain characteristics such as halide pitting resistance or oxidation resistance. Sulfur or selenium may be added to certain grades to improve machinability.

Austenitic types represent the largest of the groups of stainless steels and are produced in higher tonnages than any other group. They have good corrosion resistance in most environments. Strengths are equivalent to those of mild steels, approximately 30 ksi (210 MPa) minimum yield strength at room temperature, and are not transformation hardenable. Cold working can strengthen austenitic stainless steels significantly. Low-temperature impact properties are good for these alloys, making them useful in cryogenic applications.

Typical applications include:

Austenitic alloys are more expensive than martensitic and low-to-medium chromium ferritic grades, due to the higher alloy content of these alloys. Weldability is considered excellent; however many austenitic stainless types are prone to intergranular attack and intergranular stress corrosion cracking in the heat affected zone after welding.