By: Dave Olsen
Austenitic stainless steels are a form of stainless steel that contain significant amounts of chromium and nickel, often manganese, molybdenum, and nitrogen as a supplement to the iron base. The addition of nickel to otherwise ferritic chrome-iron alloys yields predominately austenitic alloys. The microstructure change brings a marked increase in ductility and toughness.
The family of austenitic stainless steels is, by far, the most widely used of the stainless alloys in industrial markets. That is because corrosion resistance provided by austenitics is generally the best of all standard stainless types. Materials are non-hardenable (hardness ranges 130 to 200 BHN), non-magnetic to slightly magnetic, and are readily weldable and machinable.
As workhorse alloys, each offers some slightly different performance expectations:
- CF8 (MTEK 304) combines strength and ductility with good corrosion resistance at relatively low cost. The alloy retains high impact strength to -400ºF / -240ºC. This general purpose corrosion resistant alloy used for flanges, rolls, sleeves, marine and sanitary fittings and valve parts.
- CF8M (MTEK 316) offers resistance to reducing corrosives and chloride pitting attack due to an addition of molybdenum. Like CF8, this alloy has good machinability, but requires re-annealing after welding for maximum corrosion resistance. The presence of controlled ferrite, CF8M exhibits stress corrosion resistance superior to wrought material of the same alloy. Uses include evaporator parts, marine fittings, pump parts, rolls, flanges and valve parts.
- CG8M (MTEK 317) provides exceptional strength combined with corrosion resistance. This alloy delivers cost effective performance in more highly stressed components operating in chemical processing equipment such as centrifuge bowl shells and parts.
- CN7N (MTEK 20) delivers especially good resistance to sulphuric acid and many reducing chemicals. It resists hydrochloric acid, and chloride salt solutions. Excellent machinability and fait welding characteristics. Well suited for flanges, rolls, pump parts, ball valve bodies and parts, and centrifuge parts for chemical processing.