Materials for use at sub-zero temperatures should be ductile, tough and strong at their use temperature. Only a limited number of materials, among them most of the austenitic stainless steels, satisfy all of these requirements. The austenitic stainless steels not only maintain their toughness and ductility, but they also increase in yield and tensile strengths as temperatures decrease. By choosing the right austenitic stainless steel, the demands of many cryogenic temperature applications can be satisfied.

The familiar type 300 series austenitic stainless steels have been used satisfactorily for many years as materials of construction for liquid oxygen tanks and accessories as well as liquid hydrogen handling equipment. Other applications include components containing liquid carbon dioxide, acetylene, methane, argon and nitrogen. Hence, service temperatures ranging from -80°F to -320°F (-62°F to -196°F) are typical based on the boiling points of these liquids.

Type 201 austenitic stainless steel has been available for over 50 years and has gained acceptance in a number of applications. Compared to the 300 series alloys, the lower-nickel 200 series alloys offer an economical way to obtain superior mechanical properties. ATI Allegheny Ludlum has created a special composition of type 201 specifically for sub-zero temperature service as welded tanks and vessels. This alloy, designated ATI 201LN, also identified by the Unified Numbering System Designation S20153, has replaced familiar 300 series stainlesses such as type 301 or type 304 in many applications based upon technical equivalency and economic considerations. Consequently, ATI 201LN alloy is often a good choice for use at temperatures down to -320°F (-196°F).

ATI 201LN alloy is also suited for many ambient temperature structural applications, such as railroad freight cars, truck trailers, coal handling and other bulk transport equipment where there is a need for a good combination of corrosion resistance, strength, toughness and ease of fabrication.