ATI 2205™alloy (UNS S31803 and/or S32205) is a nitrogen-enhanced duplex stainless steel alloy. The nitrogen serves to significantly improve the corrosion resistance of the alloy; especially in the welded condition. Earlier duplex alloys have had moderate resistance to general corrosion and chloride stress corrosion cracking, but suffered a substantial loss of properties when used in the as-welded condition. To impart the metallurgical benefits of nitrogen to both improved corrosion performance and as-welded properties, the ATI 2205™ alloy is produced to a 0.15% minimum nitrogen content compared to the ASTM range of 0.08-0.20% for S31803 and 0.14-0.20% for S32205. The minimum Cr, Mo and Ni contents of ATI 2205™ alloy (22.0, 3.1 and 5.5% respectively) satisfy the requirements of both the UNS S31803 and S32205 composition specifications. The typical high Cr, Mo and Ni contents of ATI 2205™ alloy give it a high PREN (Pitting Resistance Equivalent) of 35.8, further enhancing its corrosion resistance. The PREN of ATI 2205™ alloy exceeds those of types 316L and 317L stainless steels.

When heat-treated properly, the composition of ATI 2205™ alloy produces a microstructure that consists of a nearly equal mixture of austenite and ferrite phases as shown in the photomicrograph above right. The microstructure and composition of the ATI 2205™ alloy provide corrosion resistance to many environments that is superior to Types 316 or 317, and a minimum yield strength that is more than double that of conventional austenitic stainless steels.

The microstructure and phase balance of ATI 2205™ alloy have been designed to facilitate the production of pipe and tube products. All ATI 2205™ alloy is metallographically examined to ensure that the as-shipped product is essentially free from the presence of detrimental precipitate phases such as sigma.

The ATI 2205™ alloy is the most widely used of the duplex stainless steels and is often used in the form of welded pipe or tubular components. The alloy has also been applied as a formed and welded sheet product in environments where resistance to general corrosion and chloride stress corrosion cracking is important.