Stainless steel are magnetic like carbon steel. They are problematic to weld due to grain growth in the heat affected zone which reduces ductility and may result in cracks. Increasing chromium and molybdenum contents increase corrosion resistance as it does for austenitic stainless steels, however, this high alloying results in the precipitation of embrittling intermetallic phase upon welding. These microstructural problems due to welding restrict the use of ferritic stainless steels to very thin thicknesses and thus are not used in the construction of large heavy walled vessels and tanks, and structures like austenitic stainless steels. Common ferritic grades are: Type AISI
Duplex stainless steel Duplex stainless steel Duplex stainless steels is the most recent family of stainless steels. They are called duplex (or austenitic-ferritic) grades because their metallurgical structure consists of two phases, austenite (face-centered cubic lattice) and ferrite (body centered cubic lattice) in roughly equal proportions. They are used for their good mechanical properties in the as-cast (and therefore as-welded condition) and/or their excellent corrosion resistance properties (particularly to stress corrosion cracking). They tend to be divided in three sub groups: Grade 1.4462 which has been the grade initially developed. and reperesents the "mid-range" of properties and is perhaps the most used today