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
Stainless steel Hydrochloric acid will damage any kind of stainless steel, and should be avoided. All types of stainless steel resist attack from phosphoric acid and nitric acid at room temperature. At high concentration and elevated temperature attack will occur and higher alloy stainless steels are required. In general, organic acids are less corrosive than mineral acids such as hydrochloric and sulfuric acid. As the molecular weight of organic acids increase their corrosivity decreases. Formic acid has the lowest molecular weight and is a strong acid. Type 304 can be used with formic acid though it will tend to discolor the solution.