Ferritic Stainless Steels...

Ferritic Stainless Steels Ferritic stainless steels are high chromium (Cr), magnetic stainless steels that have low carbon (C) content. The chromium content of these stainless steels varies from 10.5 % to 29 % taking into account a very wide range of applications. Ferritic stainless steels can also contain other elements such as molybdenum (Mo), titanium (Ti), aluminum (Al), and niobium (Nb) etc. It is a cost saving material since most of the grades do not have expensive nickel (Ni) additions. Their market share has grown in the recent past and they represent already about 30 % of total global stainless steel production. In comparison to austenitic stainless steels, which have a face-centered cubic (fcc) grain structure, ferritic stainless steels are defined by a body-centered cubic (bcc) grain structure. In other words, the crystal structure of such steels is comprised of a cubic atom cell with an atom in the center. This crystal structure is the same as that of pure iron (? iron) at room temperature. Although the Schaeffler diagram (Fig. 1) is mainly used for welded structures, it is very useful to illustrate the different areas of stability of stainless steel microstructures. Fig 1 Schaeffler diagram The ferritic grades  Ferritic grades are usually classified into five groups (Fig 2) consisting of three families of standard grades and two of ‘special’ grades. By far the greatest current use of ferritic stainless steels, both in terms of tonnage and number of applications, is centered on the standard grades.    Fig 2 – Classification of ferritic stainless steel grades Group 1 – These have the lowest chromium content (10 % to 14 %, grades 409 and 410L) of all stainless steels and are ideal for slightly corrosive environments where localized rust is acceptable. These stainless steels have...