The classification of stainless steels is made possible by their different microstructure. Of the four categories, the two most popular are ferritic and austenitic stainless steels. The microstructure of these alloys is the internal arrangement of crystals. The arrangement of crystals determines the mechanical and chemical properties of the alloy. The microstructure of ferritic stainless steel is composed of ferrite crystals. Ferritic crystals are a form of iron that contains trace amounts of carbon, up to 0.025%. Ferritic crystals tend to absorb a limited amount of carbon. This is because of its body centered cubic crystal structure. The arrangement is such that there is an iron atom in each corner except for one in the center. The ferrous atoms in this center give the ferritic stainless steel its magnetism. Austenitic stainless steel, on the other hand, is γ -phase iron, which is an allotrope of iron. At high temperatures ranging from 1674 to 2541 degrees Fahrenheit, alpha iron undergoes a phase transition. Therefore, α iron is transformed from body centered cube or BCC structure to face centered cube or FCC structure. This altered structure of iron is called austenite.
