If the steel is tempered rather than normalized , two microstructures, other than perlite, can be produced by the inhibition of the eutectoid transformation: 1. Bainite is the constituent which can be formed when the austenite is cooled rapidly to a certain temperature, usually in the range of 200-400 ° C, and maintained therein. Bainite is a dispersion of submicroscopic carbides in a highly deformed matrix containing more than 0.02% C; 2. Martensite is the constituent that can be formed when the austenite is cooled rapidly to temperatures lower than those in which the bainite would form. It is an extremely hard and fragile phase in which all carbon is trapped in a supersaturated solid solution. The excess carbon distorts the crystalline structure, making it a tetragonal centered body (TCC) (See Chapter 3), the amount of distortion (measured by the mean value of the c / a ratio, being at the height and at the side of the tetragonal unit cell ) approximately proportional to the carbon content.