Abstract
Complex phase (CP) concept is justified based on the improvement of stretch flangeability (hole expansion) due to replacement of martensite, at least partially, by bainite. Relationship between microstructure and mechanical properties of CP steels is presented as well as recommended for processing parameters to obtain bainite fraction, keeping in mind effects of chemical composition on phase transformations. Effects of alloying/microalloying on mechanical properties of complex phase steels are discussed.