TRIP-assisted multiphase steels with niobium additions. Microstructures and properties

It seems completely clear that the combination within the same microstructure of various steel phases (ferrite, bainite, martensite) and the existence of the TRIP effect (i.e. a mechanically induced martensitic transformation) improves in a large way the properties of strength and ductility of low-alloy steels. TRIP-aided multiphase steels have been studied for several years and arouse a growing industrial interest. This project deals with the influence of a large Nb addition on the microstructure and mechanical properties of TRIP-assisted multiphase steels. It is shown that Nb influences in a large way the different phase transformations as well as the recrystallisation of the ferrite matrix occurring during the heat-treatment of cold-rolled TRIP-aided steels. As a consequence, the mechanical properties also depend on the parameters of the thermomechanical process and on the content and stability of the retained austenite.