The use of molybdenum and niobium in ultra-high strength multiphase steels

Multiphase steels such as DP (Dual Phase), TRIP (Transformation Induced Plasticity) and CP (Complex Phase) can be produced either directly from the as rolled heat or via an additional heat treatment, usually after cold rolling. The latter has become the dominating route in automotive steel production. The primary effect of Mo alloying is to modify the phase fields in the CCT diagram in such a way that a sufficiently large processing window enables stable production with little property scatter in the final product. Niobium microalloying can improve the strength of multiphase steels in various ways. It is also particularly beneficial with regard to the phase morphology and homogeneity leading to a significant improvement of the mechanical properties. This paper will show processing strategies involving Mo and Nb and explain their metallurgical effects. (AU) Copyright © 2014 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved.