Table of Contents
Journal of Metallurgy
Volume 2010 (2010), Article ID 647198, 16 pages
Research Article

A Dislocation-Based Theory for the Deformation Hardening Behavior of DP Steels: Impact of Martensite Content and Ferrite Grain Size

1YB Materialteknik, Knäppgatu 12, 78395 Gustafs, Sweden
2Product Development/Materials Research, SSAB, 78184 Borlänge, Sweden

Received 30 April 2010; Revised 25 August 2010; Accepted 22 October 2010

Academic Editor: Yuri Estrin

Copyright © 2010 Yngve Bergström et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A dislocation model, accurately describing the uniaxial plastic stress-strain behavior of dual phase (DP) steels, is proposed and the impact of martensite content and ferrite grain size in four commercially produced DP steels is analyzed. It is assumed that the plastic deformation process is localized to the ferrite. This is taken into account by introducing a nonhomogeneity parameter, , that specifies the volume fraction of ferrite taking active part in the plastic deformation process. It is found that the larger the martensite content the smaller the initial volume fraction of active ferrite which yields a higher initial deformation hardening rate. This explains the high energy absorbing capacity of DP steels with high volume fractions of martensite. Further, the effect of ferrite grain size strengthening in DP steels is important. The flow stress grain size sensitivity for DP steels is observed to be 7 times larger than that for single phase ferrite.