Processing Route Effects on the Mechanical and Corrosion Properties of Dual Phase Steel

The mechanical and corrosion behaviors of low carbon DP steel were studied based on different processing routes: (1) intercritical annealing (IA), (2) step quenching (SQ) via austenitization and quick transferring of the sample to the second furnace, and (3) Slow SQ via furnace cooling to the desired temperature. The properties were found to be highly dependent on the volume fraction of martensite (V_M) and the density of ferrite/martensite interfaces. However, at the same martensite content, the mechanical properties of Slow SQ sheet were inferior than those of SQ and IA sheets, which were related to the relatively poor work-hardening behavior due to the severe partitioning of Mn between ferrite and martensite phases. The latter was also responsible for an increase in the corrosion current density (i_corr) via galvanic corrosion. These results were analyzed based on the polarization curves and Nyquist plots obtained from the electrochemical impedance spectroscopy test. This study revealed that the SQ route can result in both better mechanical performance and higher corrosion resistance.