Effect of Ferrite/Martensite Phase Size on Tensile Behavior of Dual-Phase Steels with Nano-Precipitation of Vanadium Carbides

Abstract

This study investigates the effect of ferrite/martensite phase size and dispersion of nano-precipitates in ferrite on strength, ductility, and fracture behavior of dual-phase (DP) steels. Dispersion of nano-precipitates in ferrite improves the strength with keeping sufficient uniform elongation and post-uniform elongation, while decrease in ferrite/martensite phase size has a little effect on the increase in strength in the phase size range investigated. However, the refinement of phase size significantly improves the post-uniform elongation and reduction in area. It is concluded therefore that a simultaneous combination of refinement of ferrite/martensite phase size and dispersion of nano-precipitation in ferrite is effective to significantly improve the strength and strength–post-uniform elongation in DP steels. Quantitative analysis of void formation reveals that fracture by martensite cracking is a primary fracture mechanism in coarse phase-sized DP samples, while ferrite/martensite interface decohesion becomes a dominant fracture mechanism in fine phase-sized DP samples. It is suggested that the refinement of phase size is a promising strategy to change the fracture behavior from brittle to ductile manner, leading to an enhancement of local deformability after the necking.