Three-dimensional finite element analysis of representative volume elements for characterizing the effects of martensite elongation and banding on tensile strength of ferrite-martensite dual-phase steels

Abstract

In this study, we numerically analyzed the effects of martensite elongation (i.e., fibering) and banding on the macroscopic stress-strain curves and microscale damage evolution in dual-phase (DP) steels using three-dimensional finite element analyses to obtain insights into designing more ductile, higher-strength DP steels. Representative volume elements (RVEs) composed of equiaxed, elongated, and banded martensite grains embedded within a ferrite matrix were employed for the simulations. A modified Voronoi diagram technique was applied to generate these virtual martensite grains in the RVEs. The analyses revealed that equiaxed martensite concentrated strain in certain parts of the ferrite phase, whereas martensite elongation caused a homogenous strain concentration in the ferrite phase, which, in turn, acted as a newly generated hard phase. Therefore, the tensile strength was lower than for equiaxed grains. On the other hand, martensite banding did not decrease the ferrite strain concentration, but induced a high degree of strain partitioning in the martensite grains. This behavior resulted in remarkably high yield stresses over the entire strain region, including at the peak values. Martensite elongation also resulted in a high degree of damage in the martensite grains. Nevertheless, the elongated martensite bands exhibited smooth surfaces with few concavities. These bands prevented damage concentration during martensite elongation and banding, in contrast to the case for the banding of the equiaxed martensite grains.