Microvoid Formation of Ferrite-martensite Dual-phase Steel via Tensile Deformation after Severe Plastic Shear-deformation

One of the objectives for development high-strength dual-phase (DP) steel is improving stretch-flangeability. Large-strained sheared edges are deformed and frequently cracked during stretch-flange formation. Considering shearing as first deformation, deformation may be regarded a secondary deformation. To improve stretch-flangeability DP steels, many researchers have analyzed microvoid However, in these analyses, process was not considered. With this background, ex-situ mini-bending tests combined with scanning electron microscopy (SEM) monitoring formation were conducted Prior to several microvoids observed on surface fine subgrains formed ferrite. During preliminary present at ferrite-martensite interface propagated into ferrite phase. In contrast, behavior reamed which without Furthermore, initiated grains that interface, martensite islands This result noteworthy because cracking main factor involved initiation, absence shearing. Electron backscattering diffraction analysis revealed work hardening ferrite, prior caused deviation strain concentration sites from those found Therefore, study elucidated surfaces via provided insights material considering deformations materials.