Damage Evolution in Complex-Phase and Dual-Phase Steels during Edge Stretching

Abstract

The role of microstructural damage in controlling the edge stretchability of Complex-Phase (CP) and Dual-Phase (DP) steels was evaluated using hole tension experiments. The experiments considered a tensile specimen with a hole at the center of specimen that is either sheared (sheared edge condition) or drilled and then reamed (reamed edge condition). The damage mechanism and accumulation in the CP and DP steels were systematically characterized by interrupting the hole tension tests at different strain levels using scanning electron microscope (SEM) analysis and optical microscopy. Martensite cracking and decohesion of ferrite-martensite interfaces are the dominant nucleation mechanisms in the DP780. The primary source of void nucleation in the CP800 is nucleation at TiN particles, with secondary void formation at martensite/bainite interfaces near the failure strain. The rate of damage evolution is considerably higher for the sheared edge in contrast with the reamed edge since the shearing process alters the microstructure in the shear affected zone (SAZ) by introducing work-hardening and initial damage behind the sheared edge. The CP microstructures were shown to be less prone to shear-induced damage than the DP materials resulting in much higher sheared edge formability. Microstructural damage in the CP and DP steels was characterized to understand the interaction between microstructure, damage evolution and edge formability during edge stretching. An analytical model for void evolution and coalescence was developed and applied to predict the damage rate in these rather diverse microstructures.

Experimental Study on Failure Mechanism of Advanced High Strength Steels in Air Bending Process

“…Due to the compressive pressure, no void was detected on the inner region. The experimental results with regard to the initial crack of both metal sheet types are consistent with Pathak et al [9] and Zhao et al [10]. The results are in good agreement.…”

Microstructure, Crystallographic Texture, and Stretch‐Flangeability of Hot‐Rolled Multiphase Steel

“…The martensite and MA grains could not be clearly distinguished as well as ferrite and bainite due to the high level of deformation caused by the punching process. The martensite and MA will be called “hard microconstituents” and ferrite and bainite “soft microconstituents.” The LCR and HCR samples showed microvoids nucleated at grains fractured of hard microconstituent and hard/soft microconstituent interfaces in the shear and fracture zones as reported for dual phase steels and complex phase steels . In addition, a nucleated crack at hard/soft microconstituent interfaces that propagated through the interfaces following the banded microstructure direction can be observed.…”

“…Microvoid nucleation occurs at the ferrite/martensite interfaces and through martensite cracking . In addition, microvoid nucleation near the hole edge‐punched occurred by fracture of large TiN particles and at bainite/martensite interfaces …”

“…The hole expandability of AHSSs has been investigated . However, a detailed characterization of the microstructure of the sheet and the changes at the hole edge‐punched has not been deeply realized.…”

Reduction of Induced Central Damage in Cold Extrusion of Dual-Phase Steel DP800 Using Double-Pass Dies

“…As explained in [15], this was a serious problem in the mid-1960s for automotive companies which encountered important problems of axle shaft breakage leading to 100% inspection. Although fractures are important, there is a growing interest of the scientific community to study the appearance and evolution of damage in general, particularly in dual-phase steels [16][17][18], as it can lead to failure. Damage can affect the mechanical properties of a component under service loads [19].…”