Strain localization and damage in dual phase steels investigated by coupled in-situ deformation experiments and crystal plasticity simulations

Abstract

a b s t r a c tFerritic-martensitic dual phase (DP) steels deform spatially in a highly heterogeneous manner, i.e. with strong strain and stress partitioning at the micro-scale. Such heterogeneity in local strain evolution leads in turn to a spatially heterogeneous damage distribution, and thus, plays an important role in the process of damage inheritance and fracture. To understand and improve DP steels, it is important to identify connections between the observed strain and damage heterogeneity and the underlying microstructural parameters, e.g. ferrite grain size, martensite distribution, martensite fraction, etc. In this work we pursue this aim by conducting in-situ deformation experiments on two different DP steel grades, employing two different microscopic-digital image correlation (lDIC) techniques to achieve microstructural strain maps of representative statistics and high-resolution. The resulting local strain maps are analyzed in connection to the observed damage incidents (identified by image post-processing) and to local stress maps (obtained from crystal plasticity (CP) simulations of the same microstructural area). The results reveal that plasticity is typically initiated within ''hot zones'' with larger ferritic grains and lower local martensite fraction. With increasing global deformation, damage incidents are most often observed in the boundary of such highly plastified zones. High-resolution lDIC and the corresponding CP simulations reveal the importance of martensite dispersion: zones with bulky martensite are more susceptible to macroscopic localization before the full strain hardening capacity of the material is consumed. Overall, the presented joint analysis establishes an integrated computational materials engineering (ICME) approach for designing advanced DP steels.

Identifying Structure–Property Relationships Through DREAM.3D Representative Volume Elements and DAMASK Crystal Plasticity Simulations: An Integrated Computational Materials Engineering Approach

“…With typical experimental equipment, these quantities cannot be readily determined at all (in the case of stress), or the acquisition requires significant efforts (in the case of strain, where, e.g., digital image correlation techniques are needed [38][39][40] ). The local distributions of equivalent true strain (e vM ) and stress (r vM ) at the final loading state, i.e.…”

Local strain analysis of the tertiary oxide scale formed on a hot-rolled steel strip via EBSD

“…1) also suggests that the effect of crystallographic orientation could be more dominant than the effect of grain size for the initiation of plasticity in this case. It is noted that trigonal α-Fe 2 O 3 rather than cubic Fe 3 O 4 is strongly anisotropic and involves different microscopic mechanisms such as mechanical twinning and dislocation glide [44,45]. Thus, the mismatch between α-Fe 2 O 3 and Fe 3 O 4 are often considered to be responsible for various peculiar features of plastic flow [46].…”

Hydrogen Embrittlement Behavior of Ultra-high Strength Dual Phase Steel Sheet under Sustained Tensile-loading Test

“…Strain concentration in dual phase steels as a result of uniaxial deformation has been observed in ferrite neighboring martensite. 18,[22][23][24] In dual phase steels having a high volume fraction of martensite, the martensite is also deformed when large strain is applied, 25) and this deformation of the martensite may enhance hydrogen embrittlement. However, since the applied strain in this study was small, the strain is probably concentrated in the ferrite neighboring the martensite, as shown in Fig.…”