Dislocation density crystalline plasticity modeling of lath martensitic microstructures in steel alloys

Abstract

A three-dimensional multiple-slip dislocation density-based crystalline formulation, specialized finite-element formulations and Voronoi tessellations adapted to martensitic orientations were used to investigate large strain inelastic deformation modes and dislocation density evolution in martensitic microstructures. The formulation is based on accounting for variant morphologies and orientations, retained austenite and initial dislocation densities that are uniquely inherent to martensitic microstructures. The effects of parent austenite orientation and retained austenite were also investigated for heterogeneous fcc/bcc crystalline structures. Furthermore, the formulation was used to investigate microstructures mapped directly from SEM/EBSD images of martensitic steel alloys. The analysis indicates that variant morphology and orientations have a direct effect on dislocation density accumulation and inelastic localization in martensitic microstructures, and that lath directions, orientations and arrangements are critical characteristics of high strength martensitic deformation and behavior.

WITHDRAWN: Dislocation-based constitutive modeling of martensitic/ferritic steels at elevated temperatures. Part II: Cyclic behavior without hold time effects

“…Assuming the short-range and long-range dislocations as macroscopically immobile and mobile, respectively the model has adequately described the overall stress-strain behavior of grade P91 steels under LCF loading without any further (microstructural) consideration. Recent modeling efforts have also indicated the importance of considering both the mobile and immobile dislocation densities in a constitutive relation for predicting microstructural evolution during plasticity (Austin and McDowell, 2011;Gao and Zhang, 2012;Hatem and Zikry, 2009). This implies that stress evolution within any crystalline material upon loading can be closely represented by just con- sidering the evolutionary trends of macroscopic and localized plasticity (or equivalently, the model indices).…”

“…Although quite a few constitutive LCF models exist for martensitic/ferritic steels in general (Aktaa and Petersen, 2011;Aktaa and Schmitt, 2006;Hatem and Zikry, 2009) and grade P91 steels in particular (Koo and Kwon, 2011;Koo and Lee, 2007;Saad et al, 2011;Taguchi et al, 1990;Yaguchi and Takahashi, 2000), only a small number of them have both the evolution of dislocation densities and their interactions as the fundamental basis of their formulation (Fournier et al, 2011;Fournier et al, 2005;Sauzay et al, 2008;Sauzay et al, 2005). The last set of cited modeling efforts are however based on relatively different assumptions and their robustness mostly depends on the careful selection of model parameters that are accordingly modified depending on the nature of loading.…”

Subgrain lath martensite mechanics: A numerical–experimental analysis

“…During quenching from austenite, body centered cubic (BCC) laths form and group together according to a specific orientation relationship (approximately Kurdjumov-Sachs) with the parent austenite face centered cubic (FCC) lattice. The lath morphology and the crystallographic relation between multiple martensite subgrains can influence the local and overall anisotropic mechanical behaviour (Hatem and Zikry, 2009;Mine et al, 2013;Maresca et al, 2014). Also, since the martensitic transformation is never complete (Koistinen and Marburger, 1959;van Bohemen and Sietsma, 2009), thin interlath austenite films may be retained at lath boundaries.…”

Dynamic shear–strain localization and inclusion effects in lath martensitic steels subjected to high pressure loads

“…The parent austenite grain is assumed to be oriented based on the loading plane of (0 0 1) g , and the loading direction of [0 1 0] g . As noted by Hatem and Zikry (2009a) the [0 1 0] g is the direction can result in shear-strain localization. The K-S relation is adapted as the martensite OR, and {1 1 1} g is assumed as the habit plane.…”

“…To address these limitations and to obtain greater predictive capabilities, we have extended the dislocation-density based crystalline models proposed by Zikry and Kao (1996), Ashmawi and Zikry (2000) and Hatem and Zikry (2009a, 2009b, 2009c to investigate dynamic shear-strain localization in lath martensite steels. Within those formulations, we account for martensitic transformations and parent austenite crystalline orientations for an accurate OR description of lath microstructure.…”