Microstructure Modelling of Dual-Phase Steel Using SEM Micrographs and Voronoi Polycrystal Models

Abstract

The microstructure of dual-phase (DP) steels is composed of a matrix of ferrite reinforced by islands of martensite and the common interphase boundaries. To study the mechanical behavior of DP steels, steel with 45% ferrite and 55% martensite was fabricated and tested in the laboratory. Two types of finite element models were then created based on SEM images. The first model directly created the grains and boundaries from the SEM images, while the second model used a Voronoi type algorithm to construct geometries which are statistically similar to the SEM images. The models consider the measured morphology of ferrite, martensite, and their phase boundaries. The Gurson damage model was then used for the ferrite and boundary regions. The obtained results correctly predicted the failure mechanisms in a DP material. The results indicate that the deformation is localized due to microstructural inhomogeneities and the nucleation of voids in the boundaries between the ferrite and martensite grains. The good correlation between the numerical and experimental observations from SEM micrographs shows the efficiency of the proposed models in predicting the failure mechanism of DP steels.

A GPU-based caching strategy for multi-material linear elastic FEM on regular grids

“…Our approach ( Fig 1 ) is based on a number of assumptions about the mechanical problem. In most problems with a limited number of discrete materials [ 11 , 38 , 40 ], the global stiffness matrix contains many redundant entries. Firstly, there are often large regions of uniform material.…”

Non-destructive measurement of microstructure and tensile strength in varying thickness commercial DP steel strip using an EM sensor

“…Typical SEM images of the DP600, DP800 and DP1000 steels are shown in Fig 2 . As can be seen, the microstructure of dual phase (DP) steels consists of a ferrite matrix containing a second phase in the form of islands (martensite, bainite and/or tempered martensite) [24]. Different volume fractions of ferrite and martensite / bainite are present in the different grades of DP steels, used to give the different strength levels [4,5,24].…”

“…At room temperature, yield stress (σy) depends on the inverse square root of the grain size, i.e. the Hall-Petch relationship [24][25][26][27][28] and also grain size affects the tensile strength [29]. It is known that the ferrite grain size affects the magnetic properties in low carbon steel as the grain boundaries act as effective pinning points to magnetic domain movement [30][31][32].…”

Voronoi Diagram-Based Microstructure Modeling and Micromechanical Analysis of Quenched C35 Steel

“…If we divide the region in such a way that the distance from a given point to the point under consideration is the minimum, the result will be Voronoi diagram [37]. Kant et al developed statistically similar microstructure of a duel-phase steel from SEM images using Voronoi diagram and successfully predicted the failure mechanism [38]. A two-dimensional model based on Voronoi algorithm is used to model microstructure of ferrite-pearlite steel and is used to investigate the plastic behavior under biaxial loading [39].…”