“…As experimentally [3,8,57] and numerically [9,10] found by several authors, the material state after quenching is not homogeneous in DP. Due to the volume change, the dislocation density decreases with an increasing distance from the martensitic areas.…”
Section: Stress and Plastic Strain Statesupporting
confidence: 54%
“…Starting from an austenitic-ferritic microstructure, the martensitic transformation can be simulated to create a suitable initial stress-strain state for the following loading test. Usually, this is done by a virtual martensite transformation, without resolving the underlying martensitic structure [9,10]. Controlled by a temperature decrease, a volume expansion is imposed on the austenitic regions, so that plastic hardening occurs in the neighboring ferritic regions.…”
On the mesoscopic length scale, dual-phase steel (DP) consists of hard and brittle martensitic inclusions, which are embedded in a soft and ductile ferritic matrix. On the macroscopic scale, this composite-like structure is responsible for the attractive combination of good formability and high tensile strength. In order to improve the properties of DP, computer models can be used to investigate the effects of various influencing factors during the production chain. As an extension to our previous work (Schoof et al 2018 Int. J. Solids Struct. 134 181-94), we include a J 2 -viscoplasticity formulation into a multiphase-field framework to study plastic effects in an EBSD-based DP microstructure during the martensitic phase transformation. The hardening behavior of each phase is modeled using a nonlinear function. The effect of the plastic relaxation rate on the microstructure formation and the residual strains is investigated. Two different models for introducing a yield criterion into a diffuse interface framework are discussed, and the results are compared. In this context, a plastic driving force is formulated, and its influence on the microstructure evolution is evaluated. The model not only predicts high values of accumulated plastic strain in ferritic regions, close to ferrite-martensite grain boundaries, but also within martensitic islands.
“…As experimentally [3,8,57] and numerically [9,10] found by several authors, the material state after quenching is not homogeneous in DP. Due to the volume change, the dislocation density decreases with an increasing distance from the martensitic areas.…”
Section: Stress and Plastic Strain Statesupporting
confidence: 54%
“…Starting from an austenitic-ferritic microstructure, the martensitic transformation can be simulated to create a suitable initial stress-strain state for the following loading test. Usually, this is done by a virtual martensite transformation, without resolving the underlying martensitic structure [9,10]. Controlled by a temperature decrease, a volume expansion is imposed on the austenitic regions, so that plastic hardening occurs in the neighboring ferritic regions.…”
On the mesoscopic length scale, dual-phase steel (DP) consists of hard and brittle martensitic inclusions, which are embedded in a soft and ductile ferritic matrix. On the macroscopic scale, this composite-like structure is responsible for the attractive combination of good formability and high tensile strength. In order to improve the properties of DP, computer models can be used to investigate the effects of various influencing factors during the production chain. As an extension to our previous work (Schoof et al 2018 Int. J. Solids Struct. 134 181-94), we include a J 2 -viscoplasticity formulation into a multiphase-field framework to study plastic effects in an EBSD-based DP microstructure during the martensitic phase transformation. The hardening behavior of each phase is modeled using a nonlinear function. The effect of the plastic relaxation rate on the microstructure formation and the residual strains is investigated. Two different models for introducing a yield criterion into a diffuse interface framework are discussed, and the results are compared. In this context, a plastic driving force is formulated, and its influence on the microstructure evolution is evaluated. The model not only predicts high values of accumulated plastic strain in ferritic regions, close to ferrite-martensite grain boundaries, but also within martensitic islands.
“…The inhomogeneous deformation and work hardening behavior of DP steels were studied by Rieger et al. [13] in 2015 utilizing an Electron Backscattered Diffraction (EBSD) based on a full-field RVE and a mean-field model respectively. On the other hand, tremendous efforts have been put on the effects of microstructure properties (i.e.…”
“…At an increasing plastic strain, the higher dislocation densities are found from crack tip to the ferrite/martensite boundary. It is expected as a result of dislocation glide across the grain interiors to form pile-ups and accumulation near the ferrite/martensite interfaces [20,21]. Figure 5 In-situ TEM observation on the coalescence of microcracks.…”
In this paper, the microcrack evolution in DP590 dual-phase steel was observed by in-situ straining in straining transmission electron microscopy. It was found that a void initiated ahead of a main crack. After the load was applied, a thinned area was nucleated ahead of the void tip, and it grew gradually into shallow nanovoid, penetrating nanovoid, and then new void. Meanwhile, the old void connected with the main crack. The repetitions of the procedures resulted in the continuous propagation of a crack. Interaction between microcracks was observed. The propagation direction of one microcrack may change, affected by other microcracks. Voids were observed between microcracks and have a significant effect on the coalescence of microcracks.
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