Kazuki Mori

Microstructure-Based Multiscale Analysis of Hot Rolling of Duplex Stainless Steel Using Various Simulation Software

We proposed a microstructure-based multiscale simulation framework using various commercial simulation software and applied it to analyze the hot rolling of duplex stainless steel. According to the Integrated Computational Material Engineering (ICME) concept, we established a procedure to bridge various simulation software from nano- to macroscopic length scales. Using our framework, first, microstructure evolutions by multiphase field (MPF) simulations coupled with the Calculation of Phase Diagrams (CALPHAD) database were performed. In our application, we simulated the columnar and equiaxed solidification during the continuous casting of duplex stainless steel. In the MPF simulations, the temperature field in the slab was calculated by heat conduction analysis using a finite element method (FEM). Then, the macroscopic elastic and plastic mechanical properties of the microstructure obtained by the MPF simulations were estimated by the virtual material test using a nonlinear FEM based on the homogenization method. Because the elastic constants of single δ-ferrite and γ phases in the microstructure are necessary for the virtual material test, they were calculated by molecular dynamics and first principle calculations. Furthermore, the plastic stress–strain properties of the single phases were estimated on the basis of the results of nano-indentation and uniaxial tensile tests. Subsequently, the hot rolling of the slab was simulated using an elastoplastic FEM with the mechanical properties obtained by the virtual material test. Finally, the static recrystallization in the rolled slab was again simulated by the MPF method.

Development of Microstructure-Based Multiscale Simulation Process for Hot Rolling of Duplex Stainless Steel

Recent improvement of multi-phase field method enables us to simulate microstructure formed by various material processes and homogenization method attracts attention as the way of bridging microstructure and macro homogenized material properties. We have proposed microstructure-based multiscale simulation framework and it was applied to the simulation of hot rolling process of duplex stainless steel. In the framework various commercial software, not only multi-phase field method and homogenizaiton method but also nanoscale molecular dynamics simulation and finite element method was bridged. Multi-phase field method coupled with CALPHAD database was used to simulate microstructure evolution by columnar and equiaxed solidifications during continuous casting. Elastic property for the constituent phases in the duplex stainless steel was calculated by molecular dynamics simulation and first principles calculation. Plastic property was obtained by nano-indentation tests. Homogenization calculation gave macro elastic property from microstructure and property of each phase and virtual material test performed by finite element method served homogenized plastic property. With the material properties hot rolling process was simulated by dynamic explicit simulation of finite element method. Recrystallization by hot rolling process was performed by multi-phase field method. In this paper, the results are discussed to reveal the usefulness and problem for performing microstructure based multiscale analysis. Further discussion is given for the framework here: the method for obtaining material property of each micro phase, anisotropy of homogenized elastic constants, three-dimensional recrystallization calculation. Through these discussions, our simulation framework becomes more reliable.

Solidification Simulation of Fe–Cr–Ni–Mo–C Duplex Stainless Steel Using CALPHAD-Coupled Multi-phase Field Model with Finite Interface Dissipation

A multi-phase field (MPF) model with finite interface dissipation proposed by Steinbach et al. is applied to simulate the dendritic solidification in Fe–Cr–Ni–Mo–C duplex stainless steel. This MPF model does not require an equal diffusion potential assumption and can take into account a substantial non-equilibrium interfacial condition. We develop the MPF code to couple with the CALPHAD thermodynamic database to simulate two-dimensional microstructure evolutions in multi-component alloys using the TQ-interface of Thermo-Calc. The message passing interface parallelization technique is adapted to the program code development to reduce computational elapse time. Solidification calculations were performed in two cases of quinary compositions: Fe–16Cr–2Mo–10Ni–0.08C and Fe–17Cr–2Mo–9Ni–0.08C. We confirm that the developed MPF method can be highly applicable to microstructure evolution simulation of the engineering metal alloy solidification.

Nano Simulation Study of Mechanical Property Parameter for Microstructure-Based Multiscale Simulation

We proposed a microstructure-based multiscale simulation of duplex stainless steel by using the multi-phase field method and finite element method software. Use of an accurate elastic constant is the key to the success of these simulations. However, it is difficult to obtain the elastic constant for the each constituent phase in multicomponent steels from a database and datebook. Herein, the elastic constant of each constituent phase of duplex stainless steel (Fe–Cr–Ni alloy) was calculated by first-principles and molecular dynamics (MD) simulation. The commercial software VASP was used to estimate the elastic constants of the bcc structure. On the other hand, the open-source MD software LAMMPS was used to estimate the elastic constants of the fcc structure. Calculations were performed using 10,000 models in which the Cr and Ni atoms were repositioned at random by MD simulation. The elastic constant volumes showed a Gaussian-like distribution, and this was explained using a radial distribution function. The calculated elastic constants C11, C12, and C44 were good agreement with experimental values.