Modelling the density of Al2O3–CaO–MgO–SiO2 system using the CALPHAD approach

The density of Al₂O₃–CaO–MgO–SiO₂ system is calculated using a model for molar volume. The model is similar to the one used for enthalpy of a multicomponent solution in the CALPHAD approach. The expression for molar volume consists of two terms: one representing the volume contribution from pure components and the other the volume of mixing. The molar volume of mixing takes into account of the binary and the ternary interactions. A total of 565 experimental density data for the constituent unary, binary and ternary systems were collected from the literature. These were used as input to simultaneously optimise the model parameters describing the molar volume, after ensuring that the data belong to a fully molten state. During the optimisation 48 data points that showed significant deviation from the average trend were excluded. The optimised model parameters for the unary, binary and ternary subsystems were used to calculate the density of the quaternary system. The calculated results were compared with experimental data. Finally, it is shown that the volume of mixing of binary systems correlates well with the corresponding enthalpy of mixing.     

Predictive computations of intermetallic σ phase evolution in duplex steel. I) Thermodynamic modeling of σ phase in the Fe–Cr–Mn–Mo–Ni system

Thermodynamic modeling of the σ phase was revised according to the three sublattice model developed for the Fe–Cr system (Fe,Cr)₁₀(Fe,Cr)₄(Fe,Cr)₁₆ in the view of simulating thermodynamics and kinetics for duplex stainless steels. The alloying elements Mn, Mo and Ni relevant in duplex steels were added to the σ phase model and their thermodynamic parameters were optimized. As a consequence of the change of thermodynamic model and parameters for the σ phases, alloy phases were also re-optimized. The present work include re-optimization of binaries and ternaries sub-systems in order to build a consistent bottom-up Calphad dataset for the thermokinetic simulation of duplex steels.     

Invited Paper Computer-aided alloy designs of grade 600 MPa reinforced steel bars for seismic safety based on thermodynamic and kinetic calculations: Overview

In order to satisfy the demands for both safety and global warming reduction, a high-strength seismic reinforced steel bar is required in the structural steel market. Recent developments in computational thermodynamics and related application software have made it possible to design a suitable material as well as support engineers of steel manufacturing companies in the production of the designed material with minimum benchmarks in practical operations. This paper reports our recent success in developing grade 600 MPa reinforced steel bars for seismic safety in South Korea. First, conventional alloy design based on CALPHAD-type computational thermodynamics was carried out. For this purpose, a typical alloy system of Fe-0.30C-0.23Si-1.37Mn-0.14V-0.22Cu (in wt%) was selected, and thermodynamic and kinetic calculations were carried out using MatCalc and JMatPro software. Second, in order to reduce V content in the steel for economic reasons, a cooling process designed using finite element (FE) simulation based on the thermodynamic database was performed. For this application, Fe-0.34C-0.22Si-1.34Mn-0.04 V (in wt%) alloy was chosen, and the FE software ABAQUS was applied for modeling the TempCore process. The mechanical properties of the steel products with a diameter of 32 mm produced based on the simulated results satisfy the required properties for grade 600 MPa seismic reinforced steel bars.     

A model for 1D multiphase moving phase boundary simulations under local equilibrium conditions

Two previously suggested simulation models, for multiphase simulations (Larsson and Engström, 2006; Larsson and Höglund, 2009) and diffusion controlled growth (Larsson and Reed, 2008), respectively, are unified to form a generalized model for 1D simulations of diffusion controlled growth under local equilibrium conditions where multiple phases are allowed on either side of an interface.     

Thermodynamic description of the Ni–Sc system

The Ni–Sc system was thermodynamically assessed by the CALPHAD approach based on the available experimental data including the thermodynamic properties and phase equilibria. The excess term of the Gibbs energy of the solution phases (liquid, b.c.c., f.c.c. and h.c.p.) was assessed with the recent exponential temperature dependence of the interaction energies by Kaptay (Calphad 28–2 (2004) 115–124; Calphad 32–2 (2008) 338–352; Mat. Sci. Eng. A 495 (2008) 19–26) and compared with Redlich and Kister (Ind. Eng. Chem. 40 (1948) 345–348) polynomial equation results. The intermetallic compound Ni₂Sc in this binary system which has a homogeneity range, was treated by a two-sublattice model (Sundman et al., Calphad 9 (1985) 153–190; Hillert and Staffansson, Acta Chem. Scand 24 (1970) 3618). The others compounds were modeled as stoichiometric. A consistent set of thermodynamic parameters was optimized to give account of the available experimental and thermodynamic data.