Thermodynamic Assessments of the Fe-Si-Cr and Fe-Si-Mg Systems
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INTRODUCTION
THE Fe-Si-Cr and Fe-Si-Mg systems are among the most important subsystems in steels. Silicon steels (Fe-Si-based alloys) as soft magnetic materials are widely used in energy transportation and electromagnetic energy conversion due to their combined low magnetostriction and high saturation magnetization.[1] Cr and Mg are commonly added in the Fe-Si alloys to modify the microstructure and mechanical and magnetic properties. Cr can promote the formation of CrSi and CrSi2 compounds with high thermal stability that benefits the high-temperature applications of Fe-Si electrical steels.[2] Mg can be used for the refinement of austenite grain size,[3] and magnesium treatment can improve the hydrogen-induced cracking resistance and possibly hot cracking resistance.[4] In addition, stainless steels (Fe-Cr-based alloys) are widely used for industrial applications because of their good mechanical properties and corrosion resistance.[5] The phase diagram, phase equilibria, and thermodynamic properties are of fundamental importance for the understanding of the various phenomena and the designs of new Fe-based alloys. Such information was previously optimized by Chart et al.,[6] Lindholm,[7] and Miettinen[8] for Fe-Si-Cr and Du et al.[9] for Fe-Si-Mg within the framework of the CALPHAD (CALculation of PHAse Diagram) approach. Chart et al. only considered the isothermal section at 1173 K (900 °C). Lindholm’s optimization predicted a much lower liquidus temperature than the experimental data and SENLIN CUI and IN-HO JUNG are with the Department of Mining and Materials Engineering, McGill University, Montreal, PQ, H3A 0C5, Canada. Contact email: [email protected] Manuscript submitted December 15, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
showed an error in the distribution of Si between the solid and liquid. Later, Miettinen revised the liquid, bcc, and fcc phases of the Fe-Si-Cr system to improve the quality of the thermodynamic description. However, the optimization was only limited to the low Si region. So far, no comprehensive thermodynamic modeling of the Fe-Si-Cr system has been performed. In the case of the Fe-Si-Mg system, the thermodynamic and phase diagram information was well reviewed and optimized by Du et al. Recently, the present authors[10] reoptimized the Fe-Si system with a better description of the thermodynamic properties of the system. The thermodynamic description of the Fe-Cr system by Andersson and Sundman[11] was revised also by the present authors[12] for a better description of the solid/liquid equilibria. Besides, the Cr-Si system was also revised in a recent article[13] using the modified quasi-chemical model (MQM) for liquid with improvement in the thermodynamic properties of liquid and compounds. The present work will reoptimize the Fe-Cr-Si and Fe-Mg-Si systems based on the new thermodynamic descriptions of subsystems.
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CRITICAL EVALUATION OF LITERATURE INFORMATION
A. Fe-Si-Cr System 1. Phase diagram information Phase diagram information in the Fe-Si-Cr system was previousl
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