Thermodynamic Self-interaction of Si in Ferritic Fe-Si Alloys
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https://doi.org/10.1007/s11661-019-05392-w The Minerals, Metals & Materials Society and ASM International 2019
In order to appropriately control alloying elements and inclusions, knowledge of thermodynamic properties, such as the interaction parameters of alloying elements, even in solid Fe is required. In fact, there are many studies on the thermodynamic interaction parameters between alloying elements in liquid Fe.[1] In solid Fe, however, the interaction parameters of solutes have been rarely reported. Even the few reported values of interaction parameter in solid phase are mostly related to carbon and nitrogen, rather than metallic alloying elements. Wada et al. determined the thermodynamic properties of carbon in Fe-(Ni, Mn, Si)-C alloys by equilibration with controlled CH4-H2 atmosphere.[2,3] As for the interaction parameters between other elemental solutes besides carbon, there is an example about the interaction parameter of Si and Ti in both austenitic Fe and ferritic Fe at 1273 K based on equilibrium experiments between solid Fe and liquid Ag by one of the present authors.[4]
SUJIN LEE and YOUNGJO KANG are with the Department of Materials Science and Engineering, Dong-A University, Busan 49315, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted March 28, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Si has been used as a deoxidizing agent in steelmaking of many typical steel grades to reduce bubbles of oxygen from molten steel. For semi or fully killed steels, addition of Si should be achieved, which is in molten steel Si must be a role as essential alloying element. Not only in molten steel but also in solid steel, Si has significant impact on the properties and process of steel products. Si helps to improve mechanical properties and protect an oxidizing layer formed on high-strength steel grades, e.g., transformation-induced plasticity steel during annealing or rolling process.[5,6] In particular, electrical steel grades, which contain more than 3 wt pct Si for minimizing eddy current loss, are widely used in many industries. These steels are specifically utilized in transformers and electric motors due to their excellent magnetic properties, such as low core loss and high permeability. For improvement of their magnetic properties, the control of grain size during heat treatment has significant importance. In addition, various and small precipitations of inclusions such as AlN and MnS are utilized as inhibitors in secondary recrystallization. The interaction between solute elements in the solid phase has an impact on the grain growth of Si steels and thus the thermodynamic driving force to develop secondary inclusions and particles which may result in undesired nucleation and unexpected growth of smaller grains can be controlled.[7] Therefore, information on the interactions between solutes in solid phase is important to clearly understand formation conditions of the precipitates. The influence of Si on the solute elements, particularly in solid Fe containing co
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