Abstract
This work reports on experimental and numerical results of the gray-to-white transition (GWT) during solidification of a hypereutectic gray cast iron (GCI) in a casting test using a stub-to-carbon (STC) connection assembly. Since in this process non-uniform cooling rates are produced, the mechanical properties are expected to spatially vary due to the development of different microstructures along the thimble. The twin aims of this work were to (1) experimentally validate the GWT prediction capabilities of the microstructural model proposed earlier by the authors in the rodding process of a hypereutectic GCI-STC, and (2) estimate, from the numerically obtained microstructure and ultimate tensile strength (UTS), the local hardness of the alloy after the numerical predictions of the microstructure were experimentally validated. To this end, the final microstructure at different points of the thimble and the hardness profile along its radial direction were measured for validation purposes. Moreover, this rodding process was simulated using an extension of a thermal microstructural model previously developed by the authors and the GWT was superimposed on that simulation. The computed results encompass cooling curves, the evolution of gray and white fractions, eutectic radii and densities and, in addition, the hardness profile. A detailed discussion of the experimental and numerical results is presented. Finally, the computed GWT was found to adequately reproduce the experimental data.
Highlights
The Hall-Héroult smelting process is the most widely used method to reduce alumina to aluminum via electrolysis
Due to the large amounts of electrical energy involved to overcome the strong chemical bond existing between the aluminum and oxygen present in the raw material, one of the most important factors affecting the efficiency of the process is related to the total cell voltage drop caused by the electrical resistances of the various materials as well as the several electrical connections encountered in the current flow path
Some recent studies [1,2,3,4] have focused on a gray cast iron (GCI) thimble, which is part of what is known in the industry as the stub-to-carbon connection (STC), Metals 2017, 7, 549; doi:10.3390/met7120549
Summary
The Hall-Héroult smelting process is the most widely used method to reduce alumina to aluminum via electrolysis. Some recent studies [1,2,3,4] have focused on a gray cast iron (GCI) thimble, which is part of what is known in the industry as the stub-to-carbon connection (STC), Metals 2017, 7, 549; doi:10.3390/met7120549 www.mdpi.com/journal/metals This is an electrical connection in the anode assembly between the stub and the carbon anode (C-anode) which are linked by the thimble, and is responsible for energy loss from. Thimble, and is responsible energy with anfrom air gap forms the rodding process whenat the thimble contracts and Joulethat heating dueduring to an imperfect contact that exists the solidifying anode-thimble interface This is associated with an air gap fact that that formsthimbles during the rodding process when the shrinksimperfect onto thecontact stub.
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