Corrosivity study in Usiminas continuous casting machines segments
Geiciele Mafra de Souza; Meire Guimarães Lage; Alexandre de Freitas Gomes de Mendonça
Abstract
Volatile fluorine compounds are generated in continuous casting processes that use mold flux containing fluorine. The reaction of these compounds with the superheated steam from the secondary cooling system forms hydrofluoric acid, which is corrosive to the metallic structures of continuous casting machines (CCM), mainly in the first segments because there are greater contact between the steam and the fluorine compounds. To obtain knowledge about corrosivity in Usiminas’s CCM and to support taking actions to reduce costs with maintenance, the characteristics of the secondary cooling water were evaluated (pH, alkalinity and ion concentrations) and corrosion coupons were exposed inside the CCM. From the results, it was verified that the water flows and mold flux used in the CCM, which are specific to each type of steel, have a great effect on the water parameters that comes into contact with the structures of the CCM. The corrosion products were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) techniques and. It was observed a predominance of alveolar corrosion and high corrosion rates in the first segments of the CCM. These results helped in the implementation of actions to minimize corrosion in CCM, such as pH monitoring during the process and strict control of sodium hydroxide used in the first segments.
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Submetido em:
10/09/2023
Aceito em:
31/03/2024
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