Studies on the corrosion behaviour of wear resistant hardfacing alloys

Hardfacing alloys are used extensively in the mining, mineral processing, thermal power plants and iron and steel industries. They usually have high concentrations of Cr (>20%), C (2-5%) and Mn (up to 3%). Whilst the primary purpose of these alloys is to provide wear resistance, they are also used in situations requiring both high corrosion and erosion resistance, such as that present in the alumina processing industry. The wear resistance is given by the formation of hard primary carbides (MxCy) embedded in martensitic and austenitic matrices. In this study, hardfacing alloys were deposited on carbon steel by Plasma Arc Welding Process. Hardfacing welding electrodes with different chemical compositions were used, resulting in the production of several microstructures with diverse MxCy stoichiometry. Electrochemical potentiodynamic polarisations and potentiostatic tests were conducted in alkaline environments resembling alumina processing (i.e. Bayer processing). Results show a strong influence of microstructure and alloying elements on the corrosion behaviour of the alloys. The interface between the carbides and the matrix corroded due to galvanic effects, presumably due to depletion of chromium at the interface between carbide and matrix. Moreover, results compare to similar reports that indicate preferential corrosion of the metal matrix in some microstructures and MxCy susceptible to damage under oxidising conditions.