Studies on the corrosion behaviour of wear resistant hardfacing alloy

Hardfacing alloys are used extensively in the mining and mineral processing industry. They usually have high concentrations of Cr (25%), C (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 the present in the alumina processing industry. The wear resistance is given by the formation of hard primary carbides (M7C3) embedded in an austenitic–eutectic matrix. In this study, hardfacing layers 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 M7C3 stoichiometry (i.e., Cr, B, Si and Ti carbides). Immersion, electrochemical potentiodynamic polarisation and potentiostatic tests in alkaline and acidic environments show a strong influence of microstructure, phase distribution and alloying elements on the corrosion behaviour of the alloys. It has been found that the interface between the carbides and the matrix corroded due to galvanic effects. The galvanic effect was 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 under reducing conditions and M7C3 susceptible to damage under oxidising conditions. Finally, the overall corrosion behavior has been correlated to the M7C3 volume fractions as well as the amount of Cr and other elements in the matrix.