Comparative analysis of corrosion resistance in Ni-, Cu- and Co-based alloys in synthetic mine water

To address the corrosion of mild steel in aggressive mine water environments, nickel-chromium-iron (Hastelloy^® G30), copper-nickel-tin (ToughMet^® 3), and cobalt-chromium-tungsten (Stellite^® 6B) alloys were evaluated for their corrosion resistance. The study examined their behaviour in synthetic mine water at pH levels 6, 3 and 1 using potentiodynamic polarisation, alongside microstructural, hardness, and X-ray diffraction (XRD) analyses. Hastelloy^® G30 had equiaxed γ grains with Cr₃C₂ precipitates, ToughMet^® 3 displayed large, irregular grains, and Stellite^® 6B showed γ grains with Cr₃C₂ at boundaries and twinning. Hastelloy^® G30 and Stellite^® 6B demonstrated active-passive transitions with localized corrosion, while ToughMet^® 3 showed pseudo-passivation with severe pitting across all pH levels. Hastelloy^® G30 achieved the lowest corrosion rates at pH 6 (0.63 ± 0.01 µm·y^–1) and pH 3 (0.74 ± 0.05 µm·y^–1) but performed poorly at pH 1 (7.75 ± 0.64 µm·y^–1), with a hardness of 180 ± 10 HV₂. Stellite^® 6B had low corrosion rates at pH 3 (1.32 ± 0.34 µm·y^–1) and pH 1 (5.61 ± 1.13 µm·y^–1), with a hardness of 368 ± 13 HV₂. ToughMet^® 3 showed high corrosion rates, particularly at pH 1 (118.78 ± 8.00 µm·y^–1). Stellite^® 6B is the most promising alternative for harsh mining environments, offering optimal hardness and corrosion resistance.