How the multi-phase microstructure of a novel tool steel determines its corrosion behaviour in sulphuric acids

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The corrosion behaviour of a Fe81Cr15V3C1 steel was analysed compared to commercial X90CrMoV18 (1.4112) in 0.01-1 mol/L H2SO4 solutions. The rapidly cooled steel comprises martensite dendrites, carbide networks (M7C3, MC) and austenite interdendritic areas. Electrochemical measurements with surface analysis (SEM, EDX, AES, GD-OES) revealed the phase impact on corrosion. Active corrosion of austenite occurs at martensite-carbide boundaries leading to narrow bands. A unique oxidation between passivity and transpassivity with dissolution along lamellar carbides and vanadyl(IV) cation release enhances with increasing acid concentration. Both steels exhibit similar corrosion resistance, a superior mechanical performance of Fe81Cr15V3C1 explains its potential for tool manufacturing.