Corrosion behavior and mechanical properties of hot-rolled ultrahigh-strength steel alloys in alkaline and acidic environments

The corrosion behavior and mechanical properties of three hot-rolled ultrahigh-strength steel (UHSS) in alkaline (pH 11) and acidic (pH 5) environments were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. Results were analyzed in terms of the corrosion potential, corrosion current density, impedance modulus, and phase angle. The effect of amount and distribution of ferrite, bainite and cementite, as well Mo, and V alloys percentage content was assessed. The results of electrochemical techniques indicated that main type of corrosion was continuous anodic dissolution with a passivation tendency; this corrosion behavior was driven by charge transfer, charge concentration, and activation polarization. The redox reactions and the type of corrosion products, along with the Mo and V contents, determined the behaviors of the impedance modulus and the phase angle mainly due to the effect of galvanic micro-pairs. The hot-rolling process does not significantly alter the mechanical properties of the as-prepared steels. However, the corrosion current density of alloys is reduced. The UHSS with the highest corrosion resistance and best mechanical properties in both solutions was the L3 alloy.