POTENTIOSTATIC STUDY OF LOW ALLOY STEELS PITS FORMATION

Pitting corrosion of low-alloy steels containing Cr up to 5 % (mass.) has been studied by the potentiostatic polarization method. The essence of this method is potentiostatic polarization of steels specimens in the potential’s range of active-passive transition and following analyzing of current oscillation by Fourier analysis. The characteristic frequencies corresponding to different periods of pits growth have been obtained by this method and the relationship of current oscillation on the experimental chronoamperograms with pits growth has been determined. Revealed peculiarities of time distribution of characteristic frequencies demonstrate that pit growth can be represented as consisting of three main stages: firstly oxide films form, later these oxide films growth accompanies by local spots of dissolution formation and at last dissolution of particular pits occurs. Moreover the process of pits dissolution is periodical (oscillatory) too.