Influence of HNO3 treatments on the early stages of pitting of type 430 stainless steel

Abstract The effect of HNO3 surface treatment on the early stages of pitting of Type 430 stainless steel has been studied by AC impedance method. At a given low potential, the Warburg impedance coefficient σ, which is calculated from impedance plots, is a maximum after wet polishing, and decreases with increasing HNO3 concentration in the solution of surface treatment. It has been suggested that the surface becomes more passive and the most susceptible sites for pit nucleation are eliminated after HNO3 treatments, and that increasing the HNO3 concentration in treatment solution results in increasing the resistance of the steel to metastable pitting. The critical potential (Em) at which metastable pit or pits start to grow on the surface of the steel depends on HNO3 concentration in treatment solution. The higher the HNO3 concentration in treatment solution, the higher the Em values, showing that the nucleated pit or pits proceeding to metastable growth stage becomes more difficult.