The Behavior Of Metastable Pitting Of Stainless Steel And The Relation Between Metastable Pitting And Stable Pitting

Potentiodynamic polarization method was employed to study the behavior of metastable pitting and stable pitting on 304 stainless steel and 316L stainless steel in NaCl solution. The influence of pre-polarization on metastable pitting was studied as well.In addition, the inhibition of some anions on metastable pitting and the relation between metastable pitting and stable pitting were studied.Compared with 304 stainless steel, the behavior of metastable pitting of 316L stainless steel has some properties: the number of metastable pitting was lower, Em(the potential at which the first metastable pit emerged) and Eb(the potential at which the stable pit emerged) were higher, and the growth rate of metastable pitting and pitting were lower.As the sample was pre-polarized ,Em and Eb shifted positively, the number of metastable pits droped and the value of peak current decreased , the life time of metastable pits shortened. The higher the pre-polarization potential, the higher Em, and the less the number of metastable pits.In cerain range of Cl" concentration, both Em and Eb reduced with ci in a way of linearity, and the concentration of Cl- had little effect on the difference between them, we could get the Eb value by measuring Emvalue. With the addition of SO42", PO43" and CrO42" in NaCl solution , Eand Eb obeyed normal distribution. And not only was Eb obtained by Em, but the growth rate of stable pitting was just in the growth rate range of metastable pitting.