Abstract: The pitting corrosion of austenite stainless steels and alloy 800 in sodium chloride aqueours has been studied by the rapid scratch technique. The critical potential of the bare metal surface (E_c) obtained by the rapid scratch technique is an accurate potential value. The mechanism of pitting corrosion on the bare metal surface has been discussed and the physical sense of E_c has been proposed. E_c changes linearly with the logarithm of chlorion concentration. E_c is compared with breakdown potential (E_b) and protection (E_p) obtained by potentiodynamic technique. E_c and E_b change in the same way within a large pH range. In order to explain it, the coefficients of repassivation are measured.