Abstract
The new evaluation test method, CCS （Continuous Current Step） method, for crevice corrosion propagation of stainless steels was proposed. This CCS method is based on the crevice corrosion propagation mechanism of stainless steels in natural seawater. The steady state potential （EOUT） is measured galvanostatically on CCS test. The data sets of EOUT－i were obtained for various stainless steels. It was considered that this EOUT reflected the state of active corrosion in anolyte of inside crevice under the constant current density.
The EOUT－i data was analyzed by the exponential decay curve. When the current density i was under 1× 10－5 A cm－2（ ≈0.1 mm/y）, the obtained potential EOUT was considered as the repassivation potential called ER（CCS） in this test. The crevice corrosion propagation was regarded as stop at less noble potential of ER（CCS）.
The effects of Cr, Ni, Mo and Cu on the EOUT－i relations were tested in artificial seawater. ER（CCS） related to the metal composition and was described as one equation by using the new index, CCR（Crevice Corrosion Propagation Resistance Index）.
CCR＝[Cr]＋0.95[Ni]＋0.74[Mo]＋2.03[Cu]
ER（CCS）＝－317＋13.75 CCR（mV vs.SHE）
This new index, CCR, succeeded in unification of the crevice corrosion propagation （ER（CCS）） for various stainless steels.
