Noise Spectra of Passive Current for Sensitized SUS 304 Stainless Steel

Abstract

The passive current noise of sensitized SUS 304 was analyzed by the FFT method in 0.05M H₂SO₄ to investigate correlation between the degree of the sensitization and electrochemical noise pattern, comparing with results obtained by the electrochemical potentiokinetic reactivation method (EPR method). It was found that the sensitization effect appeared markedly in an early stage after polarization start, on the power spectral density (PSD) of lower frequency region (∼0.2Hz), when the specimen was polarized at a less noble potential, +0.2V vs. Ag/AgCl. Also, in the early stage (∼5h), the burst type noise with small amplitude was very frequently observed on the passive current, which corresponding to local dissolution of sensitized SUS 304. The micronized and local dissolution at grain boundaries and its neighborhood was concluded to bring mainly the higher level of PSD in the early stage for sensitized SUS 304. Further, the comparison of the PSD level in the early stage gave a possibility to estimate the degree of the sensitization.