Acoustic emission monitoring of micro cell corrosion testing in type 304 stainless steels

Abstract

A new method of acoustic emission (AE) monitoring was proposed to study the corrosion and stress corrosion cracking (SCC) by chloride ion. It is a combination of the small chloride droplet corrosion, SCC testing method and AE waveform measurement system with a high sensitivity AE sensor, all of which have been developed by our group. Three types of corrosion were observed in the corrosion testing, which were the open pitting, the covered pitting and snake-like corrosion, respectively. There were many AE events in the covered pitting and snake-like corrosion. On the contrary, there was no AE event in the open pitting. Meanwhile, the cross section of the snake-like corrosion was analyzed by EBSD. It shows that under the corrosion surface, there were some cracks at the {111} interface of Σ3 coincidence boundary and annealing twins. Based on these experiment results, it indicated that the microstructure generated by the covered pitting and snake-like corrosion during corrosion is the initiation site of stress corrosion cracking. Besides, the micro cell corrosion and SCC testing in thin plate specimens of SUS304 stainless steel by the AE monitoring were effective for evaluation of the progression process of them.