| Title |
Localized Corrosion Behavior of UNS N07718 in a Solution Simulating a Diluted-sour Environment |
| Authors |
이예진(Ye-jin Lee); 이준섭(Jun-seob Lee); 권순일(Soon Il Kwon); 신정호(Jungho Shin); 조영태(Young Tae Cho); 김석(Seok Kim); 이재현(Je-hyun Lee) |
| DOI |
https://doi.org/10.3365/KJMM.2023.61.8.553 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
localized corrosion; UNS N07718; carbide; scanning kelvin probe; acidic chloride; diluted-sour environment |
| Abstract |
The localized corrosion behavior of precipitation-hardened UNS N07718 was investigated by immersion tests in 6 wt% FeCl3 + 1.0 wt% HCl and the use of electrochemical techniques in a simulating solution of a diluted-sour environment of 25 wt% NaCl + 0.5 wt% CH3COOH. The Ti carbides and Nb-Mo carbides with 1-10 μm size were distributed in the alloy. After immersion at a solution temperature higher than 45℃, localized corrosion with a depth of over 25 μm was identified, and the critical pitting temperature was determined to be 45℃. Potentiodynamic polarization showed that the surface of the UNS N07718 was immediately passivated in the experimental solution. The passivity-maintaining current density was gradually increased with increasing solution temperature, and finally, localized corrosion was initiated or propagated at 0.5 VSSE in 80℃. The localized corrosion was initiated or propagated at the interface between the Ti and Nb-Mo carbides and the alloy substrate. Scanning Kelvin probe microscopic images revealed that the contact-potential difference values were in the order of Ti carbide > Nb-Mo carbide > alloy substrate, indicating that the carbides and alloy substrate act as a cathode and an anode, respectively, forming a micro-galvanic couple. Therefore, it is concluded that localized corrosion is initiated at the interface between the carbides and substrates in UNS N07718.(Received 15 September, 2022; Accepted 8 May, 2023) |