화력발전소용 슈퍼 듀플렉스 스테인리스 강(STS 329J4L) 조관 튜브 및 핀-튜브재의 부식거동

• Published in: Corrosion science and technology Vol. 22; no. 6; pp. 435 - 446
• Main Authors: 박진성, Jin Sung Park, 김용현, Yong Hyeon Kim, 홍승갑, Seung Gab Hong, 김성진, Sung Jin Kim
• Format: Journal Article
• Language: Korean
• Published: 한국부식방식학회 31.12.2023
• Subjects: Corrosion; Fin-tube; Heat treatment; Phase transformation; Super duplex stainless steel; Fin-tube; Phase transformation; Heat treatment; Super duplex stainless steel; Corrosion
• ISSN: 1598-6462

Corrosion behaviors of laser-welded super duplex stainless steel (SDSS) tubes after exposure to an actual power plant environment for one year and those of fin-tube welded SDSS were evaluated. Results showed that corrosion damage on the back side of the SDSS tube in the direction of hot air was higher than that on the front side regardless of weldment location. However, corrosion damage showed no difference between weldment and base metal due to recovery of phase fraction in the weldment through post weld heat treatment (PWHT). Nevertheless, the SDSS tube showed severe corrosion damage along grain boundary due to surface phase transformation (δ → γ) and Cr 2 N precipitation caused by PWHT with a high N 2 atmosphere. Corrosion resistance of the SDSS tube was recovered when degraded surface was removed. Corrosion sensitivity of a fin-tube increased significantly due to pre-existing crevice, unbalanced phase fraction, and σ phase precipitation adjacent to the fusion line. Although corrosion resistance was improved by recovered phase fraction and sufficient dissolution of σ phase during PWHT, corrosion reaction was concentrated at the pre-existing crevice. These results suggest that welding conditions for fin-tube steel should be optimized to improve corrosion resistance by removing pre-existing crevice in the weldment.