한국표면공학회지 (54권5호 248-259)
Effects of post weld heat treatment conditions on localized corrosion resistance of super duplex stainless steel tube used for thermal power plant applications
화력발전용 슈퍼 듀플렉스 스테인리스 강 조관재의 용접 후 열처리 조건이 국부부식 저항성에 미치는 영향
이준호a, 박진성a, 조동민a, 홍승갑b, 김성진a,*
Jun Ho Leea, Jin sung Parka, Dong Min Choa, Seung Gab Hongb and Sung Jin Kim a,*
a순천대학교 신소재공학과, b포스코 기술연구원
a Department of Advanced Materials Engineering, Suncheon National University, Jungang-ro, Suncheon 57922, Republic of Korea b POSCO Technical Research Laboratories, Pohang 790-704, Republic of Korea
This study examined the influence of post weld heat treatment (PWHT) conditions on corrosion behaviors of laser-welded super duplex stainless steel tube. Due to the high cooling rate of laser welding, the phase fraction of ferrite and austenite in the weld metal became unbalanced significantly. In addition, the Cr2N particles were precipitated adjacent to the fusion line, which can be susceptible to the localized corrosion. On the other hand, the phase fraction in the weld metal was restored at a ratio of 5:5 when exposed to temperatures above 1060 oC during the post weld heat treatment. Nevertheless, the high beltline speed during the PWHT, leading to the insufficient cooling rate, caused a precipitation of σ phase at the interface between ferrite/austenite in both weld metal and base metal. This resulted in the severe corrosion damages and significant decrease in critical pitting temperature (CPT), which was even lower than that measured in as-welded condition. Moreover, the fraction of σ phase in the center region of post weld heat treated steel tube was obtained to be higher than in the surface region. These results suggest that the PWHT conditions for the steel tube should be optimized to ensure the high corrosion resistance by excluding the precipitation of σ phase even in center region.
Super duplex stainless steel, Corrosion, Cr2N, Sigma phase, Post weld heat treatment