한국표면공학회지 (54권3호 102-111)
Corrosion Behaviors of Laser-welded Super Duplex Stainless Steel(UNS S32506) Tube with Post-Weld Heat Treatment Conditions
슈퍼 듀플렉스 스테인리스강(UNS S32506) 레이저 조관용접 튜브의 용접 후 열처리에 따른 부식거동
조동민1 · 박진성1 · 홍승갑2 · 황중기3 · 김성진1,*
Dong Min Cho1, Jin-seong Park1, Seung Gab Hong2, Joong-Ki Hwang3, and Sung Jin Kim1,*
1순천대학교 신소재공학과, 2포스코 기술연구원, 3동명대학교 기계공학부
1Department of Advanced Materials Engineering, Sunchon National University, Jungang-ro, Suncheon 57922, Republic of Korea 2POSCO Technical Research Laboratories, Donghaean-ro, Pohang 37859, Republic of Korea 3School of Mechanical Engineering, Tongmyong University, Busan 48520, Republic of Korea
The corrosion behaviors of laser-welded super duplex stainless steel tubes with post-weld heat treatment(PWHT) conditions(950, 1000, 1050, 1100 ℃ for 5 and 30 min) were evaluated by electrochemical potentiodynamic polarization and critical pitting temperature measurements. This study showed that the critical metallurgical factors affecting the degradation of corrosion resistance of a steel tube in as-welded condition were the unbalanced phase fraction(ferrite:austenite = 94:4), Cr2N precipitation, and phase transformation from the austenite phase to ɛ-martensite(via stress-induced phase transformation). The improvement in the corrosion resistance of the welded specimen depends greatly on the PWHT conditions. The specimens after PWHT conducted below 1000 oC showed inferior corrosion resistance, caused by precipitation of the sigma phase enriched with Cr and Mo. At 1100 oC for a longer duration in PWHT, the ferrite phase grows, and its fraction increases, leading to an unbalanced phase fraction in the microstructure. As a result, pitting can be initiated primarily at the interface between the ferrite/austenite phase, particularly in base metal.
Super duplex stainless steel, UNS S32506, Corrosion, PWHT, Laser welding
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