Journal of the Korean institute of surface engineering (한국표면공학회지)

The Korean Institute of Surface Engineering (한국표면공학회)
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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

  • Cho, Dong Min (Department of Advanced Materials Engineering, Sunchon National University) ;
  • Park, Jin-seong (Department of Advanced Materials Engineering, Sunchon National University) ;
  • Hong, Seung Gab (POSCO Technical Research Laboratories) ;
  • Hwang, Joong-Ki (School of Mechanical Engineering, Tongmyong University) ;
  • Kim, Sung Jin (Department of Advanced Materials Engineering, Sunchon National University)
  • 조동민 (순천대학교 신소재공학과) ;
  • 박진성 (순천대학교 신소재공학과) ;
  • 홍승갑 (포스코 기술연구원) ;
  • 황중기 (동명대학교 기계공학부) ;
  • 김성진 (순천대학교 신소재공학과)
  • Received : 2021.04.06
  • Accepted : 2021.05.20
  • Published : 2021.06.30
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Abstract

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 ℃ showed inferior corrosion resistance, caused by precipitation of the sigma phase enriched with Cr and Mo. At 1100 ℃ 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.

Keywords

Acknowledgement

This work was supported by a Research promotion program of SCNU.

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