Journal of Advanced Marine Engineering and Technology

The Korean Society of Marine Engineering (한국마린엔지니어링학회)
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Effects of alloy elements on electrochemical characteristics improvement of stainless steel in sea water

해수환경하에서 스테인리스강의 전기화학적 특성 개선을 위한 합금원소의 영향

  • Lee, Jung-Hyung (Division of Marine Engineering, Mokpo Maritime University) ;
  • Choi, Yong-Won (Division of Marine Engineering, Mokpo Maritime University) ;
  • Jang, Seok-Ki (Division of Marine Engineering, Mokpo Maritime University) ;
  • Kim, Seong-Jong (Division of Marine Engineering, Mokpo Maritime University)
  • Received : 2014.07.14
  • Accepted : 2014.09.12
  • Published : 2014.09.30
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Abstract

Austenitic stainless steel is widely used in various industries due to its excellent corrosion resistance. However, Cr carbides precipitation along the grain boundaries after heat treatment or welding may develop Cr depleted zone, which acts as a preferential site for intergranular corrosion attack. To resolve this, carbon stabilizing element such as Ti or Nb are added to suppress formation of Cr carbides. However, there are few reports on corrosion characteristics under seawater environment of the stabilized stainless steel. This study investigated the effects of alloying contents on the electrochemical characteristics in seawater of stainless steel containing stabilizing element(Ti and Nb). To achieve this, the changes on the microstructure due to alloying were observed with microscope, and the electrochemical characteristics were determined by measurement of natural potential and potentiodynamic polarization experiments. The microscopic observation revealed that all specimens had inclusions other than the austenite matrix phase due to the addition of alloying elements. Such inclusions are considered to have different electrochemical characteristics from those of the matrix, and thus a clear distinction was found according to the type of stabilizers and the contents. The results of this study suggest that it is important to consider the effects of alloying contents on the electrochemical characteristics in seawater with the addition of Ti or Nb into austenitic stainless steel.

오스테나이트계 스테인리스강은 우수한 내식성으로 인해 다양한 산업에 널리 적용되는 재료이다. 그러나 열처리나 용접 실시 후 입계에 크롬 탄화물 생성으로 크롬 결핍대가 형성되어, 입계의 내식성이 상대적으로 취약해지는 문제점이 있다. 이를 해결하기 위해 Ti 또는 Nb과 같은 탄소 안정화 원소를 첨가하여 크롬 탄화물 생성을 억제한다. 이러한 안정화된 스테인리스강에 대한 해수환경하에서의 내식성에 관한 연구는 적은 실정이다. 본 연구에서는 안정화 원소(Ti 및 Nb)를 함량 변수로 첨가한 스테인리스강에 대해 해수환경하에서 전기화학적 특성을 평가하고자 하였다. 이를 위해 합금원소 첨가에 따른 미세조직의 변화를 관찰하였으며, 자연전위 측정과 동전위분극 실험을 통해 전기화학적 특성을 파악하였다. 미세조직 관찰 결과, 모든 시편에서 오스테나이트 기지상 이외에 합금원소 첨가에 따른 개재물이 관찰되었다. 이러한 개재물은 기지 조직과 상이한 전기화학적 특성을 가지는 것으로 판단되며, 안정화 원소의 종류 및 함량에 따라 뚜렷한 전기화학적 특성 차이를 나타냈다. 본 연구 결과 오스테나이트계 스테인리스강에 내식성 향상을 위해 첨가되는 Ti 또는 Nb은 첨가량에 따라 서로 다른 전기화학적 특성을 나타내므로, 이를 고려한 합금 설계가 중요할 것으로 사료된다.

Keywords

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