안정화 원소 첨가에 따른 스테인리스강의 기계적 특성과해수환경 하에서의 전기화학적 특성
Effects of stabilizing elements on mechanical and electrochemical characteristics of stainless steel in marine environment
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Ti과 Nb과 같은 안정화 원소가 첨가된 스테인리스강은 입계부식 방지 효과가 있어 해양 및 조선 산업에 널리 사용되는 내식성 재료이다. 본 연구에서는 STS 304 주성분에 탄소 안정화 원소인 Ti(0.26%, 0.71%)와 Nb(0.29%, 0.46%,0.71%)을 농도 변수로 첨가한 시편을 제작하여, 안정화 원소 함량에 따른 기계적 특성 및 전기화학적 특성을 평가하였다. 합금 원소 첨가에 따른 재료의 기계적 특성 파악을 위해 마이크로 비커스 경도기를 이용하여 경도 측정을 실시하였다. 재료의 전기화학적 특성을 파악하기 위해 타펠분석, 사이클릭 분극(Cyclic polarization) 실험, 정전류 실험을 실시하여재료별 내식성을 상호 비교하였다. 실험 결과, Nb 첨가 시편의 경우 Nb 함량 증가에 따라 경도 향상을 나타냈으나, Ti의경우 경도 향상 효과가 미미한 것으로 나타났다. 전기화학특성의 경우 Nb 함량 증가에 따라 대체적으로 전기화학적 특성이 개선되는 반면 Ti의 경우 오히려 전기화학특성이 열화되는 것으로 나타났다. 결과적으로, 안정화 원소의 종류와 함량에 따라 전기화학적 특성이 큰 차이를 나타내며, 해수환경에 적용되는 스테인리스강 강종 개발시 이를 고려한 설계가중요할 것으로 사료된다.
Abstract
Stainless steels stabilized with Ti or Nb are largely used in offshore and shipbuilding industries due to its excellentcorrosion resistance. In this study, carbide stabilizers, Ti and Nb, were added to stainless steel 304 specimens with differentconcentrations(Ti: 0.26%, 0.71%, Nb: 0.29%, 0.46%, 0.71%), and their mechanical and electrochemical characteristics wereevaluated. Micro-Vickers hardness testing was employed to characterize the mechanical characteristics with alloying elements. Electrochemical evaluation techniques including Tafel analysis, cyclic polarization experiment, galvanostatic experiment were utilizedto compare the corrosion characteristics of the specimens. The result of hardness tests revealed that Nb containing specimensshowed increasing hardness with increasing alloying contents while adding Ti had little effect on increase in hardness. Inthe case of electrochemical measurements, the electrochemical characteristics of the specimens were enhanced with increasingNb contents while they were deteriorated with increasing Ti contents. As a result, different stabilizers and their contents mayproduce significant differences in electrochemical characteristics, and therefore such effect must be taken account of in developmentof stainless steels for marine environment.
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