Effects of alloying elements (Mn, Si, Cu) on the passivity and repassivation kinetics of stainless steel alloys = 스테인리스강의 부동태 및 재부동태 거동에 미치는 합금 원소 (Mn, Si, Cu) 의 영향

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High Mn-N stainless steels (SSs) are being developed to replace the expensive austenitic stainless steels $(\gamma-SSs)$, containing high Ni content (8~12 wt. % Ni). Ni in these SSs is replaced with a combination of Mn and N. Mn (a γ-stabilizer) is not only 7 to 8 times cheaper per ton than Ni but it also increases the nitrogen solubility, and these two together compensate for the Ni deficiency in these new high Mn-N SSs. Nitrogen in addition of functioning as an austenite stabilizer also improves corrosion properties and has several other benefits such as increased strengthening and retardation of sensitization. The addition of Si (a ferrite former) and copper (an austenite former) in SSs can also have a substantial effect on the passivity and electrochemical properties. So therefore, effects of these alloying elements (Mn, Si, Cu) on the passivity, repassivation kinetics and stress corrosion cracking (SCC) behaviour of stainless steels are of considerable importance. The effects of these alloying elements on the repassivation kinetics and SCC behaviour of SSs were investigated by rapid scratch electrode technique (RSET) and slow strain rate test (SSRT). The structure and defect density of the passive films was investigated by photoelectrochemical technique and Mott-Schottky analysis. Polarization experiments and electrochemical noise analysis (ENA) of the high Mn-N SSs, showed that as Mn content of the alloys was increased, localized corrosion resistance was decreased as confirmed by decrease in pitting potential $(E_{pit})$ of the alloys. The repassivation kinetics, measured in terms of the current density i(t) flowing from the scratch as a function of the charge density q(t) that has flowed from the scratch, showed that, the addition of Mn decreased the repassivation rate of the alloys in 0.5M NaCl solution at $80^\circ C$. During the initial stages of repassivation, passive film nucleated and grew according to place exchange model in which log i(t) is l...
Advisors
Kwon, Hyuk-Sangresearcher권혁상researcher
Description
한국과학기술원 : 신소재공학과,
Publisher
한국과학기술원
Issue Date
2008
Identifier
295371/325007  / 020034512
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 신소재공학과, 2008.2, [ 160 ]

Keywords

stainless steel; high Mn-N; Stress Corrosion Cracking; Repassivation; Corrosion; 스테인리스강; 고망간질소; 응력부식균열; 재부동태; 부식

URI
http://hdl.handle.net/10203/49700
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=295371&flag=dissertation
Appears in Collection
MS-Theses_Ph.D.(박사논문)
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