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Korean Journal of Metals and Materials > Volume 55(12); 2017 > Article
Korean Journal of Metals and Materials 2017;55(12): 870-879. doi: https://doi.org/10.3365/KJMM.2017.55.12.870
Nb 활용 탄질소 스테인리스강의 부동태 및 대기산화 피막 보호성 연구
이창근1,2, 하헌영2, 이태호2, 조경목1
1부산대학교 재료공학과
2재료연구소 철강재료연구실
Evaluation of the Protective Ability of Air-formed Oxide and Passive Films Formed on Nb-Bearing High Interstitial Stainless Steels
Chang-Geun Lee1,2, Heon-Young Ha2, Tae-Ho Lee2, Kyung-Mox Cho1
1Department of Materials Science and Engineering, Pusan National University, Busan 46241, Republic of Korea
2Ferrous Alloy Department, Korea Institute of Materials Science, Changwon 51508, Republic of Korea
Correspondence  Heon-Young Ha ,Tel: +82-55-280-3422, Fax: +82-51-510-3218, Email: hyha2007@kims.re.kr
Kyung-Mox Cho ,Tel: +82-55-280-3422, Fax: +82-51-510-3218, Email: chokm@pusan.ac.kr
Received: 5 July 2017;  Accepted: 25 September 2017.  Published online: 4 December 2017.
ABSTRACT
The effects of Nb on grain refinement and the pitting corrosion resistance of Febalance18Cr10 Mn0.3C0.3NxNb (x = 0.1 and 0.2 wt%) high interstitial alloys were investigated through microstructure analysis and potentiodynamic polarization tests. The resistance to pitting corrosion of the two alloys, covered with a passive film and an air-formed oxide films, was also examined. As the Nb content increased from 0.1 to 0.2 wt%, the grain size decreased, the volume fraction of Nb(C,N) particles increased, and the pitting potential was elevated. In addition, the two alloys covered with the passive film exhibited higher pitting potentials than the alloys with the air-formed oxide films. The physico-chemical and electronic properties of the passive film formed in an aqueous environment, and air-formed oxide of the two alloys were examined using X-ray photoelectron spectroscopy and Mott-Schottky analysis. As a result, it was revealed that the defect density level in the passive film was the dominant factor in determining the pitting corrosion resistance of the specimens. Nb addition was found to promote the formation of a protective passive film with low defect density, which resulted in the increase in the pitting potential. Moreover, the fact that the point defect density of the passive film was smaller than the air-formed oxide films was observed in both alloys, which can explain the higher pitting corrosion resistance of the passivated specimen than the specimen covered with an air-formed oxide film.
Keywords: high interstitial alloys, Nb, grain refinement, pitting corrosion, Mott-Schottky analysis
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