Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575

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Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation
Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation
Masashi NishimotoIzumi MutoYu Sugawara
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JOURNAL OPEN ACCESS Advance online publication

Article ID: TETSU-2021-009

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Abstract

Pitting corrosion behavior of SBHS500 steel in boric-borate buffer solutions containing chloride ions was investigated by macroscale and microscale polarization, immersion tests, optical microscopy, and scanning electron microscopy. Calcium sulfide inclusions (CaS) existed in the SBHS500 steel. When the specimen was immersed in a boric-borate buffer solution (pH 8.0) containing 10 mM NaCl for 24 h at 25°C, the steel matrix was not corroded. However, partial dissolution of the CaS inclusions was observed. Pitting occurred after the wet-dry corrosion test, and calcium and sulfur were detected near the center of the pit. From the results of the microscale polarization measurements, the pitting initiation sites for the SBHS500 steel were determined to be the CaS inclusions. No pitting was observed at the microscale electrode area without inclusions. In a boric-borate buffer solution containing 10 mM NaCl, the depassivation pH at the microscale electrode area without inclusions was 6.0. The depassivation at the microscale electrode area with the CaS inclusions occurred at approximately pH 6.6. The CaS inclusions in the SBHS500 steel were found to be a trigger of the depassivation of the steel matrix surrounding the inclusions.

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© 2021 The Iron and Steel Institute of Japan

この記事はクリエイティブ・コモンズ [表示 4.0 国際]ライセンスの下に提供されています。
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