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Impedance of Cr18Ni10 stainless steel in sulphate solutions after a low‐temperature plasma nitriding
Author(s) -
Flis J.,
Kuczynska M.
Publication year - 2003
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200303761
Subject(s) - nitriding , nitrogen , corrosion , supersaturation , passivation , materials science , austenitic stainless steel , electrochemistry , anode , austenite , analytical chemistry (journal) , metallurgy , plasma , inorganic chemistry , chemistry , microstructure , electrode , layer (electronics) , composite material , chromatography , organic chemistry , physics , quantum mechanics
The 00Cr18Ni10 stainless steel was examined before and after plasma nitriding in a 80%N 2 /20%H 2 gas mixture at 425°C for 30 h, resulting in the formation of a supersaturated solid solution of nitrogen in austenite ( S phase) with 12.9 wt.% N at the surface. Electrochemical measurements were made on the as‐nitrided surface and after abrasion to various depths. Polarisation curves and impedance were measured in 0.1 M Na 2 SO 4 acidified to pH 3.0; some measurements were also made at pH 6 and 9. It was found that nitrogen decreased the corrosion resistance of the steel in the acidified solution (pH 3.0), but increased it in the neutral and near‐neutral solutions (pH 6.0 and 9.0). The deleterious effect of nitrogen at pH 3.0 was at potentials of the active state much stronger and more dependent on the nitrogen concentration than in the passive state. It was suggested that the increased anodic reactivity of the nitrided steel in the active state is inherent for the lower thermodynamic stability of the supersaturated solid solution of nitrogen, whereas the increased corrosion resistance in the neutral and near‐neutral sulphate solutions is associated with the effect of nitrogen on anodic films.