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Localised corrosion behaviour of high and low nitrogen Cr‐Mn steels
Author(s) -
Srinivasan Ahila,
Reynders Brigitte,
Grabke Hans Jürgen
Publication year - 1995
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199501151
Subject(s) - nitrogen , corrosion , metallurgy , pitting corrosion , x ray photoelectron spectroscopy , chloride , materials science , ammonium , ammonium chloride , electrochemistry , sodium nitrate , sodium , chemistry , chemical engineering , electrode , organic chemistry , engineering
It is well established that addition of nitrogen to steels improves the pitting corrosion resistance of steels. To elucidate the role of nitrogen, electrochemical and surface analytical studies were carried out on Cr‐Mn steels with low (0.0075 %) and high (0.9 %) nitrogen contents. The incubation time for pitting, measured in sodium sulphate solutions containing different concentrations of chloride was higher for the high nitrogen steel. The pit initiation process was found to be first order with respect to chloride concentration. The passive current density was one order lower than that of nitrogen free steel. The grain broundary attack observed in low nitrogen steel was not present in high nitrogen steel. XPS analysis indicated nitrogen enrichment at the surface in the passive layer. This may be one reason for the higher pitting resistance of nitrogen containing steel besides formation of ammonium ions and rising pH.