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On the influence of microstructure and carbide content of steels on the electrochemical dissolution process in aqueous NaCl‐electrolytes
Author(s) -
Haisch T.,
Mittemeijer E. J.,
Schultze J. W.
Publication year - 2002
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 - 10.1002/1521-4176(200210)53:10<740::aid-maco740>3.0.co;2-j
Subject(s) - materials science , dissolution , metallurgy , microstructure , carbide , ferrite (magnet) , anode , electrolyte , cementite , austenite , electrode , composite material , chemical engineering , chemistry , engineering
The electrochemical dissolution behaviour of armco‐iron and of the steels C15, C45, C60 and 100Cr6 in concentrated sodium chloride media has been investigated. Anodic metal dissolution experiments have been carried out using the flow channel cell (parallel plate reactor), the rotating cylinder electrode (RCE) and the capillary cell. The microstructure of the steel has been varied through variation of carbon content and heat treatment (e.g. soft annealed with globular carbides or pearlitic). Current‐efficiency values have been obtained by gravimetric measurements in the current‐density range from i = 5 to 60 A/cm 2 . For the soft annealed steels, the divalent ferrite dissolution in combination with electroless cementite removal dominates. For the pearlitic steels, the occurrence of oxygen evolution at electronically conductive metal carbides or trivalent ferrite dissolution, depending on the current density applied, was detected. Microstructure dependent potentiostatic current transients and potentiodynamic polarization curves have been presented. Polarization resistances, R pol , were measured in dependence on NaCl concentration and the applied anode potential. For pearlitic steels (with carbon contents ≥ 0.45%) R pol exceeds that of the analogous soft annealed steels. The topographies of the steel surfaces after anodic dissolution show microscopic structures, based on inert metal carbides, which are the result of preferential ferrite dissolution. Qualitative metal dissolution models explain the electrochemical dissolution behaviour of soft annealed and pearlitic steels on the basis of the formation of solid films at the substrate surfaces and recognizing the role of the inert metal carbides in the steel matrix. In these models, the role of a polishing layer forming between the solid particles has been taken into account.