Pitting Corrosion of Some Stainless Steel Alloys Preoxidized at Different Conditions

S.S. Mahmoud* and M.M. Ahmed

^a Chemistry Department, University College of Girls for Arts, Science and Education, Ain Shams University, Heliopolis, Cairo, Egypt

Received 8 February 2006; accepted 30 April 2007

 

Abstract

The pitting corrosion of some stainless steel alloys (preoxidized at different conditions) in 3.5% NaCl solution was studied. The alloys are: one ferritic (15.05% Cr) (alloy1) and two austenitic stainless steel alloys (17.9% Cr,7.08% Ni) (alloy2) and (20.45% Cr, 8.3% Ni) (alloy3). Potentiodynamic anodic polarization and galvanic current-time measurements were used in these investigations. The susceptibility of the alloys to pitting corrosion decreases with the increase of chromium content of the alloy and with the presence of nickel in the alloy. The preoxidation of the alloys in different media improves their resistance to pitting corrosion in NaCl solution. The resistance to pitting corrosion for the investigated alloy increases according to the order: no oxidation < oxidation in air < oxidation in molten alkali nitrates < oxidation in molten alkali carbonates. This resistance to pitting corrosion may be due to the formation of a protective oxide film on the alloys’ surface. The composition of this film greatly depends on the chemical composition of the alloy, on the condition of the preoxidation process, and on the temperature.

Keywords: stainless steel alloys, pitting corrosion, molten alkali nitrates, molten alkali carbonates

 

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* Corresponding author. E-mail address: : drsohairr@hotmail.com