Ductile and Gray Cast Irons Deterioration with Time in Various NaCl Salt Concentrations
Engineering and Technology Journal,
2008, Volume 26, Issue 2, Pages 154-168
AbstractGray cast iron is used in wide engineering applications especially pipes
and these pipes are exposed to failure in most cases so that ductile cast iron is used
instead of it later.
This project deals with the study of microstructure characteristics and
chemical analysis for both materials in order to use them in the analysis of the
microstructure after the corrosion tests involving immersion, polarization in
different sodium chloride concentrations (0.01%, 0.58% and 3.5% NaCl).
Immersion results indicate that the corrosion resistance of both types of
cast irons is excellent and ductile iron is better than gray cast iron and the
reduction in corrosion rates for both materials is related to barrier layer deposited
on the surface which is more uniform on ductile iron surface.
The electrochemical tests involve measurement of corrosion potential in
open circuit using the same solutions for both materials and potentiostatic test is
used to measure cathodic and anodic polarization in the above solutions. The test
started from cathodic region to the anodic region with sweep rate of 10 m V/min to
obtain the general behavior and measure the polarization parameters for both
The measured corrosion potentials of the open circuit in all solutions are
more noble values for gray iron than that for ductile iron. Corrosion potentials on
polarization measurements point out to the same indication but the ability to
start and form barrier layer in ductile is better than in gray iron.
Microstructure observations after the electrochemical tests indicate
the presence of uniform layer on ductile surface and graphitization process is
obtained on gray iron.
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