Ductile and gray cast irons deterioration with time in various nacl salt concentrations

Abstract EN

Gray 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 are 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 catholic and anodic polarization in the above solutions.

The test started from catholic 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 materials.

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.