Corrosion Study on High-Alloyed White Cast Irons in Acidic and Chloride Containing Solutions

In many applications engineering components deal with both erosion and corrosion attacks. Alloyed white irons are used mostly in wear predominant services due to their limited corrosion resistance. Some higher alloyed white irons showed much improved corrosion resistance. However, the understanding on corrosion behaviors and mechanisms of alloyed white irons is still very limited.

In this study, the corrosion behaviors of standard and specialty high-chrome white irons in acidic and chloride containing solutions have been investigated through immersion exposure and electrochemical corrosion testing and optical/electron microscope examinations. General corrosion rate and pit penetration rate were evaluated at different pH and chloride levels. Results showed that the mass loss rate dropped rapidly during the first several hours of exposure, reaching a relatively steady corrosion rate after approximately 20 hours.  This behavior did not seem to be significantly affected by chloride levels. Observation indicated that pit depth decreased with increasing chloride concentration. It may be explained that higher chlorides create “ion-crowding” in the boundary layer between the target material and the solution. SEM-EDS analysis revealed chromium depletion at phase boundaries, which agrees with the location of preferential pit formation. Some other corrosion aspects of alloyed white irons have also been discussed.