Influence of graphite morphology on electrochemical corrosion behaviour in cast irons

Cast irons are widely used in the automotive industry due to its excellent castability, fluidity, machinability and wear resistance. Industrial applications include automotive and machinery industries, production of tubes, rolls in sugar cane mills and even nuclear waste containers. Cast iron parts with different graphite morphologies and mechanical properties are available in the market; grey cast irons (flake graphite particles), compacted cast irons (worm-like graphite particles) and ductile cast irons (spheroidal graphite particles). In this last case, the heavy-section parts produced are prone to form a graphite degeneracy called chunky graphite which shows a negative effect on mechanical properties. Despite their widespread use, electrochemical studies of the effect of these different graphite morphologies on the corrosion behaviour of these materials are very scarce. The present research focusses on comparison of the electrochemical corrosion behaviour of cast irons with three of the graphite particle morphologies mentioned above (nodules, flakes and chunky graphite). These three cast iron types were characterised by Optical Microscopy, Scanning Electron Microscopy and Electrochemical Tests. This last was performed in a medium designed to simulate the condition encountered in sugar cane mills. 

The results obtained in the present investigation show that all cast irons have similar values of current density (Icorr). However, the alloy with flakes graphite had a significantly higher corrosion potential value (Ecorr) than those with nodules and chunky graphite. 

The corrosion products formed in grey cast iron present different morphologies compared to the corrosion products formed in spheroidal and chunky cast iron.