Gaphite corrosion (spongiosis) lamellar gray cast iron

Spongiosis (spongy dissolution) is a form of selective corrosion of cast iron in which the corrosive attack progresses along the graphite-matrix interfaces and dissolves the iron matrix. Usually this corrosion mechanism only occurs in spheroidal graphite cast iron, here we could also identify it in a lamellar graphite casting. Because of the long graphite lamellae, as in this pearlitic lamellar grey cast iron, deep penetration of the corrosion is possible. The graphite remains and holds the corrosion product together. The original shape of the casting is retained, but the black “iron sponge” (mainly FeOOH) no longer has any strength.