corrosion vs pitting

corrosion and pitting both are nouns.

Word	Noun	Adjective	Verb	Adverb
corrosion	Yes	No	No	No
pitting	Yes	No	No	No

As nouns, pitting is a hyponym of corrosion; that is, pitting is a word with a more specific, narrower meaning than corrosion:

corrosion: erosion by chemical action
pitting: the formation of small pits in a surface as a consequence of corrosion

Other hyponyms of corrosion include indentation, roughness, rust, rusting.

corrosion (noun)	pitting (noun)
erosion by chemical action	the formation of small pits in a surface as a consequence of corrosion
a state of deterioration in metals caused by oxidation or chemical action