noun (n)

• a state of deterioration in metals caused by oxidation or chemical action(noun.state)

  source: wordnet30
• erosion by chemical action(noun.process)

  Synonym:
  corroding, erosion
  

  source: wordnet30
• The action or effect of corrosive agents, or the process of corrosive change; as, the rusting of iron is a variety of corrosion.(noun)

  source: webster1913