What are some signs of alloy corrosion?

Corrosion is a form of chemical reaction which will form a corrosion product. In a plain carbon steel, the corrosion product is widely recognised as ‘rust’. However, in a far more corrosion-resistant stainless steel, nickel or copper alloy then the corrosion product is likely to be less widespread and less prominent (although stainless steels still contain iron, so you will see some ‘red rust’).