Rusting Grasp Spell
D&D Description of the Rusting Grasp Spell : Any iron or iron alloy item you touch becomes instantaneously rusted, pitted, and worthless, effectively destroyed. If the item is so large that it cannot fit within a 3-foot radius a 3-foot-radius volume of the metal is rusted and destroyed. Magic items made of metal are immune to this spell.
You may employ Rusting grasp in combat with a successful melee touch attack. Rusting grasp used in this way instantaneously destroys 1d6 points of Armor Class gained from metal armor (to the maximum amount of protection the armor offered) through corrosion.
Deeper info on this Dungeons & Dragons Rusting Grasp Spell