Corrode Metal

Choose a manufactured non-magical metal object, such as a metal weapon or a suit of heavy or medium metal armor, that you can see within range. You cause the object to corrode, and the weapon or armor takes a permanent and cumulative −1 penalty to damage rolls/DC bonus. If its penalty drops to −5, the weapon is destroyed. Until the spell ends, you can use a bonus action on each of your subsequent turns to corrode the metal object further.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the penalty increases by -1 for each 2 slot level above 2nd.