From Pathfinder Rage of Elements, which isn't enabled.

Rustbringer

ITEM 10

DISARM MAGICAL METAL SWEEP TRIP

Price 900 gp

Usage held in 1 hand

Bulk 1

Category martial

Group flail

Damage 1d6 bludgeoning

The handle, chain, and spiked ball of this +1 striking corrosive flail are all made of iron so rusted that the weapon appears nonfunctional at first glance. On Strikes against a creature that's primarily made of metal, it gains the deadly d10 trait.

Activate—Rusting Disarm

Trigger You critically succeed at a Disarm attempt with the flail against a metal weapon

Effect Flakes of acid-laden rust are deposited on the disarmed weapon. The weapon takes 2d6 damage, ignoring the weapon's Hardness.

Pathfinder Rage of ElementsOGL