Steel is forged by striking at it with a hammer in the forge, shaping it into new forms. The warhammer too shapes the enemy's armour, using their innards as the anvil, into a laminated coffin.
EFFECT:
Hammers ignore Armour Saving Throws. Instead, each point of ARM the enemy possesses reduces a hammer's Damage Dice Rolls by -2 (4d6 -> 2d6).