Master Blacksmith (5e Feat)
From D&D Wiki
Prerequisites: Proficiency with smith's tools
You are an expert at smithing armor and weapons, gaining the following benefits
You double your proficiency bonus on checks made with smith's tools.
Weapons and armor that you craft have a chance to be imbued with additional properties. When you successfully craft an item roll smith tool check again when you make a DC 20 the item becomes +1, a DC 25 item becomes +2, and a DC 30 item becomes +3