You will find rusted weapons during each mission in Fire Emblem Warriors: Three Hopes. These have low stats and are beyond usage in battles.
You might be thinking of scrapping any rusted weapons you find to make room in your inventory. The thing is that you can repair them to bring them back up to their maximum proficiency.
The following guide will show you how to repair rusted weapons in Fire Emblem Warriors: Three Hopes.
How To Repair Rusted Weapons In Fire Emblem Warriors: Three Hopes
If it was not obvious, you need to take your rusted weapons to a Blacksmith for repairs. You will find a Blacksmith at your Base Camp.
There is a cost attached to each repair. You will need to pay in Gold and Smithing Stones, but their amount is subject to change depending on the rusted weapon you are trying to repair.
Each weapon has a grade in Fire Emblem Warriors: Three Hopes. Hence, repairing a B-grade rusted weapon will be far more costly than repairing a D-grade rusted weapon.
Whatever the cost, it is worth paying to have rusted weapons repaired because they then become Steel Axes, Steel Swords, and Steel Bows with higher stats and attributes. A rusted weapon when fully repaired will always be better than a standard weapon you purchase from the Item Shopkeeper.
How To Repair Higher Grade Weapons In FEW: 3H
You will only be able to repair low-grade (D-grade) rusted weapons at first. If you want to repair high-grade weapons, you must upgrade the Blacksmith.
To do this, you can simply talk to the Facilities Master at the Base Camp. You can collect the required upgrade materials by completing missions. Take the materials back and upgrade the Blacksmith to start repairing higher-grade rusted weapons.