Scrap Iron

It's old and rusty but can be smelted and used again.
Overview
Scrap iron is a metal resource found in Valheim, primarily in the 

Scrap iron can also be found buried underground in the Swamp. The Wishbone, which is dropped by 
In addition to swamp sources, Scrap iron can be found in chests inside Sunken Crypts. It is also dropped by Oozers that spawn at night in the Swamp and during events. In the 
- Main source: Muddy scrap piles in Sunken Crypts.
- Hidden source: buried deposits in the Swamp, located with the Wishbone.
- Other sources: chests in Sunken Crypts, Oozers, ancient sword and armor remains in the Mistlands, and some dwarven buildings.
- Sunken Crypts are accessed with the Swamp Key, which is obtained by defeating The Elder.
- Buried scrap piles are often searched for with the Wishbone, dropped by Bonemass.
Scrap iron is therefore a key mid-game material tied closely to the Swamp biome and to progression through Valheim’s boss line.
Official description
It's old and rusty but can be smelted and used again.