About Captain America's Shield
About Captain America's shield is not actually a lump of pure iron. The inside is actually composed of very sophisticated mechanical structures.
The mechanical structure inside the shield is the secret of the shield's unbreakable strength. And not simply because the metal is hard.
A lot of other Marvel fanfic writers get this wrong, simply thinking that Vibration Gold or Adelmanium is incredibly strong. But it's not like that.
Leave the comics aside and just watch the movies with the widest audience. Cap's shield also exhibits several different properties.
For example, the rebound after impact can also activate the super cutting damage ability without rebound. And solid defense.
These characteristics cannot be achieved by a simple pure metal shield.
This point comes from the original setting rather than my personal nonsense. If you don't read comics, you can take a look at Tony Stark's 1:6 workbench model produced by hottoys.
Among the Iron Man series models, there is one that Tony disassembled Rogers' shield for maintenance.
It roughly depicts the details of the internal structure of the shield.
I think it's better to explain it above.