This is an older short story.
I think that a piece of metal fell in a junkyard. Then the story shifts to a room where men are saying that all metal will be indestructible. At first, the military is excited that things won't wear out, but the man explains that in a few years, no one will be able to work any new tools due to it being indestructible. They decide to shift to a pre-1900 agricultural society to survive.
Juggernaut by A. E. van Vogt.
Previously identified in Indestructible iron bar falls out of thin air, ends war and Short story about an infectious indestructible metal bar? I first read it about 50 years ago in The Best of A. E. van Vogt but it has been published many times so there are lots of anthologies that contain it.
You can read the story on archive.org here. it starts:
The man—his name was Pete Creighton, though that doesn’t matter—saw the movement out of the corner of his eye, as he sat reading his evening paper. A hand reached out of the nothingness of the thin air about two feet above the rug. It seemed to grope, then drew back into nothingness. Almost instantly it reappeared, this time holding a small, dully glinting metal bar. The fingers let go of the bar, and drew out of sight, even as the metal thing started to fall towards the floor.
THUD! The sound was vibrant. It shook the room.
Creighton sat jerkily up in his chair, and lowered his paper. Then he remembered what he had seen. Automatically, his mind rejected the memory. But the fantastic idea of it brought him mentally further into the room. He found himself staring at an ingot of iron about a foot long and two inches square. That was all. It lay there on the rug, defying his reason.
As you remember Creighton sends the bar to a scrapyard where it starts infecting all the metal it touches with it's indestructibiliy.
