World Trade Center.
Steel from foreign suppliers was used to cut costs.
https:// sites.lafayette.edu/vast265-sp12/steelopedia/q-z/world-trade-center-contract-and-bethlehem/
The evidence suggests that some foreign steel was used.
News today shows that one manufacturer lied about its certifications.
I don't want to slide the thread. Maybe some of the steel used in the WTC was weaker than certified, I would NOT suggest that this was the cause of the collapse though. There is plenty of contradictory information, please inform yourself and make your own opinion.