Steel

On Earth, during the 13th century, Humans were still perfecting the mechanical clock and using steel crossbows in battle at the time the Promellians were building interstellar warships. (TNG: "Booby Trap")

The emergency baffles used in the ventaliation system at the facility on the trellium mining planet were steel plates. These plates would be locked into place during maintenance cycles. (ENT: "The Xindi")

During the ecological attack caused by the Whale Probe that visited Earth in 2286, steel plates were utilized to reinforce the windows at Starfleet Command. (Star Trek IV: The Voyage Home)

In explaining the appeal of the game of darts to Quark, Miles O'Brien stated that it involved "No lasers, no holograms; just steel tips and feathers." (DS9: "Visionary")

The level of metallurgic technology achieved by the species who inhabited the class L planet, in the Delta Quadrant, that B'Elanna Torres crashed on in 2376 were not yet able to produce steel, as they were still at the Bronze level of development. (VOY: "Muse")