Daniel 2:33
its legs of iron, its feet part of iron, and part of clay.
Daniel 2:40-43
The fourth kingdom shall be strong as iron, because iron breaks in pieces and subdues all things; and as iron that crushes all these, shall it break in pieces and crush.
Daniel 7:7-8
After this I saw in the night visions, and behold, a fourth animal, awesome and powerful, and extremely strong. And it had great iron teeth. It devoured and broke in pieces, and stamped what was left with its feet. And it was diverse from all the animals that were before it; and it had ten horns.
Daniel 7:19-26
Then I desired to know the true meaning concerning the fourth animal, which was different from all of them, exceedingly terrible, whose teeth were of iron, and its claws of bronze; which devoured, broke in pieces, and stamped what was left with its feet.