Daniel 2:33
its legs of iron, its feet part of iron and part of clay.
Daniel 2:40-43
And the fourth kingdom shall be strong as iron: forasmuch as iron breaketh in pieces and subdueth everything, and as iron that breaketh all these, so shall it break in pieces and bruise.
Daniel 7:7-8
After this I saw in the night visions, and behold, a fourth beast, dreadful and terrible, and exceeding strong; and it had great iron teeth: it devoured and broke in pieces, and stamped the rest with its feet; and it was different from all the beasts that were before it; and it had ten horns.
Daniel 7:19-26
Then I desired to know the certainty concerning the fourth beast, which was different from them all, exceeding dreadful, whose teeth were of iron, and its nails of brass; which devoured, broke in pieces, and stamped the rest with its feet;