'Brass' in the Bible

I will go before you, and make the rough places level: the doors of brass will be broken, and the iron rods cut in two:

Because I saw that your heart was hard, and that your neck was an iron cord, and your brow brass;

In place of brass, I will give gold, and for iron silver, and for wood brass, and for stones iron: and I will make Peace your judge, and Righteousness your overseer.