According to an article by John Welch, at various times in history when iron was scarce, it was used as a precious decorative metal. Welch cites a recent article by Alan R. Millard ("King Og's Iron Bed--Fact or Fancy?") that documents the early use of iron to decorate beds (see Deuteronomy 3:11) and thrones, as well as bracelets and jewelry, weapons and royal swords. Such things were not of solid iron, but they were plated, veneered, or studded with the metal. He relates that because iron was hard to obtain it was "highly prized"; The product of a difficult technique, a bed or a throne, could be a treasure in a king's palace.
With this point in mind, we can reread the account of King Noah, who built many elegant buildings and "ornamented them with . . . all manner of precious things, of gold, and of silver, and of iron" (Mosiah 11:8).
Thus, although iron was present in the city of Nephi during Noah's time, it was apparently rare and precious. This was probably always the case in Book of Mormon society, for all New World references to iron in the book mention it together with gold and silver and other precious things (see 2 Nephi 5:15; Jarom 1:8; Ether 10:23). [John W. Welch, "Decorative Iron in Early Israel," in Reexploring the Book of Mormon, F.A.R.M.S., p. 133] [See the commentary on Jarom 1:8]