Iron bars are items used to create iron tools, weapons, minecarts, rails, shears, buckets and pistons. These are part of Vanilla minecraft, and the ore is unchange by Metallurgy textures.
Iron bars can be created by mining iron ore blocks and smelting them in a furnace, or a smelter (added in the Nether ores submod). Each ore will give a single iron bar. This can be doubled by crushing the ores first in the crusher (as this will give two dusts) and then smelting the dusts (using a furnace). Each dust will smelt into one ore.