Hot rolling is the most common hot-working technique. The metal is forced through pairs of revolving steel drums that produce long sheets or strips of metal. While iron and steel are usually forged hot, after the initial hot working they and many other metals may be worked cold. Cold working strengthens and hardens the metal and gives it a fine finish. Molten metal may be cast, or poured into simple molds, for further working.
Molten iron is poured into molds to make bars of pig iron.
Sometimes metal is poured into a single cast and shaped to its final form. Although this method is cheaper, it results in a lower-quality product. Metallurgists are trying to find new, more efficient ways of casting steel continuously. Powder metallurgy, a method of forming metal, has developed rapidly since the 1950s. In this process, the metals to be used are first made into powders.