text: In the 17th, 18th, and 19th centuries, wrought iron went by a wide variety of terms according to its form, origin, or quality.
  While the bloomery process produced wrought iron directly from ore, cast iron or pig iron were the starting materials used in the finery forge and puddling furnace. Pig iron and cast iron have higher carbon content than wrought iron, but have a lower melting point than iron or steel. Cast and especially pig iron have excess slag which must be at least partially removed to produce quality wrought iron. At foundries it was common to blend scrap wrought iron with cast iron to improve the physical properties of castings.
  For several years after the introduction of Bessemer and open hearth steel, there were different opinions as to what differentiated iron from steel; some believed it was the chemical composition and others that it was whether the iron heated sufficiently to melt and "fuse".  Fusion eventually became generally accepted as relatively more important than composition below a given low carbon concentration. Another difference is that steel can be hardened by heat treating.
  Historically, wrought iron was known as "commercially pure iron"; however, it no longer qualifies because current standards for commercially pure iron require a carbon content of less than 0.008 wt%.