Wrought iron of good quality is neraly pure iron; its carbon content seldom exceeds 0.035%. In addition, it contains 0.075%-0.15% silicon, 0.10 to less than 0.25% phosphorus, less than 0.02% sulfur, and 0.06%-0.10% manganese. Not all of these elements are alloyed with the iron; part of them may be associated with the intermingled slag that is a characteristic of this product. Because of its low carbon content, the properties of wrought iron cannot be altered in any useful way by heat treatment.
(from "Iron alloys" in McGraw-Hill Encyclopedia of Science and Technology vol 9 p 448 [1997])
Wrought iron had a dominant position in meeting the need for a forgeable, nonbrittle, ferrous metal, from before the time of historical record until the advent of the age of steel [mid-19th c, with Bessemer and Siemens innovations]...The vital demarcation between the puddling and steelmaking furnace was the limited temperature of the former. The puddling furnace was below the 2700F (1482C) needed to keep the refined iron molten...
A distinguishing characteristic of wrought iron is a fragmented or irregualr fracture, as contrasted with a fibrous or crystalline type in steel...
The development of steelmaking processes prompted prediction of the doom of wrought iron. Puddling required hard manual labor, with low output both in unit mass and total tonnage, and accompanying high cost. However, although wrought iron once held competitive merit in certain uses, notably where corrosion- and shock-resistance were important, very little wrought iron is produced today.
(from "Wrought iron" in McGraw-Hill Encyclopedia of Science and Technology vol 19 p 610 [1997])