Wrought iron | Properties, Uses & History | Britannica (original) (raw)

wrought iron, one of the two forms in which iron is obtained by smelting; the other is cast iron (q.v.). Wrought iron is a soft, ductile, fibrous variety that is produced from a semifused mass of relatively pure iron globules partially surrounded by slag. It usually contains less than 0.1 percent carbon and 1 or 2 percent slag. It is superior for most purposes to cast iron, which is overly hard and brittle owing to its high carbon content. Dating back to antiquity, the first iron was smelted directly from iron ore by heating the latter in a forge with charcoal, which served both as a fuel and a reducing agent. While still hot, the reduced iron and slag mixture was then removed as a lump and worked (wrought) with a hammer to expel most of the slag and weld the iron into a coherent mass.

In Europe it was found that wrought iron could be produced indirectly from cast iron made in a blast furnace. One of the most widely used such indirect methods, called the puddling process, was developed by Henry Cort of England in 1784. It involved melting cast iron in a hollowed hearth and then agitating it with a bar so that the carbon in the cast metal was removed by the oxidizing gases of the furnace. As the carbon was removed, the proportion of solid decarbonized iron progressively increased, and the resulting thick mixture of metal and slag was then run through a squeezer, which removed much of the excess slag and formed a rough cylinder for subsequent rolling into a more finished product.

Wrought iron began to take the place of bronze in Asia Minor in the 2nd millennium bc; its use for tools and weapons was established in China, India, and the Mediterranean by the 3rd century bc. The chief advantage of iron was simply its far greater availability in nature than that of copper and tin. Wrought iron continued to be used for the proliferating implements of peace and the arms and armour of war for many centuries. In the 19th century it began to appear in building construction, where its strength in tension (resistance to pulling apart) made it superior to cast iron for horizontal beams. The invention of the Bessemer and open-hearth processes led to the supplanting of wrought iron by steel for structural purposes. The use of wrought iron in the 20th century has been principally decorative.

Wrought-iron railings, doors, balconies, grilles, and other exterior fittings have been handcrafted since early times; the European Middle Ages were especially rich in handcrafted wrought-iron work. The church screens of the 15th–16th century are especially noteworthy, as is the decorative body armour of the same period.

This article was most recently revised and updated by Amy Tikkanen.