Wrought iron

Chinese fining

Puddling furnace

A231 - Optical micrograph of wrought iron

Wrought iron is a form of iron that is characterized by its very low carbon content compared to other forms of commercial iron and steel. Historically, it was known for its toughness, malleability, and ability to be welded, making it a popular material in the construction of early tools, weapons, and architectural structures. The term "wrought" is an archaic past participle of the verb "to work," thus wrought iron literally means "worked iron."

Production

Wrought iron is produced by heating iron ore in a blast furnace where it is refined to produce pig iron. This pig iron is then further refined to reduce its carbon content. In traditional methods, this was achieved through a process known as puddling, where the iron was heated in a reverberatory furnace and stirred with rods, which allowed the carbon to oxidize and separate from the pure iron. The resulting iron, with a very low carbon content, was then hammered or rolled to expel slag and consolidate the iron. The labor-intensive nature of this process gave wrought iron its characteristic fibrous texture due to the slag inclusions.

Properties and Uses

Wrought iron is known for its ductility, malleability, and resistance to corrosion, which made it an ideal material for various applications. Before the development of effective methods of steelmaking, wrought iron was the most common form of malleable iron. It was widely used for making nails, wires, chains, horseshoes, railings, balconies, and many types of decorative ironwork. Its ability to resist corrosion also made it suitable for outdoor use, particularly in wet or marine environments.

In architecture, wrought iron has been used for centuries, notable in the construction of iconic structures such as the Eiffel Tower and numerous Victorian-era bridges and buildings. Its malleability allowed for the creation of intricate designs, making it a favored material for decorative elements like gates, fences, and grilles.

Decline and Modern Use

The production of wrought iron began to decline in the late 19th century with the advent of steel-making technologies, which could produce steel with properties similar to wrought iron but at a lower cost and with greater scalability. The introduction of the Bessemer process and later the open hearth furnace made steel more economical to produce, leading to its dominance in construction and manufacturing.

Today, wrought iron is no longer produced on a commercial scale, having been replaced by mild steel for most purposes. However, it is still made for restoration projects and by craftsmen for artistic and decorative uses. The term "wrought iron" is sometimes incorrectly used to describe ornamental iron products, regardless of the actual type of iron or steel used.

Conservation and Preservation

The conservation of historic wrought iron structures and objects is an important field within cultural heritage and conservation science. Techniques for cleaning, protecting, and repairing wrought iron must take into account its susceptibility to corrosion and the need to preserve its historical integrity.

See Also

• Iron
• Steel
• Bessemer process
• Pig iron
• Conservation science

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