While wrought iron remains a popular material for decorative applications--gates, fences, outdoor stairs and railings--it is for that very reason that it is one of the most mislabeled building materials around today. Wrought iron has not been made in the United States since 1969, and many of the new "wrought iron" products are called that simply because they are a traditional application of wrought iron. Does this Spark an idea?
Content
Wrought iron is commercially pure iron, which is to say it has a carbon content so low as to not qualify as steel. This gives it the quality of being tough but malleable. "Wrought" itself is an outmoded English word that is almost synonymous with "worked," so "wrought iron" can be read to literally mean "worked iron."
Process
In 1925, American James Aston developed the last major innovation in making wrought iron. This involved pouring very hot molten steel onto a pool of cooler slag. The sudden contact with the cooler slag causes the steel to rapidly drop in temperature and expel gasses that are dissolved into its matrix, purifying it into wrought iron. While this was the most economical process developed for the production of wrought iron, by the 1960s steel had become so cheap that wrought iron could no longer compete with low-grade, mild steel. The last wrought-iron plant in the United States closed its doors in 1969.
Misconceptions
Since wrought iron is no longer made in the U.S., much of the products that are supposedly made of wrought iron are, in fact, made of steel with a very, very low carbon content. This steel is close enough that, given how much cheaper it is to make, it is more economical even if it is not as good in certain applications. The term "wrought iron" continues to be used for those products that were traditionally made out of wrought iron.
Common Uses
Examples of some common items that are still said to be made of wrought iron include certain kinds of chain, horseshoes, handrails, ornamental ironwork, railway couplings and rivets. Other products that were once always made of wrought iron--nuts and bolts, for example--are no longer described this way, since they are obviously made of something else (steel, stainless steel or brass, in the case of nuts and bolts).
Advantages
Wrought iron has a number of useful characteristics relative to steel or cast iron. It is malleable and tough at the same time, which means it can be readily deformed into different shapes with a very low risk of fracture. Steel, on other hand, is harder and stiffer, and therefore not always as malleable. Cast iron is very brittle. Wrought iron becomes soft at a low level of heat (low for iron, that is), making it useful to blacksmiths and for welding. It also has a rough microscopic surface, making it better for holding platings or coatings. For example, if you were to paint a wrought-iron bridge or silver-plate a wrought-iron statue, it would hold more material on its surface than if it were made of steel.
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