Wrought iron

Wrought iron literally means Worked iron. my. As irregular past-tense forms in English have historically been phased out over long periods of time, wrought became worked. Belonging to me.
Word Origin: The word “wrought” is the old past tense of the verb to work. Wrought iron products as described in routine commercial transactions usually refer to mild steel products which are also described as ornamental iron work.

In old, very rusted pieces of wrought iron, the grain is revealed, making the iron bear a striking resemblance to reddish-brown wood. This grain makes wrought iron especially tricky to smith, as it behaves much like wood grain--prone to spontaneous splitting along the grain. The strengths across the grain would be about 15% lower. "Treble best" could reach 28 tons per square inch (386 MPa).

"Best" bars would have a tensile strength along the grain of about 23 tons per square inch (317 MPa). Faggoting resulted in impurities within the metal ending up as long thin inclusions, creating a grain within the metal. Wrought iron which had been faggoted twice was referred to as "Best"; if faggoted again it would become "Best Best", then "Treble best", etc. Historically, this would be followed by faggoting.

This process took time to develop, but by the 1750s a number of oxides had been identified that would react with the excess carbon to produce carbon dioxide, which bubbles out. In order to use it in ironmongery, it had to first be converted to a form similar to what the bloom/wrought process produced. However the product of a blast furnace, pig iron, had a very high carbon content and was very brittle. Soon iron prices were dropping rapidly as production shot up.

Not only was the fuel much cheaper, but it also could be burned in a "lump" instead of a thin sheet, allowing the furnaces to be much larger. The introduction of the the much less expensive coke for use with the blast furnace by Abraham Darby I in 1709 changed ironmaking and replaced charcoal. As wrought iron lacks the carbon content necessary for tempering, it is believed that cultures that never discovered how to make steel would cold work wrought iron tools in order to harden them. Hammering a piece of wrought iron cold causes the fibers to become packed tighter, which makes the iron both brittle and hard.

The fibers of wrought iron gives it some interesting proporties, however. Also due to the slag, it has a fibrous look when broken or bent past it's failure point. These slag inclusions give it a "grain" like wood, and distinct look when etched. As a result of this process, many strands of slag are mixed into the metal.

This process gives rise to the name "wrought", as the iron was pounded, twisted, and folded. The bloom was then mechanically worked to break off the masses of slag and impurities. In a bloomery, the fire does not get hot enough to melt the iron completely, so you are left with a spongy mass containing iron and silicates from the ore; this is iron bloom from which the technique gets its name. This way little carbon entered the iron directly.

As the ore melted it would be reduced (ore is iron oxide, or rust), mixing with the charcoal to release carbon dioxide. The heat produced would melt the ore. Air was blown onto the charcoal after lighting it on fire. Bloomeries used charcoal-heated smelters, typically in the form of small pots or ladles, into which the ore was poured and then covered with a thin layer of charcoal.

Wrought iron was originally produced by a variety of methods today known as a bloomery. Wrought iron has been used for thousands of years, and represents the "iron" that is referred to throughout history. When formed into bars, it is known as "bar iron". However, it is too soft to make blades and swords.

It is tough, malleable, ductile and can be easily welded. Wrought iron is a very pure form of commercial iron, having a very small carbon content.