Wrought Iron's uses and characteristics

Wrought iron lantern in Copenhagen from around 1880

This page includes information on the characteristics and uses of wrought iron. The page also  describes problems associated with wrought iron.

Iron (Fe) is a common dark grey metal. Iron is the main element in a range of materials including wrought iron, cast iron, carbonized iron and steel. Each of this materials has its own properties that differentiate them from each other.

Iron was first used during the iron-age as a material for tools and weapons. Iron objects have been found in Egypt dating from around 3500 BC. The ancient Hittites, from present days' Turkey, were the first to smelt iron from its ores around 1500 BC and thus began the iron age. Its uses have since grown to include items for domestic use to architectural building components. 

Wrought iron ornamentation on a fence in Copenhagen from around 1905

Wrought iron differs from cast iron and steel in its carbon content:

1. Wrought iron contains very little carbon (less than 0.035%)

2. Steel contains a moderate amount of carbon (between 0.06% and 2%)

3. Cast Iron contains a high amount of carbon (between 2% and 4%)

Wrought Iron is characterized by being soft, magnetic and strong with high elasticity and tensile strength. It is also malleable and can be heated and reheated and worked into various shapes. 

Wrought iron is strong when tension is applied whereas cast iron is only strong when compression is applied.

Wrought iron is produced the following way:

1. "Pig iron" is smelted in blast furnaces and subjected to a condition when it boils until virtually no carbon remains. The boiling iron is worked continuously during this process so that impurities are being removed from the iron. The process makes the iron stiffer. This process ends when the carbon monoxide stops bubbling through the iron. 

2. The iron is then being formed into balls. 

3. The iron balls are then being hammered with a shingling hammer, to expel surplus cinder and slag. 

4. Then as the iron is still bright red, it is being passed through rolling mills, becoming more elongated and thinner after each pass, and finished as puddled iron bar. The bars are reworked and heated to  increase the ductility and tensile strength.

Wrought iron was used for fences during the 18th, 19th and beginning of the 20th century

Uses

Wrought iron was being used for fences, gates, and railings, balconies, porches, verandas, lamps, lanterns and hardware during the 18th, 19th and beginning of the 20th century.

It wasn't however used for building facades or columns. Cast iron was more suitable for that.

By the beginning of the 20th century, the use of wrought iron for structural purposes had been superseded by steel.

Wrought iron balcony

Problems with wrought iron

Chemical corrosion

Corrosion may attack the metal surface evenly or the metal surface in selected areas. When a metal is not homogenous throughout, certain areas may be attacked in preference to others.

The process may attacks areas in a metal which were stressed during metalworking and were later exposed to a corrosive environment. Old, hand wrought iron items are more likely to be affected than are machine rolled wrought iron pieces. 

Rust is a common form of chemical corrosion of wrought iron. It occurs when the metal is exposed to oxygen and water. Carbon dioxide, sulfur compounds, soot, and fly ash will exacerbate the corrosion of the iron, as will airborne salts.

If wrought iron is exposed directly to copper or zinc, and to a lesser extent galvanized iron or steel, it will cause galvanic corrosion (rust).

The Eiffel Tower, made of wrought iron

Mechanical or physical deterioration

Even wrought iron may fail if it has been repeatedly stressed beyond its elastic limit. Wrought iron is generally fatigue resistant but it has limits. 

Defects in the wrought iron itself may cause failures. 

 Wrought iron will distort and fail if exposed to heat e.g. from a fire.