11 Jan Wrought Iron VS Cast Iron
People often assume that cast iron and wrought iron are interchangeable terms for early iron work, but there is world of difference. Wrought Iron is iron that has been heated and then worked with tools. Cast Iron is iron that has been melted, poured into a mould, and allowed to solidify.
The fundamental distinction between cast iron and wrought iron is in how they are produced. The differences can be found in the names: wrought is a past participle of work (“worked iron”), and cast describes anything formed by the casting process. The different methods of production create metals with varying strengths and weaknesses, which is why you rarely see a cast iron fence or a wrought iron frying pan.
Wrought iron is composed primarily of elemental iron with small amounts (1-2 percent) of added slag (the by-product of iron ore smelting, consisting of a mixture of silicon, sulphur, phosphorous, and aluminium oxides). Wrought iron is made by repeatedly heating the material and working it with tools to deform it.
Wrought iron is highly malleable, allowing it to be heated, and re-heated, and worked into various shapes – wrought iron grows stronger the more it’s worked and is characterized by its fibrous appearance. Wrought iron contains less carbon than cast iron, making it softer and more ductile. It is also highly resistant to fatigue; if large amounts of pressure are applied, it will undergo a large amount of deformation before failing.
The term “wrought iron” is often misused today; it is commonly used to describe designs similar to historical wrought iron pieces – regardless of the metal used. Mild steel that has been machine-bent into shape in a cold state or cast steel and iron pieces that have been painted black both regularly mislabelled as wrought iron work. To be truly designated as wrought iron, however, a metal piece must be forged by a blacksmith who heats it and hammers it into shape.
Cast iron can refer to a range of iron alloys, but it Is most commonly associated with grey iron. Despite having the name iron, it isn’t pure elemental iron (Fe on the periodic table) – its actually an alloy containing 2-4% carbon, plus small amounts of silicon and manganese. Other impurities, such as sulphur and phosphorus, are also common.
Cast iron is formed by smelting iron ore, or melting pig iron (an intermediate product of iron ore extraction), and mixing it with scrap metals and other alloys. The liquid mixture is then poured into moulds and allowed to cool and solidify.
The final result is strong but brittle. Due to the higher carbon, cast iron solidifies as a heterogeneous alloy, meaning it contains multiple constituents, or materials in different phases, within its microstructure.