Wrought iron has little carbon content, it is tough, malleable, ductile and easily welded. It was traditionally smelted at a low temperature to produce a sponge-like mass of metal called ‘bloom’. The impurities are then hammered off as ‘liquid slag’ hence the name ‘wrought iron’, which means ‘worked’ iron. Now that the wrought iron is pure it is not susceptible to corrosion from weathering.
Cast Iron or ‘pig’ iron
Cast iron has 2% to 3.5% carbon, is strong under compression, but brittle under tension. Cast iron is smelted at a much higher temperature than wrought iron till it is in liquid form. From the furnace fuel, the iron is saturated in carbon (up to 5%). Then the liquid iron is poured into a mould (hence the name cast) to produce blocks of iron. Therefore cast iron is not suitable for manipulation or ‘shaping’.
Ductile iron is a combination of many materials such as Carbon, Silicon, Manganese, Magnesium, Phosphorus and Sulfur. Due to its make-up of nodular graphite inclusions such as the creation of spherical nodules rather than flakes means the material is flexible and elastic.