A Brief History of Iron & Steel

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 These notes are from memory so please do not quote us but it should give you the basics. 
First, the smelting of ironstone with coke and limestone in a blast furnace to produce cast iron.
Cast iron, iron with about 4% carbon, is ideal for castings as it flows well into the mould, it is strong in compression but weak in tension and can be quite brittle.
Heating molten cast iron reduces the level of carbon but the melting point of pure iron / steel is a lot higher than cast iron and these higher temperatures could not be obtained in a large furnace.
The production of steel (about1-2 % carbon) could only be achieved in small high temperature crucible furnaces producing small amounts of very expensive steel.
Wrought iron is produced by heating cast iron to remove as much carbon as possible until the rising melting point causes the molten iron to thicken, it is now called a bloom. 
The hot bloom is hammered flat and folded over, repeated many times, the iron oxide scale that forms on the surface is also folded in forming layers of carbon rich iron and iron oxide. The carbon is drawn from the iron and combines with the oxygen in the scale resulting in layers of near pure iron and slag.
The term wrought iron refers to the hammering and folding process.
Puddled iron is produced by heating cast iron in a refractory furnace, it has a "lid" to keep the heat in, iron oxide scale is add and mixed by hand with iron rods, the carbon and oxygen combine. Often called puddled iron or puddled wrought iron.
The Bessemer Converter came into use in the 1850`s, the converter is charged with molten cast iron, air or oxygen is forced through holes in the base and burns with the carbon, it is this rapid burning that causes an increase in temperature high enough to keep the resulting steel in a molten state. The cost of steel dropped many fold due to this simple yet efficient process.
Wrought iron tends to have nice square corners, steel tends to have rounded corners.
A company name or initials stamped on the bars, not common but when found is a good pointer to wrought iron.
Corrosion, steel tends to have a random pitted surface while corrosion of wrought iron tends to follow the layers of iron and slag producing lines along the bar. Very heavily corroded wrought iron, old ships anchor for example, will show these lines very clearly to the point that the forged welded joints can be seen. The fracture test, wrought iron will fracture to show the layers of iron and slag, not unlike snapped wood but a fracture in steel will resemble a broken brick.