Process
The process begins with wrought iron and charcoal. It uses one or more long stone pots inside a furnace. Typically, in Sheffield, each was 14 feet by 4 feet and 3.5 feet deep. Iron bars and charcoal are packed in alternating layers, with a top layer of charcoal and then refractory matter to make the pot or "coffin" airtight. Some manufacturers used a mix of powdered charcoal, soot and mineral salts, called cement powder. In larger works up to 16 tons of iron was treated in each cycle.
Depending on the thickness of the iron bars, the pots were then heated from below for a week or more. Bars were regularly examined and when the correct condition was reached the heat was withdrawn and the pots were left until cool—usually around fourteen days. The iron had "gained" a little over 1% in mass from the carbon in the charcoal, and had become heterogeneous bars of blister steel.
The bars were then shortened, bound, heated and hammered, pressed or rolled to become shear steel. Alternatively they could be broken up and melted in a crucible using a crucible furnace with a flux to become crucible steel or cast steel, a process devised by Benjamin Huntsman in the 1740s.
Read more about this topic: Cementation Process
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