Sunday, June 23, 2013

Simple Discussion about Making Medieval Steel

Catalan Forge located in Andorra and called “Farga Rosell”
Image also posted by miquel on the forums. 

Making steel during the medieval period was a bit of a gamble. On one end you have your basic iron on the other you have cast iron. In between these two you have steel. The only difference between steel, iron, and cast iron is the carbon content. Too much carbon and you end up with a very brittle material known as cast iron. Too little carbon and you end up with iron also known as wrought iron. Like Goldilocks, you want the iron with just the right amount of carbon (around 1%) that way you would end up with steel. The problem is that there is no "real" control in the medieval smelting furnace. You put in a high carbon fuel (charcoal, coal, etc) and some iron ore and then you heat it up and hope for the best. This process is still used by hobbyist today and it is definitely difficult to get truly repeatable results. With time and experimentation you would be able to better predict the outcome, but you still might end up with a lot of material that was  unsuitable for your intended purposes. Even if you did end up with steel after the smelt you would still need to process the bloom into a usable piece of steel. This process was typically done through heating the bloom until a red heat and gently compressing the bloom down (either with hammers or with a press). I do mean gently compressing it, if you try to over compress it the bloom will crumble into many pieces leaving you with a whole bunch of small pieces. The purpose of compressing the bloom is to squeeze out the impurities and work the smaller pieces of steel together into a forgeable piece of steel. There are quite of few sources out there on the internet and also a couple of interesting books on the smelting process. Hopefully this may have peaked your interest and you'll look further into it.

Two images borrowed (without permission) from miquel @

miquel has been testing out the catalan style of forge with some very good results. Jesus Hernandez also did some work with this style of furnace. Some of his information can be found here

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