More Primitive Technology's explorations of the Iron Age

John Plant of Primitive Technology continues his explorations of Iron Age technology. In this video, he attempts to remove the carbon (decarburize) from some iron prills he produced using a method demonstrated in another video. His goal was to produce a malleable iron that he can hammer forge.

As always, turn the CC on to get info about what's going on.

He explains his process in the video description:

I think I figured out how to turn the brittle cast iron I've been producing into malleable iron that can be forged flat. When ever I smelt local ores it always produces cast iron prills rather than softer blooms of low carbon iron as one would expect from the bloomery process. I believe this because the prills are very hard, but when struck hard enough they shatter rather than flatten.

Cast iron is iron that has a high carbon content (when arranged by carbon content: Cast iron>Steel>iron). Cast iron has a lower melting point and is harder compared to regular iron. But it is more brittle so it's nearly impossible to forge. So I figured out how to decarburize it after some experiments.

First I tried making an ingot to work on but it didn't cast properly. Then I tried rusting the iron to oxidize the metal before melting so it would decarburize the cast iron during the melt (similar to the "wet puddling" process in metallurgy). But this gave an incomplete melt also.

The method that finally worked was simply melting the cast iron in front of the air blast till the carbon burnt out in the oxygen rich zone of the forge. This caused the cast iron prills to melt together in a single blob that I then was able to hammer flat while yellow hot.

This method is similar to the "stir fried steel/ 炒钢" process in ancient China or the "Osmond process" in Europe. It's done where ever cast iron needs to be converted to a lower carbon to be forged. I've seen videos about carburizing iron on youtube but none about decarburizing cast iron.

Thumbnail: Screen grab, YouTube, Primitive Technology.