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Dylan A. Lewis

Reducing carbon for hearth steel

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I've been wondering for a while if it's possible to make a hearth furnace that would take the carbon out of cast iron to be left with either Bloom iron or orishigane. Just curious if anyone has ever tried it

 

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It is not only possible, it was the main way wrought iron was made from around 1450 AD up to 1800 or so.  Look up "finery forge," "chafery fire," and the indirect process of making wrought iron.  You will need some slag for it to work, though. Sand can get you started, but it does better with real smelting slag.

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Also look up evenstads work on open hearth furnaces you can add or reduce carbon. Reducing carbon is much more finicky but would typically be done by lowering the air inlet closer to the base of your furnace to oxidize that cast iron more. And speaking from experience Alan is definitely correct I found the slag to work much better than the sand for this process.

 

Will

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On 12/10/2019 at 9:43 AM, Alan Longmire said:

It is not only possible, it was the main way wrought iron was made from around 1450 AD up to 1800 or so.  Look up "finery forge," "chafery fire," and the indirect process of making wrought iron.  You will need some slag for it to work, though. Sand can get you started, but it does better with real smelting slag.

Would the slag that forms on the sides of my previous attempts at adding carbon to mild steel, aswell as ore itself?

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Ore itself is better, you need the glassy iron silicate to protect the iron while you burn off the carbon.

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On 12/10/2019 at 6:43 AM, Alan Longmire said:

it was the main way wrought iron was made from around 1450 AD up to 1800 or so. 

Also called "puddling", as in a "puddling furnace". Lots of info out there on the process.

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Puddling is actually later, ca. 1790-1950s.  Finery/chafery forges are more like the Catalan forge process, in which you stir around the cast iron as it melts in an open hearth full of charcoal and slag.  With puddling the fire is separated from the iron and molten slag by a muffle wall in a closed reverberatory furnace not unlike a pottery kiln, making it much less messy and more efficient.  

 

You can easily make a finery forge from charcoal and a hole in the ground. 

 

Puddling furnaces are a substantial bit of industrial infrastructure, needing a firepit, a hearth (with doors), and a very tall chimney with top-mounted damper.  The plus side is you can use any fuel that burns well in a puddling furnace, you're not limited to charcoal.  The downside is they're sort of like the blast furnace itself in that they work best when run 24/7 until the lining starts to wear out.  Sometimes they'd even build a cementation furnace onto the chimney end of a puddling furnace to make use of the waste heat to make shear steel.  Since they were holding temperatures of 2500 degrees F in the puddling furnace for weeks at a time, it was just efficiency to use the cooler end under the chimney to cook steel for a week or two at a lower temperature, often around 1600-1800 degrees F.  

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On 12/27/2019 at 1:18 PM, Alan Longmire said:

Puddling is actually later, ca. 1790-1950s. 

Huh. Ray Rybar often refers to any carbon reduction process of hearth steel as "puddling". He often makes cast or really high carbon steel from smelts and needs to reduce it in subsequent processes. I do not know what type of furnace he uses though. Thanks for the info.

 

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It's just terminology. As I read on another forum this very day, "Nomenclature is the first refuge of pedants."  :lol:       

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