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I Forge Iron

How to add carbon to steel.


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Can you case harden it to a depth greater than you lose  from scale losses and decarburization?  I've seen a number of new smiths take high carbon steel and make into mild steel---wouldn't harden!

A common urban legend is that folding and welding increases the carbon content of steel. Actually most of the time it decreases it. Some Japanese swordmakers start out with nearly 2% C and by repeated folding and welding get 0.5% steel. (Much more homogenous though! Tamahagane  starts out as pretty much a mixture.)

Doing a long soak surrounded in high C stuff is how you make blister steel from wrought iron.  If you then pile it and weld it,  you then get shear steel.  Now you can get double blister, double shear steel; but it's costly in energy used.

If you make blister steel and then melt it you get Crucible steel, which was done about a thousand years earlier in central Asia than was done in Western Europe. Wootz is one variety of crucible steel.  Huntsman had a lot of issues with refractories that would work when melting steel.  (See "Steelmaking before Bessemer, vol II Crucible Steel" KB.)

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Huntsman had first worked in the glass making trade.

So he was familiar with the glassmaking  furnaces they used and they were run very much hotter than the standard iron and steel furnaces that were in current use.

 And  he used those higher temperatures to make crucible steel.

He also used the flux that the glassmakers used. It's identity escapes me for the moment. (I'll look for it later tonight).


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I checked through my files for further information. And these are some of the additional details concerning Huntsman's crucible steel process.

He used coke to heat the steel crucibles. This brought the temperature up  to 2.900 degrees F. (1,600 degrees C). That temperature melted the steel to produce a homogeneous mass in about three hours. The vessels were sealed with clay so as to exclude air.

A coal fire could not get to that high a temperature.

I am still searching for the flux that  he used.

Stay tuned for further bulletins,


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