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how to make an iron knife?


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#1 jake cleland

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Posted 28 November 2006 - 07:25 PM

i have a hankering to forge a knife from wrought iron, and carburise the edge. my plan is to forge the blade very close to shape, leaving perhaps 1/32 -1/16" on the edge, and build a big coke fire, with a steel tube, capped at on end, filled with charcoal - my truyere is at the back of my forge, so i figure i could run the blower quite hard, to get the coke fire up to temp, without worrying about oxidation, and have a charcoal fire for the knife to sit in. i figure i'd need about 2200f for about 20 mins to ensure full carburization. i also thought i could clay up the spine to ensure that the carbon was getting to where it was needed. then do a few normalizing cycles, take to non mag and quench. anyone tried anything like this?is it a stupid idea? am i missing something? any advice would be appreciated.
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#2 Bob Geldart

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Posted 28 November 2006 - 07:29 PM

I don't think 20 mins would give a very deep carburization.

#3 polarbearforge

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Posted 28 November 2006 - 07:30 PM

In tech school, we did this to a few pieces just for the experience. Instead of 2200 though, we just baked it at 1700(in a mostly sealed box with parts packed with charcoal). I have a chart somewhere around here that shows how much carbon moves at temperature. I'll see if I can find it. We used an electric heat treat oven though and let it bake for a lot longer, but had penetration at about 0.070 if I remember correctly.

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#4 Michael Stuart

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Posted 28 November 2006 - 07:44 PM

If I understand correctly how this works, higher temperatures do increase the rate of carbon diffusion, but they also cause greater deformation of the surface (blistering, hence, "blister steel"). Lower temperatures and longer time, up to several days, will get the carbon to move in without as much damage to the surface of the piece.

I believe some case-hardened knives would have been sharpened only on one side, like a chisel, so that the edge was always made from the hardened portion.

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#5 tell

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Posted 28 November 2006 - 07:47 PM

Good idear if it works out let me know i have about 20 old park benches in need of a new life if i remember there is a link to a guy that supplyes Satanite clay in the states he also said he can get a material for Caburising in the forge , worth a look give this guy a buzz he may be able to help

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hope you have some sucsess mate :rolleyes:

Edited by tell, 28 November 2006 - 07:49 PM.

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#6 B Finnigan

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Posted 28 November 2006 - 08:36 PM

I have also been wanting to try that but I reservations about the end strength of the iron. Since wrought is very grainy with alot of brittle silicates in stratified layers it does not seem like it would lend itself to making a strong blade given the thin structure.
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#7 Ty Murch

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Posted 28 November 2006 - 10:35 PM

Look up what's called shear steel. This is an old way of making blade steel from carburizing wrought iron. Carburize thin strips, stack, weld, fold......

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#8 mete

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Posted 29 November 2006 - 02:15 AM

Typical carburizing of steel is done at 1500-1700 F. Higher temperatures give deeper case but at the expense of grain growth. In any case it's hard to control. You could do as they did in the old days with iron and bronze work harden the cutting edges.

#9 Gérard Heutte

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Posted 29 November 2006 - 06:56 AM

Hello

Here is the curve of carbon migration speed in accordance with temperature:

diffusion01_gb.jpg
(synthesis curve with information from web and books)

I hope this helps.

Edited by Gérard Heutte, 29 November 2006 - 06:57 AM.


#10 CProkopp

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Posted 29 November 2006 - 08:33 AM

...Or you could go high tech and use Casenit.
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#11 jake cleland

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Posted 29 November 2006 - 11:19 AM

thanks for the replies guys - the reason i was going so hot is that the heat/penetration curve is pretty much exponential and at that temp/time i hope to be able to carburise right through the cross section of the edge, giving a sort of hamon effect, so you cant sharpen through the hard section. similar penetration at 1700 would take about 20 hrs. i figured that as this is about the welding temp for iron, the grain growth should be reparable with a few normalizations, pretty much like plain carbon steel. the blistering might be problematic, but as long as i get a deep enough carbon migration, i hope i can grind through it, or else a blistered edge and grain pattern spine might look pretty cool. the most important thing i guess would be to make sure my iron was homogenous enough, but i should be able to tell this from forging out the blade.
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#12 owen bush

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Posted 29 November 2006 - 04:01 PM

thanks for the replies guys - the reason i was going so hot is that the heat/penetration curve is pretty much exponential and at that temp/time i hope to be able to carburise right through the cross section of the edge, giving a sort of hamon effect, so you cant sharpen through the hard section. similar penetration at 1700 would take about 20 hrs. i figured that as this is about the welding temp for iron, the grain growth should be reparable with a few normalizations, pretty much like plain carbon steel. the blistering might be problematic, but as long as i get a deep enough carbon migration, i hope i can grind through it, or else a blistered edge and grain pattern spine might look pretty cool. the most important thing i guess would be to make sure my iron was homogenous enough, but i should be able to tell this from forging out the blade .


Jake ,
this is something that I have thought about a lot and I got some good info from an english knife maker called Dave Bud who did carburisatin of steel as part of his masters degree in experimentel archiology .I am remembering a conversation from a pub so dont rely on 100% acuracy .

There are other materials that get better carbon penatrarion than charcoal ,leather being one and horse poo being another .

You will have to take the % of migrating carbon in the steel into acount and this is not even, ie there will be a higher % at edge and this will drop as you travel further into the steel .so theroreticaly the edge may be to high carbon before the center is up to corect %.

and then some thoughts of mine

If you carburised thin section and then forge welded em together you could get a more even carbon distribution due to carbon migration .

you would also have the chance to adjust the carbon down by adding iron layers to the layer'd steel before forge welding it together .

wrought iron can be really crappy so I would either forge it down from thick section at welding temp or fold it and weld it a few times to squirt a bit of crud (silicates) out .

Alternetivly you can buy charcoal iron in uk in sheet form or pure iron to .

If you make the steel first and not try it on a knife then you would have a chance to test some and use some for a finished knife.but I like the "idea "of making a whole knife and then steeling it .

just some ideas ,Anyhow let us know how it goes ,and as I said what do I know ?
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#13 R.H.Graham

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Posted 29 November 2006 - 09:49 PM

Charcoal and sugar together works well to carburize. Id keep the temps on the low end, around 1350-1400f and hold for a couple or three hours to get a usable result.

Just to be clear, there's very little indication this was done historically to any great degree, outside of rasps, files, and scrapers, so if it's a case of doing something "historical", this ain't the way to go.

Still, carburizing is a fine skill to have worked out, it has uses, and blistersteel, as was mentioned, IS a historical method in any case.
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#14 EdgarFigaro

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Posted 29 November 2006 - 10:07 PM

As own said there was one of our smith's here on the site...I don't remember if it was by J. Arthur Loose, Jesse Frank, Alan Longmire or someone else...

They had made their own bloom, drew it out into a very long thin bar, cut it into about 5 pieces or so. He then covered the bars in veggie oil (think Crisco , recipe he was going by called for animal fat/lard). After covering the bars he bound the bars in twine with a slab of leather on each side. He then stacked them all together, encased it in a large mound of clay which he then placed in his forge/furnace.

I think he cooked it around 1900 f.
Not sure how long he cooked it though.
He forge welded and I think folded it a few times to even things out.

Oh, and another note the recipe was I think by Theophilus or some such?

BINGO! It was Jesse
http://jfmetalsmith.com/smelting2.html

There was a page before that one, but that was the bloom I remembered.

He might have taken it hotter to get more penetration.

Found the original thread!

http://forums.dfoggk....php/t4994.html
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#15 John Rigoni

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Posted 30 November 2006 - 12:37 AM

I bought some casenit two years ago, used it to case harden a hammer of mine that was originally mild steel. The problem is I don't know how deep it went into the steel and from what I've read, it wasnt much, better methods include either a cast iron box filled with bone or cooking the blade in cyanide. good luck

#16 Jesse Frank

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Posted 30 November 2006 - 12:55 AM

Heh, yeah, that was me....

I have done it several ways. One is to cook a, 1/8" thick bar in a steel can filled with charcoal at 2150f for 20 minutes, then fold it on itself and run with it. works great. You saw the way I did it in that thread, works well, too. The key to avoiding blisters is to do it in a sealed environment. If you seal it up well, it will come out sometimes cleaner than it went in.

Honestly, if it were me, I would coat the areas you don't want carbon in with satanite or something and do it that way.
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#17 R.H.Graham

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Posted 30 November 2006 - 10:34 AM

in the lower temp ranges only the thin parts will pick up any significant amount of carbon anyway.
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