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Case hardening...

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I heard you can make a high carbon shell on mild steel. Like for a hammer or a hard cased tool. I was told to take the glowing finished tool and bury it in a bed of charcoal to cool. I guess the carbon collects on the outside and case hardens it. Is this true and if it is, how well does this work?

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It is true that you can case harden mild steel. The process you described however would give a very shallow case if any. Carbon is absorbed into hot steel very slowly. To build an apreciable shell thickness requires holding the steel at high heat for many hours. If I remember correctly 12 hours would give about an 1/8'' thick case. To harden a tool with the process you described, you would need to use a case hardening compound. Case hardening chemicals contain deadly poisons and must be used with great care.
Furthermore, I would think that a hammer with a hard case would be likely to chip, which would also be dangerous.

Edited by arftist
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A book I have, I think that "The Complete Modern Blacksmith" by Alexander Weygers is the one, describes a method of case hardening where a part was wrapped in a ball of either ground animal hooves or graphite surrounded by I think plaster and tossed in a boiler fire overnight and then allowed to cool. I have wanted to try something like this but the several hour burn time has been a deterrent.

I've also read elsewhere that using this "Super-quench" will make mild quite a bit harder. I bet the recipe for it is around somewhere.

also, I found this on here:


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There are a couple of quick hardening formula on the market, Kasenit, and Cherry Heat.
These produce only a superficialy hardened surface but it is adequate for makeing wearing surfaces on mild steel. Cherry heat is less dangerous than Kasenit.

One commercial deep hardening compound, or Pack case hardening as the process is called, is Wilcarbo from Rose Mill Co. - chemicals lubricants processing.

Casehardening starts at aroun 1750 for low alloy steels and goes down with the percentage of carbon already present. The upper limit is around 1800. This is a high red to low orange depending on your eyesight and lighting conditions.

Not all alloys are equal in their ability to absorb carbon. With A36 it is a real dice roll as to how effective pack case hardening will be.

The most important things in pack case hardening is that the metal be absolutly clean, and free of scale, the media must be finely ground to dust, the item must be surrounded with the media for some depth, there must be something that acts as an early oxygen scavanger to prevent scaling early in the process. The temperature be closely controled.

Most people build a metal box to do the packing in.

When it is all said and done I prefer buy the right steel in the first place. If you just want to experiment then bone charcoal for aquarium filters and chrushed nut shells makes and good combination.

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  • 6 months later...

After your reply, Thats where I read it.

Yes, no, and maybe. The old case hardening method with carbon bearing materials, bone, leather, horn, and charcoal...was done in a ceramic or iron casing pot with a clay luted lid to keep it air tight. You wanted the casing material to not burn up. Holding for 5 to 6 hours at a red heat would give a case of a few thousandths of an inch. This is shown in the film, "The Gunsmith of Williamsburg" which I got from The Williamsburg Foundation, Williamsburg, VA.

In the old days before the mid` 1700's, steel was made from low carbon wrought iron, so called "blister steel," by the casing (cementation) process, and using charcoal. It was done on a larger scale than case hardening, and the red heat was maintained for 7 to 8 days, sometimes 11 days for high carbon heats. The problem was that the carbon content was not homogeneous throughout the mass. The resulting steel had higher carbon near the surface than in the interior. In 1746, a clockmaker named Benjamin Huntsman figured out that if he cut the blister steel into chunks and melted it, then reforged it, that he got higher quality clock springs. At the time, it was not known that carbon content was involved. Huntsman was experimenting and he did the right thing, because when molten, the carbon became uniformly distributed within the melt. The chemistry about carbon was found out at a later time.

http://www.turleyforge.com Granddaddy of blacksmithing schools
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Not to mention that all the slag in the WI would float to the top leaving a very nice clean steel below.

When I do blister steel I get a chunk of pipe with one end sealed off and fill with charcoal, bone meal, etc and shove the strips of WI into it leaving them well spaced, then closing off the open end, (often hammer flat and bend over---when done hot it's kind of fun as the powdered charcoal likes to come out and play). The chuck in the propane forge against one wall and remember to rotate it every hour as you go about your regular forging. It's possible to get the carbon content *too* high by this method!

If you are really interested in the process may I commend to your attention "Steelmaking Before Bessemer, vol 1 blister steel, vol2 crucible steel"

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  • 3 weeks later...

This is a great hardener, I hardened a piece of old wrought iron into a chisel , One fifth generation smith saw it and said " that's imposs, she canna werk I don unner stan" Here is the formula I think it was discovered by Gunther somebody ...Five gallons of water , five pounds of salt, a bottle of dawn dish washing detergent and a small bottle of jet dry, as a surfactant ( what ever that is ) anyway, mix well. When you quench use a scrubbing motion. up and down quickly I don't know why but if you don't scrub it doesn't work. I know it sounds insane but it changes the structure of the molecules , it really works, try it and prepare to be amazed.

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Called Super Quench. The soap and jet dry breaks down surface tension (that is what surfactants do) and lets the water wet the metal faster. The salt provides many many many (many?) nucleation sites for water to boil at and raises the boiling temperature of the water. All this causes very small bubbles and help prevent a vapor film. The scrubbing motion breaks up what vapor film forms, and agitates the solution bringing fresh cold solution in contact with the metal. End result is a very very high heat transfer rate out of the metal.


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