In the realm of steel

[JimCrawford]

Is it possible to ADD carbon to a lower carbon steel without re-smelting it? I know that there are legends floating around about this, but am wondering if there's any fact to the fiction.

-Jim

[ThomasPowers]

Yes; making blister steel was the common way of doing it for several hundred years.

If you can ILL a copy of "Steelmaking Before Bessemer, vol I Blister Steel" you will learn way more than you wanted to know.

Basically wrought iron bars were put into large stone chests along with carbon containing material and then heated red hot for a week to ten days---steel was *expensive* compared to wrought iron even as late as the American Civil War steel could cost 5 times more than plain wrought iron.

When it came out the surface was all covered with blisters, hence blister steel.
Now blister steel in general had a variable carbon content that would decrease as you went toward the center of the bar if it hadn't "steeled" all the way. To get things better homogenized you could take blister steel bars and weld them together and draw it out to be shear steel. If you repeated this you could get double sheer steel. So the most expensive highest carbon version was double blistered double shear steel---spec'd only for razors and objects wehre the very high carbon would be OK.

Now if you wanted to get a much more homogenous material you could take the blister steel and melt it in a crucible and get crucible steel---in the west Huntsman came up with this in the 18th century.

Ric Furrer gave a demo at Quad-State on 3 ways of making steel where he demonstrated blister steel, crucible steel and orishnagane (sp) a japanese method of taking small bits of wrought iron "trash" and carburising them in a charcoal forge and then welding up the resulting steel into a usable billet.

Smelting is getting the metal from the ore; I think you mean melting it.

[HWooldridge]

Any carbon rich environment that surrounds the material when it is at elevated temps will transfer some carbon, while an oxidizing environment will do the opposite. A fuel rich gas forge will add a bit of carbon - an oxidizing atmosphere will remove it and cause excessive scaling.

Case hardening adds carbon to steel on the surface so carried to extremes, the carbon will migrate farther into the bar and become more than a skin treatment. As Thomas said, heavy forging and/or welding will then distribute the carbon throughout the bar.

[attlihammer]

If I am making a tool it is often cheeper and easyer to make the tool out of mild steel, and to then case harden them. This process only hardens the surface and so is not sutable for tools that are to be regularly ground. my scrolling forks have been made this way and have been in use now for several years, and are as good as new. In the uk it is possible to buy case hardening compound. My case hardening compound goes under the brand name of "hardenit" and is obtainable from- Glendale forge, monk street, thaxted, essex CM6 2NR. I assume there is a us eqivalent.

[John B]

A very old method of surface hardening mild steel,
Take a spoonful of wholemeal flour, add two spoonfuls of salt, add a little water and make into a smooth paste.

Heat the end of the item to be hardened until the paste will stick to it, when you have the item coated where you want it, heat the area to a bright red heat and plunge the item into cold clean soft water. The coated are will be appreciably harder.

An ideal way to make a quickie tool more hardwearing and no toxic chemicals involved

[ThomasPowers]

Perhaps an older one: In 1120 CE a german monk named Theophilus wrote of taking iron and greasing it and wrapping it in leather and then covering that with well kneaded clay, letting the clay dry and then heating the entire thing up to a good red and breaking the clay off and quenching it.

Using sugar is another.

Letting it sit in a charcoal forge that is hot but reducing is another that can get you a deeper case; basically how they make orishnahagane (sp).

[Quenchcrack]

One comment lacking in all of the above: Carbon moves into the steel at about .007" per HOUR at 1750F at a carbon potential of about .6. That means you need an atmosphere that has about six tenths of one percent carbon to get the carbon to diffuse into the iron at the quoted rate. The point is, don't plan to forge or grind the surface after you carburize it. You will either grind it all away or oxidize it away.

[bridgeport]

Kasenite, is your friend here... it works and is cheap.