Hello gentlemen. Since where I live finding good metal for armour making is almost impossible, I want to ask about your experiences with carburization, mainly of iron sheets, since that's what's available. A couple questions:
* Should one attempt to do it to the complete piece or the unhammered sheet of metal?
* Any advice on charcoal?
* Any blueprints or photos of a home made device?
* Is gas a good option for fuelling the heat? If not; which one to use?
* I read the ideal temperature is around 900Cļ and the propagation of carbon dictates that for something of around 16g an hour an a half is required. Is this the case? Which carbon content will it have at this point?

Thanks in advance for your time!
Hi Julian

First off, I haven't tried it, but I think that you should be very careful if attempting to carburize iron, because apart from the obvious danger of heating a gas in a confined space, it produces carbon monoxide, which is very toxic, so do it in a very well ventilated area. Personally I'd just work-harden the mild steel, or else find out about heat-treating it by quenching it with a surfactant mixed into the quenchant (which can apparently get it to spring hardness despite the low carbon content - but again, I've never done it).

If you want to proceed, I believe the process is quite simple in principle; something along the lines of sealing the iron bits you want to carburize in an airtight (or nearly so) fireproof container with the burning charcoal and leave it for one or more days. I don't think you will need to use an external heat source; if I recall correctly, the charcoal supplies the heat. Hopefully one of the professionals who have done it will write in to correct me (and comment on working around the safety issues).

Otherwise, more than a decade ago when I a week-long workshop practical at university, I seem to remember being told that it is also possible to do a form of carburization using an oxy-acetlene torch, provided you set the ratio of gasses just right. If you have an oxy-acetylene set and are trained in its use, that might be an easier way to go.
We sometimes case harden pieces like cervellieres. We put them into a form of steel, the outside is coated with loam, the inside filled with crushed charcoal. On the form we place a cap, which only leaves a small gap of about 1-2mm. The process needs a little bit of air, but not much. If you add to much air the piece will oxidate a lot. The thickness of the helmets are between 1-1,5mm. They stay in the electric oven at 950įC for 6 hours. You need to keep the temperature constant. The carbon content rises roughly at the following: 0,1%, at a depth of 0,1mm in 1 hour. So if you want to reach ~0,5% of carbon at the outside of a 1mm thick sheet. You need to heat it for 5 hours, when there is no carbon in the steel before. Now you should keep in mind that the carbon gets in from 2 sides, therefore the outside as well as the inside gets carburized. And you still need to grind and polish the pieces at the end. So the layer with most carbon will be removed. Therefore keeping it in the oven another hour will lead to a piece with 0,5% carbon at the outer layer.
All of this is very rough, I should look up if the formula was correct. But still 1,5 hours is by far not enough.
If you want to do this I recommend you to do this before you cut the pieces. Doing this with a breastplate, afterwards with a pair of arms, legs, helmet, backplate, each one individual is wasted fuel. Take sheets of the same thickness, place a layer of charcoal between them, put everything in a steel box, coat it with loam and put it above a fire or into an oven. I don't know if it works with gas. But I would wouldn't try, (personal opinion), I'd either use an oven or a simple fire. Both work.

Well it does work with gas, but you need a huge amount of gas to heat up all the stuff. Therefore I don't recommend it.
Mild steel is *really, really* low on carbon, and carburization only really hardens the very outside layer of the steel. Useful in small applications-- think gauntlets and other individual parts of the armour-- but frankly I would say just use the mild steel in less critical parts of your armour, save your pennies and buy some carbon steel when you can for the more important parts.

If carbon steel is absolutely not available... then go ahead and use the mild steel; unless it's completely soft and unworkable, in which case you wouldn't be using it anyway, it's going to be plenty tough enough for armour as long as you do a decent job. If you still want to attempt carburization, do so on some of the more vital parts such as the helmet crown and visor, joint protection, and the cup.
When I first started down the road to heat treating armour, I started with case hardening, using a mix of two powders, namely Kasenit and Welco 'Quick Hard'. After I got the stuff to stick to the piece (inside and outside) I heated it up to yellow, and continued to sprinkle the stuff on the piece, to keep it well covered, for about ten minutes or so, then quenched it in cold brine solution (with some other stuff I'm not going to tell you about because it's dangerous and toxic ;) ). Bracing the piece as you would to harden medium carbon steel is a good idea to prevent warping, and if you jump on the piece right out of the quench, you have about 15 minutes to correct the piece before it 'sets'. Using old hot rolled steel (strip it with vinegar overnight to get the black off) will give you better results, if they still make it the same, as it often had a higher carbon content than cold-rolled steel. On thinner pieces, it is a good idea to temper it back a bit (brown-yellow might be enough) rather than leave it full hard. It really does strengthen the metal quite a bit. Experiment on scrap first to get things dialed in for maximum effect before you use it on real pieces. Failure to temper thin pieces can result in cracking if you have flutes or other stress risers, but I didn't have any problems on helmet skulls, which were almost dent proof at 0.075" thick. Visors, better temper if you have anything around the eyes resembling a corner, or odd shaped cutouts.
@ Andrew Gill: Yes, I doubt I will use gas, just seeing what options are available. Iím afraid thereís no steel whatsoever here, not 1050 nor 1010, just iron and stainless steel.

Do you think that will be enough? So far I have read that you need to keep temperatures over 900C.

I donít. But I will look into it!

@Peter Spštling: Thatís really good info! Do you have any images of this setup? How heavy duty do you think the box should be? Have you done this with a fire? If so; how do you make sure the temperature stays constant and how do you feed it for 5 hours?
Yes, gas seems like a bad idea.

@Jeffrey Faulk: No steel is available, no carbon nor mild. Just stainless, if lucky.

@ James Arlen Gillaspie: First of all; Big fan of your work! Loved it since I saw it years ago in the book Techniques of Medieval Armour Reproduction by Brian R. Price.
Do you think the techniques you talk about could work for rising the carbon content of iron? Iím interested in getting my hands in mild steel not only for making tougher higher quality pieces, but also to learn to heat treat them.
I know modern mild steels are lower in carbon than they used to be, but I think hot rolled steels might still have a little more. Anybody into materials science, please comment! I don't know of anyplace that is producing pure iron, and only pure iron, for common use. Pure iron is pretty specialized and difficult to come by; I wanted some once upon a time for something. In any case (no pun intended), the powders will definitely help. You will have to play around some on sample pieces to find out what you like best. I mixed powders to get better properties.
Julian, where exactly is "here"?

It may be a hassle, but I'm sceptical that you'll find that is is not available anywhere.
A good option is looking for aviation repair suppliers, who often stock 4130 spec sheet.

Its certainly less hassle than trying to carburise steel yourself...
@ James Arlen Gillaspie: Here galvanized iron is the easiest one to come by they have just iron too. Iíll look if itís possible to make them. Would be happily surprised if they are sold here!

@ JG Elmslie: Argentina.

Well, I checked all the suppliers I could find, from the capital, my area and cities with heavy industry. I also asked artisans, smiths, knife makers and medieval enthusiast living in the country. I have not checked with aviation suppliers though!

Oh, I know, I would be really happy if I could walk to my local metal supplier or hardware store and buy it, but it seems itís not feasible here, so I either learn, make inferior products or quit. I still wish our industry grows and we start getting it or I find a super cool supplier that can get me some though.
Hi Julian

As someone else commented, most of what is sold as "galvanized iron" or "iron" is actually mild steel - 1018 or something similar. Sometimes it is made from recycled steel, so the composition varies quite a bit. Appaerntly some pieces even contain enough carbon to be heat-treatable, although I wouldn't bank on it.

Otherwise, you could try scavenging. I have found old lawnmower blades to be a good source of small flat pieces of medium-carbon steel - they're great for small knifemaking projects, though perhaps too small for plate armour unless you weld several together. So are saw blades and many other tools. If you happen to have a sawmill nearby, go and ask for some of their old bandsaw or circular saw blades, some of which are quite large and probably big enough to be useful for armour.
I would like to insert a safety note here:

If you work with any GALVANIZED metal, DO NOT heat it without adequate ventilation and protective equipment!

The galvanization cannot take the heat, it will come off the metal in the form of HIGHLY TOXIC fumes. They will NOT do you any good if you breathe any of it in! You CAN heat it up, but please only do it outdoors or in a space with a very efficient fume hood.

One way I have heard of working with galvanized metal is to put it in the middle of a large fire in the outdoors. This will both anneal the metal and burn off the galvanization, so it can be a good move. However you can never be quite sure that all the galvanization is burnt off, so keep on being careful with it.

Sheets of mild steel should be easily obtainable if you can find a scrap-yard; car hoods and trunks, for example, would be a reasonable source, requiring some disassembly though and of course you would have to remove any paint and greasy build-up since neither of those will like fire at all.
Often car hoods and trunks have a fair amount of carbon. Good idea! Galvanization can be removed with muriatic acid, but beware of the fumes! Outdoors, only!
I spoke with a couple of Argentinean armourers I vaguely know, and they suggested talking to this company, as they might be able to supply suitable steel sheet:

- good luck, I hope that helps.
@ Andrew Gill: The sawmill idea is good, Iíll ask around and research what type of metal those blades are made of.

@ Jeffrey Faulk: Thanks, Iím aware of that, the times I needed to remove zinc submerging the metal in apple vinegar did the trick, a chemist buddy vouched for the method.

The fire seems like a good idea for bigger pieces.

I thought about that, but donít you think they might be a bit too thin? I heard most cars have 19 gauge upwards.

@ James Arlen Gillaspie: Yes, sir. Safety first.

@ JG Elmslie: Thank you very much! I will contact them for sure.

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