So on Sunday, I used my DIY, concrete forge, to heat treat my India Origin frizzen. I used charcoal, and a battery operated charcoal "fire starter" as my air source. Luckily years ago I hoarded some Kasenit, hardening compound, which these days has been replaced by stuff called Cherry Red.

Anyway I got the part heated to the proper color, applied the Kasenit, let it do its thing, then quenched it in water. Followed this with a repeated application as per directions.

Then I took the slag off the front of the Frizzen, and was careful to wipe, not polish the frizzen face, and tested the lock. YEP it worked. Nice sparks.

I don't think it did more than added carbon to the Frizzen, since from what I was taught by a master lock maker, the color wasn't bright yellow to get the steel properly hard enough on its own. This particular frizzen is a tad thin, so I don't think I'd try that for fear of cracking the steel, or worse.

It will probably need a treatment again in the future. No telling when, but Kasenit or Cherry Red doesn't put the carbon very deep into the steel. They are surface hardening compounds.

I am thinking of actually refacing the frizzen with a piece of 1090 carbon steel, in the future. The classic way is to make a new face that matches the contour of the frizzen. Then you harden that. Then you silver solder that into place, as the silver solder melts at a much lower temp than that used when heat treating the new face, so does not mess with the hardness. The trick is to get the balance right on the newly repaired frizzen without having to muck about with the frizzen spring.

LD

I've not done it myself, but I've heard of quenching the frizzen in old motor oil or transmission fluid. I don't know if this adds more carbon to the metal or not.

No, it shouldn't but it should get a harder quench. My friend who does commercial frizzens, uses an oil "quenching compound" that is sold for that purpose.

LD

My grandfather advised me to quench in used motor oil as he said it adds more carbon content, which I assume is from the carbon within the used oil. I really have no idea but did listen as he was an old blacksmith.
Walk

Well, I don't think it would hurt.

I think too there is a difference from using wrought iron in a tool application, and getting it harder by quenching in used motor oil, and taking steel and adding more carbon to the steel (short of bringing it up to a liquid point and adding it that way.) Otherwise none of the hardening compounds would be needed, right?

LD

Your right Dave. Wrought iron cannot be hardened except by case hardening. Motor oil, used or new, is a very poor quenchant having poor cooling qualities, and gives off very toxic fumes when it burns. It is formulated to be a lubricant and not a coolant. No carbon is added by any carbon in the used oil. If you are going to oil quench, use a vege cooking oil, of which canola is the fastest cooling of all available, and will work well enough with all the 10xx steels. You can add carbon to iron by layering thin strips or sections with layers of common carbon, then cook covered at a high heat, in the range of 1500° plus. In colonial times, the steel might get cooked 24 hrs per day for a few days to a week per batch. This is how blister steel is made, and was the only steel available until crucible steel was rediscovered around 1740. Shear steel was available and is but simply blister steel folded and forge welded into a billet much the same as Damascus, but of a single type steel. In perfect light, and clean metal, you can see the layers in some shear steel.