How do you avoid scaling when hardening a carbon steel frizzen?

[Rolf]

Chambers and L&R frizzens are made of carbon steel.
How do you avoid scaling when hardening a carbon steel frizzen?

Best regards
ROLF

[T*O*F]

How do you avoid scaling when hardening a carbon steel frizzen?

Control your heat better!  You are either heating too fast or too hot.  Steel will enter the non-magnetic state before scaling forms and should be quenched at that point.  If you watch your part carefully, you can actually see the scale start to form.  Pull your heat and drop the part into the quench.  At this point, any scaling that has formed after quenching should be able to be flaked off with your fingernail or a light hit on the wire wheel.

[Dphariss]

Chambers and L&R frizzens are made of carbon steel.
How do you avoid scaling when hardening a carbon steel frizzen?

Best regards
ROLF

I usually coat the part with Kasenite to prevent surface de-carb then avoid over heating the part.
Scaling as TOF indicates usually means the part was too hot.
Dan

[Jay Close]

If using an oxy-fuel torch, make sure you have a neutral flame or even one that is slightly fuel rich. If using a solid fuel forge (coal/coke or charcoal), heat in the upper reaches of the fire where the fuel is burning in a neutral or slightly reducing part of the the heat column.  And as the other gentlemen said, don't over heat and don't hold it any longer than necessary at the critical temperature.

[Acer Saccharum]

You can also charcoal pack in a closed container.

Flint era cowboys hardened their frizzens in old bean cans, packed in mesquite charcoal.

[JCKelly]

In the US, brownells.com sells a product called ANTI-SCALE COATING, $15 for a pint. Paint it on, let it dry. Knivemaker guys use it I believe. I have no personal experience.

There is another compound, which would have to be home-made, that for years was used to prevent the very fine teeth of a file from decarburizing (and certainly from scaling) during the 5 minutes or so it was heated around 1440F (782C) to harden.

This was called "cyanide loaf". No, it is not all that toxic though I'd not eat it nor inhale the dust. One takes potassium ferrocyanide (formula K4Fe(CN)6, also known as "yellow prussiate of potash"), mix it with salt, flour,bone black and water. It was painted on the soft, freshly cut file before it went into a molten lead bath for heat treat. This file manufacturer rinsed the files after heat treatment and kept the rinsewater in a pond. I don't recall if the pond had fish. Really not especially dangerous but our OSHA is not known for keen intelligence.

My guess is that with enough potassium ferrocyanide you may have mixed up a version of Kasenite.

Whichever you use, I would let the coating dry completely before heating the part.
And make sure to use exactly the right chemical, K4Fe(CN)6. Don't get acid (such as vinegar) on it, that will make cyanide gas which is poison.

[Rolf]

I use a an electric, programable, thermostat controlled heat treating oven for making knives. I've calibrated it with color change sticks so I know it is correct. I've been using it for 12 years. The oven contains normal air (21% oxygen). This is what causes the scaling. Steel starts scaling at about 650^oC (1200^oF). This is lower than than the hardening temp/nonmagnetic temp which is 775^o(1427^oF). I file and sand my knives after annealing. This is the same procedure all Norwegian smiths follow. On a knife this is not to much work.

With springs, I've been following Kit Ravenshear spring  booklet and hardening at 1500^oF and annealing at 700^o F. I leave the scale on. Most of it cracks and falls off when the spring is used . What sticks on does not seem to interfear with the function.
But a frizzen is something else. The scaling has to be removed and is a $#*! of job.
 
Most of you seem to be avoiding scaling by heating in a neutral/reducing flame . I don't have acsess to a forge any more, and therefore want to use my oven. Coating the parts with kasenite or packing in charcol would solve the problem. I am a bit afraid  that adding carbon to the frizzen would make it more brittle and prone to crack at the toe. I think I'll experiment a bit with one of the anti-scaling compounds. It seems no one has tried to use them on frizzens. They are not sold in Norway. Hope Brownell will ship them to Norway. It has been a problem to get them to ship chemicals.

Best regards
Rolf

[Jay Close]

Rolf:

Seeing as you have a heat treating furnace, I think there is a stainless steel foil that is sold (by Brownells?) to tightly wrap a part in for heat treating. The idea is to exclude oxygen during the heating but I don't know how it might impact the quench.  Just a thought. I wouldn't worry too much about a charcoal pack or Kasenite over carburizing as standard procedure (at least for me) would be to draw the foot and pan cover pretty soft.

[Mike Gahagan]

The way that Jim Chambers taught me was to heat the frizzen,springs,etc to where the metal starts to turn blue and then cover it in boric acid until it has a clear glassy looking crust forms on it.Then reheat it again like you normally would to harden and quench in oil.To get the layer of crust back off you can soak it in hot water for awhile.Works great and it will hardly turn the color of the metal to where you can re-polish it with just some scotch bright.

[JCKelly]

Brownell's does sell 321 (EN 1.4541) stainless for for wrapping parts to be heat treated. Price $20.99 for a 61cm square (24 x 24")  0.05mm (0.002") thick. Should work. My former employer sold a much higher nickel grade for that purpose until the 1980's.

Add a little charcoal to the pack to use up the oxygen. Don't worry about carburizing the toe. You need only heat for a few minutes, surely less than 1/2 hour, before quenching. Very little depth of carburization can occur in this time. And, as posted above, it is well to temper the toe through pan cover a bit hotter to avoid breaking. It is surprizing when one pulls the trigger & the frizzen, part of it anyway, flys off.

I had forgotton about stainless foil. Much less messy than "cyanide loaf" Nothing magic about Brownell's foil, if Outokumpu has stainless foil locally available it should be just fine.

Slightly off-topic & as a knife maker you already know this: my college Prof used to work at Springfield Armory, when the US used to make real military rifles. You'd think they would have known this for centuries, but he did pass on to us that a bayonet must be quenched straight in to the oil/water, if one expects it to come out straight. If it hits the quench on edge or on its side it will bend. Also, for those working with plain carbon steel, one gets less distortion, less chance of cracking & a little more hardness by quenching in salt water, than in pure water. About a 10% solution of sodium chloride (table salt) in water will do it.

[Dphariss]

It only takes one bent blade or spring the learn this lesson.
Dropping properly  into the quench is critical in pack hardening as well. How the parts are put into the pack controls how they fall into the quench and can determine a straight or warped part.

Dan