Carbon shealding in HT oven

JTknives

JTknives

Joined
Jun 11, 2006
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8,651
After my last post about "burning" the oxygen in a heat treat oven I have been doing some testing. I first tryied using it at high temp with foil to see if it helped prevent foil burn through. It seamed to help to an extent, by that I mean I was not burning through foil anymore at real high temps. Next test was on some 15n20 and it also showed a great improvement on surface scale. The final test was on an actual knife and after a conversation with a customer I decided it was time. He hand finishes his blades and had problems removing the little circles and lines that come from scaling. So he sent me a small blade that looked just about finish sanded and I figured no was the perfect time to try and save his finish.

I heated the oven to 1475° and once the oven was at temp I tossed in a charcole BBQ Briquette and closed the door. After a few min I opened the door and the charcole caught fire and I put the blade in the oven and closed the door. Once the oven reached 1475° again I gave it a soak 10-15min. I then opened the door and the briquette caught fire again and I snagged the blade and quenched in parks 50. After wiping off and cleaning I noticed there was no scale just a even pitch black smooth finish on the blade. I can't feal any pits or finish issues. I then tested the hardness and from past experance any carbon steel that gets a soak has issues with hardness testing without grinding a spot to test. Well the tang of this blade tested at 66-67rc over a few tests. It then got a temper and is sitting at 61-62rc now.

I can't be anything but happy with the results and I will continue to test this to see how this continues to work out. Here are some pictures.

Photo%20Mar%2005%2C%206%2029%2024%20PM.jpg


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Photo%20Mar%2005%2C%206%2040%2026%20PM.jpg
 
That's interesting. I might try that next time just to see what results I get. Thanks for the update

Sent from my SM-N915V using Tapatalk
 
Good think there JT - I guess the high heat with charcoal fills the oven with CO2 (?). Is there much fumes/order given off? My oven is inside and wouldn't want too much fumes inside. On the few occasions I HT carbon steel, I cover good with roach poison powder (borax) which works pretty good.

Good thinking JT -

Ken H>
 
I imagine the hardness test is the result of a little bit of carburizing from the CO given off.
 
MBurks said:
When you say PCB my mind instantly goes to "printed circuit board ", so what is PCB?.
Click to expand...

My mind instantantly thought Polyclorinated Biphenol.
The transformer crew used to all but bathe in the stuff. Now a minor spill means 'Haz-Mat dig up & haul away anything it contacted.

Anyway, I think anything is good if it consumes or shields oxygen from the steel. Its common in industry by a plethora of methods.
Btw, coal should work also, but maybe leave behind contaminates.
 
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There was a little smell but not bad becaus it smelled like BBQ lol. I'm sure there is lots of stuff I could but a bag of briquettes is cheep and has a ton of then in the bag. One lasts in the oven for a while and you could easily heat treat lots of blades for hrs with one. But no readion to be cheep thy don't cost a lot. I'm going to make a briquette holder that I can take in and out with tongs. Now I don't know the affect this might have on the heating elaments but so far so good. Thy don't look any worse then befor I started this test.
 
I'm famous! Thanks for another bang-up job JT. I'm glad the new process worked. This is the blade for the thread I made about paring knife handle flaws. Admittedly, i've never used another HT service, but it's hard to imagine anyone else giving little-old-me-and-my-newbie-knives more professional attention.
 
JT, did it make inside of oven black? Since you said the blade was black, just wondering about oven.

Ken H>
 
I may have gotten that wrong. I should have said the liquid anti-scale compound, like the ATP 641 that Brownells sells.
 
ATP - now that makes sense. Like MBurks said, PCB is a printed circuit board to me. Making them by etching with ferric chloride, or with a CNC machine.

Ken H>
 
Cute oxygen purging technique. I'd like to think about using it for oil-quenched carbon steels, because kiln+foil+oil is the most complicated and riskiest combo.

Is there any risk of deposition on the heating element? What else could go wrong?
 
I'm kind of thinking the elements Will self clean, but maybe colder parts of oven may develop a little build up after a while.

Just a guess though.
 
I don't see any buildup of anything in the forge, just the little ash pile where the briquette was. At that temp I'm thinking everything is burning and turning into gas. Plus the briquette is mostly carbon, I'm sure there are a few things in it that are not carbon. I'm going to have to do more research and ask people smarter then me about what gas we actually have in there. I came across a paper that talked about carbon monoxide and how Reactive it is with nickle. I'm holding off any more testing till I can figure out if I'm making poisonous gas. Here is a blurp from the paper.

Ni (s) + 4 CO (g) -> Ni(CO)4 -> Ni (s) + 4 CO (g)

Carbon monoxide is so reactive with nickel that within a couple of minutes it will have etched the surface. Ni(CO)4 is highly toxic with a musty smell. As well as being flammable this tetrahedral complex decomposes easily into its constituents. Carbon monoxide is acting as a ligand towards the transition metal through the lone pair on the carbon atom. Diatomic carbon monoxide has a triple bond between its atoms. One of the bonds forming the triple bond is a dative covalent bond.
Click to expand...
 
Fwiw,
If you wonder what chemistry content of your brand of briquettes, You can look up their MSDS sheet.
All manufacturers publish one.
 
Ken H> said:
ATP - now that makes sense. Like MBurks said, PCB is a printed circuit board to me. Making them by etching with ferric chloride, or with a CNC machine.

Ken H>
Click to expand...

It's PBC* anti-scale compound. It's a dark grey powder that you sprinkle on to coat the blade when it reaches about 450F and it becomes a black glass type coating at austenitizing temps. It's comes off easily in boiling water... hot tap water, not so much lol.

I use it sometimes on blades to thermal cycle that I want to then clean up quickly and add clay to for clay hardening.

http://usaknifemaker.com/pbc-regular-anti-scale-powder-1lb.html (I never really knew what they were showing in that picture, but for me it came in a baggy.)

Anyway, just thought I'd share that.

As you were.. ;)

~Paul
My YT Channel Lsubslimed
... (It's been a few years since my last upload)
 
Try natural chunk charcoal instead. Most bricketts are chock full of additives. Good chunk charcoal should be about cure carbon
 
JT -- Google "Study of Reduction Behaviour Of Iron Ore Lumps". It's a PDF I came across while doing research at work awhile back. While the subject of the paper isn't exactly about what you're trying to accomplish, the chemistry and reactions discussed might be useful...

Jesse
 
Brownell's PBC is now just called Brownell's non-scaling compound

The old name was so often misspelled as PCB that they changed it. The acronym was for Protective Blade Coating.

It works great.
 
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