Carbon in the heat treat oven

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
Joined
Jun 11, 2006
Messages
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So I was looking over my gole of running shealding gas in my oven. In researching I found that Co2 is commonly used as a shealding gas for MIG welding. That got me thinking and wondering about using somthing to turn the O2 into CO2. I know from past threads on the forum people say CO2 is bad for electric elaments, but Why? Why not use a charcoal briquette to burn off the O2 and generate CO2. This would put less CO2 in the oven then if you injected it. I know heating elaments build up an oxide layer on there skin and maybe the CO2 reacts with it. Like I said I have seen posts in the past about C02 + elaments are not good but I'm looking for an actual reasion why that can be proven not just rumours.
 
The CO2 would only last as long as the carbon supply does. At 1500F that probably wouldn't be very long. The increased CO2 atmosphere will affect the coils just like an increased O2 atmosphere would.
 
CO2 is an oxidizer, they do use it in welding, however, they put deoxidizers in welding alloys.

Hoss
 
Stacy E. Apelt - Bladesmith said:
The CO2 would only last as long as the carbon supply does. At 1500F that probably wouldn't be very long. The increased CO2 atmosphere will affect the coils just like an increased O2 atmosphere would.
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Stacy , I've mentioned in another topic that HT oven from my friend is isolated from the inside.You can not see coils ? Maybe that is solution ?
 
Perhaps a little bit of a side note, but I was recently reading through this thread: http://community.ceramicartsdaily.org/topic/5193-how-to-make-an-oxygen-sensor-for-your-kiln/
where a guy made a homebrew O2 sensor with a few dollars worth of parts. Might be something worth exploring? You could then monitor the oxygen, or possibly even get a similar CO2 sensor as well?

Flow over the sensor MIGHT be a bit of a tricky issue, I can't say for sure, but if you had meter-able numbers, you could monitor how efficient one method over another might be.

Just thinking out loud, as usual. ;)
 
But inside the forge the extra CO2 from burning propane rich shields the steel form oxidising why would I not work the same way in a oven?
 
Because you are supplying a constant source of fuel to burn up the oxygen with. That is why it creates the dragon breath once its outside the forge and mixes with additional oxygen. Like Stacy pointed out if you put a charcoal brick in the kiln it will burn up quick. I suppose you could keep shoveling charcoal into your kiln but obviously that is not very realistic.

-Clint
 
JTknives said:
But inside the forge the extra CO2 from burning propane rich shields the steel form oxidising why would I not work the same way in a oven?
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It's not the CO2 that creates a reducing atmosphere. It's CO that does it. CO is generated by the fuel rich mixture burning, CO at high temperature grabs free radical O molecules from the forge and creates CO2 as it exits the forge.
 
By the way, what happened to the sandpot? Get that working and this is a non issue yeah? Hopefully your still working on it, that was interesting stuff.

-Clint
 
I'm still working on it.
But in order to burn the carbon you need oxygen. Once the carbon burns up the oxygen that is in the oven as long as the oven is mostly sealed I would think the carbon would last as long as fresh air is not flooding in. Kinda like when you put paper in the foil pouch with your blade. All that's left is a sheet of carbon if there was no air.
 
JTknives said:
I'm still working on it.
But in order to burn the carbon you need oxygen. Once the carbon burns up the oxygen that is in the oven as long as the oven is mostly sealed I would think the carbon would last as long as fresh air is not flooding in. Kinda like when you put paper in the foil pouch with your blade. All that's left is a sheet of carbon if there was no air.
Click to expand...

JT , maybe it's easier to make vacuum inside oven ?
 
Ok I get what you are saying now. I honestly can't say other than I would like to think someone would have tried this by now as opposed to other more costly solutions I have seen people implement such as argon. I have an evenheat and it is pretty air tight but I doubt it is so air tight that i could burn something up during a heat treat session and not have any oxygen in the system.

That said I have nothing scientific to back this. Also I have no idea much oxygen is a problem when heat treating. In theory what you are saying may work if your oven is close to air tight.

Easy enough to test if you are willing to take the risk. If it were me I would heat treat a stainless coupon in foil like you normally would. Heat treat a second coupon with no foil with the same variables as the first. Finally heat treat a third coupon with no foil and a piece of charcoal or whatever in the kiln and compare the three. See how close the last one got to the one in foil and I think you will have a good idea how much oxygen is in the kiln.

Now one other thing I will say. Is if you burn up all coils or damage your thermocouple and the sand pot falls through. You may have spent enough money on all that to have just went with salts :) Food for thought anyway. Good luck and keep us posted if you try it.

-Clint
 
As Devin said with welding the CO2 comes apart in the plasma stream and is a oxidizer. It's known as a hot gas because it does burn a small amount of the base material increasing heat. I'm not sure what temperature it comes apart at and it's not completely uncontrolled so at minimum there should be a large reduction in oxidation. Maybe it's enough to be worth it. Nitrogen could work depending on if it's going to affect the alloy. Someone who knows way more than I could chime in but I don't think Nitrogen should affect most blade steels detrimentally. I my world it's a austinite former and that's bad for welding austenitic stainless. Does that affect blades. I guess I need to go read a few more books
 
The Simple Solution is Dry Nitrogen Gas......No need for a science project and its a proven process.
 
Ok I tested it and it might be working.
I snagged a small chunk of carbon from the wood stove that was about the size of 1/2 stick of butter. Put it on some foil and put it in the oven when it was close to temp. Once the oven hit 1475 I put some 15n20 in the oven and gave it a soak. I then I quenched in water. It came out of the quench super clean with no visable scale. I then went and tested it for RC. I chose 15n20 because I have test coupons that where heat treated the same way but with out the carbon. I grabbed my 1480° coupon and tested it and the surface that was ground to remove decarb measured 66rc. I then tested the other end that still had decarb and it measured 63rc. I figured these would be perfect comparisons to the carbon heat treat. I grabbed my carbon test and tested the hardness and hot damn 66RC. I tested it a few more time and still 66RC. Here is a picture of the coupon and the carbon test. The carbon lump had a little tiny flame when I first put it in but then went out. When I opened the oven door it was glowing but still there and hardly any gone.

Photo%20Feb%2008%2C%2019%2031%2020.jpg
 
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I did some quick math to see if I could actually see how much shealding the carbon could give us. Here is how my thought process went.

1 briquette is 180 grams
CO2 is 44.01 g/mol
1 mol CO2 is 24.465 L
Carbon has an atomic weight of 12.011
Oxygen has an atomic weight of 15.999
Air is an average of 20.95% Oxygen
Oxygen is 64g/mol
Oxygen is 22.4L/mol

First thing I did was calculate how much of C02s weight was carbon. 12.011/31.998= 37.54%
Next what's the carbon weight in one mol of CO2. 44.01x.3754=16.52gr
We know one Briquette is 180 grams so how many mols of CO2 will that make if we are in a perfect world. 180/16.52=10.896mol C02
Now convert that to liters, 10.896x24.465=266.57liters co2
We know 37.54% of Co2 weight is carbon so that means 100-37.54 = 62.46% of CO2 weight is O2
This means 180grams of carbon needs (1.6246x180) 292.428 grams of O2 to become CO2.
292.428g O2 is (292.428/64) 4.57mols which is also (22.4x4.57) 102.35 liters
Air is an avarage of 20.95% Oxygen
This means (100/20.95) 4.77x102.35=488.21liters of air is needed to supply the required oxygen to burn 180 grams of carbon.
My oven is right at 13 liters in size which means one briquette would consume all the oxygen in this oven (488.21/13) over 37.5 times.

Now I could be way off with my numbers, it is late and I just scribbled this all down on a note pad. But it kinda get the idea across, and that is while there is still carbon in the oven our atmosphere will be about 80% nitrogen and 20% CO2. This is assuming we get just CO2 and no C0. One thing we completely forgot to calculate is the expansion of gasses at that temp. This expansion from 68° to 1500° is just under 4 times (3.714) which means we could assume a hot oven would actually need (3.714x488.21) 1,813 liters of air to burn 180gr of carbon. That's a whopping (1813/13) 139.46 times the volume of my oven.
 
Hey, just found this thread after some googling because I had the same idea. JT, did this work out for you long-term? Have you done it more than just once to test?
 
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