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Possible decarb? - gas vs solid fuel?

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I've made a few knives before using coal/charcoal for the forging and heat treat. After the quenching a new file would skate nicely. Some time ago, the club I belong to had a gas forge build that I got into. I've attempted 2 knives recently in the gas forge. In neither case has a file skated after quenching. On the first one, I kept getting a little hotter and a little hotter until I ended up with about a bazillion pieces and huge grain. The one I just quenched, I tested with a magnet.
So I'm wondering why the file doesn't skate the same and the only thing I can come up with is I get more decarb. in the gas forge than working with solid fuels. Thoughts?
For the record I'm using 1095 I ordered from Jantz a couple years ago and it was also what I used in the coal/charcoal fire. I've used both vegetable oil and water for quenching depending on my mood and the knife.

Thanks for any thoughts you have on the matter.

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A gas forge running lean will cause more decarb than a gas forge running neutral. A gas forge running neutral will cause more decarb that a gas forge running rich. If the forge is rich enough it can prevent scale and increase the carbon content.

A gas forge running rich kicks off a lot of carbon monoxide, which is part of why it tends to not cause scale and decarb. Make sure you have enough positive ventilation that you are not affected by carbon monoxide, that stuff can kill you. If you feel like a headache is starting, or flue-like body aches then you are getting carbon monoxide poisoning.

I think your forge is running lean.


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Note too that the tuning of your gas forge *changes* as it heats up so what might be right at the start of a session will be off when the forge reaches steady state. A regulator helps keep things steady as the tank runs down.

Since i like blades I tend to tune a bit rich and so I have lots of ventilation in my shop---2 10' x 10' roll up doors, one per each end of my shop along the general wind path in our valley, In the dirty shop I have the gables open and the ridgeline open as well as one 20x10' end...

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I have a suspicion that all else equal, gas forges may cause a little more decarb because you generally heat the entire blade during each heat, despite the fact that (depending on the size of the blade) you're probably not actually working the entire blade after each heat. In a solid fuel forge, at least the way I use one, you generally only heat the portion of the blade that you intend to work during your next trip to the anvil. So I think that in gas forges the entire blade spends more time at elevated temps, on average, than in a properly managed solid fuel forge.

With that said, yes, atmosphere is a critical factor.

Even if you do have decarb, it shouldn't be very thick. Take a few strokes with the file and see if you get down to hard steel. If so, decarb is likely your culprit. If not, there's probably something else going on.

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So, I did run the file over it some more. After 4 or 5 strokes it started skating like I'm used to. Therefore I'm concluding, in it absence of other evidence it suffered decarb. It's going through the final tempering cycle now. If I don't get too busy, sometime next week I'll know if it'll make a good knife, right now I think so. But next week is looking busy. When done I'll put pics up.

I have a regulator for the forge and I open doors and windows when working, so far no indications of CO poisoning. It wouldn't surprise me if I'm running lean. I haven't had as much time to play with settings as I'd like.

Thank you for all the information you've provided.


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I think one of the resions gas forges are accused of greater decarb is because the smith has a tendancy to leave material longer in gas than would be prudent in a coke forge .

Hey...I was just going to get a drink of water, but coffee seemed better and you need cake with coffee and.......hey where did my knifeblade go and who left this pile of scale in my forge?

I did leave a bar of pattern-weld in the forge at a nice heat for too long...when I returned I could not see it vs the forge lining and when I fished it out and hit it on the anvil..it broke...the grain was larger than huge..bigger than big.
So...I stacked the two and did another weld and forged it down....grain size fixed.

As to carbon loss.....take a bar of steel and grind a long wedge (like the wood shims you can buy). Place it in the forge along with a knifeblade you are forging and take the wedge out when you forge on the blade and put them both back in when heating....when the blade is all forged quench the wedge and cut (break/grind whatever) it the long way, polish and etch...you will see the color change if you have lost carbon and you know how deep that loss is for you.
With good forge practice and a gas forge that is not making work drip with scale....you will only have to be concerned with thickness less than about 3/32 or so for the edge. Since most forge thicker than that it is generally not an issue..or rather...not a great issue.

That said..it is up to you to verify under your conditions.

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