Heat treat w/o oxidation

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Does anyone know of a way to heat treat a blade without it oxidizing and having to re grind it? Would covering it in clay beforehand work?
 

DeadboxHero

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Does anyone know of a way to heat treat a blade without it oxidizing and having to re grind it? Would covering it in clay beforehand work?
ATP 641 anti scale for oil hardening

For air hardening, use 321 or 309 Stainless steel foil wrap.
 
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There are several ways. One is to make a paste of boric acid and alcohol, apply it to the blade everywhere you don't want oxidation. Heat as normal and quench as normal.

Another is to pack the blade in a stainless foil pouch with a scrap of paper inside the bag with the knife blade. The paper will burn, consuming all the free oxygen in the pouch leaving you with no oxidation on the blade, but you need to work quickly when it's time to quench to cut the pouch open so you can get the blade into the quenchant sans pouch.

Yet another is to use either a vacuum furnace or alternatively an argon purge in your furnace while it's heating the blade.

All of these work, all have their plusses and minuses. I'd try the boric acid paste first.
 

DeadboxHero

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There are several ways. One is to make a paste of boric acid and alcohol, apply it to the blade everywhere you don't want oxidation. Heat as normal and quench as normal.

Another is to pack the blade in a stainless foil pouch with a scrap of paper inside the bag with the knife blade. The paper will burn, consuming all the free oxygen in the pouch leaving you with no oxidation on the blade, but you need to work quickly when it's time to quench to cut the pouch open so you can get the blade into the quenchant sans pouch.

Yet another is to use either a vacuum furnace or alternatively an argon purge in your furnace while it's heating the blade.

All of these work, all have their plusses and minuses. I'd try the boric acid paste first.
What's the mixing ratio? Any hardness measurements on the surface to to check for decarb after hardening?
 
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Mix to make a paste that is heavy enough to stay put when applied. The alcohol will evaporate leaving the boric acid behind. Doesn't hurt to leave the item submerged in a small dish type container with excess boric acid/paste either.

Hardness testers generally aren't very accurate at shallow hardness differentiation. A better test is to make a sample and harden it, then clean-up grind the outside of the part and test it. Then grind off a bit more and test again. Repeat the process if the hardness is significantly different between the two.
 

Stacy E. Apelt - Bladesmith

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Just to make it clear - coatings and foil packets will reduce decarb, but not totally eliminate it. Additionally, the edge should be left fairly thick pre-HT and then the final bevels ground after tempering. Finally, the blade will need finish sanding to bring it to its final surface look.
So, short answer, - You should always re-grind the blade post HT.

If making a boric acid coating, this is a better formula that the saturated solution mentioned:
Mix 8 ounces yellow ochre, 6 ounces boric acid, 3 ounces satanite, and 1 ounce gum tragacanthin. then add enough denatured alcohol to make a medium thick paint. Paint on the blade and let dry before putting in the forge. You can play with the ingredients ratios if you want, but this is what I have found works well. This is similar to Turco, which is a very good commercial anti-decarb product, but pricy.
NOTE - only use boric acid coatings for basic carbon steel HT done below 1600°F. At higher temperatures it becomes corrosive and will damage the blade surface.

Ways to reduce decarb:
The number one way to reduce decarb is to use a HT oven
. A forge is just about the worst place to do HT as far as decarb goes. That doesn't stop many folks ( including me from time to time) from using the forge to do HT in. You just have to grind a few thousandths more away post-HT.

Salt pots. These come as close as possible to no decarb. These are not amateur devices and are expensive.

Sand pots, safer than salt, but more expensive.

Vacuum ovens - expensive commercial machines.

Argon purge ovens, they work fairly good reducing decarb, but argon is an added expense. (Some folks use nitrogen)

Stainless foil packets - these are what most bladesmiths use. The cost is fairly low per-knife and use is simple. They can only be used with a HT oven.

Blade coatings - Turco, ATP, Brownell's, satanite/clay, and many others all work fairly well. Using one of these is important if you HT in a forge.
 

DeadboxHero

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Good post
Just to make it clear - coatings and foil packets will reduce decarb, but not totally eliminate it. Additionally, the edge should be left fairly thick pre-HT and then the final bevels ground after tempering. Finally, the blade will need finish sanding to bring it to its final surface look.
So, short answer, - You should always re-grind the blade post HT.

If making a boric acid coating, this is a better formula that the saturated solution mentioned:
Mix 8 ounces yellow ochre, 6 ounces boric acid, 3 ounces satanite, and 1 ounce gum tragacanthin. then add enough denatured alcohol to make a medium thick paint. Paint on the blade and let dry before putting in the forge. You can play with the ingredients ratios if you want, but this is what I have found works well. This is similar to Turco, which is a very good commercial anti-decarb product, but pricy.
NOTE - only use boric acid coatings for basic carbon steel HT done below 1600°F. At higher temperatures it becomes corrosive and will damage the blade surface.

Ways to reduce decarb:
The number one way to reduce decarb is to use a HT oven
. A forge is just about the worst place to do HT as far as decarb goes. That doesn't stop many folks ( including me from time to time) from using the forge to do HT in. You just have to grind a few thousandths more away post-HT.

Salt pots. These come as close as possible to no decarb. These are not amateur devices and are expensive.

Sand pots, safer than salt, but more expensive.

Vacuum ovens - expensive commercial machines.

Argon purge ovens, they work fairly good reducing decarb, but argon is an added expense. (Some folks use nitrogen)

Stainless foil packets - these are what most bladesmiths use. The cost is fairly low per-knife and use is simple. They can only be used with a HT oven.

Blade coatings - Turco, ATP, Brownell's, satanite/clay, and many others all work fairly well. Using one of these is important if you HT in a forge.
 
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Mix 8 ounces yellow ochre, 6 ounces boric acid, 3 ounces satanite, and 1 ounce gum tragacanthin. then add enough denatured alcohol to make a medium thick paint. Paint on the blade and let dry before putting in the forge
Does this mixture work better than heating (around 350F) the blade to melt boric acid to form the "glass" layer over the material?
 

Stacy E. Apelt - Bladesmith

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I found that straight boric acid will rub/scrape/drip, etc. off the blade in HT. It is a bit more complex that just melting boric acid on the blade, too.

Here is what happens with Boric acid (H3BO3) on a blade in a forge.
1) The boric acid melts around 350°F.
2) The H3BO3, decomposition around 750°F, it becomes Boron tri-oxide and water vapor ... B2O3 + H2O.
3) The Boron tri-oxide turns into a liquid at 850°F. The good thing about B2O3 is it won't boil away until, well over 3000°F. The bad thing about it is liquids drip, flow, and rub off easily. It can expose places on the blade.
4) If the B2O3 gets much above 1600°F it becomes corrosive and will attack the steel. You don't want this to happen, so good forge temperature control and using only carbon steels is important.

In the mix with the clays, the ochre and satanite act as a binder to lock the B2O3 over the blade. The gum tragacanthin helps the mixture stick to the blade until the clays dry and set.
 
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I generally do more small tool parts than knife blades, so I use a little dish/boat made of stainless steel wrap to keep the parts mostly submerged, that works well but isn't so practical for larger knife blades. Good advice Stacy.
 
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