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JamesK

Do I have the "Ok" to Temper?

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Yesterday evening I finished and heat treated my mini tomahawk head made from an old rusted prybar, and it successfully hardened to my surprise. I just did some research on tempering and wish I knew to temper the blade sooner, or that I had time to do it after the quench, but now it's the next morning and I don't know if tempering would be safe. The steel is fine and did not crack overnight and everything seems to be okay, but can critial damage be done during a temper similar to that of a heat treat? I heard 400F for 3 hours, cooling it every hour is the way to go, but this late after a treat I'm not sure how dangerous that would be, any suggestions? Thanks!

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Nope, tempering only relieves stress. It does not increase it. I am no expert but 400° seems a bit low for a hawk? Anyone care to jump in?

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"Tempering" is the act of softening a blade after the quench. "Drawing it back" to remove the brittleness caused by the hardening quench. You cannot "temper" a blade, axe or other, before it is quenched. Before you quench you may thermal cycle or heat treat to refine the grain structure, depending on the steel but this is different than tempering. Most folks like to temper immediately following the quench as soon as they do a file test to make sure it had hardened. It is not unusual for a blade left untempered to spontaniously crack from the stresses induced by hardening, therefore, IMO, it is a good idea to immediately give it at least a hour in the oven at the lower end of the tempering level you are aiming for immediately to relieve the stresses. Remember, the lower the tempering temp the harder the blade and you can always go back in the oven at a higher temp to soften a blade that is too hard. I too would think, depending on the steel, that you mighy want a bit higher temp for an axehead but starting low won't hurt .

ETA. To make it simple, tempering a fully hardened blade is generally a "must do" whether 24 minutes or 24 hours after quenching. If the blade hasn't cracked then no practical harm was done as long as it gets tempered.

Edited by Vern Wimmer

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2 hours ago, Vern Wimmer said:

"Tempering" is the act of softening a blade after the quench. "Drawing it back" to remove the brittleness caused by the hardening quench. You cannot "temper" a blade, axe or other, before it is quenched. Before you quench you may thermal cycle or heat treat to refine the grain structure, depending on the steel but this is different than tempering. Most folks like to temper immediately following the quench as soon as they do a file test to make sure it had hardened. It is not unusual for a blade left untempered to spontaniously crack from the stresses induced by hardening, therefore, IMO, it is a good idea to immediately give it at least a hour in the oven at the lower end of the tempering level you are aiming for immediately to relieve the stresses. Remember, the lower the tempering temp the harder the blade and you can always go back in the oven at a higher temp to soften a blade that is too hard. I too would think, depending on the steel, that you mighy want a bit higher temp for an axehead but starting low won't hurt .

ETA. To make it simple, tempering a fully hardened blade is generally a "must do" whether 24 minutes or 24 hours after quenching. If the blade hasn't cracked then no practical harm was done as long as it gets tempered.

Yea the axe head is pretty hard, but it’s very small. So you think I should temper it?

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Certainly temper it. IMO it is a "must". If a file skates on it, indicating it is properly hardened, how would you sharpen it ? Not to mention it would be brittle. "Pretty hard" isn't much of a "tell" either, after cutting through any decarberization layer, a file won't cut the steel (indicating full hardness) or it will (indicating it is not hardened or the material isn't hardenable). 

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Without knowing the steel that was used in the pry bar that you used to make the tomahawk head from it's really hard to advise on tempering temperature.  The bar probably wasn't low carbon steel but you can't tell.  It could be a medium carbon steel, on the order of 1040 which might be usable as an ax head with a low temper tempering, maybe around 325°-350°,  It could, but not likely, be a high carbon steel that you would want to temper above 400° to get a softer temper for the use as an ax/tomahawk head.

I know that all the "coulds" and "probablys" might be a little aggravating but not know the steel we're dealing with here it's the best that we can do.

Doug

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Prybars tend to run on the medium-high side of carbon, 1070 is a decent guess.  I'd temper on the hot side, 450-500 degrees F.  Axe-like objects need to be tough rather than hard, you absolutely don't want them to chip and you do wantto be able to sharpen them with a file.

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8 minutes ago, Alan Longmire said:

Prybars tend to run on the medium-high side of carbon, 1070 is a decent guess.  I'd temper on the hot side, 450-500 degrees F.  Axe-like objects need to be tough rather than hard, you absolutely don't want them to chip and you do wantto be able to sharpen them with a file.

Ok, thanks so much everybody for advice, just recently I learned about tempering and now I understand the purpose of it, thanks

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