At what temperature will a blade's heat treat be compromised?

Joe Duder

Joe Duder

Joined
Jan 22, 2013
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I put this in this forum (not the General Knife Discussion forum) because I've seen a lot of people do at home spa treatments, buffing, and grinding on their blades. Some knife makers say that this type of tinkering on their blades voids their warranty. I can't say I blame them. It's a given, overheating a blade will compromise the blade's heat treat.

My questions are:

How hot do you have to get a blade and how long at that temperature/heat does the blade have to be kept to ruin a heat treat?

Let's say you over heated a blade, how will you know that the heat treat is ruined?

I mostly use my knives very lightly to:Clean fish, slice, dice and chop veggies, and the occasional wood carving, feather sticking and light kindling batoning.
Should I notice a significant change in the ability to perform those light tasks with a blade with a ruined heat treat?

This is a little off topic, but what's the difference between tempering and heat treating?

Any advice or short & to the point link(s) would be greatly appreciated.

Keep in mind that I mostly play with 01, A2, 1075-1095, CPM-154, CPM3v, S30V.

Thanks guys and gals.
 
400 degrees for carbon steels. Higher for stainless steels.
Heat treating involves HARDENING the steel to maximum hardness, then TEMPERING it back to useable hardness.
 
Bill DeShivs said:
400 degrees for carbon steels. Higher for stainless steels.
Heat treating involves HARDENING the steel to maximum hardness, then TEMPERING it back to useable hardness.
Click to expand...

Thanks for input.

So the second it hits 400 degrees, the heat treat is ruined?

I mostly use my knives very lightly to:Clean fish, slice, dice and chop veggies, and the occasional wood carving, feather sticking and light kindling batoning.
Should I notice a significant change in the ability to perform those light tasks with a blade with a ruined heat treat?
 
Joe Duder said:
Thanks for input.

So the second it hits 400 degrees, the heat treat is ruined?

I mostly use my knives very lightly to:Clean fish, slice, dice and chop veggies, and the occasional wood carving, feather sticking and light kindling batoning.
Should I notice a significant change in the ability to perform those light tasks with a blade with a ruined heat treat?
Click to expand...

to ruin the heat treat, the steel will have to be exposed to the heat for a period of time usually couple of hours.
 
Just take as much precaution as you can to not even let it get close to 400 F . If you're gonna do some buffing or grinding etc. just always do one pass then dip in a bucket of water and agitate it (preferably cold water on an already heat treated and finished knife). It can take less than a second to ruin the heat treat if the blade gets any hotter than the final tempering cycle temperature was at for that specific blade, mainly at the very apex of the edge because it is so thin, and is where all the actual cutting happens at. It may not always be catastrophic damage to the blade and may only be a small portion of the edge, but I say it's just better not to even take a chance to let it get close. Like I said a bucket of cold water after every pass of a buffer etc. is pretty easy to do to help prevent any damage.

-Paul
www.youtube.com/Lsubslimed
 
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coldsteelburns said:
Just take as much precaution as you can to not even let it get close to 400 F . If you're gonna do some buffing or grinding etc. just always do one pass then dip in a bucket of water and agitate it (preferably cold water on an already heat treated and finished knife). It can take less than a second to ruin the heat treat if the blade gets any hotter than the final tempering cycle, temperature was for that specific blade, mainly at the very apex of the edge because it is so thin, and is where all the actual cutting happens. It may not always be catastrophic damage to the blade and may only be a small portion of the edge, but I say it's just better not to even take a chance to let it get close. Like I said a bucket of cold water after every pass of a buffer etc. is pretty easy to do to help prevent any damage.

-Paul
www.youtube.com/Lsubslimed
Click to expand...

I use sandpaper, strops and polish to sharpen and doll up my blades. I don't use machinery. I'm just wondering how sensitive blades are to heat and how significant a ruined heat treat is to a blade that does light tasks.

I have thrown some large ferro sparks that have landed on the bevel on my blades though. They burned out after a few seconds, but they did burn pretty hot on the blade in their short life.
 
Carbon steel doesn't take a couple of hours. The 400 degree remark was a very general approximation.
A thick piece of steel will take considerably more time to heat up than a thin edge will.
 
It really depends on the steel. Most carbon steels are tempered in the 400F range, so a temp over that may ruin the temper. But you also need to consider that if you overheat a blade when buffing or something, you really can't reliably measure the temperature you got the steel up to. The closer you get to the cutting edge, the thinner the steel and the easier it is to overheat.

If you think you've overheated something, you can use the brass rod test on the cutting edge to see if the area you believe to have overheated behaves any differently. That will tell you more about whats going on with the steel than guesswork over how hot you think you got it.
 
I have reconditioned many knives and when I was a young man worked in a machine shop. It goes without saying if you change the color of the steel you have gone too far. I would agree with the 400 degree benchmark. Like others have said that temp is used to temper so it has to be causing some changes. The AVERAGE human hand will pull away from 150 degrees so that is what I do when buffing. When it gets so I can't hold my hand on it I quench it. The temp is way lower than 400 so no worries about the heat treat. Go slow and keep checking the temp if you burn the crap out of your hand you may have gone too far.
 
Hairlesstwinkie said:
to ruin the heat treat, the steel will have to be exposed to the heat for a period of time usually couple of hours.
Click to expand...

Very bad advice. The steel only needs to reach temperature to alter the steel. The only reason people temper multiple times for hours (what you may be thinking about) is to make sure its evenly and properly heated.
 
If the over heated edge areas are more easily rolled than other areas, indeed the affected areas are softer. The duration of over heated exposure determine the depth of such undesirable blade softening. Keep in mind, that only a thin sheet of metal from apex directly up toward the spine is where cutting actually done, so if over-heated other parts won't affect the performance of your blade much or at all.

Ferro spark is hot, so after a few seconds of burn, the affected area could be quite deep. For low Chromium steels (carbon), the affected area more/less annealed. Alloy steels with secondary hardening hump/curve (around 1000F), the affected area will be smaller and less deep. It's not a problem, if the affected steel doesn't intersect with the cutting core.

:grumpy: No fun - keep chopped up my text until BF let me post.

edit: ok, I notified support of posting hung/time-out due to BF sql inject removal code. http://www.bladeforums.com/forums/s...-posting-difficulties?p=13720817#post13720817
 
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