Heat or temperature?

ron_m80

ron_m80

Tempered Member
Joined
Mar 1, 2009
Messages
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Which is it that actually tempers a (destroys a tempered) blade?

I am certain its a bit of both, but i percieve so much conflicting information given out.

Grinding a blade, and a few hundred degrees could damage your temper.

Bending hot kydex is fine (recent post), but the temperature was about the same as grinding, and maybe even greater.

So I am starting to think it has more to do with heat than temperature, based on the context of the repsonces here in BF.
 
It, uh... wait, huh?

Your use of the word heat verses temperature doesn't make sense to me. Temperature is a measure of heat, no? That is like saying, is it your speed or your MPH that most affect your travel time. Doesn't make sense.


Raising the temperature of the steel above the temperature it was tempered at will draw back the temper. For example, a blade that was tempered to 450 degrees will become softer if it is ever heated to 475 degrees.

Something to consider is a blade that can be held in the hand can easily achieve very high temperatures at the very edge while grinding. Even red heat at the very edge (over 1000)

A 300 deg piece of plastic can cause no harm.
 
Most blades (carbon steel) are tempered at around 400 degrees after around a 1500 degree quench. Kydex forms around 325 to 350 degrees max so it really isn't an issue as far as I know. Some stainless is tempered even higher (CPM154 is tempered around 1000 degrees after an 1950 degree quench). When grinding a hardened and tempered blade, do it bare handed. If it's too hot too touch (hold) then dip it in water to cool. Your fingers will burn long before you damage the HTing...well, unless you overheat the edge. If it turns blue, it's too late.
 
Tempering is a temperature /time operation. However the grinding operation creates heat through friction and on an edge and especially the tip the temperature can reach above critical !! Uneven grinding [ side to side ] can also produce stresses that can warp a blade. I've had a few quality knives that tips broke off. I can only attribute this to overheating from grinding.
 
Heat is the energy transference of objects; temperature is the average internal energy of an object. This for normal life is the same thing for us practically, the transfer of energy is monitored as temperature which is called heat. Scientifically they are different things but it doesn't apply for our daily life. When you heat the blade you increase the temperature of that blade which can ruin the temper. No one cares how you transferred the energy to the blade, the most important thing is the internal energy level of the steel which we want to keep it lower than tempering temperatures. You may transfer (heat) the blade by friction (grinding) or radiation or other ways doesn't matter, those all rise the internal energy of the steel. If something is hotter than tempering temps. and in contact with the HT'd blade you may ruin the temper in some time. Time depends on heat conductivity of the medium between heat source and the blade. If in contact the time is defined by the steel's conductivity. You may heat the blade with a 3000 F heat source for a second and you might get away without ruining the temper because the steel wont have enogh time to increase the internal energy to the tempering temps. But you can ruin the temper with a 600 F heat source in a minute. I hope this answers your question...
 
I just thought it was strange that people were saying grind this or that, and bend this or that its ok, when the temperatures were not so far apart in some cases. And not to harp on them at all. it just inspired some thoughts.

like how is 350 degree kydex ok, but 400 degree grinder is not, temp is temp. And 50 degrees isn't that much. To develop a 400 degree surface temp on a skinny blade is not nearly the same thing as a 1/4" chopper. If i had to choose which one got dropped on my hand for an extended period i pick the skinny one, because it will cool much faster, due to its internal heat cannot be greater than the thicker blade exposed to the same conditions until 400 degree. So the absence of reference to heat made me curious. And I wanted to hear what everyone thought about heat. I am not so sure if one were to wrap a fillet knife in kydex it would retain the temper, if the material were tempered around 350 degree.

Galadduin, said what i was getting at, temperature would be the magnitude of the heat, and heat would be the total thermal energy the mass has.
 
Actually, depending on the steel, a fillet knife most likely would be tempered at an even higher temperature to create the springiness. Say raising the RC to around 53-55 instead of 58-60 (my numbers are probably off, I'm not sure what a RC a fillet is best). Regardless, 350 is 350 no matter how close, in my example, to 400 it is. Tempering is meant to create toughness so a few degrees here and there make no matter. Large amounts are what create issues.
 
I'm sure it could be dependant on the steel to some degree, but i had no idea that Rc and tempering temp were inversely related, I kinda always asssumed the springiness was resultant of less time or temp.
 
Regardless of the semantics, don't get the blade hotter than the temperature used for tempering, and you won't have to worry. And as for temp/Rc, the higher the temperature of the temper, the softer the steel in Rc and thus the less brittle, more tough.

--nathan
 
silver_pilate said:
Regardless of the semantics, don't get the blade hotter than the temperature used for tempering, and you won't have to worry.

--nathan
Click to expand...

Well thanks for tolerating my questions gents. Yes I think that would be the key, and since i have no tempering experience it likely leads to all my confusion and questions. I am seriously just trying to grasp the process a bit.
 
When you harden, say O1, it will be 62-63 Rc after quench and brittle. The tempering then at, say, 425-450 will decrease the Rc to 59-60. Tempering is not to reduce the Rc, it's just an effect during the conversion (at least, to my understanding). :D
 
If the Kydex is 350, and the temper of the blade is 400. Nothing will happen. Even if the Kydex were 450 and the temper was 400, most likely nothing would happen because the plastic would cool as the steel heats, and the steel would not likely exceed the 400 deg temper. So it is a fairly safe thing.

Grinding the same blade and reaching a temp of 400 would also cause no problem. But the reality of grinding is the temperature can rise 50 deg in a fraction of a second and there is no stabilizing theoretical upper limit (no asymptote). So you need to maintain a much larger margin of error. If you can get water to sizzle on a tempered blade - in theory you may have only reached the low 200's. But the reality is you're really pressing your luck. And the worst part about it is there is no easy way to know if you exceeded your temper temperature because a lot of steel won't run any color at all if over heated for only a second. But the damage is done. So you have to be very careful with heat when grinding a finished blade. 300 is too much simply because it means you may have reached a lot more than that at the very edge.
 
ron,
What you are asking ( I think) is :
"How can grinding a blade ruin the temper when the blade does not get all that hot?"

When grinding a blade, the whole blade may get to 300F, and that would not be a problem. However, the heat is often being generated at the edge. The edge can easily jump to 500-600F ( and turn blue) or go right to a glowing red ( around 1100F). This is because the thin section has much less ability to transfer the heat to the rest of the blade. Dunking the blade in water constantly, and avoiding too much pressure help. Sharp belts are a must on grinding blades after HT.
If the edge turns blue when grinding, chances are you have damaged the temper. The tip is the worst offender, and can turn blue quickly if not being carefully watched.

Hope this helps.
Stacy
 
bladsmth said:
ron,
What you are asking ( I think) is :
"How can grinding a blade ruin the temper when the blade does not get all that hot?"

When grinding a blade, the whole blade may get to 300F, and that would not be a problem. However, the heat is often being generated at the edge. The edge can easily jump to 500-600F ( and turn blue) or go right to a glowing red ( around 1100F). This is because the thin section has much less ability to transfer the heat to the rest of the blade. Dunking the blade in water constantly, and avoiding too much pressure help. Sharp belts are a must on grinding blades after HT.
If the edge turns blue when grinding, chances are you have damaged the temper. The tip is the worst offender, and can turn blue quickly if not being carefully watched.

Hope this helps.
Stacy
Click to expand...

Thanks for following some of my questions Stacy, this was born from the same train of thought, though i quite understood the grinding bit and actually was fairly happy with the result, the edge I chose to do by hand with arkanasas stone, and a small bit of removal with a dremel. the bulk of the removal was from the spine of the blade. I have some Green / black linen (i meant mikarta, but think it was actually g10) on order, and will be making a handle for my modified machete.

I was actually starting to wonder about how tempers don't get effected by some things and not others. And by asking, getting a better handle on what bladesmiths concider a large temperature differential, and a minor one.

So really i was hoping to narrow down my own personal knowledge (whatever thats worth) of heat and temperature, and use answers from the folks with experience to help me learn what was actually happening to the steel.

But semantical discussions being sort of a peave of mine, I backed off the questions when i got called on making one of my own ;)
 
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