How much heat does it take to ruin temper?

[p3pe]

How much heat does it take to ruin or effect the temper of VG10 and s90v?Please in celsius if you can.

[p3pe]

Correction: heat :)

[p3pe]

The problem is related to Militec-1 and a 1600w hair dryer.

[bada61265]

from what i can see depending on specific alloy`s anywhere from 450 deg F to 1500.
if you got it hot enough to change color youve probubly tempered it.

[p3pe]

No noticeable colour change. It just got to hot to handle for more than a fraction of a second. but I did not get burned, so I hope I didnt interfere with the temper.

Militec-1 is probably best left unheated with folders..

[The Mentaculous]

I've heard that generally, any heat above what a person could tolerate on their skin momentarily without injury or serious pain has the potential to mess up the heat treat. Even the highest temperature that tap water can get to has the potential to mess up your edge (that's one reason they say not to put knives in the dishwasher). Remember, it doesn't have to remove the heat treat on the whole blade--just the edge, which is the thinnest part, and therefore the most susceptible to temperature change.

Edit:Maybe Bada's right--he certainly sounds like he knows what he's talking about, and I don't really--I'm just repeating what I've heard. I have heard several times though that a dishwasher can mess up the heat treat in the edge of a knife, but maybe that's after repeated uses?

[The Deacon]

I've heard that generally, any heat above what a person could tolerate on their skin momentarily without injury or serious pain has the potential to mess up the heat treat. Even the highest temperature that tap water can get to has the potential to mess up your edge (that's one reason they say not to put knives in the dishwasher). Remember, it doesn't have to remove the heat treat on the whole blade--just the edge, which is the thinnest part, and therefore the most susceptible to temperature change.

Edit:Maybe Bada's right--he certainly sounds like he knows what he's talking about, and I don't really--I'm just repeating what I've heard. I have heard several times though that a dishwasher can mess up the heat treat in the edge of a knife, but maybe that's after repeated uses?

Nope, dishwashers will damage knives, but not by ruining the heat treat. First is that the spraying jets of water move items around, and the knife's edge will inevitably bang against other metal objects. Second is that the combination of very hot water and a detergent far harsher (more caustic) than normal dish detergent can etch (pit) the steel and eat away at the edge. It can cause other damage to knives as well, for example loosening handle slabs.

[FLYBYU44]

Though I'm not sure of exact numbers (trying to recall them from when I took heattreating in college) I'm pretty sure a dishwasher and hairdryer will come nothing close to causing a loss in temper however. Grinding on the blade for a extended period of time will cause a loss in temper, but I don't think indirect heat will.

[The Mentaculous]

Nope, dishwashers will damage knives, but not by ruining the heat treat. First is that the spraying jets of water move items around, and the knife's edge will inevitably bang against other metal objects. Second is that the combination of very hot water and a detergent far harsher (more caustic) than normal dish detergent can etch (pit) the steel and eat away at the edge. It can cause other damage to knives as well, for example loosening handle slabs.

Interesting--makes complete sense. I stand corrected.

[Evil D]

So exactly what happens when the heat treat is damaged? Does it not take an edge as good or..?

[The Deacon]

So exactly what happens when the heat treat is damaged? Does it not take an edge as good or..?

Might actually take an edge better, but the edge will roll very easily, and dull very easily.

[O,just,O]

So exactly what happens when the heat treat is damaged? Does it not take an edge as good or..?

Damage to a heat treat will be to normalise the steel. That is to take it back to before hardening & then tempering.
Hardening, hardens to as hard & brittle as the steel can be.
Tempering, tempers some of this hardness off to a usable hardness which is usually a compromise between edge holding & edge chipping if too hard. This is a place above normal for the given steel.
Annealing is to soften below normal.
If any of these states were achievable with a 1600 watt hair dryer then I would no longer need a forge or propane torch or kiln.
It is a Spydie p3pe you will have to do better than that to ruin it.
Think of it this way. If that hairdryer could ruin your knife, it would have burnt all your hair off long ago. :eek: :D
O.

[Joshua J.]

Might actually take an edge better, but the edge will roll very easily, and dull very easily.

AKA the steel goes soft.

[Koen Z]

O,just,O Stated it good.

The lowest temperature that will mess with your hardening is the temperature at witch your blade is annealed.

For a simple carbon steel like O-1 that is about 200 degrees Celsius.
For other types of steel like HSS are annealed above 500 degrees Celsius.

[Evil D]

So then...can it be reversed? Sorry i don't know a lot about this part of steel.

[JNewell]

Though I'm not sure of exact numbers (trying to recall them from when I took heattreating in college) I'm pretty sure a dishwasher and hairdryer will come nothing close to causing a loss in temper however. Grinding on the blade for a extended period of time will cause a loss in temper, but I don't think indirect heat will.

That can happen, but it's because the local temperature at the edge can get very, very high. That kind of temperature would melt every part of a hairdryer and all or most of a dishwasher. :eek: :D

[JNewell]

The problem is related to Militec-1 and a 1600w hair dryer.

You cannot possibly have drawn the temper on that blade with a hairdryer. :cool:

At least, you can't have done so without doing something like shorting the mains with the blade. :eek:

[O,just,O]

So then...can it be reversed? Sorry i don't know a lot about this part of steel.

YES, but.
The blade will have to be rehardened & then retempered, then ground & polished.
If it comes to this it would be cheaper & better to buy a new one.
O.

[p3pe]

I feel a little relieved. But on some part of one side of the blade, I can se some slight change in colour, and this makes me annoyed. It looks like it could just be polished off, so it might not have anything to do with the tamper, just the finish on the blade.

[RLR]

Discolouration is a stain, no more, no less.
Temper is not affected by boiling water, autoclave, etc.

You can ruin a blade by friction heat - sharpening on a grinder and not cooling blade. So, don't sharpen on a grinder.

Anything else, stirring spaghetti with your knife, pulling out a tea bag with your knife, putting your knife in a dishwasher AWAY from anything it can bang into, is OK.

Use it and don't worry about it.