Tempering and Heat Treating Knives

[MichaelBikel]

I have heard of guys tempering knives in their oven but how does this work? For example I just re-profiled a kitchen knife to make a drop point knife. Assuming that I drew out the temper during cutting/sanding (which I was careful to avoid) can I just stick it in the oven for two hours?

I also recall seeing a bit of information saying that you want to sharpen AFTER you temper and not before. Is that correct? I don't see how sharpening before would make any difference.

 

[scooternut]

It is very complicated. But, the tempering, or oven, actually serves to draw DOWN the hardness. The heat treating, or proper hardening of some knife steels creates a steel that is actually too hard and brittle. Baking in an oven "tempers" the steel, aka, brings the hardness down.

Your issue, did you over heat the steel. If you are not VERY careful with properly tempered knife steel when sharpening, then you've ruined the "temper."

Easy to overheat with power tools, Sanders, grinders, etc. Too hot to hold bare hand? Then you've probably altered the hardness requiring re-hardening. Hardening in most steels requires heating to critical temperature, or about 1400 degrees. Though, it is far more complicated than simply heating, and all steels require a different heat treatment.

Hope this helps




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[Danno1]

.


A kitchen knife is prob made of 440A or 440C stainless steel. A good one might be made of S30V. You would need to anneal first (to soften to a starting point), then heat treat (to harden), then temper (to bring the hardness down from too hard and brittle to hard and not so brittle).



The following link is heat treats for tool steels, but at least gives you an idea of the process.

http://www.mcmaster.com/#=145h15s



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[MichaelBikel]

Okay, all good information here. So making a knife does not solely consist of tempering and it includes annealing which I assume happens in the process of forging? Then would be heat treating and tempering would be quenching and setting in some kind of controlled environment?

So in my case, working on a properly treated knife if I drew the temper out I would need to start the heating/cooling process from square one? AKA annealing, heat treating then tempering?

Edit: One last thing, since it has been mentioned that some of us use power tools to shape knives, what is the best way to avoid drawing out temper? Is it possible to use water or oil to disperse heat, or is it really more about going slow? The second knife I shaped I ended up chopping minimal amounts off and submerging in water for about 5+ seconds between cuts or sanding.

 

[lazer50]

Your knife is likely not s 30 v steel but you could probably google the brand and see what they use.then go to blade forum .com there are all kinds of topics there but i seen an area dedicated to heat treating so im sure that will help you will just have to look around the forums there.

 

[kazlx]

Yes, tempering is reducing the hardness of the steel after initial heat treating. Most steels have a chart that can be found online showing the initial heat treat cycle, usually 1500-2000 degrees. Then you would temper afterwards to get your desired hardness (reducing the hardness to make the knife less brittle). Most tempering is around 400* F or less, so it could be done in a home oven.

Not hard to keep a knife cool while working it. Just keep a bucket of water next to your grinder. When it starts to get warm, just dunk it.

Sharpening is the very last step. You would want to do it after temper because the edge could move a little. Usually you want to keep as much meat as possible on the edge while doing any heat treating or tempering.

1.Blank out rough shape
2. Grind to rough shape, can rough grind bevels, or not.
3. Add holes, features, etc. Quite a bit easier before heat treat
4. Heat treat
5. Temper
6. Finish grind
7. Sharpen

 

[skunkape1]

I hope I'm not jacking the thread here...
My dad threw his deer knife in the fire a couple years ago. It was wrapped in paper we had been using for butchering. When I figured out what happened, I pulled the knife out of the fire. The leather washer handle was gone and the blade plus tang was cherry red. Obviously the temper is gone, the steel is very soft. I want to restore the knife if possible. It is a "Case" knife that belonged to my Grandpa originally and there is a very "interesting" story about how the knife was lost and miraculously found again during a Wyoming deer hunting trip in the 60's. I have rehandled knives with leather and birch washers so I have that covered.

I assume I need to start over in effect and bring to critical temp (no longer magnetic), and then temper at oven temps to get back to close to original hardness. It is possible isn't it? Or is the blade a goner? Thanks

 

[scooternut]

Most important is what kind of steel it is and what is the recipe. You have what is "mystery steel," at least to you and me. Perhaps you can find out since you have a name brand.

If it is a seriously important knife, I'd find a knife maker in my area and ask him to harden.

Otherwise, I'd say that you could get it hard by the usual backyard method. How hard is just a guess. Heat to critical temp, quench in oil. Then temper in oven. Also, prior to this I "normalize" by three cycles up to critical tempt with a slow cool down in the air.

CAUTION: I leave my knives about the thickness of a dime before I heat treat. I read that anything thinner that you risk warping during the quench. I do my final grinding hard using sharp belts while tediously dunking in water almost every pass on the SHARP belts to keep cool. Hand sanding to finish.

I'm no expert,taught myself reading on the net and made some really nice things for myself, friends and family.

 

[Tim Kennedy]

Try and contact Case themselves --- not sure but they may have a service to re-condition knives --- worth a shot --- least they could say is no.

 

[skunkape1]

Try and contact Case themselves --- not sure but they may have a service to re-condition knives --- worth a shot --- least they could say is no.

I did contact Case and they do re-condition their knives. At the time the price I was quoted, although very reasonable, was cost prohibitive for me. They were even going to feature the story of the knife and the many traumas it suffered on their website. Case is an awesome ALL-AMERICAN company. Maybe I'll contact them again i'ts just my pride doesn't allow me to have others fix things that I can likely fix myself.

 

[Fcvapor05]

I did contact Case and they do re-condition their knives. At the time the price I was quoted, although very reasonable, was cost prohibitive for me. They were even going to feature the story of the knife and the many traumas it suffered on their website. Case is an awesome ALL-AMERICAN company. Maybe I'll contact them again i'ts just my pride doesn't allow me to have others fix things that I can likely fix myself.

Unless you have a gas forge, quenching setup, and enough experience to know how to use them, you can't fix this yourself.

My advice would be to let Case take care of it.

 

[MichaelBikel]

I did contact Case and they do re-condition their knives. At the time the price I was quoted, although very reasonable, was cost prohibitive for me. They were even going to feature the story of the knife and the many traumas it suffered on their website. Case is an awesome ALL-AMERICAN company. Maybe I'll contact them again i'ts just my pride doesn't allow me to have others fix things that I can likely fix myself.

What was their quote to you if you don't mind my asking?

 

[skunkape1]

What was their quote to you if you don't mind my asking?

It was about 50 bucks if I remember correctly. It was 20 less than the most similar current production CASE knife at the time. The original knife was/is a 5 in. clip blade w/leather handle.

I will be contacting the good people at Case again rather than play with fire.

 

[Maine Coon]

I may be wrong, but I think it's done at 800 °C

 

[gungatim]

I would definitely pay the $50 just to add to the great story of that knife. and some documentation by them is provenance...may prove to be a good investment in the end...