Metal tempering without an oven

[MisterJohn]

Hello I'm new to the whole knife making process and when I wached all the videos on knife making they always temper their knifes after quenching in an oven. And I currently don't have an oven and I wondered if its possible to temper a blade in a campfire forge and how hard would it be

[BartW]

Hello;

 

Yes, it's possible, and it isn't hard. Clean up a part so you can see bare steel; and allow the heat to creep up slowly, and judge by the tempering colours. That's everything below dark grey in the picture below.

 

[anvil]

It is done easily. However it's critical to have a constant light source. Those colors in that chart change depending on the light. Heat treating outside takes a lot of experience. It's best done inside.

[ThomasPowers]

Also remember that the thin edge will heat faster than the thick spine producing exactly the opposite temper than you want. 

I've tempered with a small cheap propane torch playing it on the spine and running the colours to the edge and then quenching.  I've also taken a chunk of heavy scrap steel and heated it in the forge to red and placed the spine on it leaving the tip hanging off in the air.  What I like best is to use tempering tongs---tongs with a set of cross bars welded onto the tips that you heat in the forge and grab the spine of the knife with to transfer heat.

So there is no kitchen oven anywhere near you?  If the blade is well cleaned after quenching---and especially if you quenched in a vegetable oil then there should be no issues tempering it in a kitchen oven.  Get an oven thermometer as kitchen ovens are notorious for being "off" from the markings on the dial and remember that ovens cycle the heat so they may go too high---too low.  Heating a container of sand can help get a more constant temperature. (Stick your blade into the sand.)

You may notice that I prefer to differential temper for plain HC steels.  The high alloy blades get sent to a pro!  I will sometimes use an oven for snap tempering. (Tempering to a lower temp to make sure a freshly quenched blade doesn't self destruct waiting for the full tempering cycles.)

[MisterJohn]

Thanks for the input I was scratching my head all morning wondering how will I get by without a oven, but if it's possible to do it in a charcoal forge I'm up for it, just I have a question when I get it to the right color in the charcoal forge do I let it just air out and cool down, or do I quench it again? I saw someone quenching it after tempering it in a forge so I got a bit confused

[Steve Sells]

it doesnt mater

[ThomasPowers]

The issue is that; when tempering without an oven or using differential tempering the edge may get heated higher than you want and so quenching "freezes" it at he correct temperature.  If you use a temperature controlled oven and a uniform temper you can set it to the correct temp, and then once it reaches that let it air cool as it won't get hotter than the set temperature.

[MisterJohn]

Ok thanks that cleared up some things that where really confusing for me.

[BartW]

If you're considering tempering something like a knife in a charcoal forge; Keep the edge out of the fire (as the fire is WAY too hot; and your spine of your knife will be WAY too hot too); and quench in water as soon as you get to the right colour. The difficult part is getting the colour uniform; but this comes with pratice. 

Kitchenovens or professional heat treating ovens; you set a temperature, and it will stay at that excact temperature; so no need to quench off excess heat build up in the spine.

[ThomasPowers]

Just remember that kitchen oven gauges are notoriously inaccurate and the temp does cycle up and down---it does NOT stay at an exact temperature!

[pnut]

I have a three dollar toaster oven I found at the thrift store and a nine dollar digital thermometer I found at walmart. For anything except knives I just quench the tool and use the residual heat for tempering. After the hardening quench I quickly polish the cutting edge and when the edge gets to the color I want I quench it again. It usually takes about two or three times at least before the temperature gets low enough for the colors to stop running. 

Pnut

[Frosty]

My $5 shop toaster oven is 12" long inside and handles everything I need to temper. I have a good thermometer for it and the oven itself is pretty accurate. LOTS more accurate than the new toaster oven in the kitchen. 

Frosty The Lucky.

[Scalebar]

I'm thinking of trying torch tempering because for one small piece every week or so running the oven for hours doesn't make a lot of sense. Why does tempering in an oven take much longer? 

[ThomasPowers]

It depends on how you do it.   If you are placing the blade such that it's getting heated by the ambient temperature of the air in the oven then you have 150 to 200 degC Air transferring heat to the blade. If you use a torch you have 1980 degC flame transferring heat.  As heat transfer is a power function of temperature difference it would seem that the torch would be much faster!

Now if you can preheat a material in the oven and use conduction, then heat transfer will be much higher.  (Say 2 slabs of metal that can squeeze the blade between them.)   There are other methods using highly toxic substances that are even faster to transfer heat in an oven---if you don't like yourself or anyone in the neighborhood!

Have you looked at high temp and low temp molten salt mixtures that are used for fast heating of blades?

[Scalebar]

Thanks, and yeah I've looked at some of the bewilderingly complex - and outright dangerous treating regimes some people use. I think I'll keep it simple ( although... I do have access to dry ice and liquid nitrogen) 

[Charles R. Stevens]

Cutting up a coffee can and setting it over a gas burner works as well. It’s how I temper wood chisels

[anvil]

I've done that, if this is what you are doing. Reroll the coffee can into a cone. Put the wide end over your coke. Use the heat coming out the narrow end for a localized heat source