Can you temper a knife with a blowtorch?

H

Hermanelldena

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Feb 28, 2018
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Hello everyone, I'm planning on taking a challenge to make a knife in 4 hours, and I was just wondering, after hardening the blade, can I just slowly heat it up with a blowtorch until it gets a straw color? Because I don't have time to put in the ownen of course. What is the difference between a temper done with a blowtorch and a temper done with an ownen? (except for the eveness of course)
 
I'll start this off with a question :
Do you have a couple of fire brick to reflect the heat back onto the blade ?
 
Steel processing is measured using [time at temperature]. Without the time part you are doomed to failure, unless you have a couple of hours with the torch. It would be the same for fully annealing a blade.
Some one will come along who will give you the technical.
Regards, Fred
 
A metallurgist could do it ! :rolleyes: :D
Typical tempering is one or more stages for two hours at temperature .A kitchen oven would be far better .Some details could improve that .
 
I'm sure you could, but the knife edge may not be as useful and who knows how it will perform.
I can tell you that I have propane torch tempered a slip joint spring a year ago and it works just fine.
If you want to temper quickly you could flash temper but you would need to choose the right steel to work with and know how to go about doing this.
I flash temper all my blades which are laminated steel.

good luck making a knife in 4 hours :), I don't think I could do it.
 
What metal? I'd think a simple alloy like 1080 type. What knife shape? I'd suggest heating from spine of blade watching colors move down toward edge. That seems to give best control.
 
what steel? if using 80CrV2, i got good results with 2 15 minute tempers with cold water quench in between. so counting time in furnace and oil quench, that is about 45 minutes.
 
The real answer is YES … and NO.
Yes - you can lower the hardness by a temper low alloy steel with a torch. Yu heat it slowly along the spine with the torch and watch the "temoper colors" walk down the blade to the edge. Dip in water once the straw color hits the edge. Repeat down the blade as needed, sand to bright steel and repeat a couple times. That will give a simple temper.

NO - in the fact that what you have done is soften the blade, but not converted structures fully.

The better way - bake in a pre-heated kitchen oven at 400-450F for one to two hours, take out and cool off to room temp (just run cold water over it), put back in, and bake a second hour or two. This will give you a full temper.
 
If I may be so bold :
You could save time by running it full hard.
Does this knife have to survive some endurance contest after you make it ?
Otherwise full hard is going to cut stuff and look good for the Paparazzi right ? ;)
PS: don't drop it on the floor before all the press have left :eek: :p
 
I re-read your first post. I missed that it was a challenge. If doing a challenge to make a finished knife in 4 hours, then a torch temper will be suitable. Use the method I listed above.

If you are trying to copy Forger in Fire, their blades are tempered in an oven overnight between the first and second parts.
 
Stacy E. Apelt - Bladesmith said:
The real answer is YES … and NO.
Yes - you can lower the hardness by a temper low alloy steel with a torch. Yu heat it slowly along the spine with the torch and watch the "temoper colors" walk down the blade to the edge. Dip in water once the straw color hits the edge. Repeat down the blade as needed, sand to bright steel and repeat a couple times. That will give a simple temper...
Click to expand...

So you should be able to do this blowtorch method to REDUCE hardness on an edge, yes? E.g., take an edge from say 60RC to 50RC? (Reason/Use Case: so the edge doesn't get chipped as much during fencing aka sparring with other blades - Ideally you want two blades with the same edge hardness against each other and neither too hard, so 50RC vs 50RC is pretty ideal.)
 
I have heard of using a heated bar to provide the heat. This might be a good use for tempstik crayons. If you use heat colors just remember that they are oxides and won't show up until you move the flame away.
 
Torch tempers work just fine. They are way less than ideal, but for your purposes, it will work ok. That being said, in this case, I would probably edge quench (5160 is very forgiving in the HT so it edge quenches pretty easily). Have a flap disk sitting next to the oil. as soon as the knife is quenched, use the disk (only the disk, no angle grinder) to expose some bare metal all the way down the edge and wait for the dark straw color to reach the edge. Fully quench the blade as soon as it does. If you want to get a second round of tempering after that, resand and use a torch or heated steel plate to reintroduce heat. That is probably the best option for a very compressed tempering schedule.

A flat edge, like a standard seax or similar would be ideal for this style of that treatment.
 
I'm sure that controlled oven tempers are best. I use an oven to temper my knife blades.
BUT- I have made literally thousands of leaf springs from 1095, using a torch to both harden and temper. 4 have broken and they were from the same piece of steel. Springs are not knife blades, but if my tempering were less than optimal, more springs would have failed.
 
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