Heat treating and tempering knife blades

C_Claycomb

Moderator staff
Mod
Oct 6, 2003
7,627
2,701
Bedfordshire
How much draft does the chimney part of the chimnea create? I too am surprised that something the bulk of a blade would reach 800+degC unless there is some air being drawn through. Makes me curious though. I have a platinum thermocouple for my forge and am tempted to try it in a wood fire the next time I have a chance.

We all tend to use O1 here in the UK because it is so easy to get, and many other simpler steels are not so available. O1 is pretty forgiving, but as far as proper heat treating goes, it is actually a more complex steel, a "tool steel" not just a "carbon steel". As such, it will not get fully hard by simply taking it to non-magnetic (hate the term cherry red, nothing that was what I think is cherry red was ever non-magnetic or ready to quench) and quenching. That will work for 1084 and similar steels, but O1 is meant to be soaked at a consistent, controlled temperature for 10-15 minutes to fully dissolve the carbon which in the annealed state is tied up with the more complex alloying elements.

First time I read that, I didn't want to believe it, after all, I was getting hardness, I thought, files skated and I could temper at 170degC and get something that would cut and the edge would not deform too much against a brass rod. However, when fully hard, O1 needs a higher temperature to temper it. That I was tempering at 170 meant that I was not getting full hardness. There was LOTS of stuff on the internet forums where other makers were heat treating with torches or forges and all getting similar results, sort of a collective self reinforcing shared opinion. We all made knives that worked, but we don't get the full performance of the steel that way. There is something to be said for trying to get a simpler steel that will heat treat correctly with the simple tools and heat sources available to the beginner.

Multiple quench cycles do help with getting more carbon into solution with O1. Not ideal and a bit of a bodge dodge, but better than simply getting hot once and quenching once.
 
Last edited:

punkrockcaveman

Full Member
Jan 28, 2017
1,457
1,516
yorks
[video]https://m.youtube.com/watch?v=0uxoZoEWZC4[/video]

Sorry about the quality guys, but hopefully you will see how I harden my blades. I'll stick up a link to a youtube slideshow of the knife that this blade has made.
 

juttle

Nomad
Feb 27, 2012
465
10
Devon
You don't need to get anywhere near 800c to heat treat simple carbon steel, 01, 1095, 15n20, etc. Which is what most one carbon steel knives or Damascus is made from. You need a heat source, garden BBQ will be fine, you need fuel, charcoal is fine, and you need a device to tell you when the temp is right, a magnet! Heat the blade until the magnet won't stick to it, nowhere near bright red or orange, more of a dull red, depending on the available light, etc, hence the magnet. When the magnet won't stick to the blade, remove it from the fire and quench in warm veg oil. When cool enough to touch test the edge with a file, if it bites heat treat it again, but leave it in the fire slightly longer, if, as usually happens, the file slides along the blade without biting, proceed to temper. A domestic oven is fine, 230 degrees C. for an 1.5 hours should do it.
 

Stew

Bushcrafter through and through
Nov 29, 2003
6,610
1,406
Aylesbury
stewartjlight-knives.com
You don't need to get anywhere near 800c to heat treat simple carbon steel, 01, 1095, 15n20, etc. Which is what most one carbon steel knives or Damascus is made from. You need a heat source, garden BBQ will be fine, you need fuel, charcoal is fine, and you need a device to tell you when the temp is right, a magnet! Heat the blade until the magnet won't stick to it, nowhere near bright red or orange, more of a dull red, depending on the available light, etc, hence the magnet. When the magnet won't stick to the blade, remove it from the fire and quench in warm veg oil. When cool enough to touch test the edge with a file, if it bites heat treat it again, but leave it in the fire slightly longer, if, as usually happens, the file slides along the blade without biting, proceed to temper. A domestic oven is fine, 230 degrees C. for an 1.5 hours should do it.

So what temperature are you suggesting is the curie point for O1?
 

juttle

Nomad
Feb 27, 2012
465
10
Devon
Ah, oops, you do need to be approx 800c, but the right temp is indicated by the magnet. Every time I heat treat 01 or damascus, it becomes non magnetic at far darker a colour that the "forged in fire" cameras show for hardening. What I was trying to get across was that there's no need to get your blade to a temperature that's just about sparking!
 

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