Advice Request for Machete Build

polish avenger

polish avenger

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So, my step son requested that I make a machete for him (gonna be his graduation gift). I have some 1/8" 15N20 and would like thoughts on heat treat. I know that this steel is tough at fairly high hardness....but how tough is it when hardness drops to what are considered "machete hardnesses"? Is it tougher? Is it "bendy"? What should I be aiming for here?
This isn't a super-long piece. Blade is sitting at 16 1/2" with a max blade height of 2". Process is completely stock removal. Heat source is an Evenheat, quench is Parks.
I'd like to end up with something that can have the crap beaten out of it like a 22 year old can do without my worrying if half the blade will end up staying in a sapling in the wilds of Oregon.
Thanks all!
-Mark
 
I'd follow Larrin's heat treatment protocol and temper to +-59HRC.

I wouldn't temper higher than 400f-425f to avoid tempered martensite embrittlement (which means lower hardness and lower toughness). I'm not smart enough to explain how tempered martensite embrittlement works but Larrin talks about it in his site.

Same as fillet knives, the bendiness comes from the geometry of the knife rather than hardness.
 
I read Larrin's work on nickel bearing steels before posting, but still kind of questioned the high hardness in a longer blade. The part about martensite embrittlement scared me pretty good.
I appreciate the replies, y'all.
 
Don't let martensite embrittlement scare you. It is not a thing most knives need to fear. It also isn't a light switch that turns on instantly at, say, 435°F. It is a range where toughness decreases. It also doesn't mean the steel suddenly becomes brittle as glass as you enter the range. It is just less tough and more brittle as you get deeper into the range. For 15N20, a temper at 450°F would not be a problem. For your use as a machete, 400°F would be just right anyway. There may be other opinions, but I consider any temper done below 450°F perfectly safe.
 
Stacy E. Apelt - Bladesmith said:
Don't let martensite embrittlement scare you. It is not a thing most knives need to fear. It also isn't a light switch that turns on instantly at, say, 435°F. It is a range where toughness decreases. It also doesn't mean the steel suddenly becomes brittle as glass as you enter the range. It is just less tough and more brittle as you get deeper into the range. For 15N20, a temper at 450°F would not be a problem. For your use as a machete, 400°F would be just right anyway. There may be other opinions, but I consider any temper done below 450°F perfectly safe.
Click to expand...
Thanks, Stacy! I will take this into consideration!
 
I've made quite a few machetes. While I haven't used 15N20, I've used a ton of 52100, which is lower in toughness. I run the 52100 around 59-60RC and spring temper the spines. I would not recommend tempering the whole knife down to classic machete hardness of ~53-55RC. Keep the edge around 60. It will make a way better tool and there is plenty of toughness there.
 
A English gentleman, "Da Main Mouse", made a 15n20 machete (more than one) and his heat treatment was: "The blade was differentialy heat treated in a coke forge using exhaust paste clay, with a pre heated oil quench approx 110c. tempering was x2 2hours at 250c". No word about hardening, I'm sorry. All temperatures are in degrees Celsius.

The result seems pretty satisfying:


Although this gentleman achieved a very satisfactory result, I would follow Larrins recomendations:

knifesteelnerds.com

How to Heat Treat Nickel Knife Steels - 15N20, 8670, L6 - Knife Steel Nerds

Thanks to the new Knife Steel Nerds Patreon supporters! Fikes Lee, Dennis Toland, mlknhny, Immenreiner, Robert Pearce, Andrew Lakey, and Scott Amstutz. It is thanks to your support that I can do experiments like the ones you find in this article. YouTube Video Here is a video version of the...
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