8670, Oyster Knife, Torch Treating....

D

donnie1822

Joined
Nov 23, 2021
Messages
3
Long time lurker. This site has been incredible in kicking off my experience making custom prison shanks, slowly progressing to a knife. I have a couple of serrated bread knives under my belt, and a lopper/machete thing. The bread knives obviously receive negligible use, but I have approached it as practice in finishing work.

I finally picked up my first known steel at Blade Show in ATL this year. Two sticks of 8670.
I think my main crutch is not having any kind of oven or means to gauge heat temp. All I have for heat treating is an oxy/acetylene torch and the kitchen oven.

My first 8670 bread knife was heated to non-magnetic and quenched in corn oil. Then cycled in kitchen oven to 400, held for an hour, and cooled off to ambient. This was done twice(2). I then read online.... that I could flatten it by pinning between two flat surfaces and running through temp cycle again, but with cooling in sink each time. I did this and it came out damn near straight.
The knife seemed harder than when it was raw, but still file-able for the serrations. The problem is that it can bend and hold that bend EASILY. I find myself straightening it out with my hands.

Where did I lose the spring?

I want to make a oyster knife and will inevitably just go for it, but as you could imagine I would like to avoid blatant waste when experimenting.

Any tips on treating for tough/spring with my given limitations? Normalize in sand a few times? Quick quench then straight into clamped surfaces? Drastically different oven temp? Adopt a new religion?

I appreciate your time,
Donnie
 
You may have to go hotter for it? Sometimes non magnetic isn't the same as austentizing temperature? Most 8670 shows 1500 for Aus temp. Or the oil may have been too slow to quench properly?

knifesteelnerds.com

How to Heat Treat 8670 - Knife Steel Nerds

8670 is a popular steel for being easy to work and heat treat. We did a study on how to optimize its toughness and hardness.
knifesteelnerds.com knifesteelnerds.com
 
Did you only focus on heating the edge or was the whole knife an even color/temp?
 
Not sure about the oil being too slow but I could certainly change it up.

I tried heating the whole blade (12") and a little into the handle. I did not worry about heating all the way to the butt as it was inherently hard to to keep the whole blade one color waving a torch over it. Would it be more practical to just try the cutting edge?

Donnie
 
donnie1822 said:
Not sure about the oil being too slow but I could certainly change it up.

I tried heating the whole blade (12") and a little into the handle. I did not worry about heating all the way to the butt as it was inherently hard to to keep the whole blade one color waving a torch over it. Would it be more practical to just try the cutting edge?

Donnie
Click to expand...
Chances are you may have hardened the edge but not the spine which is why it’s taking a set and not flexing, I’d suggest sending a few blades to be heat treated professionally and save up for a oven or forge, the longer the blade the harder they are to harden with a torch
 
Maybe you can do a two brick forge with a hole for your torch? Or do the plain old charcoal fire and hair dryer methof. I think its the way most of us started with but moved quickly to forge HT, professional HT services and/or buying/building HT oven. Consistency is one of the main goals and that's hard with the minimalistic approach.
 
Welcome Donnie,
Fill out your profile. There may be another maker near you who will invite you over to do the HT right.
 
Austenizing temp for 8670 is around 1475 I think, which is a shade hotter than non-magnetic. I will tell you from experience that cooking oils are waaaay to slow for 8670. If your funds allow it, I recommend getting some Parks 50 quench oil in the near future.
 
TheEdge01 said:
Austenizing temp for 8670 is around 1475 I think, which is a shade hotter than non-magnetic. I will tell you from experience that cooking oils are waaaay to slow for 8670. If your funds allow it, I recommend getting some Parks 50 quench oil in the near future.
Click to expand...
Austenizing for 8670 is between 1500-1600, I prefer 1525
 
Thanks for the input guys. I'll be purchasing some Parks 50 after the holidays and will be shopping around or building a gas forge for even heating.
 
You must log in or register to reply here.
Back
Top