Hardening/Tempering

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BChou-E29

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Dec 4, 2009
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I've been messing around with some hardening methods and I came across differential hardening. I like the idea of a hard edge + tough spine so I'm thinking about trying it for a new knife. I've never done a differential harden before and I wanted to ask if my method would be appropriate. I'm using O-1 tool steel and motor oil as a quench medium.

1. Heat blade till demagnetized
2. Quench cutting edge area ONLY in oil
3. Let the rest of the blade (spine, tang) slowly cool to allow carbides to return to carbon.

I thought this method would be good in concept since it would eliminate the need for tempering. Any ideas?
 
I think if you do that in motor oil it will flare up bad. But that method will work. Try putting clay or satanite on the spine and quench the whole blade. Instead of motor oil maybe try olive oil it doesn't seem to flare up as bad and don't stink near as bad. I don't think it eliminates the need for tempering at all. I think it should be done anyway to take some stress out of the hardening process. I'm no expert by far especially on O-1 but through my research this is what I have found.
 
1, O1 is not a steel you would typically use to differentially harden - use 1084 or 1080.

2, if you want a tough spine, harden it and draw it back with a torch while the edge is dipped in a pan of water.

3, heat till demagnetized is not hot enough, O1 needs a soak to get it's full potential. If you don't have good controls over temperature and time for soaking use a simple steel like 1080, 1084.

4, Eliminate need for tempering?? Could you elaborate on this?
 
BChou-E29 said:
I've been messing around with some hardening methods and I came across differential hardening. I like the idea of a hard edge + tough spine so I'm thinking about trying it for a new knife. I've never done a differential harden before and I wanted to ask if my method would be appropriate. I'm using O-1 tool steel and motor oil as a quench medium.

1. Heat blade till demagnetized
2. Quench cutting edge area ONLY in oil
3. Let the rest of the blade (spine, tang) slowly cool to allow carbides to return to carbon.

I thought this method would be good in concept since it would eliminate the need for tempering. Any ideas?
Click to expand...

no offence, but this is hardly a new idea.........

you're still going to want to temper it though
 
and the reason you will still need to temper is even if you get a soft spine and a fully hardened edge, your edge would chip if left fully hard. Heating 01 to non magnetic will probably not get you a fully hardened edge though. You will end up with a mixture of pearlite and martensite, which is not as good as pure martesite that has been tempered. I lost my ht files when I had the fire but I think O1 needs too go to something like 1500f for 10 minutes to get full conversion. Your magnet will quit sticking at about 1350f. For maximum edge holding you want maximum martensite
 
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I agree. I heat treat O-1 at 1475F for 20 minutes, quenching in AAA oil (a medium speed oil), For O-1, probably any oil will work ok if you agitate. I used to use canola. Heat to non-magnetic and quench will not get you a fully hardened blade in O-1. The heat has to be higher, and you need at a minimum a 5 minutes soak at that heat.

I also prefer the fully hardned blade and spine and use a torch to draw back the temper in the handle/spine after a regular temper if I feel it's needed. That being said, many makers still do an edge quench as you're describing. O-1's not the best to edge quench, but it will work. You should look up Brian Goode (blgoode) and ask him about his technique. I believe he uses a torch to differentially harden O-1.

--nathan
 
theoretically he's right it could eliminate the need for tempering, as the spine of the blade would be hot enough to re-heat the edge to a temperature that would temper the blade. however I would still temper it, maybe not as much (as high a temp)

oh and everybody is right about the heat treat temp it needs to be several hundred degrees above magnetic
 
Theoretically, maybe. You'd have to do an interrupted quench for an auto-tempering effect to occur, I would think. If you do as most makers and quench the edge and leave it there in the oil or rock it back and forth on a limiting plate, you should get a decent conversion to martensite at the edge that is going to need to be tempered. There's just no good way to assure an appropriate or consistent tempering through conductive heating from the spine. You'd get a mixture of over-tempered martensite at the quench line and likely under or non-tempered martensite at the edge.

Either way, I would still do a temper at the appropraite temperature for what hardness/toughness characteristics you're looking for.

--nathan
 
I see... By the way, SShepherd, I am aware that this method is not new but I was wondering if I could get similar results if I did so without a tempering. But I see this is not the case. Anyways, thanks everyone for your insight.
 
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