I have a question about carbon steel blades guys.

L6steel

L6steel

Joined
Sep 23, 1999
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I know most of you heat treat your carbon steel blades by edge quenching them which basically leaves the rest of the blade annealed. I know the reasoning behind this is flexibility is better than stiffness. It'll bend instead of break when put under pressure.
Well, I don't really get it.
I just finished a big bowie and you can see where the edge was quenched, what folks call the hamon I guess and it does look neat, but the rest of the blade is so soft you can ding it up easily and it's much more prone to rust than it would be if it were completely hardened and tempered. This bowie got a light dusting of rust on the tang edges over night just from me handling it. I know, I forgot to wipe it down with an Outer's cloth but it you're out in the field that's going to happen a lot.
Another reason it seems to me it would be better to harden and temper the entire blade is that by having only the thinnest part of the blade hard and the rest soft, aren't you setting it up to break at the grind? It looks like where the hardened steel ends and the soft steel starts there would be a weak spot just begging to break.

Please don't eat me alive, I'm just posting some concerns. :D
 
That's a fair enough concern. Have you considered hardening the entire blade then heating up the back to a spring (blue) temper? That's certainly harder than annealed and less ding prone.

"It looks like where the hardened steel ends and the soft steel starts there would be a weak spot just begging to break."

I think this was a problem Cold Steel had for a while. The best way around this that I know of is to "feather" the spot where hard steel ends and soft steel begins. That is - don't let it be a "harsh" transition from hard to soft, but a bit more gradual. Does that make sense? I don't think you can get a good hamon or temperline from this, but can't speak definitively on that.

Tim
 
Thanks for the reply Tim!!
Right now I'm sending my carbon blades out for heat treat. My oven isn't big enough for them. I'm thinking about ordering a bigger oven and selling the one I have so I can do them myself. That way I can experiment with them too. I just use L6 so maybe I can come up with a heat treat method for it that will make a butt kicking blade.
 
You say the spine is too soft ? What type of steel ? did you differentially harden (if so what did you start with) or differentially quench ? My tutorial www.knivesby.com/robert-cella-1.html lists all the combinations, you have to decide what you want.
 
Come on smithies, where are you on this one, I wanna know what you have to say on this!
 
I just want to make a knife in my forge that will not break.

Im told that to harden only the cutting edge area would allow the spine of the blade to remain strong and soft. And so that's what I do.

Now yes, I don't know for sure how this will affect the amount of rust on the blade in the future, but remember Im not using carbon steel based on its ability to resist a little rust in the first place.

While having a nice shine on a blade to show my friends is at times a neat thing to have, what I actually make my knives for is to help guys at their work.

When I actually draw my knife in the field or on the jobsite, what matters most to me at the time is that I can cut what I need to cut, and that the knife is safe and will not let me down when I need it.

I don't harden the spine so that I can trust my knife will not break when pushed a bit over the limit. Sometimes I have to use my knife to reach into dug up underground drain pipes and cut out a ball of tree roots. At such times when working in darkness and being unable to see what I am doing, it's nice to be able to trust that the blade I have in my hand will not suddenly snap in two on me.

Yes, it might come out of the hole with a bit of rust on it, but both it and my hand come out in one trip.
 
There's alot of opinions on which was is best. I'm still new at this myself, but personally I think that differentially tempered is superior to diff hardened. Both are better then a fully hardened non-diff tempered, but diff tempered should be more likely to spring back into position rather then take a set if it bends too far. In any reasonable use though, both should be more then good enough if done well. Also Hamons are really cool.
 
Michael A. Cooper said:
I know most of you heat treat your carbon steel blades by edge quenching them which basically leaves the rest of the blade annealed. I know the reasoning behind this is flexibility is better than stiffness...
Click to expand...

I will leave the whole edge quenching thing alone since there are so many different opinions about it (I can say that I think your original thoughts are in the right direction, in my opinion). But I will take time here to point out that you shouldn't worry at all about "flexibility", since heat treatment has no bearing on flexibility or stiffness whatsoever. You adjust that with the grinder. All heat treat can do is determine how easy the blade will permenantly bend or eventually break. And a fully hardened blade, if properly heat treated, will take some serious effort to break (but it is all about nailing that heat treat ;) ).
 
One method I've read about and used is doing a full quench with a clay coat with a little thinner spine coating. This will harden the spine a little without messing with your hamon. It also prevents rapid curving which can cause edge cracks.
 
I was wondering if edge quenching might come from back in the day when good steel was rare so smithies forge welded lesser steel to a section of good steel to make a knife so the only part of the blade that needed quenching was the edge. Ie.. you can't harden junk steel anyway so why bother quenching it.
With the steels we have nowadays that doesn't count.
 
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