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Differentially heat treated composite blade

bodog

bodog

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There's been a lot of discussion about ZT producing the 0560CBCF with s110v at 59 hrc. Has anyone thought about or attempted to differentially harden the blade to protect the braze and spine? I got an email from them saying that no one has mentioned the idea.
 
The idea of the composite blade is to give you a harder cutting surface with a softer spine material. It's two completely different types of steel.
 
crom said:
The idea of the composite blade is to give you a harder cutting surface with a softer spine material. It's two completely different types of steel.
Click to expand...

Yea, I know they're different steels, that's why they didn't harden the entire blade more than 59 hrc, because the braze would've melted and it would've ruined the sandvik. My question is whether the same process used to differentially HT a blade would work on a composite blade, as referenced in the title, and protect the spine made up of a steel that can't really handle the higher HRC and the braze which would melt, as referenced in the first post.

I'm not really familiar with HT processes, so I could be way off base here, but seems like it might be possible. Or would it be better to just get a full blade of s110v and DHT that in order get the edge to 62+ hrc while keeping the spine softer?

Just a question about capability. I'm happy with my ZT as is, but in my mind it doesn't hurt to ask so I can learn something. Isn't that part of the reason for this forum being here? Please don't patronize me by telling me there are two different steels when I mention outright in the beginning that I'm referencing a composite blade.
 
I, uh, ok not sure how to proceed. My assumption was that you had never seen a Kershaw composite knife before and was under the impression the blade was made of one type of steel. The easiest answer I can give is the differential hardening is kind of achieved by using the softer steel in the spine portion. I watched a video a long time ago on how they make these, IIRC the two pieces are hardened separately before being braised together. Settle down man, I was trying to help.
 
It's a really interesting idea. I'm not sure how difficult it would be to pull off, especially with a production knife. The S110 part of the blade is very close to the spine metal near the base.

The composite blade looks beautiful, but I think I'd prefer just a solid S110V blade.

I still haven't tested the S110V at 59Rc enough to know how well it performs. Hopefully someone will give it a good test. I reprofiled my edge to 30 degrees (15dps), and it took a nice edge. The steel seems to be a very aggressive cutter. Maybe 59Rc is enough, but I'd have liked it a bit harder.
 
I would imagine that the additional labor to differentially harden the composite blade edge area, would exceed the cost of using solid s110v. I'm no expert though.

Tom
 
Obviously all that is needed to this is to keep the brazen material at the temperature below it's melting point. So the question is, is the temp. needed to raise S110V from 59 to it's optimal hrc (mid 60's?) excessively more than the original heat treat temp? I don't know but my guess is no so it seems highly possible.
 
I'm thinking that's why they used a composite blade to begin with, well, excluding costs. Sandvik can take a pretty good beating so I'm wondering if this is a production effort of a "differentially hardened" blade. Without worrying about the joining line so much, as long as the hardening line is well below the braze, then I think it could work. I wouldn't want to test it unless the heat treater was very experienced in not only stainless steel differential hardening, but one as highly alloyed as s110v, and even then, he'd have to be very exact in where the hardening line extended to. I searched and searched and I haven't found anyone who has talked about even attempting something like this. ZT says they haven't heard of it either.

It'd be a way to pull more out of a s110v production knife without insane costs or brittleness of a through hardened blade made of s110v from a custom maker.
 
The short answer is, it would be a complete waste of time and money.

The purpose of differential hardening is to get a blade with a tough spine and a hard, wear-resistant edge, as we know. This works very well with low-alloy "carbon" steels, because they are in essence shallow-hardening and once brought to heat, require a rapid and fairly severe quench to reach full hardness. This means we can (for instance) take a 1095 blade that's fully hardened and tempered back to 61Rc, protect the very edge from heat, and re-heat the spine to several hundred degrees... allowing the reheated section to cool in air (instead of quenching it again) results in a much softer temper.

Composites like this one achieve that same general effect, using high-alloy steels by mechanical design. That's the whole point. There is no need to differentially-harden a composite blade.

Attempting to do so would be very costly; chromium-rich air-hardening steels like these are specifically made to harden-through without the need for severe quenching (contrary to popular lore, that's precisely why they were originally developed, not so much for their corrosion-resistance... although it quickly became clear that "stainlessness" was a very nice side-effect). This very property makes them extremely difficult to selectively temper in the way one can with simpler "carbon" steels. If they're reheated again, they will want to re-harden again unless cooled extremely slowly.

It's reportedly been done, but it's crazy expensive and the few people who claim to have accomplished it are not sharing their secrets.

S110V is much more wear-resistant than 14C28N, even at the same Rc hardness, by virtue of its massive amounts of carbides. (All those vanadium, niobium, molybdenum and even the chromium carbides are much harder than any plain steel can get.)

So, this knife already has a tough spine and a harder (in a practical sense) edge.
 
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Can you even differentially heat treat stainless steel? I have only ever seen it done to tool steel.

Either way, no way could it be done practically in a production setting even if it is possible.
 
bodog said:
I'm not really familiar with HT processes, so I could be way off base here...
Click to expand...

Yes, you are way off base. I'm not trying to be patronizing, it's just a basic misunderstanding of the process.
 
you know, I didn't even think about s110v or 14C28N being air hardening steels. Would it work for oil or water quenching steels? Just play along and say that the combo they used didn't already accomplish the goal (which is what I assumed from the beginning more than cost savings) of giving a tougher spine over a harder edge. I never understood why Kai never came out and said it. They always talk about why they hardened the s110v to 59 hrc but never about why they made a composite blade to begin with. Honestly, I just wanted to know if differential re treating could raise the hardness, but with the steel being designed for air hardening, it's a no go from the gate.

Thanks for the answers, guys.
 
Scurvy092 said:
Can you even differentially heat treat stainless steel? I have only ever seen it done to tool steel.

Either way, no way could it be done practically in a production setting even if it is possible.
Click to expand...

There are a few guys that say they do it and some claim to produce mild hamons.
 
bodog said:
Would it work for oil or water quenching steels?
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Absolutely. A skilled maker could make it look really cool by using a nickle-bearing steel like 15N20 for the edge portion and a very simple steel like 1084 for the spine and then etching them after HT (including differential tempering, if so desired) and polishing. Just like damascus, the 1084 would get very dark and the 15N20 would stay bright and shiny.

There's another way to achieve a similar look... low-alloy steel laminated between two bars of stainless. In that case, again there would be no real need for diff HT, and it would be problematic at best. Here's an example by Karl Andersen:

CDSM1.jpg


In that example the low-carbon 416 out layers provide toughness (and corrosion resistance, plus it just looks cool) and is not hardenable anyway; the 1095 core is hardened normally and provides a hard, wear-resistant edge.

One advantage of both the above approaches is they don't require brazing; the different steels can be forge-welded together and then forged and/or ground in the normal fashion, much like a homogenous bar.
 
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james terrio said:
Absolutely. A skilled maker could make it look really cool by using a nickle-bearing steel like 15N20 for the edge portion and a very simple steel like 1084 for the spine and then etching them after HT (including differential tempering, if so desired) and polishing. Just like damascus, the 1084 would get very dark and the 15N20 would stay bright and shiny.

There's another way to achieve a similar look... low-alloy steel laminated between two bars of stainless. In that case, again there would be no real need for diff HT, and it would be problematic at best. Here's an example by Karl Andersen:

CDSM1.jpg


In that example the low-carbon 416 out layers provide toughness (and corrosion resistance, plus it just looks cool) and is not hardenable anyway; the 1095 core is hardened normally and provides a hard, wear-resistant edge.

One advantage of both the above approaches is they don't require brazing; the different steels can be forge-welded together and then forged and/or ground in the normal fashion, much like a homogenous bar.
Click to expand...

Yea, I'm actually really, super impressed with the look of Burt Foster's San Mai. I guess being a master bladesmith means that they're really good at what they do.
 
James Terrio has forgotten more about this stuff than I ever knew. Thanks for your explanation.
Sonnydaze
 
bodog said:
Yea, I'm actually really, super impressed with the look of Burt Foster's San Mai. I guess being a master bladesmith means that they're really good at what they do.
Click to expand...

The ABS doesn't just hand out JS or MS stamps willy-nilly. Those cats are definitely really good at what they do, and they have proven it to their peers :) They are among the finest knifemakers the world has ever known... and yes, that includes semi-mythical smiths like the Japanese, Middle-Eastern and European makers of history.

Sonnydaze said:
James Terrio has forgotten more about this stuff than I ever knew. Thanks for your explanation.
Click to expand...

You're very welcome, and that's very kind of you to say. I learned (and continue to learn!) by doing my own research and asking (sometimes "dumb") questions of the best makers in the business... and sorting out the answers that make sense ;)
 
Once again I am reminded of how little I know about knives and steel, but I sure do enjoy the learning. And appreciate the time that those of you experts take to share your knowledge and experience. Thanks.
 
We are all living in the True Golden Age of cutlery, and we stand on the shoulders of giants. :)
 
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