Edge quenching

bobbywett said:
I'm learning a lot from this thread, especially Stacy's recent summation. If I am to interpret correctly, the consensus is a thinner geometry, martensite edge, fine pearlite transition, from slow a drawback blade will yield better under lateral stress? If this is true, than a thinner blade (possible 3/16" or thinner) with a wider profile fully hardened and then drawn back....would be the best bet for the J.S. performance test?
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I think that is a fair statement. The idea behind the JS Performance test is to see if the maker has control of heat. You can shoot for a blade that returns back to true after a 90deg flex, but as Kevin so bluntly put it to me, "WHY?... there are no extra points for wow-factor.". If the only goal of the 90deg flex test is to not have your blade break, why would you risk it by fighting the yield point? Temper that baby back! I feel it is just as bad to have the mixed structure of a differential HT that in essence, creates a place for failure to begin. I see blades that crack at the edge and bend at the spine and yes, they will pass if the crack is less than 1/3 of the blade width. BUT why not have a blade that yields without cracking at all? Fully martensitic, tempered accordingly is the way to go, IMHO.
 
This is all true, only IF “everything else is equal“,… geometry, steel type etc., and that’s a big IF. From this standpoint, I don’t think we can say that a full quenched blade is “always” superior to an edge quenched blade,… IF other aspects of the comparison are not equal. In the real world “everything else being equal” is seldom the case.

So, in reality an edged quenched blade could out perform a full quenched blade, but it would likely be a better steel with better geometry and/or with more mass.

… seems obvious, doesn’t it?

Although the term edge quenching is often applied to differentially hardened blades, what would you call a blade that is quenched past the center line, but not all the way to the top of the spine? It’s beyond an “edge quench”, but just short of a full quench.

Just saying there are a lot of variables in this and over simplifying it may not be the best way to try and resolve it. I haven’t said much for a while, but this might be one of those times to apply some lateral thinking.

If we place the parameters at “everything else being equal” in order to make a point, then we ignore the possibility and likelihood that everything else may not be equal.
 
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I think the point Tai makes is reasonable. There are many variables involved... that is a given. It is also why we chose to use statements like "everything else being equal". Otherwise, nothing comes from these conversations. You have to get to the root of the discussion, while still acknowledging that it isn't that simple. But to say everybody is right because nothing is equal, gets us nowhere. If we don't set parameters to make points, it is pointless.:p Sometimes all things are equal, within reason.
 
If you are trying to prove theoretically that your full quenched blades perform better than other maker’s edge quenched blades,… you’re out of the realm of science. In order for the science and/or logic to apply, everything else has to be equal. I suppose that’s a given,… but just want to reiterate that point.

It is pointless... because the parameters, conditions, variables etc., can always change. You can put those where ever, when ever and how ever you like, and/or any way that circumstances dictate hypothetically in the real world... That's what heat treating is really all about.

I don’t think it’s realistic to conclude that one way is always better than the other, depending on the variables. When it gets down to what’s better, it becomes a subjective discussion. What’s “better” can vary in an infinite number of ways.

Both methods have there place.
 
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I'm losing your meaning, Tai... Are you basically saying that proof is in the use, not the construction?
 
Rick,.. I'm basically just talking, but not saying anything. I'm leaving it open to interpretation, which is how I think it should be. ;)

You answered the question when you said the microstructures are "different". That's true.
 
If memory serves, retained austenite is a problem due to it gradually transforming over time. Any comments on minimizing retained austenite?
 
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Michael Kemp said:
If memory serves, retained austenite is a problem due to it gradually transforming over time. Any comments on minimizing retained austenite?[/QU

More tempering cycles spread over several days will address this. There is a point of diminishing returns.
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I think Tai is getting needlessly defensive about edge quenching because that is how he does most of his blades. I don't think that pointing out the metallurgical superiority of a properly full quenched blade in any way devalues any of Tai's work, I don't think people buy it for its metallurgy, I think his work is valued as art.

From a performance perspective a fully hardened properly tempered blade will be superior to an edge quenched blade made of the same materials with the same geometry. A properly tempered blade has the strength of the entire blade reinforcing the edge, wheras the edge quenched blade will have the spine yield prematurely to torsional stress possibly causing the edge to crack and chip out

-Page
 
Each and every blade smith has the hardware and materials to answer these questions for himself. Just use the blade for what it was intended. If hard use is your goal, put it to the extreme test and see how it does. If strength and flex is what you seek as well as edge toughness and cut test your own blades, put a torque wrench on the blade and see what it takes to flex to where it does not return to straight, then test it to destruction and you will know for yourself. Theory is great, but usually based on traditional concepts that may or may not pertain to knife.
 
Page, I use both full quenching and edge quenching (and everything in between) equally, on different blades for different reasons. I don't have a preference here, just trying to be fair to both sides.

In fact, I do "custom heat treating" to clients preferences, within reason... full quench, edge quench etc. It just depends what someone wants and expects from a blade. I try and give people what they want, within reason. It's all within reason if done well and accordingly. The last thing I want to do is try and force one way down everyone's throat.

If it seems like I’m defending one, it’s just because I see it as being unequally represented.

It's not my fault that my differentially hardened blades currently seem to get the most recognition and exposure. Before that, it was my pattern welded blades, all fully hardened...
 
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Ed Fowler said:
Each and every blade smith has the hardware and materials to answer these questions for himself. Just use the blade for what it was intended. If hard use is your goal, put it to the extreme test and see how it does. If strength and flex is what you seek as well as edge toughness and cut test your own blades, put a torque wrench on the blade and see what it takes to flex to where it does not return to straight, then test it to destruction and you will know for yourself. Theory is great, but usually based on traditional concepts that may or may not pertain to knife.
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What heat treat is best for a blade to flex and return completly straight. I am more of looking for what takes the most strength to crack or bend.
 
chad2 said:
What heat treat is best for a blade to flex and return completly straight. I am more of looking for what takes the most strength to crack or bend.
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The answer is contained within this post:



Each process leaves you with a different microstructure. My preference is a homogenous hardening process(full quench) with tempering to suit the intended function(Full or differential, depending...). That is not to say that edge quenching or differential heat treating doesn't have a place in knifemaking.

Flex is a product of geometry within the elastic range... not the absence of hardness. If there is any "flex" beyond the elastic limit(which is the same for like geometries, regardless of hardness) it is a result of hardness(martensite) and the resistence against plastic deformation(strength) not the ability to deform without breaking(toughness).

I may have butchered that last bit of technical talk(Modulus of Elasticity)... lol. Page will probably come along and slap my peepee.

All I know, is that I would rather have a blade that requires 2 guys and a cheater bar to break, than one that can bend back and forth under my own power. I abuse my knives and don't mind that they get abused buy my customers. It is a compromise for me. Some would never expect that from a knife(by standard definition)... which IMO, makes edge quenching/differential hardening an even harder sell... from a practical standpoint.

There are good makers who use different methods for different reasons and as long as they aren't misrepresenting facts, I am fine with it.

Last edited by Rick Marchand; Yesterday at 06:33 PM.
 
Tai and Rick:
If this gets into a philosophy/theory of everything debate or a "You said ,I said " rant, I'll lock it.

The OP wanted to know what the flex vs strength was in different techniques. All have a reason that is a plus, and all have a disadvantage.
This is one of those places where there may truly be no one right or wrong answer. Lets keep this about the OP question.
 
Page,

Going back to the Zoweda/Cashen demo; do you happen to remember the split on the required force - specifically where the annealed bar yielded vs where the hardened bar snapped?

I understand they used PG O-1, but I've played around with this informally with my own straight 1084 and 1084/15N20 PW blades. At this point, I would hazard a guess at about 2.5X more force required to break a full-hard/untempered cross section than to plastically bend an edge-quenched/back drawn, but otherwise similar, profile.

I'm curious because this difference has been my primary reason for full-quench (that, and I was wisely advised a few years ago to stop flaming my Parks #50), but I've yet to see any empirical data.

Thanks man.
AWL
 
Empirical data - I don't have....but I agree with your guesstimate. It takes a lot more force to break a fully martensitic blade than it does to permanently bend a pearlite body blade.
 
bladsmth said:
Empirical data - I don't have....but I agree with your guesstimate. It takes a lot more force to break a fully martensitic blade than it does to permanently bend a pearlite body blade.
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I am in the process of building a contraption to measure a more realistic ft/lbs torque of resistance a blade generates while being laterally flexed.
 
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bladsmth said:
Empirical data - I don't have....but I agree with your guesstimate. It takes a lot more force to break a fully martensitic blade than it does to permanently bend a pearlite body blade.
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It would just take more steel on the differentially hardened blade to achieve the same amount of strength. ;)
 
chad2 said:
What heat treat is best for a blade to flex and return completly straight. I am more of looking for what takes the most strength to crack or bend.
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As high a hardness (strength) and as thin as you can make it without loosing too much weight to do it's job, and as long a blade as you can get without being awkward. A uniform heat treatment would be desirable, ie no edge quenching, soft back draws, etc.
 
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