13 Myths about Heat Treating Knives

Larrin

Larrin

Knifemaker / Craftsman / Service Provider
Joined
Jan 17, 2004
Messages
4,970
Thank you so very much. I don’t have the words to thank you enough. Great work that sheds light on a conversation otherwise based on simple opinions.
 
Alright, can't wait to read. Thanks Larrin!

edit: Love #12. That's a particularly poorly understood phenomenon, especially as it relates to "bend tests" of knives. You often can see people extolling how a particular knife did when being bent to 90 degrees and back while making no note of how sharp the bend radius is or how thick the steel is. Those factors have way more of an effect on how a knife handles bending than anything else.
 
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I think you're setting up a false argument. You acknowledge that geometry, steel alloy and heat treat are all important, but the thrust of your argument comes down to this: "But if we were to pick one factor that is the “most important” I’m not sure that heat treatment would be the one."

Trying to pick which one of those three factors is most important is like asking which leg of a three-legged stool is most important. Yes, geometry cuts, but steel alloy and heat treat determine how much geometry a blade can support.

I have a S30V blades that chip easily. I have S30V blades in the same geometry that don't chip with the same use. The difference is in the heat treat.

I bought a large custom blade in CPM 3V that dented and rolled with every strike into soft, clear-grained Doug fir. I have a large custom blade in the same steel and same geometry that isn't affected by the same use.

The difference is heat treat.

Ed Fowler, in Knife Talk, describes complex, multi-quench heat treats that "resulted in an increase in cutting performance of 300 percent over previous 52100E blades from virgin steel... ." He said, "One of the blades was flexed back and forth a full 180 degrees 6 1/2 times before the edge cracked." How many 52100 blades can achieve that level of performance?

I have two EDCs that I use for chopping. One blade is Vanax SuperClean, a beautiful steel but not especially tough when compared to carbon steels. I have another blade in A8(mod), a super tough steel with the same geometry.

The Vanax can chop all day long without damage. The tougher A8(mod) blade failed quickly in the same use. The problem isn't the steel, but rather something that went wrong in the heat treat. Here's a shot of the A8(mod) blade after some light chopping:
2v2HtjqHGxAWtWs.jpg


Just as steel alloy and geometry will exhibit huge differences in knife performance, so can heat treat.
 
Twindog said:
Ed Fowler, in Knife Talk, describes complex, multi-quench heat treats that "resulted in an increase in cutting performance of 300 percent over previous 52100E blades from virgin steel... ."
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How can anyone actually verify the claims made here? That sounds just like Jay Fisher claims I've seen on his website.

Twindog said:
He said, "One of the blades was flexed back and forth a full 180 degrees 6 1/2 times before the edge cracked." How many 52100 blades can achieve that level of performance?
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As I noted above, this is not a commonly well understood demonstration. Any piece of steel can bend however you want, repeatedly, given the right geometry and a basic heat treat. The stress at any point on the blade will be determined by where in its cross section you are interested in, how thick the blade is, and what the radius of curvature is. Assuming the very edge is in line with the centerline of the blade, that's a location of essentially zero stress while in bending. This is not a demonstration of heat treatment so much as geometry, as a thicker blade would not perform the same way no matter the heat treatment.

Twindog said:
I have two EDCs that I use for chopping. One blade is Vanax SuperClean, a beautiful steel but not especially tough when compared to carbon steels. I have another blade in A8(mod), a super tough steel with the same geometry.

The Vanax can chop all day long without damage. The tougher A8(mod) blade failed quickly in the same use. The problem isn't the steel, but rather something that went wrong in the heat treat. Here's a shot of the A8(mod) blade after some light chopping:

Just as steel alloy and geometry will exhibit huge differences in knife performance, so can heat treat.
Click to expand...

Those are two different steels at different hardnesses and levels of strength. How is your comparison supposed to single out heat treat as the differentiating factor?
 
marrenmiller said:
How can anyone actually verify the claims made here? That sounds just like Jay Fisher claims I've seen on his website.



As I noted above, this is not a commonly well understood demonstration. Any piece of steel can bend however you want, repeatedly, given the right geometry and a basic heat treat. The stress at any point on the blade will be determined by where in its cross section you are interested in, how thick the blade is, and what the radius of curvature is. Assuming the very edge is in line with the centerline of the blade, that's a location of essentially zero stress while in bending. This is not a demonstration of heat treatment so much as geometry, as a thicker blade would not perform the same way no matter the heat treatment.



Those are two different steels at different hardnesses and levels of strength. How is your comparison supposed to single out heat treat as the differentiating factor?
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Ed Fowler is not Jay Fisher. Ed documented his heat treating performances in his book, which included independent analysis by a metallurgist.

The A8(mod) vs Vanax blades were both the same hardness and the same geometry. But you miss the point. The A8 alloy is much, much tougher (resistant to chipping and cracking) than the Vanax ally. Normally, it should not crack before the Vanax. But something wasn't right in the heat treat, so a normally low-toughness steel could outperform a high-toughness steel. That's how much difference heat treat can make.

If you just compare routine heat treats of a steel, you won't see a lot of difference. But heat treats can dramatically increase blade performance or dramatically lower blade performance -- just as changes in geometry or steel alloy.
 
The myth listed was specifically to argue with a focus on only one aspect of knife design, as the most common thing I see is that heat treatment is what controls performance. Heat treatment is important, we shouldn't ignore edge geometry and steel choice, and it is my view that edge geometry is more important than heat treatment.
 
I think folks love love love the idea that somehow they've got a knife with a bit of black magic mixed into the blade that gives miraculous performance.

Nothing wrong with custom blades or most of the folks that make them but once you start to believe the hype it's not good.
 
Twindog said:
Ed Fowler is not Jay Fisher. Ed documented his heat treating performances in his book, which included independent analysis by a metallurgist.

The A8(mod) vs Vanax blades were both the same hardness and the same geometry. But you miss the point. The A8 alloy is much, much tougher (resistant to chipping and cracking) than the Vanax ally. Normally, it should not crack before the Vanax. But something wasn't right in the heat treat, so a normally low-toughness steel could outperform a high-toughness steel. That's how much difference heat treat can make.

If you just compare routine heat treats of a steel, you won't see a lot of difference. But heat treats can dramatically increase blade performance or dramatically lower blade performance -- just as changes in geometry or steel alloy.
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I understand he's not Jay Fisher. I'm saying that this claim is hard to justify, just as Jay Fisher's often are.

I think you've missed the point, actually. Impact toughness isn't the only thing that determines damage to an edge, nor is it always the case that tougher steels will take damage before less-tough steels. See: many examples like this, where extreme strength of A11 class steels shrug off damage that "tougher" steels might not. BBB did a number of demonstrations with Rex45/K390/Maxamet and with M4 and showed that, while impact toughness between the steels were wildly different, the lower toughness steels resisted rolling and chipping better than M4, even when using production knives. Also demonstrated many times is that the ability to resist damage, like when cutting a nail in half, can be dependent on strength/hardness, toughness, and in particular geometry. Just changing the edge thickness a bit can be enough to resist damage where it might be catastrophic otherwise.

Impacts are hard to quantify and are hard to directly compare. The exact loading cases matter when comparing damage, and that's even assuming that we can take it on good authority that your knives indeed have identical geometry. That is also without knowing for certain that your knives were treated the same way, as just about any steel can chip if it hits something like minerals embedded in wood. Even if everything is completely identical, all that you would manage to demonstrate with your example is that a faulty heat treat can make a tougher steel less resistant to damage. If that tougher steel was slightly more thick at the edge or had a more obtuse edge angle, how do you know the results wouldn't have been significantly different? That is the basis behind the claim that geometry matters more.
 
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I think the thing being missed here is that geometry offers the largest potential for difference in performance than any of the other factors. A 12-15 dps edge vs a 30 dps edge will almost always offer more improvement in edge retention than jumping to another steel, or having a better or worse heat treatment. In terms of cutting performance, a paper thin knife will go through most mediums with significantly less effort than one that's .030"+ at the edge, regardless of what steel or heat treatment they have.

If you want to push that to logical extremes, I'd be willing to bet that an annealed piece of 420HC with a .010" thick edge would offer better cutting performance and edge retention at 20 dps than any knife you can make with a thicker edge and a blunt 45 dps edge.
 
Danke42 said:
I think folks love love love the idea that somehow they've got a knife with a bit of black magic mixed into the blade that gives miraculous performance.

Nothing wrong with custom blades or most of the folks that make them but once you start to believe the hype it's not good.
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So, are you saying that 3V isn't as tough as S30V or, that Aus 8 will last just as long as S110V in edge retention?
I'm being serious. Ive always been led to believe that certain steels performed better in different areas, like toughness and edge retention for example.
 
Another insightful and useful study, thanks! (Now, if only I had been properly heat treated, maybe I wouldn't have needed this new hip...:D)
 
MacLaren1 said:
So, are you saying that 3V isn't as tough as S30V or, that Aus 8 will last just as long as S110V in edge retention?
I'm being serious. Ive always been led to believe that certain steels performed better in different areas, like toughness and edge retention for example.
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No I'm saying people love to believe in magical thinking like a spiel from some custom builder who can only heat treat knives during a planetary alignment because the extra gravity waves help organize the carbides by height and in alphabetical order.

There's no doubt that super steels are super.

The hype comes into this when someone pretends that what they do is the long lost secret of the Damascus steel or whatever. Instead of selling on their attention to detail of balancing the right steel with the correct heat treat protocol and effective blade shape and edge. In other words; boring.

Jay Fisher is obviously the Guinness World Record holder for making outsize claims but he's not the only one.
 
Any of these factors -- geometry, steel alloy or heat treat -- can make a huge difference or virtually no difference.

I usually sharpen at 15 dps. Someone with a Lansky is likely to use 17 dps. There is not going to be much difference.

The heat treat of S30V by Spyderco or Benchmade is not going to make a lot of difference.

A blade made of 154 CM or VG 10 is not enough of a difference for me to notice.

But when you get into larger differences, each of these variables can make huge differences:

10 dps vs 30 dps
Rex 121 vs 420J
A heat treat by a new knife maker using his toaster oven or a professional heat treat by a renowned knife maker.

And all of these factors have a dynamic interplay, and that interplay can vary greatly with the type of use the knife receives. A three-legged stool needs all three legs.
 
Twindog said:
Any of these factors -- geometry, steel alloy or heat treat -- can make a huge difference or virtually no difference.

I usually sharpen at 15 dps. Someone with a Lansky is likely to use 17 dps. There is not going to be much difference.

The heat treat of S30V by Spyderco or Benchmade is not going to make a lot of difference.

A blade made of 154 CM or VG 10 is not enough of a difference for me to notice.

But when you get into larger differences, each of these variables can make huge differences:

10 dps vs 30 dps
Rex 121 vs 420J
A heat treat by a new knife maker using his toaster oven or a professional heat treat by a renowned knife maker.

And all of these factors have a dynamic interplay, and that interplay can vary greatly with the type of use the knife receives. A three-legged stool needs all three legs.
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I don't think anyone is saying they're not all important. I do, however, think it's fair to say that geometry is the most important if you had to choose between them, which is what Larrin's comment seemed to say. Rex121 with a world-class heat treat won't cut if it's a dull brick.
 
Larrin said:
And if we use "sharpness" as one aspect of edge geometry (controlled by the edge width/radius so technically true) then it becomes very difficult to argue against edge geometry being the most important factor.
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Why not. I mean you can make a perfectly refined 45 dps edge which will probably still feel dull.
 
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