Friction Forged Blades : CATRA tests

[Cliff Stamp]

One major disagreement I have is that Cliff's definition of edge retention is normalized by the original edge sharpness.

No it isn't. I define a cutting advantage as the ratio of material which can be cut until the blades degrade to a level of blunting. Since the responce of blunting is nonlinear this cutting advantage is dependent on where you fix the stopping point. As I have noted specifically which steel is superior can actually invert depending on if you look at high sharpness or low sharpness.

The initial sharpness is just one of the variables in the models. The reason the numbers are so normalized is simply because it makes them easier to look at visually. But you don't compare them in this manner as noted in the above. You look either at the absolute sharpness at a specific amount of material cut, or at the absolute amount of material cut to reach a given level of degredation.

Of you look at the fitted variables and make inferences accordingly, but that is more difficult, but I have discussed that in detail as well.

All the steels were sharpened on 600 grit diamond belts, with a mechanical fixture used to establish sharpening angle. The wire edge, or burr was then removed on a cardboard wheel with chromium oxide compound.

It has nothing to do with games, different steels will require different methods to sharpen. There is a big difference between high vanadium and high chromium steels in regards to sharpening. With the initial sharpness so different it should have raised an obvious question as to why the CPM steels were so dull. The first thing to do would be to check them under low magnification to inspect for proper burr removal. Why did the edge not form to the optimal sharpness which is about 0.1 microns or so.

I repeat, every steel that was tested, including the FFD2, was sharpened with the same procedure ...

That is the problem and shows a fundamental lack of understanding of steels. You can not sharpen 420J2 and 1095 the same way for example. One will create a very sharp edge and the other highly burred under the exact same method. Now you can easily pick a method which will favor one steel over the other.

Thanks for the raw data, I will see if I can't model it the weekend and produce the cutting advantage ratios for the steels in question.

Clilff,
Have you ever actually observed the grain size in a piece of properly hardened D2?

I have broken Doziers and several other production/custom knives, so yes. The austenite grain of steels is limited more by the heat treatment than the compostion of the steel. The general stock heat treatment for D2 leaves a large austenite grain. To refine the grain you want a higher heat and a very tight control of the time so as to minimize the growth of the austenite and get the carbides in at the minimial size.

But you can forget about the specifics here and just argue in general. For example, the grain size of 1095 is much finer than D2, with both having stock heat treatment. Now D2 still easily has a much higher wear. By doing this with different steels you can easily model edge retention on the basic of carbide volume/grain size parameters. I proposed this to CATRA many years ago.

Now if you just think about this it again becomes difficult to understand where the high performance comes from. Do a simple wear test on the new D2 vs S90V and see what happens. Is the claim here than this process somehow obliterates the huge advantage of the vanadium carbides in S90V or does S90V still have much more wear but the edge is more stable in the new D2. Because you can test edge stability independently of wear resistance as Landes has shown and check this as well.

These are the reasonable questions which would be asked and a sensible way to proceed if you wanted to really understand the behavior of the steel. This is not black magic, where is the performance coming from, measure that physical property specifically. The above PDF file does none of that and answers none of the obvious questions about performance. Now quite frankly I know there were metallurgists involved in the process and I know these questions had to be asked because they are blatently obvious. So what are the answers?

Now if you just want promotion then that is fine, but the above offers nothing significant in terms of actual understanding of the performance of the steel or even any logical attempt to explain it. Of course I would not really expect that in such a document which is why I started the thread here to see if such information could be attained and to show why the above is flawed from such a viewpoint.

Do you realize that .5 micron is so small that it looks like a blank piece of paper at 1,000X?

Yes I understand the meaning of a micron. About 100 microns is the limit of the human eye.

Most knives are used in a slicing mode, rarely by being pushed straight through something.

If this is the case then you would not use the CATRA sharpness testor to measure sharpness as it tests on a push.

-Cliff

 

[Kohai999]

Now you understand why I "explained" Cliff and his methods to you, I just didn't want you to think this was a typical friendly online discussion.

He will also edit himself multiple times if he is found to have his dick swinging in the wind.

Best Regards,

STeven Garsson

 

[cds4byu]

Cliff writes: The initial sharpness is just one of the variables in the models. The reason the numbers are so normalized is simply because it makes them easier to look at visually. But you don't compare them in this manner as noted in the above. You look either at the absolute sharpness at a specific amount of material cut, or at the absolute amount of material cut to reach a given level of degredation.

Why not look at the absolute amount of material cut to reach a specified level of sharpness, which is what we showed in the paper?

In his treatise on edge retention, Cliff writes:
The 420HC blade with the "Edge 2000" profile radically outperforms the BG-42 blade with the more obtuse edge profile until the blades have seriously degraded. The "Edge 2000" process was an enhancement by Buck to increase the intitial cutting ability and cutting lifetime of their knives. The exact defination is given on their website. It basically reduces the angle to 14.5 degrees per side and uses a hard cardboard wheel to replace a cloth wheel so there is less rounding or convexing of the final edge bevel. Note when all blades are given the same enhancement the BG-42 blade no longer has a significant disadvantage early and pulls ahead strongly after significant cutting.

You state that the advantage of the E2K profile is just in the profile, and that when the other blades are sharpened to the same geometry, the best steel wins out. But you complain when we sharpen all our test blades of various steels to the same geometry. Why do you have such a problem with our method?

As far as the metallurgy, and the cause for the extra performance, we're trying to determine that. The grain structure is so fine that we can't use optical metallurgy, and we haven't yet been able to develop the right specimen preparation for electron microscopy. We're working on it, and hope to have better reports out in the future.

In almost every technological advance, the advance comes before the science is fully understood. I believe there's a real advance here, and I hope to get the science there eventually.

Carl

P.S. It's just plain Carl, not Professor Sorensen, since we're not in the classroom.

 

[Kohai999]

You state that the advantage of the E2K profile is just in the profile, and that when the other blades are sharpened to the same geometry, the best steel wins out. But you complain when we sharpen all our test blades of various steels to the same geometry. Why do you have such a problem with our method?

My guess is that he is going to roll out something from Roman Landes on this one.

Best Regards,

STeven Garsson

 

[tnelson]

Broos,
No apology needed. I am just another dumb Norwegian, but I am not sure I make much sense. And Thanks to everyone else for the welcome.

Regarding the FF technology: Dr. Sorensen (Carl) and I want to get as much information/data about the technology out and available to everyone. We hope that knife enthusiasts will evaluate the data and the performance of this new technology. We also hope that people will provide us with constructive feedback and discussion.

Cliff,

I don’t know where to start: You’re a legend in your own mind. When others provide constructive criticism (also called peer review) you quickly move to discredit it before considering it.

I’m too tired tonight. So I’ll address some of the errors in your last post tomorrow.

TN

 

[Kohai999]

Cliff,

I don’t know where to start: You’re a legend in your own mind. When others provide constructive criticism (also called peer review) you quickly move to discredit it before considering it.

TN

Virtual high-five and chiclets sent!!!

You guys will drive the Dragon Cliff from the village!!!!!

Best Regards,

STeven Garsson

 

[Roman Landes]

@ppl,

The method is basically a remelting process.
These kind of processes are very well known for decades in the field laser and electro beam remelting.

The new FF process to me, offers the advantage that much more volume can be remeltet with a easy way to do it on a construction part.
Using a 3D multiple axis power unit its makes it interesting for numerous parts.

No doubt, great stuff for industrial applications! Hence I will bare it in mind for future professional applications in my work.

Basically every remelting process offers some well known and interesting opportunities.

1. Refinement of the ausgrain since the gradients for heating and cooling are nearly infinite...

2. Refinement of the carbide structure since the temperatures reach beyond liquidus and thus the distribution and the size of the carbides gets leveled out to a certain extend.

3. The amount of solved alloys are enhanced in a high saturation witch in terms of D2 enhances the corrosion resistance in the treated area.

4. High hardness can be reached since also more C gets into solution.

All together these effects make a “known steel” with elevated properties such as shown in the presentation of FF. (see chapter 3.1 in my book)

It makes it to a non-nonsense application for many interesting parts and alloys.

Of course there are some challenges.
And of course this is not a process for home use.
• The method needs a very expensive equipment usually only accessible to the industry.
• The operator needs very good knowledge of metallurgy to apply onto different steel the right method and parameters
• The process is limited to the ability to reach every corner of the part in dependence of geometry
• A counterforce is necessary against the rotating head to get the process going WO too much plastic deformation of the part
• Cost towards a industrial application might be reasonable but it is definitely beyond private use with a few parts a year, thus u have to rely on a supplier to do the stuff for you.

And for knives...

We still have a huge amount of carbides un-dissolved, but in a much more capable matrix. Not as many as S90V or S 30V witch will give him its advantage as shown.
Thus the matrix is stronger to keep the carbides there which give it of course more edge stability over conventional treated blades.
But still there are many carbides in the size of 10 to 20 times larger than AEB-L hence the tear out will be there as well, although dampened. The large carbides will still break intra crystalline just like the ATS edge shown in the book.

If one would like to compare, AEBL as one example, well treated, will still be ahead in terms of corrosion resistance, edge stability for push cutting, and durable sharpness plus, it can be purchased and treated with low budged compared to the pimped D2.
Hence, it brings already many desirable properties along with its genes.
Of course one could employ the same method on this steel to improve its properties…

One can also reach improvement with D2 by using PM. If done right carbide size can be lowered and levelled out maybe even more.
But than, you still need to have a HT, that can provide these high gradients of heating and cooling (e.g. inductive, laser, electro beam,…) to reach superfine ausgrain.

In the end its a matter of money you want to spend and what you are looking for.

Finally the remelting process and its outcomes are known for decades. The FF offers additional opportunities such as to penetrate lager sections of material with lower costs due to its simple equipment compared to the Laser and e- beams.

There is no doubt for me to pimp an steel, with remelting such as D2 is definitely beneficial towards its properties and especially for either the mechanical and corrosion side.
Although there is improvement you still have the alloy you started with and not a new steel.

Thus the right choice of the steel for the application and environment given, in combination with the proper treatments, to me, is the lever of performance I prefer for knives in a uncompromising design-to-fit-approach.

But of course if I had the opportunity, to easily access to remelting equipment I would definitely use it myself for knives.

RGDS Roman

 

[Cliff Stamp]

Why not look at the absolute amount of material cut to reach a specified level of sharpness ...

I do as noted, that is one of the two ways. However as I further noted what you get is a nonlinear curve as as responce to that criteria, it isn't a constant. The curve can also invert showing one blade is superior and then change depending on what you set the final sharpness (degredation) level. Thus you can show either blade is superior and be perfectly valid. You just have to clearly state what you are concluding/proving.

But you complain when we sharpen all our test blades of various steels to the same geometry. Why do you have such a problem with our method?

My issues was not with the geometry (that does have problems but are secondary I'll mention that shortly) but with the SHARPENING methods. As noted you can easily pick a sharpening method which favors one steel over the other. I am speaking of abrasives used, pressure, number of passes, etc. . This is why you would need to make sure the intitial sharpness was the same OR verify the reason for it not being so sharp by checking the edge under magnification. The edge will form at the 0.1 micron level so it is not difficult to resolve.

In regards to geometry. As a specific example, if you compare ATS-34 vs AEB-L with edge angles of 30 degrees then ATS-34 is superior both in the long term and short term and thus this shows that it is a superior steel for edge retention. However this is ONLY at 30 degrees. If you compare them at 10 degrees then something different happens. Thus an unbiased comparison would show that the AEB-L knife would hold a higher sharpness better at low angles and the ATS-34 would hold a higher sharpness better at high angles.

Generally you could check 10,20,30 to cover the range of steel behavior from those that have a very high edge stability (AEB-L) to those that are very low (440C/D2). This of course would be for an exhaustive report. If you wanted a particular angle for your knives you would just use that and say that for my geometry this is superior but be very careful to note the constraints of the superiority. That is unbiased reporting.

As I noted, you don't need to resolve the structure, you just need to test the physical properties. Test the edge wear resistance directly, test the edge stability directly and those would give you a solid physical basis to argue for superior edge retention. If you were going to move beyond light cutting you would do torsional/charpy impacts as well.

-Cliff

 

[cds4byu]

Roman wrote: The method is basically a remelting process.
These kind of processes are very well known for decades in the field laser and electro beam remelting.

Actually, it's not a remelting process. The steel never reaches the melting temperature during Friction Forging. This means that the cooling gradients are even higher than remelting, and there is no solidification shrinkage. The microstructure is wrought, not cast.

The alloy is still D2, but it's a non-equilibrium alloy; there's more Cr dissolved in the matrix than in traditional D2. Hence the stainless edge (and it is stainless).

It's true that the home bladesmith can't run the process in his garage or shop.

I find it interesting that you've never tested FFD2, but you're sure that well-treated AEB-L will be ahead of FFD2. Isn't this a biased position _against_ FFD2? We've put our data out, and the data was prepared in the most unbiased way we knew. Perhaps there ought to be some burden of proof on those who seek to discredit the data?

Carl

 

[cds4byu]

This is why you would need to make sure the intitial sharpness was the same OR verify the reason for it not being so sharp by checking the edge under magnification. The edge will form at the 0.1 micron level so it is not difficult to resolve.

We can examine initial edges under the microscope in the future. But we did check to see that the initial sharpness was equivalent, as measured by the REST cutting force, which appears to me to be a better standard than just looking at the burr width. But I've learned something about data you want to see, so the next time I do tests, I'll follow up.

As I noted, you don't need to resolve the structure, you just need to test the physical properties. Test the edge wear resistance directly, test the edge stability directly and those would give you a solid physical basis to argue for superior edge retention.

I thought that's what we were doing. We measured initial sharpness with the REST, then wore the blade by cutting through hemp rope, and measured edge stability by looking at the decrease in REST sharpness (or increase in REST force). That's why we're arguing for superior edge retention.

If you wanted a particular angle for your knives you would just use that and say that for my geometry this is superior but be very careful to note the constraints of the superiority. That is unbiased reporting.

OK, I'll amend our statements. For the geometry tested, FFD2 is superior. We also have anecdotal evidence that it's superior for some other geometries, but we don't have sufficient data to make that claim.

If you were going to move beyond light cutting you would do torsional/charpy impacts as well.

We can't do Charpy impacts, because the FFD2 specimens are too small. Full-size Charpy specimens are 10mmx10mm; sub-size specimens are 5mmx5mm. Our FFD2 specimens are 3mm thick as processed. If we make them bigger, we'll get different properties, because of the different quench rate in larger specimens. People who understand Charpy testing would just laugh at 3mm thick specimens.

I'm not sure what you mean by torsional impacts. We've done manual blade bend tests similar to the fallkniven test (followed the ABS journeyman bladesmith procedure). We got higher bend angles for FFD2 than for any other steel we tested. And when the blade finally broke (at an angle of about 120 degrees), there was no edge fracture or damage other than at the point where the blade broke. The edge in the bent region still shaved.

We hope to assess toughness in the future by means of a high-load indentation fracture test, which is a technique used to measure toughness of ceramic materials. We aren't sure yet if it will work, but will get more info out once we've done the test.

I keep getting accused of biased reporting, but I'm not hiding anything. I try to answer all of the questions posed, and provide whatever data I have supporting those answers. You obviously have more experience with blade sharpening than I do. I have more experience with FFD2 than you do. At what point does your insistence that our work is biased marketing hype become bias on your part? Until you've actually tested a knife with a FFD2 edge, aren't you speaking out of ignorance about its performance? I have no problem with you expressing concerns about our test procedures and asking for clarification. But it seems that you're on a mission, not to find out whether our testing procedures and results are correct, but to prove that they're incorrect. And that, to me, is a biased approach.

Carl

 

[Roman Landes]

I find it interesting that you've never tested FFD2, but you're sure that well-treated AEB-L will be ahead of FFD2. Isn't this a biased position _against_ FFD2? We've put our data out, and the data was prepared in the most unbiased way we knew. Perhaps there ought to be some burden of proof on those who seek to discredit the data?

Im not interested in promotiong steel at all, nor for any producer nor do I disregard your results if you read thorogly. I actually support your position.

The prediction vor the FFD" vs proper HT AEBL is prittey simple.

Even in maximum solution, there is not enough Cr in D2 to call it stainless, and in your pictures you show residual carbides that contain for sure considerable amounts of chrome.

Altough the carbide size is definately improved through the process, it shows no evidence that it comes near AEBL as a standard razorblade steel.

If you got time just make a simple test.

Manufactue a razorblade withwith your FFD2 and with identical geometry to the ones that you can buy from gillette or schick and compare them and you will see.

Tanks for the info.

 

[cds4byu]

Even in maximum solution, there is not enough Cr in D2 to call it stainless, and in your pictures you show residual carbides that contain for sure considerable amounts of chrome.

According to the AISI, 10.5% Cr is the minimum to call a steel stainless [1] But we call it stainless not because of its composition, but because of our tests. The edge won't etch with nitric acid. It won't pit or rust when submerged in salt solution for weeks, although the spine of the knife will. This may be partly due to galvanic action between the FFD2 and regular D2, but at any rate, the edge is truly stainless according to simple tests. More complex tests, such as EPR tests, are planned for the future.

If you got time just make a simple test.

Manufactue a razorblade withwith your FFD2 and with identical geometry to the ones that you can buy from gillette or schick and compare them and you will see.

Because I don't have the expertise to make razor blades, I'll probably not follow your proposed test. But I have requested a factory-heat-treated 3mm thick by 50mm wide blank of AEB-L from the factory, and plan to make a knife with which to compare edge holding of AEB-L and FFD2.

Thanks for the suggestions.

Carl

 

[tnelson]

Steven,

Virtual chiclets were good.

Roman,

Thanks for your thought and discussion. I agree that there are still a significant amount of carbides in the FF material, but these have been refined relative to the original base metal. D2 has sufficient Cr to be considered “stainless”. However, some of the Cr is tied up as Chromium carbides (most likely Cr23C6 type), which reduces the Cr level in the matrix rendering D2 a non-stainless steel.

During the FF process, some of the carbides (especially Cr carbide) dissolve and the Cr and C diffuse into the matrix. Under traditional heat treating practices, it would take significant time for the Cr and C to diffuse into the matrix because the diffusion distances are very large (on the order of at least ½ the grain size). However, during FF, the metal undergoes very high deformation rates at elevated temperature. The combination of high temperature and deformation continually refine the microstructure to the submicron level.

Now our hypothesis is that at grain sizes of the order of 500 nanometers or less, the diffusion distance are very short. This combined with the elevated temperature and high amount of deformation during the process increase the kinetics substantially. As a result, the Cr and C can redistribute in the austenite matrix much faster. Based on the nitric acid etching (shown on page 24 of the presentation Carl posted) and other corrosion tests we will publish later, there is good evidence the FF region is stainless.

Like I said, this is our hypothesis. It has been supported by some simplified testing and analysis. We plan to do the electron microscopy this summer to quantify the amount of Cr in the matrix, grain size and carbide redistribution and size. We will publish it later this summer.

TN

 

[gunmike1]

What was the final edge angle on the blades that were tested?

Mike

Edit to add: Has CPM D2 been tested against the FF D2? Now that Spyderco and I am sure several others are going to be putting CPM D2 out to the masses it would be interesting to see how the CPM D2 compares to the FF D2.

 

[Phil Wilson]

Carl, Could you provide more information on the CPM S90V test blade? How was it heat treated and to what hardness. I have worked (struggled) with this steel pretty much since it was first introduced and know from experience that heat treatment and hardness make difference on how this one performs. I saw a range of hardness values, 58 to 62 I think it was but not what the actual test blade was. I am guessing that hardness was probably closer to 58 since I know it is difficult to get a finished tempered hardness much over 60 on this one. Thanks, Phil

 

[cds4byu]

<Responding to Carl's comment "Why not look at the absolute amount of material cut to reach a specified level of sharpness, which is what we showed in the paper?"> I do as noted, that is one of the two ways. However as I further noted what you get is a nonlinear curve as as responce to that criteria, it isn't a constant. The curve can also invert showing one blade is superior and then change depending on what you set the final sharpness (degredation) level. Thus you can show either blade is superior and be perfectly valid. You just have to clearly state what you are concluding/proving.

I thought that we did just that. We set the final sharpness level to be a REST value of 3.0, which corresponds in our test to an approximate definintion of "loss of shaving sharpness". All of our results are based on that final sharpness level. If we weren't clear before, I hope we are now.

Carl

 

[knarfeng]

The grain size in standard hardened D2 is 5 microns, the Friction Forged D2 has a grain size of .5 microns.

Actually, it's not a remelting process. The steel never reaches the melting temperature during Friction Forging. This means that the cooling gradients are even higher than remelting, and there is no solidification shrinkage. The microstructure is wrought, not cast.

So you start with metal that has a grain size of 5 microns and are able to break the grains into pieces 1/10 the initial size by your process?

I'm not doubting. I don't know enough metallurgy to doubt. I'm just trying to understand.

Thanks

 

[Cobalt]

I think it lends a lot of credibility to this process when carl, wayne and tracy all come out and answer questions and open up their doors to whatever anyone wants to ask. This goes a long way in my book, towards the credibility of a product.

No forging process ever gets a steel back up to melting temperature as that defeats the whole purpose of forging. However, the part I am not understanding is that this seems to be more of a "Localized Forging process" not a standard forging process. Is this correct. How many annealing cycles does it take to get rid of the induced stresses from such a localized strengthening process. If the entire steel part is friction forged, then pardon my misunderstanding of the process.

 

[cds4byu]

So you start with metal that has a grain size of 5 microns and are able to break the grains into pieces 1/10 the initial size by your process?
Thanks

Yes, that's correct. The rotating tool generates frictional heat, and the material must deform to move around the pin. It's essentially a local forging process, with extremely rapid heating and cooling. The rapid heating, deformation, and cooling combine to make grains 1/10 the size of the grains in the parent metal.

Carl

 

[cds4byu]

What was the final edge angle on the blades that were tested?

I believe the angle was 20 degrees per side, but I'll have to get the formal information. I didn't do the sharpening.

Edit to add: Has CPM D2 been tested against the FF D2? Now that Spyderco and I am sure several others are going to be putting CPM D2 out to the masses it would be interesting to see how the CPM D2 compares to the FF D2.

The CPM D2 we tried was more brittle than the regular D2. But we're not experts at working with CPM D2, so we may not have got it up to the performance that you and Spyderco have been able to achieve.

In our application, we wanted the toughest material possible for the blade, and the longest-lasting, sharpest possible edge. Based on our tests to this point, regular D2 with a Friction Forged zone on the edge gives us the best results so far.

Carl