Friction Forged Blades : CATRA tests

Phil Wilson said:
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
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Phil,

We used commercial heat treaters to treat all the blades, so we probably don't know all the secret tricks for individual alloys in knife manufacturing. We heat treated according to manufacturers' recommendations.

I will obtain the specific hardness measurements for all the blades on Monday, when I'm in my office. I believe I have that data there. If not, I'll get it from the lab that did the testing, and post it when I get it.

Thanks,

Carl
 
Knarfeng,

You are correct. The original base metal has a grain size of 10-15 microns. Under the heat and plastic deformation of the FF process, the grains are subdivided multiple times. You can see this in the presentation that Carl linked on the previous page. On page 21 of the presentation you can see three micrographs taken at 1000X optical magnification. The top picture is the base metal. The large white (10-15 microns) and medium (3-7 microns) islands are chromium carbide. The small grey islands about 1-2 microns in size are most likely Vanadium carbides. These are all dispersed through out the martensite matrix (grey background). In the grey background you can see black lines which subdivide the gray background. These black line define the grain size of the matrix.

In the two figures below the base metal are photomicrographs of the FF D2 at the same magnification. In the photo on the left, you can see that the large chromium carbides (white blocky islands) have been reduced in size relative to the picture above. In this photo, the matrix grain size is now on the about 1-5 microns. In the photo on the right, the matrix grain size can no be resolved. We had to use electron microscopy (page 22 of the presentation) methods to measure this grain size.

We are able to vary the final FF grain size in the D2 by changing the process parameters. This is evident in the photos just described above. We have been successful at achieve grains size in the FF D2 ranging from 3 microns down to as small at 80 nanometers (0.08 microns).

Hope this helps.

TN
 
Cobalt,

Yes it is a "Localized" forging process producing a region about 1/2" wide. We process a blank along the location of the knife edge. Then we manufacture the knife so that the final blade edge is close to the middle of the FF zone.

We have not performed post FF process annealing. We get a little bit of in-situ annealing. All tests to date have been on as-processed blade, no annealing. Will will be investigating the value of annealing this summer.

Thanks,

TN
 
Cobalt said:
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.
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Thanks for the kind words. If some of you would like to see the process in action, I imagine we could arrange for that. I would also expect that you could observe our testing methods. Right now, however, I think the current emphasis is on production, so the testing is temporarily on the back burner.

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.
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It is a localized forging process, and there are some residual stresses left over from the process. No annealing cycles are used. The residual stresses are low enough that the blade does not distort. And the residual stresses appear to be low enough that they do not adversely affect the life of the blade.

Thanks,

Carl
 
Have you used the FF process on any other steels? How did you decide on useing D2?
 
thanks for the responses.

I am going to pull another analogy of what I have seen in differentially Ht'd 5160, 52100, O1 and D2 over many years. I do know that the knives were all high quality well made blades but they all seemed to have one common failure, except 5160. All these blades were between 1.5 inch and 2 inches wide and all were differentially Ht'd from low 40's at the spine to high 50's (56- 59) at the edge. The differential hardenning lines were noticeable and about 1/2 inch from the edge on nearly every knife. I noticed th same failure in every knife and that is while chopping wood and hitting hard spots like knots, I ended up getting a chunk missing out of the blades that was nearly half dime/nickle size and the highest point just seemed to terminate at the temper transition from the edge hardness to softer section. This lead me to believe that there was induced internal stresses that were never Ht'd out by an annealing cycle. This happened many years ago and the brands of knives is irrelevant now, but suffice to say that they were not cheap.

By contrast, I have chopped wood with swamp rats SR101, which is differentially hardenned and similar to 52100, and have had no major chipping and definitely no chunks comming off the blade. Swamp rat also used D2 and they too tested one to destruction and it never chipped along the temper line, but I do not recall if this one was differentially hardenned or not.

In any case, this is what I was wondering about, by this localized process. Not sure if the process itself gives an annealing effect, but the only way to test this is to perform an edge endurance test similar to chopping into hard woods or knots or bone. Damage will occur in any blade, but it is interesting to see what kind of damage the blade takes.

thanks for all the information.
 
db said:
Have you used the FF process on any other steels? How did you decide on useing D2?
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We've done Friction Stir Processing (which is what we call it when we're not making knives) on 304, 316, HSLA 65, X 65, HiHard Armor, and various nickel alloys.

We've tried FF on S30V, and found that the base metal was brittle enough to sometimes fracture during FF.

We tried D2 because we knew there was some extra chromium hanging around to potentially improve the properties of the FF region. We expect to do further studies with additional steels once we get FFD2 on the market.

Carl
 
Cobalt said:
The differential hardenning lines were noticeable and about 1/2 inch from the edge on nearly every knife. I noticed th same failure in every knife and that is while chopping wood and hitting hard spots like knots, I ended up getting a chunk missing out of the blades that was nearly half dime/nickle size and the highest point just seemed to terminate at the temper transition from the edge hardness to softer section. This lead me to believe that there was induced internal stresses that were never Ht'd out by an annealing cycle. This happened many years ago and the brands of knives is irrelevant now, but suffice to say that they were not cheap.
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When we made our first FFD2 blades, we went after the chop torture tests. We chopped wood, bone, antler, desert ironwood, brick, cast iron, and other knife blades.

We never observed fracture at the edge of the process zone. We did occasionally see chips in the blade, but they were far smaller in FFD2 than in any other alloy we tried.

These results weren't scientific, so we haven't included them in our paper. And I should point out that the blade geometry we had in the chop tests was more robust (thicker, and larger included angle) than in the FFD2 knives about to come out on the market.

Tracy had one of the first prototype FFD2 knives, and abused it about every way he could think of -- chopping bone, chopping wood, using it as a chisel and pounding it on the spine. He succeeded in dulling the edge when he ran it through the wood and into the concrete below. But the edge never chipped, and it's since been resharpened and is still going strong (and I'm a bit jealous, because his FFD2 knife is bigger than mine, and size matters).

Carl
 
cds4byu said:
When we made our first FFD2 blades, we went after the chop torture tests. We chopped wood, bone, antler, desert ironwood, brick, cast iron, and other knife blades.

We never observed fracture at the edge of the process zone. We did occasionally see chips in the blade, but they were far smaller in FFD2 than in any other alloy we tried.

These results weren't scientific, so we haven't included them in our paper. And I should point out that the blade geometry we had in the chop tests was more robust (thicker, and larger included angle) than in the FFD2 knives about to come out on the market.

Tracy had one of the first prototype FFD2 knives, and abused it about every way he could think of -- chopping bone, chopping wood, using it as a chisel and pounding it on the spine. He succeeded in dulling the edge when he ran it through the wood and into the concrete below. But the edge never chipped, and it's since been resharpened and is still going strong (and I'm a bit jealous, because his FFD2 knife is bigger than mine, and size matters).

Carl
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thanks
that says a lot. chipping is expected on hard items like bone etc. But serious chunks is not and it does not seem you are getting that, so it stands to reason that there are no induced stresses in the internal hardness transitions of the steel. Again thanks for the info.

Too bad you have a size complex:D
 
wouldnt it be so much easier to just buy one when the darn things come out, test it and then draw your conclusions from that?
 
severedthumbs said:
wouldnt it be so much easier to just buy one when the darn things come out, test it and then draw your conclusions from that?
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There is no substitute for that, but why not discuss what appears to be a new promising advancement in knife steel? Even more intriguing in my opinion because it is coming out of left field when compared to other previous advancements (predominantly new steel alloys).

Interesting how a process that was originated as an advancement in welding, whose main advantage was that it kept the weld area as strong (not stronger!) than the surrounding material, resulted in an advancement in knife steel at the weld. This application is far afield from the original applications.

The use of it to bend armor for use in vehicle turrets is neat - it is obvious a lot of thought has went into thinking of new ways this process (really an old process modified to be used on new materials) can improve on older technologies. Making a knife out of it had to be somewhat of an intuitive leap? Maybe while sitting in deer camp sipping a cold brew, eh?
 
Broos,

You are almost right on. The idea of applying this process to knife occurred when Charles Allen (Knives of Alaska) was paired up with Hobie Smith (Smith International) at the National Quail Congress several years ago.

TN
 
cds4byu said:
I believe the angle was 20 degrees per side, but I'll have to get the formal information. I didn't do the sharpening.
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That is pretty obtuse, it would seem to really minimize any edge stability improvements that the process adds to your steel in the comparison. Seemingly it would do better vs. the CPM steels when run more acute on all of them, so it will be interesting to see what your findings are as to exactly why the steel performs so much better than the others, especially at such an obtuse angle.


cds4byu said:
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
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I've never used CPM D2, I was just curious if you had tested it as it would also be an "improved" version of the base steel. I remember reading that Phil Wilson was working with CPM D2 in testing, and Spyderco just announced a run of knives in CPM D2, so within a few months it will be on the street. It seems like an obvious competitor, but I hadn't seen it mentioned in what I browsed through. In brittle do you mean the edge was prone to microchipping (widely complained about in S30V), the blade was subject to snapping, or both?

Mike
 
Things might have been much clearer from the beginning if you had used the proper term ,Friction Stir Processing, instead of inventing another and confusing term FF !!!
 
mete said:
Things might have been much clearer from the beginning if you had used the proper term ,Friction Stir Processing, instead of inventing another and confusing term FF !!!
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Mete,

Sorry for the confusion. We have worked with this process sooooooo long we got tired of Friction stir Welding and Friction Stir Processing terminology.

Friction Forging actually describes the process more accurately. The process is a very localized high plasticity micro forging process.

TN
 
I've been to Nelson and Sorensen's play house. They have the stuff to take all the guesswork out of testing on a scientific level.

I do it differently but get similar results with sharpness and edgeholding tests.

In order to answer some questions about blade geometry and sharpening methods I submit the following.

I specified that the cross section on the FFD2 Traditional Hunter by DiamondBlade to be as follows. The blade is 1" wide, the flat grind comes down to .015 at the edge. That is a nice thin blade for a knife intended as a hunting knife. The included angle of the blade wedge is approximately 5-degrees. I usually sharpen at 15-degrees measured from the side of the blade, that would be 17-18-degrees off of the centerline. The FFD2 test knife had the wire edge taken off with the Norton Fine India, (aluminum oxide 320 grit). The wire is taken off at an angle of approximately 30-degrees using very light abrading cuts. The land made by the stone in taking the wire edge off is an optically measured .001-.002 inch. This is the same edge I’ve used since my tests started in 1973. The test knife did 300 cuts on half-inch rope. Standard D-2, ATS34 and 154CM at 60-61Rc will do 45 in the same test.
 
Thanks for the information on your test results Wayne. I haven't used my knives yet, they are too nice.

In regards to testing: after watching your PRECISION sharpening technique last month at Tejon Ranch, I am convinced that your rope cutting test is fairly close to standardized.

Best Regards,

Tracy
 
We are in a high tech age with steel types, heat treat and all that goes into making a knife. Still, most knives being carried and used are near dull or else never as sharp as they could be. I’ve always said that a knife that is nicely made with the best steel and heat treat is no better than a ten-dollar knife from the discount store once they both get dull. I’ve taught the class you attended at the Tejon Ranch for over 30 years at knife shows. I’ve had some attend that took three or more sessions before they “got it”. I’ll be doing it in Atlanta next weekend.

My scale with the cutting platform is the low-tech equivalent of the CATRA test. Early on we decided to cut until the blade lost its bite in the rope. That was right at the point where it lost the ability to shave hair. My variance in number of cuts was right at 10%. About ten years ago I started cutting on the scale and stopped cutting at 35 lbs, that’s where the blade lost its bite. My variance went down to 5%. I like to do each blade three times and average the results.
 
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