Steel testing underway...

[TLR]

As a reference when I talked to Peter's about my cpm 3v blades they suggested I take my fixed blades to 61-62. That's what we did and I couldn't be happier to have them that hard. I have a couple of camp knives I did at that hardness and they've held up to chopping and some batonning into wood just to test them. Everything from green oak, maple and birch to dried black locust. No issues with chipping.

 

[chiral.grolim]

Assuming these blades are at least 1/8 thick, 1.25 tall and ffg to 0.013. My quick est for 50* inclusive has bevel shoulder thickness ~0.015, bevel face width ~0.0178. That's quite a lot of supporting metal behind the apex for non-chop and non-lateral/deflection impacts... my 2cents.

Yeah I agree. I've used the exact same edge geometry in the past (including during the first round of testing) and it has shown itself to be quite robust. I'm sure it could be tweaked, but I'm fairly sure that whatever issues are happening right now is quite likely to be an issue with the heat-treatment...

That IS quite robust for non-chopping. Alright, I'm convinced :thumbup:

Regarding shoulder thickness and apex support, indeed sharpening angle is key as it simply describes the thickness of the material at each point behind the apex. I ask about shoulder thickness as well, however, because even though it is so far back from the apex (certainly farther back than the damage experienced), it can still come into play in certain types of cutting since how thick the blade is can affect how much force is required to complete the cut. For example, cutting cardboard (deep cutting) is so much easier with a thinner blade; whereas a thicker blade, even sharpened to the same apex angle, will experience more stress at the apex (and faster degradation) than the thin blade because it is receiving more force (and encountering more resistance) to complete the same task.

I look forward to those images of your test edges

 

[aarongough]

As a reference when I talked to Peter's about my cpm 3v blades they suggested I take my fixed blades to 61-62. That's what we did and I couldn't be happier to have them that hard. I have a couple of camp knives I did at that hardness and they've held up to chopping and some batonning into wood just to test them. Everything from green oak, maple and birch to dried black locust. No issues with chipping.

Good to know! I thought that 59-60 sounded a little soft for a steel as tough as 3V! I'm looking forward to finding out what the current hardness is of those blades!

 

[aarongough]

That IS quite robust for non-chopping. Alright, I'm convinced :thumbup:

Regarding shoulder thickness and apex support, indeed sharpening angle is key as it simply describes the thickness of the material at each point behind the apex. I ask about shoulder thickness as well, however, because even though it is so far back from the apex (certainly farther back than the damage experienced), it can still come into play in certain types of cutting since how thick the blade is can affect how much force is required to complete the cut. For example, cutting cardboard (deep cutting) is so much easier with a thinner blade; whereas a thicker blade, even sharpened to the same apex angle, will experience more stress at the apex (and faster degradation) than the thin blade because it is receiving more force (and encountering more resistance) to complete the same task.

I look forward to those images of your test edges

I appreciate your input mate! It's always good to have a few sanity checks to make sure I'm not headed off into the woods!

 

[Andy Lewis]

...For example, cutting cardboard (deep cutting) is so much easier with a thinner blade; whereas a thicker blade, even sharpened to the same apex angle, will experience more stress at the apex (and faster degradation) than the thin blade because it is receiving more force (and encountering more resistance) to complete the same task.

Pardon me for saying, but that is simply nonsense.

No squabble that thin blades are generally expected to out cut thicker blades, at a given bevel angle. But that is because the cutting resistance is influenced more by wedging, material displacement, friction, etc. (i.e. what follows the edge, not increased resistance to the cutting edge itself).

For cutting soft materials like cardboard, shoulder thickness behind the edge/apex, at any given bevel angle, has little to do with edge stability IMHO - except possibly with bad technique while using very thin blades (a different problem not relevant to this discussion).

Can I ask why you think this is true? What am I missing here?

 

[aarongough]

Pardon me for saying, but that is simply nonsense.

No squabble that thin blades are generally expected to out cut thicker blades, at a given bevel angle. But that is because the cutting resistance is influenced more by wedging, material displacement, friction, etc. (i.e. what follows the edge, not increased resistance to the cutting edge itself).

For cutting soft materials like cardboard, shoulder thickness behind the edge/apex, at any given bevel angle, has little to do with edge stability IMHO - except possibly with bad technique while using very thin blades (a different problem not relevant to this discussion).

Can I ask why you think this is true? What am I missing here?

Yes, as I said earlier I believe that edge stability on a micro scale is largely down to sharpening angle and steel strength. On a macro level (think big visible chips out of the blade edge) then the primary factors are the thickness of the bevel and the strength of the steel.

I'm using 'strength' here to loosely refer to the combination fo hardness and toughness that a given steel provides. ie: when the steel is hard but not tough it will chip without flexing, when it is hard and tough it will flex, then roll, then chip. When it is tough but not hard it will flex and roll without chipping.

 

[chiral.grolim]

Pardon me for saying, but that is simply nonsense.

No squabble that thin blades are generally expected to out cut thicker blades, at a given bevel angle. But that is because the cutting resistance is influenced more by wedging, material displacement, friction, etc. (i.e. what follows the edge, not increased resistance to the cutting edge itself).

For cutting soft materials like cardboard, shoulder thickness behind the edge/apex, at any given bevel angle, has little to do with edge stability IMHO - except possibly with bad technique while using very thin blades (a different problem not relevant to this discussion).

Can I ask why you think this is true? What am I missing here?

This is off-topic, but I'll endeavor to explain:

Again, "because it is receiving more force (and encountering more resistance) to complete the same task." I should add, "in the same amount of time". Friction and the wedging-effect demand that the user input much more force to the cut which, while it is somewhat distributed along the bevel face, is concentrated at the apex by design. Keep in mind that the apex is part of each bevel face. The resistance experienced by the bevel faces is also experienced at the edge itself. A stable apex has thickness (diameter, sometimes larger than 10 um due to grain size) - it rubs against the material being cut along both its sides and its face doing the cutting. The identical apex-angles face the same amount of resistance at the apex, but the user is putting much more force into cutting with the thicker blade. Does all of this energy only go into the thicker portion behind the apex? On a fast cut, thicker blades generates more frictional heat, and this reaches the apex by conduction. What if the blade slips within the medium or what about after the apex exits the medium but the blade is still passing through? Every apex-impact even with only the minute abrasive particles which may be present in the medium causing wear, or with a surface behind the medium, is magnified by the acceleration. What if the user twists slightly (as is apt to happen to most any user, especially when using considerable force)? Again, the apex experiences this. As a result of thickness behind the apex, compression and fracture at the apex increase.

I am not saying that the coefficient of cutting-resistance of the medium increases, but that not all of the extra force required to complete the cut with the thicker blade is absorbed by the areas of wedging that demanded the increased force to begin with. In my experience, increased force = increased rate of degradation at an apex of the same angle.

Is this really nonsense? I am open to correction. Or perhaps we should just drop it and get back on topic?

 

[tmanifold]

This is off-topic, but I'll endeavor to explain:
Etc, etc, etc

Is this really nonsense? I am open to correction. Or perhaps we should just drop it and get back on topic?

That was an awesome post and I would love to see more discussion on it. If nothing else it might help people choose blade thickness for task specific knives in a more informed way.

However, it could easily clog up this thread. Maybe a mod could split it?

Regardless, thanks it was incredibly informative.

 

[aarongough]

It's clear you've put a lot of thought into this!

I'd definitely like to delve into that more, but I think another thread would be the place to do it if that's ok! Feel free to post a link to the thread here as a way to tie-off the conversation in this thread.

 

[aarongough]

Ok! So first batch of images from the microscope. Not the sharpest images ever, but they serve the purpose!

Here is the A2 blade from the first batch after sharpening and stropping:

Here is the A2 blade from the second batch after the same sharpening and stropping regime:

You can see that the blade from the second batch with the modified heat treat definitely took a finer edge.

--------------------------

Here is the A2 blade from the first batch after doing 100 cuts through 1/4" sisal rope (edge):

Here is the A2 blade from the second batch after 100 cuts through 1/4" sisal rope (edge):

You can see that the edge on the second blade has deteriorated a little more, although it's done so more consistently.


Here is the A2 blade from the first batch after doing 100 cuts through 1/4" sisal rope (side):

^ Note the slight deformation in the edge

Here is the A2 blade from the second batch after 100 cuts through 1/4" sisal rope (view):

^ No noticeable deformation

-----

Thoughts & conclusions: it seems that my 'feeling' that fine edge retention had gone down in the second batch is likely right. The light reflected from the edges gives us a rough idea of how wide the edge has become. We don't have enough magnification to see exactly what the failure mechanism is though unfortunately. My feeling while testing was that this deterioration happened pretty quickly.

I'm curious about whether the deterioration is going to plateau though. You can see that while the edge from the second batch has deteriorated slightly more, it hasn't deformed as much...

I'm going to do a comparison between the two blades now cutting cardboard and see what the difference is like. This test should push them both to the limits of what they're capable of...

-----

In order to get the A2 blade out of the current batch of test blades without compromising the test I covered the number of each blade with tape, and then pulled aside the tape that covered the steel identifying engraving. Once I re-tape and shuffle them I will no longer know which is which...

 

[BluntCut MetalWorks]

please bluntly tell/correct me if I goof :foot:

1. There seem to be burr on batch1 edge.
These sizable burr probably get sheared off by sisal.

2. Batch2 edge has a wire-edge.
Sisal first rolled the edge, then subsequence impacts flattened the apex. I don't see many holes (micro-chip) on the edge but a lot of reflection, which indicate rounded apex.
A quick test for wire-edge: slice newsprint (even printer paper), after 5+ slices, if the edge catches - voi'la wire-edge.

 

[aarongough]

please bluntly tell/correct me if I goof :foot:

1. There seem to be burr on batch1 edge.
These sizable burr probably get sheared off by sisal.

2. Batch2 edge has a wire-edge.
Sisal first rolled the edge, then subsequence impacts flattened the apex. I don't see many holes (micro-chip) on the edge but a lot of reflection, which indicate rounded apex.
A quick test for wire-edge: slice newsprint (even printer paper), after 5+ slices, if the edge catches - voi'la wire-edge.

Honestly I don't really have enough information to say exactly what the failure mechanism was in the second blade. The first one is clearly starting to roll/tear.

I will say though that I viewed the edge on both blades from both sides and I didn't see any real folds or rolling apart from the small ones apparent in the photos of the first blade. I don't think a wire edge was the culprit, but I simply don't have the magnification to say that definitively unfortunately...

 

[Azcountryman]

Cant see any photos but I m on my work computer so maybe they will show up at home. Will also look for your youtube channel later.Interested to see your testing. I just noticed your in Canada and I m in the USA but I have access to a RC tester and a Oxford X-MET 5100 for checking chemical make up of steels. If you cant find anything local you can send me a piece of steel or a jacked up blade and I would gladly run the test on them for you.

 

[aarongough]

Cant see any photos but I m on my work computer so maybe they will show up at home. Will also look for your youtube channel later.Interested to see your testing. I just noticed your in Canada and I m in the USA but I have access to a RC tester and a Oxford X-MET 5100 for checking chemical make up of steels. If you cant find anything local you can send me a piece of steel or a jacked up blade and I would gladly run the test on them for you.

I think I'll be getting a hardness tester tomorrow morning actually! Kind of expensive, but also exciting!

Very interested in the idea of the alloy tester though! Might have to send the whole batch off to you after the testing for that extra datapoint!

 

[Azcountryman]

I think I'll be getting a hardness tester tomorrow morning actually! Kind of expensive, but also exciting!

Very interested in the idea of the alloy tester though! Might have to send the whole batch off to you after the testing for that extra datapoint!

Very cool. They are fun. Going to find yourself testing everything you can grab. Not sure what tip you will be using but we use a diamond tip and depending on how hard your steel is you could smash it. Done that a few times.
Yeah just let me know if you want the chemical test done. Love zapping stuff on my down time. Mostly ancient coins and what not.

 

[aarongough]

So, I just finished cutting up over 500 feet of cardboard with the two blades in question.

A2 batch 1 (test blade #2) after cutting 260' of cardboard (side):

A2 batch 2 after cutting 260' of cardboard (side):

-----

A2 batch 1 (test blade #2) after cutting 260' of cardboard (edge):

A2 batch 2 after cutting 260' of cardboard (edge):

After the test I would consider both blades to be extremely dull. Neither were capable of cleanly cutting notebook paper, let alone shaving. During the test I didn't really notice any difference in terms of how fast they broke down...

I tried stropping both blades (all my stropping is done without abrasives btw) to see if either edge would bounce back. Neither one di though, they're both in dire need of resharpening.

Given the results so far I would probably take the blade from batch #1 personally, as it holds a fine edge a bit longer than the blade from batch #2.

Very interesting and fun results! I'll be interested to find out what the difference in hardness is between the two blades...

 

[BluntCut MetalWorks]

Honestly I don't really have enough information to say exactly what the failure mechanism was in the second blade. The first one is clearly starting to roll/tear.

I will say though that I viewed the edge on both blades from both sides and I didn't see any real folds or rolling apart from the small ones apparent in the photos of the first blade. I don't think a wire edge was the culprit, but I simply don't have the magnification to say that definitively unfortunately...

You probably right, I am just exploring...

It could be batch2 stropped edge was too fine/delicate for sisal cutting. Ankerson's manila rope cutting shown that coarse edge performed much better than highly refined edge. http://www.bladeforums.com/forums/s...based-on-Edge-Retention-cutting-5-8-quot-rope
If you don't mind, please test batch2 edge off 600 grit without stropping.

btw - clean 600 grit & stropped edge micrographs (see post #122, then #119) http://www.bladeforums.com/forums/showthread.php/1036649-A-balanced-strop?p=12608140#post12608140. Highly refined edges off post #119 won't do well in sisal rope cut test.

edit: thanks for clarified stropping w/o compound. lol - lurk mode, I'll go...

 

[aarongough]

You probably right, I am just exploring...

It could be batch2 stropped edge was too fine/delicate for sisal cutting. Ankerson's manila rope cutting shown that coarse edge performed much better than highly refined edge. http://www.bladeforums.com/forums/s...based-on-Edge-Retention-cutting-5-8-quot-rope
If you don't mind, please test batch2 edge off 600 grit without stropping.

btw - clean 600 grit & stropped edge micrographs (see post #122, then #119) http://www.bladeforums.com/forums/showthread.php/1036649-A-balanced-strop?p=12608140#post12608140. Highly refined edges off post #119 won't do well in sisal rope cut test.

Very nice images those! I wish my little microscope was capable of that!

The edge being too fine is for sure a possibility. If I get time I will test that tomorrow.

I'm about to head home, but my plan for tomorrow is to get the hardness tester, then test every blade from both batches and see what's what (after doing a bunch of practice tests of course!)...

My plan is to wrap up this testing this weekend so that I can get back to making knives. If anyone has any requests please let them be know tomorrow before I break the blades on Saturday night!

 

[aarongough]

Well, the new toy is in the shop. Now I just have to get it all setup, hopefully that won't take too long (though the not exactly stellar manual won't be much help!)

 

[aarongough]

So today I got the hardness tester setup and managed to test all the blades! It was very illuminating in at least one case, you'll see why shortly.

First, a disclaimer about these numbers: the hardness tester I just bought is consistently reading 2.5 points low. I tested it with high and medium hardness HRC standards that it came with and the result was about the same on each, 2.5 points low. I haven't worked out quite how to calibrate this error out yet (big surprise that the manual is no help) so I've done all the tests with the tester as-is. The numbers below are the numbers from the tester PLUS 2.5 POINTS to approximately calibrate it with what it should be reading. The actual numbers straight from the tester are included in parentheses next to each result. I know this is not ideal, I'll work out how to calibrate it and re-do this shortly, in the meantime it at least gives us a comparison between the blades.

Each blade was tested on the tang, as close to the ricasso as I could get. The tang of each blade was ground to 120 grit on the belt-grinder before running the tests to make sure the surface finish and decarb did not cause problems. Each blade was tested 4 times, each test was about 1/8" apart. The first result was thrown out, then the other 3 results were averaged to give the numbers below:

Batch 1:

[FONT=Courier New]
Steel     Compensated HRC   (Uncompensated HRC)
-----------------------------------------------
440C      59.1 HRC          (56.6 HRC)
O1 kiln   60.6 HRC          (58.1 HRC)
CPM154    59.6 HRC          (57.1 HRC)
A2        59.5 HRC          (57.0 HRC)
CPM3V     61.1 HRC          (58.6 HRC)
O1 forge  --------          ----------    (tang of blade was soft)
[/FONT]

Batch 2:

[FONT=Courier New]
Steel     Compensated HRC   (Uncompensated HRC)   Hardness gain
---------------------------------------------------------------
440C      60.0 HRC          (57.5 HRC)            +0.9 HRC
O1        61.8 HRC          (59.3 HRC)            +1.2 HRC
CPM154    62.0 HRC          (59.5 HRC)            +2.4 HRC
A2 (#1)   63.3 HRC          (60.8 HRC)            +3.8 HRC
A2 (#2)   64.6 HRC          (62.1 HRC)            (n/a because tempered lower at 360ºF)
CPM3V     60.5 HRC          (58.0 HRC)            -0.6 HRC
[/FONT]

So, a couple of interesting things come from this:

1) We've definitely seen hardness gains with our optimized heat-treats (except for CPM3V) and that is likely a result of decreased levels of retained austenite as was the goal. Many of the blades have ended up too hard because of this though and should likely be tempered back a point or two.

2) Turns out that I mixed up my A2 blades. I had two blades, one of which was tempered at 360ºF and the other was tempered at 400ºF. I must have accidentally mixed those two up though because when I was testing the A2 blades yesterday I thought I was testing the blade from batch 1 against the SOFTER of the two new blades. It interesting to see that the harder blade did not have better edge retention, in my opinion it was actually worse!

3) Because we've managed to (hopefully) produce lower levels of retained austenite in these blades, we should be able to temper them a bit higher and get equivalent hardness to batch one along with increased toughness! (correct me if I'm wrong-headed here!)

I think overall it's good things all round from this. I don't think there's any issues with the heat-treat on these blades apart from the fact that the tempers need to be adjusted a little. Here's the plan:

O1 -> Temper to ~59HRC, this is because O1 at 60HRC in the first test was not tough enough.
440C -> Temper to ~59HRC, let's see how much extra toughness less retained austenite will get us!
CPM154 -> Temper to ~60.5HRC, last time CPM154 was reasonably tough, but didn't do so well in edge retention... I'd like to see what an extra point gets us.
A2 (#1) -> Temper to ~62HRC, 2 points harder than batch #1, just because I want a nice spread of hardnesses for A2.
A2 (#2) -> Temper to ~61HRC, 1 point harder than batch #1, but hopefully also just as tough with the improved heat-treat.
CPM3V -> Leave as is. It needs all the hardness it can get!

Any thoughts and ideas welcomed!

If you know how to calibrate my hardness tester please PM me! It's the same as the Grizzly one.