I Tested the Edge Retention of 48 Steels

Larrin Larrin what's the deal with the toughness rating on m390/20cv/204p? In older articles it was up about 10, but now it's down around 5. Do you have an article about the update in toughness results? I dug around but couldn't find anything.
 
metaphoricalsimile said:
Larrin Larrin what's the deal with the toughness rating on m390/20cv/204p? In older articles it was up about 10, but now it's down around 5. Do you have an article about the update in toughness results? I dug around but couldn't find anything.
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This article talks about the changes to the toughness for m390.

knifesteelnerds.com

M390 Steel - History and Properties (and 20CV and 204P) - Knife Steel Nerds

M390 has become a very popular knife steel over the past few years. How was the steel developed? How do its properties compare?
knifesteelnerds.com knifesteelnerds.com
 
Zeunerite said:
My point is that with many people using CATRA to judge edge retention, LC200N does well to keep up with some higher end steels in rope cutting without having to rely on hardness or abrasion resistance.
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If they can sharpen it better it starts further from dull so it cuts longer.

That's what could happen when edge geometry and initial sharpeness are not being ruled out.

If we fix the angles at 15dps and start with the same sharpness and do an average of tests.

We see steels fall more inline with the hardness, carbide type and volume.
 
Larrin said:
Recently I was able to acquire a used CATRA machine, so I heat treated just about every knife steel I had, made 57 knives with the help of knifemaker Shawn Houston, and tested them all to see which cut the longest. For a few of the steels I did multiple heat treatments to look at a couple variables and to see the effect of hardness. I also compared edge retention and toughness to see which steels have the best balance of properties. https://knifesteelnerds.com/2020/05/01/testing-the-edge-retention-of-48-knife-steels/
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Thanks for all your hard work! I bought a copy of your book, but haven't started reading it yet. Being more than 400 pages it will be the thickest book i will read since college days, not counting my current book, the Bible.
 
Larrin, excellent testing, also ordered your book, as I am sure it is a good read.

Did I read correctly that the blade profile was 3dps and the edge was 15dps? Also how thick were the samples, 1/8"? Tried reading through everything this morning.

Was the cryo done as part of the HT continuously and not after the HT was done? It appears that's the case when I read it, but verifying.
 
Cobalt said:
Larrin, excellent testing, also ordered your book, as I am sure it is a good read.

Did I read correctly that the blade profile was 3dps and the edge was 15dps? Also how thick were the samples, 1/8"? Tried reading through everything this morning.

Was the cryo done as part of the HT continuously and not after the HT was done? It appears that's the case when I read it, but verifying.
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Here's a video of how I sharpened them.
 
Cobalt said:
Larrin, excellent testing, also ordered your book, as I am sure it is a good read.

Did I read correctly that the blade profile was 3dps and the edge was 15dps? Also how thick were the samples, 1/8"? Tried reading through everything this morning.

Was the cryo done as part of the HT continuously and not after the HT was done? It appears that's the case when I read it, but verifying.
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Yes 3 dps and yes 15 dps. The majority were 1/8” though a few were thinner. The constant primary and secondary grind was selected so that the stock thickness differences are irrelevant.

Yes cryo was done directly after the quench. I’ve never performed cryo in any other way, for the reasons given in my cryo articles.
 
DeadboxHero said:
If they can sharpen it better it starts further from dull so it cuts longer.
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If that were the case then many of the other low carbide steels would also perform better than expected.

Comparing S30V to LC200N paired up by sharpener used, edge angle, and final finishing.
Spyderco heat treat S30V at 59-60rc and LC200N at 57-58
Benchmade S30V is at 57.7
JhwC8Lx.png

These numbers seem fairly consistent but if there's something else I'm missing please let me know because they don't seem wrong to me.
The rope used is twisted sisal twine which is barely abrasive. During cutting most of the fibers will naturally be at an off angle relative to the edge no matter how you cut it and cause repeated lateral stresses.
LC200N having a much higher toughness would definitely help out to resist fatigue here.
 
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Zeunerite said:
If that were the case then many of the other low carbide steels would also perform better than expected.

Comparing S30V to LC200N paired up by sharpener used, edge angle, and final finishing.
Spyderco heat treat S30V at 59-60rc and LC200N at 57-58
Benchmade S30V is at 57.7
JhwC8Lx.png

These numbers seem fairly consistent but if there's something else I'm missing please let me know because they don't seem wrong to me.
The rope used is twisted sisal twine which is barely abrasive. During cutting most of the fibers will naturally be at an off angle relative to the edge no matter how you cut it and cause repeated lateral stresses.
LC200N having a much higher toughness would definitely help out to resist fatigue here.
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It's not just low Carbide volume, there are other variables, that's why I said "whatever can be sharpened better" not specifically low carbide volume etc.
 
Larrin said:
Yes cryo was done directly after the quench. I’ve never performed cryo in any other way, for the reasons given in my cryo articles.
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I figured you were doing it the correct way, but in some other industries the after the fact cryo gets more credit than it deserves.
 
Larrin - you mentioned earlier in this thread that refining grain by going above and below critical in cycles works. Do you know if anything useful happens in plain steels if steel is heated (quick, in a forge) subcritical (red, but never nonmagnetic) and then quenched, and then followed by a typical higher temp heat and quench? Will that refine grain size or is it likely doing nothing?

(this question has to do with trying to cheat and improve toughness without propagating iron carbides that don't later get dissolved - 26c3 in this case).
 
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D-weaver said:
Larrin - you mentioned earlier in this thread that refining grain by going above and below critical in cycles works. Do you know if anything useful happens in plain steels if steel is heated (quick, in a forge) subcritical (red, but never nonmagnetic) and then quenched, and then followed by a typical higher temp heat and quench? Will that refine grain size or is it likely doing nothing?

(this question has to do with trying to cheat and improve toughness without propagating iron carbides that don't later get dissolved - 26c3 in this case).
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Heating above critical means you are forming a new set of austenite grains and then cooling to form pearlite. It is the rapid formation of new grains which helps to refine grain. If heating below transformation you are not forming new grains. You may be affecting the carbide structure which can have an indirect effect on the final heat treated grain size but it’s not the same thing.
 
Your research is more impressive than watching Joey Chesnut devour hot dogs on July 4th... Thanks!
(and it didn't even make me nauseous!)
 
I do want to thank you for adding rigor, to knife edge sharpness and endurance, to what was previously nothing more than ignorance and superstition.

I remember the days when blade steels were described as “Solingen Steel”, Surgical Steel”, or a meaningless brand name such as “Queen Steel”. The consumer was ill informed, and that was the way industry liked it.

Buyer awareness of steels finally got D2 steel in customary folders. Too bad Queen went away, this has D2 blades.

iI1ru48.jpg


We have it so much better today, and your work has done a great job of educating the vast unwashed.

Personally, I am quite happy with the steels on Case knives, what ever they may be, and inexpensive D2 knives. I am a buyer around $50 to $70, but unwilling to pay more, as I lose things! Ultimate knife edge holding is not as important as restoring an edge quickly. With over a half century of free hand sharpening, while I cannot beat the edge fixtures can produce, my edges will slice Roma tomatoes. The Roma tomato slice is my standard for sharpness.

I have ordered your book today, I know I will be happy.
 
Larrin said:
Heating above critical means you are forming a new set of austenite grains and then cooling to form pearlite. It is the rapid formation of new grains which helps to refine grain. If heating below transformation you are not forming new grains. You may be affecting the carbide structure which can have an indirect effect on the final heat treated grain size but it’s not the same thing.
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I think I'm in need of an etchant. I've been advised by a chemist (I'm not the careless type, but I know there are plenty who are, so I understand the lack of availability and precautions) what the issues would be with nitric acid and methanol. that said, can you recommend any supply places in pittsburgh that would sell nital to someone off of the street? Doesn't need to be provided in a public response.

I've done a couple of samples of 1095 - these are hammered to shape by me then, ground, then heat treated in a simple small can forge, and then compared 1095 to a commercial file (they usually have nice fine grain that can be hard to match - I don't have a commercial 1095 sample to compare).

This is the file (as a starter for seeing relative grain size - the picture are optical around 50-75x (the hand scope makes fantastic claims, but the magnification is probably closer to the range I'm guessing)
https://imgur.com/CgnLghi

This what 1095 looks like if it's heated above critical (but just barely) and cycled to black in air and then cycled to room temp on the third cycle and heated (never getting more than barely above nonmagnetic - no bright oranges or anything involved after shaping is done).
https://imgur.com/XcQqRj2

This is 1095 after the cycle of "not hotter than magnetic but close" heating mentioned above.
https://imgur.com/fAEI7Xk

(by the way, I do have a proper budget metallurgical scope, but these irregular broken pieces are a no go as it's only good with dead flat surfaces vs. irregular broken-off bits)

both 1095 samples are untempered - they were cut from adjacent spots in the same piece of stock (after it was hammered to shape to become a chisel blank), just quenched in parks50, then transferred to icewater quickly and then put into the freezer. I don't have a hardness tester, but nothing above is close to being fileable.

The sample with the tiny grain is harder to break off in a vise. And separately, for confirmation, I have no furnace, so nothing is normalized - just heated to nonmagnetic, then "some more after that" and then quenched.

26c3 sees similar improvement, though there are little tiny black dots dispersed in the optical sample, which I'm assuming are carbon.

I have never done anything like this previously and have a metallurgical scope to grade sharpening stones by the edge they leave on a razor.

I *think* I'm inadvertently thermal cycling even though the steel samples are quenched in each cycle just before they would (by eye in dim light, and confirmed with a magnet) lose magnetism. The interim quenches are just done by a couple of dips in parks 50 (not fully to room temp).

I don't believe the file is a fair comparison to 1095 as I'm sure it has excess stuff in it, but it's my hurdle quenching in the shop at this point as in the past, I could break samples and tell by naked eye view that my attempts were far more coarse.

(I joined your patreon in exchange for being a nuisance)
 
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apologies that the picture show up - I tried to post them as small non-intrusive links so that not everyone would be bombarded with them, but the forum software appears to have other ideas.
 
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