I Tested the Edge Retention of 48 Steels

Larrin

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I feel that some context is important here. There is no improvement to edge retention shown in CATRA testings, but in something like rope cutting tests PM steels do tend to perform much better than their non-PM counterparts.
Ok link us to the context.
 
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I searched for a comparison of 154CM and CPM154 for the same knife model (in order to have the same approximate grind, edge and angle) but found nothing on your link. If you filter for 154CM and CPM154 you only find that Pete tested different models with different edge angles :
57GRGNmh.png


I think you cannot compare steels if the grind, edge and angle are not exactly the same.
That's why the tests performed by Larrin on standardized knives are so valuable.
 
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Yeah, I really should have checked beforehand if it had any good comparisons before I said anything.
The best example I could find in it is CTS 40CP vs 440C, same sharpener and edge angle used but no mention of hardness.
I'm thinking that maybe hardness isn't enough to explain the huge difference in there.
HD25FHW.png
 

Larrin

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Yeah, I really should have checked beforehand if it had any good comparisons before I said anything.
The best example I could find in it is CTS 40CP vs 440C, same sharpener and edge angle used but no mention of hardness.
I'm thinking that maybe hardness isn't enough to explain the huge difference in there.
HD25FHW.png
On the contrary those results are so far apart they are unlikely to be explained by the PM difference. Phil Wilson in his rope cutting has not found a difference between 154CM and CPM-154. Some makers that prefer D2 over CPM-D2 will even argue that the larger carbides make it cut more aggressively. On balance I think the safest conclusion is that there is no difference when cutting rope or in CATRA.
 
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I searched for a comparison of 154CM and CPM154 for the same knife model (in order to have the same approximate grind, edge and angle) but found nothing on your link. If you filter for 154CM and CPM154 you only find that Pete tested different models with different edge angles :
57GRGNmh.png


I think you cannot compare steels if the grind, edge and angle are not exactly the same.
That's why the tests performed by Larrin on standardized knives are so valuable.


quite fair
 
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Larrin - I have a question as it relates to this testing as we scalp some of your results for ideas in woodworking. The question is this, what are we missing in woodworking in terms of communicating fine edge holding.

For example, 3V is high toughness, and at 61 hardness, the edge gets a little stronger but at the expense of toughness. In woodworking, we hate folding edges even if they don't fail, so lower hardness and high toughness is out. But as we move toward higher ranges in tests that involve malleting chisels, etc, steel that's reportedly very low toughness ends up faring very well - like white steel, etc. At high hardness, those steels seem to have better fine edge holding and they hold up very well in a chisel test as long as they're not overhard (and that's a close tipping point if people are pushing the limits, but let's assume 65 hardness with white 2 and good edge behavior).

Is there any kind of documented measure for fine edge holding of this type? I use the term strength, but not sure what type of "strength".

this type of strength also makes a wonderful straight razor whereas something higher in toughness but slightly lower in hardness won't shave as well (I saw your article about dirtiness of razors often leading to dullness feeling, etc, but set that aside as it's not an issue with straight razors - they're wiped off and the strop gets rid of it. When I've had lower steel razors, the edges deflect more and getting a really strong fine edge requires adjusting geometry, which is at odds with the shave).

primary question, though - what is a measure of the edge holding ability, especially in regard to linear pounding (no twisting, etc) such that a steel that supposedly has a toughness of 5 ft pounds beats a much tougher steel only a few points softer.
 

Larrin

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It all depends on your failure mode. If you are losing your edge to deformation then you need more strength. Either higher hardness steel or a more obtuse edge. If you are losing your edge to wear you need more wear resistance. If your edge is chipping you need more toughness. Edges can of course see mixed modes where you want a combination of strength, toughness, wear resistance, and corrosion resistance.
 
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It all depends on your failure mode. If you are losing your edge to deformation then you need more strength. Either higher hardness steel or a more obtuse edge. If you are losing your edge to wear you need more wear resistance. If your edge is chipping you need more toughness. Edges can of course see mixed modes where you want a combination of strength, toughness, wear resistance, and corrosion resistance.

is it fair to say that some steels will have higher tested toughness at a given hardness and still fail at the fine edge? I *think* that what I accounting for is that above a certain level in woodworking, our cuts are fairly controlled and we don't do things that introduce relatively random or varying forces. Chisels are used mostly straight in, and plane irons are used without battering them, occasionally running into something that would test strength or toughness (knots or dirt or silica in wood). I'm curious as another more academic fan than me is asking if my comments about fine edge holding and "strength" in regard to things that make razor steels hold a fine edge are an attempt to make up a new type of measurement (as in "make up hot air"). I'm also curious as I've started making chisels at a high level, why I prefer things like file steel (which is probably 1.1-1.2 carbon steel, but otherwise fairly plain) - I like it because it can attain high hardness and hold up well, but it's fair to say also that abuse levering, etc, can cause edge failure.

Strength is the term that I use for the fine edge to not be moved easily, as in, I think I'm chasing strength with enough toughness rather than high toughness with strength just over the bar. And the enough toughness doesn't need to be much. And that there's a fairly simple other issue that you outlined well with blue steel (which I've seen in tools) that if you add random large carbides, it can confuse the issue a bit by making fine edge holding poor due to evacuating carbides.

I saw a chart that showed "strength" measures with a ductile steel and one considered "brittle". the latter meets the level where it deforms permanently and then fails quickly, the former may meet the point where it deforms a little more easily, but then has a long range of deformation before it fails. In woodworking, we would prefer whichever one deforms or chips least easily because folding or chipping- either requires resharpening.

One final question about AEB-L in this context - it may be outside of your wheelhouse. If AEB-L can hit 63/64 hardness and still be usable, would your expectation be that its fine edge holding in something like cardboard slicing or shaving would be as good as 26c3? Subjectively, with lower carbon, I would expect the razor edge to fail first in AEB-L, even though it's the same hardness and probably would attain a higher toughness measure. This is on a sliding scale, as AEB-L would dominate this test vs. something with coarser grain, but when I make chisels that are at a hardness where both should work well, the higher carbon of the two seems to do better with initial edge behavior - once it's worn off, then both are the same.
 

Larrin

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Strength is a term used in materials science. Yield strength and ultimate tensile strength are very common measures of strength, generally measured in the same test (tensile test). Strength can also be measured in compression. Hardness correlates with ultimate strength. Yield strength is resistance to deformation. If you have deformed an edge you have exceeeded its yield strength.
 
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Thanks. I think it's yield strength that I'm banking on, and am guessing just based on experience with things that the correlation of hardness is long proven (as you mention) but that there may be small variations in results based on alloy that seemingly cause hard higher-carbon steels to hold a fine edge really well. May aim is just figuring out what I'm seeing with chisels (as I'm forging them and making them). AEB-L is off limits as a trial at this point because I'd need it in thicker sections and would have to send it out for heat treat.

I have zero interest in being a fanatic who is looking to "discover" something, but more looking to explain what I'm seeing, and some could be my failure as a maker to do each simple steel as well, and there are outliers. 1084 plane irons worked great. 1095 are chippy. O1 and 52100 are great without overcomplicating things. All are about the same hardness. Same with chisels - all of those are great, but 1095 (from a different supplier and after attaining a very high quench hardness - chippy compared to the others).

Thanks to your book and your articles, I'm going to give 26c3 a whirl to see how it turns out. Historically, something more like silver steel in the 1% carbon range would've been used for chisels, and maybe before that, ore that had a favorable addition without knowing why (e.g., sheffield using continental european or swedish ore that may have had nickel in it). Going to the trouble to actually make things, and comparing your data to what I've seen in more rudimentary testing is very helpful and 26c3 will be an interesting trial to get this "fine edge" jones that files provide without having to constantly search for the right thick files to hot shape/thermal cycle and then finish grind and reharden. What's puzzling me is the ability of the steels like the file steels and the white steel to be able to hold up well at higher hardness where something like O1 will attain the hardness, but won't perform well until it's tempered back further (or in short, the files and white steel are better in a chisel at really high hardness - and the fine edge holding is better at high hardness).

Thanks again.
 

Larrin

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We did a new set of edge retention tests on a range of high speed and stainless steels including Rex 45, Rex 76, CPM-T15, SPY27, XHP, and 420. We also did toughness tests on several of those steels that we had not yet been tested. And we redid our Rex 121 knife with a new heat treatment that was much easier to sharpen so it got a significantly higher score. https://knifesteelnerds.com/2021/05...eels-xhp-spy27-maxamet-rex-45-420-t15-rex-76/
 

Blues

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Great addition, Larrin Larrin .

The charts are particularly instructive, (I was happy to see how well CPM Cru-Wear continues to hold up), and impressed by how well balanced your MagnaCut is proving.

I'll look forward to the opportunity to get a knife or two with it.
 

Easyrider

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I finally read your article/paper on your testing of the 48 different steels after looking at the title long enough. I must say it was both a pleasure and incredibly informative to read! I learned a lot in the process.
Thank you very much for doing the tests and posting the results of your research. :cool::cool::cool:
 
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We did a new set of edge retention tests on a range of high speed and stainless steels including Rex 45, Rex 76, CPM-T15, SPY27, XHP, and 420. We also did toughness tests on several of those steels that we had not yet been tested. And we redid our Rex 121 knife with a new heat treatment that was much easier to sharpen so it got a significantly higher score. https://knifesteelnerds.com/2021/05...eels-xhp-spy27-maxamet-rex-45-420-t15-rex-76/

Excellent information! Two questions:

1) I see that K390 has a CATRA result, but no toughness result, would you expect it to have similar toughness to Rex 45/Rex 76/ Z-Max?

2) Where would you predict H1 to fall in to the CATRA graph?

Thank you for creating this excellent data repository!
 

Larrin

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Excellent information! Two questions:

1) I see that K390 has a CATRA result, but no toughness result, would you expect it to have similar toughness to Rex 45/Rex 76/ Z-Max?

2) Where would you predict H1 to fall in to the CATRA graph?

Thank you for creating this excellent data repository!
1) My K390 is too thin for a toughness specimen. It is somewhere between 10V and Vanadis 8 when at the same hardness.
2) At the bottom
 
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