Edge Stability Part 2 - Experiments

[Larrin]

In this article I summarize and analyze the "edge stability" experiments performed by Roman Landes. What results line up most closely with the edge stability theory? What surprises are found?

https://knifesteelnerds.com/2018/09/24/ ... ty-part-2/

[blues]

Hey, nobody said there was gonna be math (this early in the morning).

Seriously though, good stuff if a bit heady before I finished my first cup o' coffee.

Interesting to see how the variables effect the outcome.

[Larrin]

Don't worry I did the math already. :)

[Bodog]

Don't worry I did the math already. :)

Were there any surprises? Hardness and resistance to fracture (toughness to most people) were the primary factors as long as the heat treatment was good and carbide volumes were low enough to not effectively reduce strength and toughness. AKA high hardness M4 or maxamet or AEBL or even 10V with appropriate heat treatment...

I think this should make apparent that S30V does not normally warrant the title of "stable edge steel" because it cannot get that hard without brittleness, is not that tough regardless of hardness, and it's carbide volume is detrimental in most media excepting soft materials that will not damage almost any edge made from quality steel with a quality heat treatment made to fit reasonable edge geometry. Literally cheap AEBL can defeat S30V in a lot of head to head competitions. That seems to very closely echo what Cliff Stamp repeatedly said and it really does contradict what some other popular reviewers say ad naseum.

I would assume, based on your findings, that most any steel that has some reasonably decent toughness at 65+ RC would be a good candidate for the description of "edge stable," as in a steel that maintains an edge in a variety of cutting media, regardless of carbide volume.

Disclaimer: i have a 10V knife at 68 RC that is very impressive. It was heat treated by Luong La. It does last longer than most steels in everything I've put it through.

Luong and Cliff, come back please. For the record i think Cliff was obstinate but he was right a lot of the time. More right than some others who battled with him, anyway.

[JD Spydo]

I'm finding that website you've shared with us to be a most interesting resource. I've been kind of doing my own ranking of blade steels for serration patterns and most especially Spyderedges. Nothing at all scientific because I don't even have a Rockwell or Vickers Hardness tester. I've just been taking a certain blade steel with serrations and/or Spyderedges and putting them through really hard uses. I also do stuff with serrations that I don't dare do with plain edges. As a result with the tests I've been doing I'm finding that Spyderedges seem to do better with blade steels that have somewhat of a "toughness" aspect to them. And I'm finding not many blade steels do exceptionally good with both edge types. VG-10 is an exception to that rule>> I do find it performs above average in both SE & PE.

Some of the steels that Spyderco has used that I've found great for serrated edges are ATS-55, AUS-8, 440V, VG-10 and the old GIN-1. And none of those steels are what anyone would call supersteels for plain edge uses. It was discovered by Spyderco themselves that supersteel ZDP-189 made a lousy serrated edge steel because it truly had some brittleness factors that didn't hold up well in SE.

My question to you Larrin >> Has that website ever done any tests on serration patterns and maybe Spyderedges in particular?

[Larrin]

Were there any surprises? Hardness and resistance to fracture (toughness to most people) were the primary factors as long as the heat treatment was good and carbide volumes were low enough to not effectively reduce strength and toughness. AKA high hardness M4 or maxamet or AEBL or even 10V with appropriate heat treatment...

I think the edge stability test correlated most strongly with hardness. The effect of carbide volume, toughness, or retained austenite is mostly speculation based on the existing information.

[Larrin]

I'm finding that website you've shared with us to be a most interesting resource. I've been kind of doing my own ranking of blade steels for serration patterns and most especially Spyderedges. Nothing at all scientific because I don't even have a Rockwell or Vickers Hardness tester. I've just been taking a certain blade steel with serrations and/or Spyderedges and putting them through really hard uses. I also do stuff with serrations that I don't dare do with plain edges. As a result with the tests I've been doing I'm finding that Spyderedges seem to do better with blade steels that have somewhat of a "toughness" aspect to them. And I'm finding not many blade steels do exceptionally good with both edge types. VG-10 is an exception to that rule>> I do find it performs above average in both SE & PE.

Some of the steels that Spyderco has used that I've found great for serrated edges are ATS-55, AUS-8, 440V, VG-10 and the old GIN-1. And none of those steels are what anyone would call supersteels for plain edge uses. It was discovered by Spyderco themselves that supersteel ZDP-189 made a lousy serrated edge steel because it truly had some brittleness factors that didn't hold up well in SE.

My question to you Larrin >> Has that website ever done any tests on serration patterns and maybe Spyderedges in particular?

Is "that website" mine or a different one? I haven't written anything about serrations, yet.

[Bloke]

Thanks yet again Larrin.

I don’t mind admitting plenty goes over my head but I learn a bit too. :rolleyes:

[Baron Mind]

A good read. I would absolutely LOVE to see further edge stability testing pursued, especially as it relates to edge retention, balancing wear resistance vs fracture resistance. It seems the issue with carbides might not be that they make your edge unstable, but that they cause issues with hardenability? So which carbides, and how much can you fit into a steel without having to settle for low hardness?

[Larrin]

A good read. I would absolutely LOVE to see further edge stability testing pursued, especially as it relates to edge retention, balancing wear resistance vs fracture resistance. It seems the issue with carbides might not be that they make your edge unstable, but that they cause issues with hardenability? So which carbides, and how much can you fit into a steel without having to settle for low hardness?

Hardenability is a measure of the cooling rate required to achieve maximum achievable hardness, which is different than the "maximum achievable hardness." In other words, 1095 and O1 have a similar maximum achievable hardness but O1 has higher hardenability and therefore only needs an oil quench rather than a water quench. Anyway, that's a detour but be careful in using the word hardenability.

High carbide and high hardness are not necessarily inversely correlated. For example, adding more carbon to a simple steel can give higher hardness and more carbide. Maxamet and Rex121 have very high carbide contents and very high hardness.

However, as you said, more carbide generally means more wear resistance but lower toughness. It's a difficult design balance.

[Bodog]

Hardenability is a measure of the cooling rate required to achieve maximum achievable hardness, which is different than the "maximum achievable hardness." In other words, 1095 and O1 have a similar maximum achievable hardness but O1 has higher hardenability and therefore only needs an oil quench rather than a water quench. Anyway, that's a detour but be careful in using the word hardenability.

Would you mind going into this a little more? Is this saying the term hardenability is speaking to how quickly it cools in order to achieve max hardness? I don't understand this. Is this saying cooling rate and the difference between oil, air, and water hardening steels?

A2 has higher hardenability than O1 and then W2 regardless of maximum hardness?

How does plate quenching get qualified? Air? How are most tool and stainless steels quenched? How does the term hardenability fit into these different steels? Does hardenability affect final performance?

[Larrin]

Would you mind going into this a little more? Is this saying the term hardenability is speaking to how quickly it cools in order to achieve max hardness? I don't understand this. Is this saying cooling rate and the difference between oil, air, and water hardening steels?

A2 has higher hardenability than O1 and then W2 regardless of maximum hardness?

How does plate quenching get qualified? Air? How are most tool and stainless steels quenched? How does the term hardenability fit into these different steels?

I wrote more here: https://www.bladeforums.com/threads/how ... h.1555442/

Hardenability is a measure of how fast the steel has to be quenched to achieve max hardness. Water quenches faster than oil which quenches faster than air. Therefore an "air hardening" steel has high hardenability.

A2 has higher hardenability than O1 and W2.

Plate quenching is generally performed on air hardening steels, but there are no steels designated as "plate quenching" steels. Most tool steels and stainless steels are air quenched. However, you can quench more rapidly than necessary, some knife makers quench air hardening steels in oil. Faster quench increases the chances of warping or cracking.

[koenigsegg]

I liked this test but I think a narrower angle and more samples would help us learn quite a bit more.

I've been meaning to ask for a while so now it's unrelated to the current topic so ignore if you want.

Does a higher PREN mean more stainless? So M4 is more stainless than 440C? Wasn't sure if this was a typo or maybe it just didn't mean what I thought it meant exactly.

[Bodog]

Would you mind going into this a little more? Is this saying the term hardenability is speaking to how quickly it cools in order to achieve max hardness? I don't understand this. Is this saying cooling rate and the difference between oil, air, and water hardening steels?

A2 has higher hardenability than O1 and then W2 regardless of maximum hardness?

How does plate quenching get qualified? Air? How are most tool and stainless steels quenched? How does the term hardenability fit into these different steels?

I wrote more here: https://www.bladeforums.com/threads/how ... h.1555442/

Hardenability is a measure of how fast the steel has to be quenched to achieve max hardness. Water quenches faster than oil which quenches faster than air. Therefore an "air hardening" steel has high hardenability.

A2 has higher hardenability than O1 and W2.

Plate quenching is generally performed on air hardening steels, but there are no steels designated as "plate quenching" steels. Most tool steels and stainless steels are air quenched. However, you can quench more rapidly than necessary, some knife makers quench air hardening steels in oil. Faster quench increases the chances of warping or cracking.

So the slower it can be cooled and still achieve maximum hardness increases the hardenability rate?

That was a good explanation you just provided in the link, by the way. Sorry, i feel a little slow today.

Take O1 vs W2. Both relatively low alloy steels. Does the speed in which it achieves maximum hardness affect performance? Before now i never assumed it affected it one way or the other, only that it was a simple property that needed to be known. Now I'm wondering if hardenability affects performance.

I ask because Luong La does very, very rapid quenching (faster than water alone) with some of the air hardening steels and the performance (due to higher than normal hardness and toughness associated with the given steel) seemed very good to me despite the fracturing and warping that seems commonplace with steels that are supposed to cool more slowly, essentially seeing high edge stability in steels really only known for wear resistance. Essentially combining the best of both worlds, high edge stability in steels not normally known for it due to the high carbide volume normally known to reduce stability.

[Larrin]

I liked this test but I think a narrower angle and more samples would help us learn quite a bit more.

I've been meaning to ask for a while so now it's unrelated to the current topic so ignore if you want.

Does a higher PREN mean more stainless? So M4 is more stainless than 440C? Wasn't sure if this was a typo or maybe it just didn't mean what I thought it meant exactly.

tool-steels-corrosion-resistance2.jpg

For those that want to read the background for this question you can read the article on corrosion resistance I wrote, where the chart comes from: https://knifesteelnerds.com/2018/06/11/ ... stainless/

PREN is a prediction of pitting resistance but is somewhat misleading as a proxy for overall corrosion resistance, for the following reasons:

1) The equation assumes that the Cr-oxide film is more or less "complete," and I've never seen it used outside of stainless steels that already have a relatively high chromium content. Some articles describe it as the Mo improving the "strength" of the Cr passive film rather than replacing it.
2) Pitting resistance is not necessarily the same as "corrosion resistance." Pitting is just one type of corrosion
3) Mo primarily (only?) improves corrosion resistance in the presence of chlorides (like salt)

[koenigsegg]

Thanks so much for your reply

Are there more resources on PREN that I missed? I'd love to know what something like H1 would be on that chart or can nitrogen steels even be compared?

[Baron Mind]

A good read. I would absolutely LOVE to see further edge stability testing pursued, especially as it relates to edge retention, balancing wear resistance vs fracture resistance. It seems the issue with carbides might not be that they make your edge unstable, but that they cause issues with hardenability? So which carbides, and how much can you fit into a steel without having to settle for low hardness?

Hardenability is a measure of the cooling rate required to achieve maximum achievable hardness, which is different than the "maximum achievable hardness." In other words, 1095 and O1 have a similar maximum achievable hardness but O1 has higher hardenability and therefore only needs an oil quench rather than a water quench. Anyway, that's a detour but be careful in using the word hardenability.

High carbide and high hardness are not necessarily inversely correlated. For example, adding more carbon to a simple steel can give higher hardness and more carbide. Maxamet and Rex121 have very high carbide contents and very high hardness.

However, as you said, more carbide generally means more wear resistance but lower toughness. It's a difficult design balance.

Thank you, I was afraid I was getting myself into trouble there. We need a catchy intuitive term for maximum achievable hardness!

So I guess what I'm really interested in right now is what properties or factors give a steel a higher maximum achievable hardness, and what properties or factors give a steel a lower maximum achievable hardness, with a special interest in the role played by wear resistant carbides. Have you written any articles on any of that yet?

[Larrin]

Take O1 vs W2. Both relatively low alloy steels. Does the speed in which it achieves maximum hardness affect performance? Before now i never assumed it affected it one way or the other, only that it was a simple property that needed to be known. Now I'm wondering if hardenability affects performance.

I ask because Luong La does very, very rapid quenching (faster than water alone) with some of the air hardening steels and the performance (due to higher than normal hardness and toughness associated with the given steel) seemed very good to me despite the fracturing and warping that seems commonplace with steels that are supposed to cool more slowly, essentially seeing high edge stability in steels really only known for wear resistance. Essentially combining the best of both worlds, high edge stability in steels not normally known for it due to the high carbide volume normally known to reduce stability.

I'm not aware of any mechanism by which quenching faster than water would lead to improved properties. High carbide volume would be the limiting factor for edge stability and toughness. In other words, even if faster quenching did improve the "matrix" in some way, the limiting factor would still be the carbides.

[Larrin]

Thanks so much for your reply

Are there more resources on PREN that I missed? I'd love to know what something like H1 would be on that chart or can nitrogen steels even be compared?

I don't know of any really good references that describe the mechanisms behind the PREN number. I gave some PREN calculations for nitrogen-steels in the nitrogen article, though H1 is not in the table. However, H1 has all of its alloy in solution so using the PREN equation with nitrogen included is easy. https://knifesteelnerds.com/2018/09/17/ ... fe-steels/

[Larrin]

So I guess what I'm really interested in right now is what properties or factors give a steel a higher maximum achievable hardness, and what properties or factors give a steel a lower maximum achievable hardness, with a special interest in the role played by wear resistant carbides. Have you written any articles on any of that yet?

Maximum achievable hardness is controlled primarily by carbon/nitrogen. You can read all about it here: https://knifesteelnerds.com/2018/04/10/ ... l-so-hard/

Wear resistant carbides don't contribute much to hardness. The much smaller tempering carbides can, however, increase hardness: https://knifesteelnerds.com/2018/04/23/ ... -of-steel/