K390 PM2 | Testing

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JuPaul
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Re: K390 PM2 | Testing

Postby JuPaul » Fri Nov 22, 2019 11:03 am

Deadboxhero wrote:
Fri Nov 22, 2019 10:45 am
Rutger wrote:
Fri Nov 22, 2019 7:35 am
Good chance that REX45 will outperform this due to the higher hardness...
It doesn't work that simple,

Rex 45 has ~8% total carbide volume in the matrix. It's 2.5% vanadium Carbides plus ~5.5% Softer M6C Tungsten Molybdenum rich Carbides.

K390 has ~16-17% volume Vanadium carbides in the matrix.

So, that k390 edge will resist being worn down and blunted smooth from lots of cutting.

The rex 45 matrix may be harder but the K390 is still more wear resistant and will cut longer.

Rex 45 is fun for how hard it is from a production company. Really enjoy the keen edge holding it offers and can drop angles lower with great stability and how easy it is to shape the apex to a very keen edge since we don't have to cut and shape as many very hard carbides.
It's crazy that we have Hap40/Rex45 in a production folder. Gotta love that "voodoo steel"

Softer K390 still has more edge aggression.

At 63.5rc, the k390 edge has what I call a "Cruwear" effect meaning it's sharpenablity is very high, I've been talking with Michael Christy about his thoughts on the Pm2 k390 edge character, I feel we both agree, it's interesting to see that sticky edge Cruwear effect at 63-64 but with the aggression of k390 it makes for a nice edge character that's fun to play with.

Larrin Thomas was flexing his Heat treatment skills and he Heat treated a K390 test knife at 68rc. I still need to test, it is impressive seeing what the maximum limit is for k390, there isn't any data for that though so no one knows what that edge is like and it is horrendous to grind so not realistic for making knives at high volume.

When the matrix is harder with hard carbides inside at high volume, it's a nightmare to grind and the abrasive cost goes through the roof, that's why it's so neat that Spyderco makes Maxamet so available, they deserve a great deal of respect for that.

About the Cruwear, I run the Cruwear softer in my customs because I like how that edge comes up in Cruwear at 62-63rc. Cruwear is capable of 65rc but it was encroaching on CPM 4v's territory and cruwear doesn't have the firepower of 4v. So, I felt the benifit to Cruwear was the edge character and sharpenablity, so I kept lower for that sticky edge that comes up easy with a variety of different stones.
Thanks so much for all this info in terms a layperson can understand! Very interesting and helpful.
- Julia

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Deadboxhero
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Re: K390 PM2 | Testing

Postby Deadboxhero » Fri Nov 22, 2019 11:22 am

Image

The Tungsten and Molybdenum in air hardning chromium (4-5%) tool steels will make M6C Carbides
These are Softer(hv, hardness vickers) than the M7C3 Chromium Carbides rich in Vanadium like those found in all the chromium vanadium rich PM steels s90v,m390, S30v etc

We have Tungsten and Molybdenum in K390 but it's all dissolved during Austenizing leaving undissolved Vanadium carbides to kick butt.

However, with precipatation strengthing after tempering, we put that tungsten and Molybdenum content to work with making M2C and M6C when we diffuse carbon with high temp tempering to increase the red hardness.

Don't get side tracked with temper carbides, it's the Undissolved Carbides after Austenizing and quenching that are the focus for what makes a steel very wear resistant not temper carbides.
These are not the sexy Tungsten carbides people think of when the get super excited about the tungsten alloy.

Tungsten is a very weak carbide former, it's outer sub shell is filled, so it's not as hungry to make bonds with Carbon to make hard carbides like the the other carbide forming elements are.

That's why non iron/steel, tungsten carbide metals are interesting, they synthesize the tungsten carbides separately and pack into a cobalt binder at very very high Carbide volumes 70-90% WC and W2C Carbides.

Brittle as all hell though and the edge is not enjoyable to sharpen since deburring can take the apex off with the burr. Rex 121 is compared to carbide materials but it's much tougher and still has the elastic nature of steel.


There are some killer articles about this on Larrin's site.

This one about Carbides is my all time favorite.
https://knifesteelnerds.com/2019/07/15/ ... fe-steels/


This is a new article about Tungsten Carbide Metals and how they work which is bizzare, works different than the Strengthing mechanism that we use for steel. Worth a read
https://knifesteelnerds.com/2019/11/18/ ... hat-is-it/
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Re: K390 PM2 | Testing

Postby Rutger » Fri Nov 22, 2019 6:03 pm

attila wrote:
Fri Nov 22, 2019 8:45 am
wrote:
Fri Nov 22, 2019 7:35 am
Good chance that REX45 will outperform this due to the higher hardness...
I was actually wondering about this and what experienced users of both steels have seen. I don't cut enough to have noticed any difference, and the only K390 I have is a lightly used Urban.

I'm guessing 65-66 hrc Rex 45 would support a fine edge longer, but may be passed up by the higher vanadium+tungsten content of 63-64 hrc K390 in extended cutting scenarios. At the same hardness, I think K390 would win hands down, but I can't be sure.

If K390 at this hardness outperforms the Rex 45 that the PM2 sprint featured, I'll consider buying the former and selling my copy of the latter.
Super Steel Steve did some testing between K390, Maxamet, REX45 and HAP40 cutting cardboard. The REX45 results were pretty impressive in my opinion considering it has a lot less carbides in it.

https://www.youtube.com/watch?v=fm0pv3JzQvo

If you don't wanna watch the whole video for the results i'll list them here:

________| HRC..... | Fine edge | Working edge
K390..... | 65.6HRC | 198.8ft... | 406.4ft
Maxamet | 66.2HRC | 189.9ft... | 362.2ft
Rex45.... | 65.7HRC | 178.9ft... | 331.3ft
HAP40.... | unknown| 130.3ft... | 251.8ft
Sadly we can't use bbcode for tables on this forum.

So K390 beats Maxamet if at similar hardness. Though most Maxamet knives are produced at higher HRC (68-69) so they beat K390 in most tests.

The surprising thing from this testing is that REX45 at similar hardness as Maxamet is within 10% difference of it's performance. Could be margin of error in testing even. So the extra carbides in Maxamet didn't matter that much. REX45 is like a Maxamet light in composition.
K390 has different carbides/composition so it performed better. But you could question how big of an impact the extra carbides will have if it is ran at lower HRC.

K390 beats REX45 at similar hardness here, but the differences aren't huge in my opinion. Now consider K390 being several HRC points lower in this PM2 version. There are even examples of REX45 Military's at 67HRC which would make the difference in HRC even bigger.

So unless K390 at lower HRC has some nice attributes in edge finish/aggression/character (like cruwear) i don't see why you would pick it over Maxamet or REX45 at much higher HRC. Certainly not for the fine or working edge holding.

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Re: K390 PM2 | Testing

Postby Deadboxhero » Fri Nov 22, 2019 6:39 pm

Rutger wrote:
Fri Nov 22, 2019 6:03 pm
attila wrote:
Fri Nov 22, 2019 8:45 am
wrote:
Fri Nov 22, 2019 7:35 am
Good chance that REX45 will outperform this due to the higher hardness...
I was actually wondering about this and what experienced users of both steels have seen. I don't cut enough to have noticed any difference, and the only K390 I have is a lightly used Urban.

I'm guessing 65-66 hrc Rex 45 would support a fine edge longer, but may be passed up by the higher vanadium+tungsten content of 63-64 hrc K390 in extended cutting scenarios. At the same hardness, I think K390 would win hands down, but I can't be sure.

If K390 at this hardness outperforms the Rex 45 that the PM2 sprint featured, I'll consider buying the former and selling my copy of the latter.
Super Steel Steve did some testing between K390, Maxamet, REX45 and HAP40 cutting cardboard. The REX45 results were pretty impressive in my opinion considering it has a lot less carbides in it.

https://www.youtube.com/watch?v=fm0pv3JzQvo

If you don't wanna watch the whole video for the results i'll list them here:

________| HRC..... | Fine edge | Working edge
K390..... | 65.6HRC | 198.8ft... | 406.4ft
Maxamet | 66.2HRC | 189.9ft... | 362.2ft
Rex45.... | 65.7HRC | 178.9ft... | 331.3ft
HAP40.... | unknown| 130.3ft... | 251.8ft
Sadly we can't use bbcode for tables on this forum.

So K390 beats Maxamet if at similar hardness. Though most Maxamet knives are produced at higher HRC (68-69) so they beat K390 in most tests.

The surprising thing from this testing is that REX45 at similar hardness as Maxamet is within 10% difference of it's performance. Could be margin of error in testing even. So the extra carbides in Maxamet didn't matter that much. REX45 is like a Maxamet light in composition.
K390 has different carbides/composition so it performed better. But you could question how big of an impact the extra carbides will have if it is ran at lower HRC.

K390 beats REX45 at similar hardness here, but the differences aren't huge in my opinion. Now consider K390 being several HRC points lower in this PM2 version. There are even examples of REX45 Military's at 67HRC which would make the difference in HRC even bigger.

So unless K390 at lower HRC has some nice attributes in edge finish/aggression/character (like cruwear) i don't see why you would pick it over Maxamet or REX45 at much higher HRC. Certainly not for the fine or working edge holding.
Fair enough, first world problems eh? So many options, all work fine.
For the spirit of testing we would have to send to Steve so he could do things similar to what he did for those other Knives.
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Re: K390 PM2 | Testing

Postby attila » Fri Nov 22, 2019 6:54 pm

Rutger wrote:
Fri Nov 22, 2019 6:03 pm
attila wrote:
Fri Nov 22, 2019 8:45 am
wrote:
Fri Nov 22, 2019 7:35 am
Good chance that REX45 will outperform this due to the higher hardness...
I was actually wondering about this and what experienced users of both steels have seen. I don't cut enough to have noticed any difference, and the only K390 I have is a lightly used Urban.

I'm guessing 65-66 hrc Rex 45 would support a fine edge longer, but may be passed up by the higher vanadium+tungsten content of 63-64 hrc K390 in extended cutting scenarios. At the same hardness, I think K390 would win hands down, but I can't be sure.

If K390 at this hardness outperforms the Rex 45 that the PM2 sprint featured, I'll consider buying the former and selling my copy of the latter.
Super Steel Steve did some testing between K390, Maxamet, REX45 and HAP40 cutting cardboard. The REX45 results were pretty impressive in my opinion considering it has a lot less carbides in it.

https://www.youtube.com/watch?v=fm0pv3JzQvo

If you don't wanna watch the whole video for the results i'll list them here:

________| HRC..... | Fine edge | Working edge
K390..... | 65.6HRC | 198.8ft... | 406.4ft
Maxamet | 66.2HRC | 189.9ft... | 362.2ft
Rex45.... | 65.7HRC | 178.9ft... | 331.3ft
HAP40.... | unknown| 130.3ft... | 251.8ft
Sadly we can't use bbcode for tables on this forum.

So K390 beats Maxamet if at similar hardness. Though most Maxamet knives are produced at higher HRC (68-69) so they beat K390 in most tests.

The surprising thing from this testing is that REX45 at similar hardness as Maxamet is within 10% difference of it's performance. Could be margin of error in testing even. So the extra carbides in Maxamet didn't matter that much. REX45 is like a Maxamet light in composition.
K390 has different carbides/composition so it performed better. But you could question how big of an impact the extra carbides will have if it is ran at lower HRC.

K390 beats REX45 at similar hardness here, but the differences aren't huge in my opinion. Now consider K390 being several HRC points lower in this PM2 version. There are even examples of REX45 Military's at 67HRC which would make the difference in HRC even bigger.

So unless K390 at lower HRC has some nice attributes in edge finish/aggression/character (like cruwear) i don't see why you would pick it over Maxamet or REX45 at much higher HRC. Certainly not for the fine or working edge holding.
I have seen that video when originally released and rewatched the results discussion a couple of times since. That's what got me thinking.

K390 only leads by 11% in fine edge holding but by 22.6% in working edge holding.

I was wondering if dropping K390 by 2 hrc points would bring it down below Rex 45 in either working or fine edge holding or in edge stability.

These questions I can't answer, but BBB's explanations above helps me get a decent idea. Considering that and the amount of carbides in each steel, I still would expect K390 at 64 hrc to outlast or at least match Rex 45 at 66 hrc in the working edge department.

I like mine to stay shaving sharp, so the working edge characteristics aren't as important.
Own: Delica, Old S30V Native, modified Breeden Rescue, Delica, HAP40 Endura, ZDP DF2, S110V Manix LW,Pakkawood Delica, Cruwear Para 3, SE H1 DF2, M4 Manix 2, HAP40 Caly 3, S90V Native 5, K390 Urban, Pakkawood DF2, Cruwear PM2, SE Pac Salt, HAP40 Jazzlica, S110V Native, P.I.T.S., DLC Manix 2, REX 45 PM2, Para 3, XHP Manix LW, SB Caly 3, 20CV PM2, Rhino, SB Calypso Jr., B70P, PMA11, K03, ZDP Stretch 2, Kapara, REX 45 Military, 154CM Manix LW, 204p PM2, Swick, SG Delica, backlock Lil'Native, AEB-L Urban, HAP40 Stretch, KC Cruwear Manix 2, Cruwear Military, M390 PM2, Cruwear Delica, 4V Lil'Native, Mantra 2, CruCarta Shaman, M390 Para 3 LW, M390 Manix 2, K390 Police 4, RexWood Shaman, DLC Cruwear Shaman, Rex 45 Manix 2, Native 5, Native LW, 204p Para 3, S45VN PM2, S90V Manix LW, 20CV Manix 2, Rex 45 Shaman, Lil’Native.

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Re: K390 PM2 | Testing

Postby Rutger » Fri Nov 22, 2019 7:26 pm

attila wrote:
Fri Nov 22, 2019 6:54 pm
I like mine to stay shaving sharp, so the working edge characteristics aren't as important.
I like super sharp fine edge holding too and most people here seem to prefer that. Cruwear is king at that and it's no wonder that that steel is so popular right now. Maybe Maxamet or K390 at higher HRC would beat cruwear at it, but i doubt they would beat it by a lot. And they for sure would take a lot more effort to sharpen up again.

So i am unsure what the place of this K390 is at this moment. Got no hands on experience with it myself. I'd like to see it as a Maxamet killer but then it has to be ran at higher HRC.

For fine edge holding i think it's better to go with a less carbide rich steel with a nice micro structure that is also easy to sharpen. That is why i like Cruwear, LC200N and REX45 a lot.

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Re: K390 PM2 | Testing

Postby The Meat man » Fri Nov 22, 2019 7:37 pm

In Pete's test (Cedric and Ada Outdoors) Maxamet beat K390 by a considerable margin, and both were way ahead of CPM REX 45.
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Re: K390 PM2 | Testing

Postby Pelagic » Fri Nov 22, 2019 7:55 pm

The Meat man wrote:
Fri Nov 22, 2019 7:37 pm
In Pete's test (Cedric and Ada Outdoors) Maxamet beat K390 by a considerable margin, and both were way ahead of CPM REX 45.
Steve's test was with an abnormally soft Maxamet knife. I think Maxamet at that hardness could definitely beat k390 by a little bit, IF, that was the hardness a skilled bladesmith was shooting for. But since they were aiming at a higher hardness and arrived 2 points low, there's a good chance the integrity of the blade is lacking in more than just hardness. And I believe that is partially why Steve predicted k390 to win. Hardness isn't everything, but an HRC of 65.6 is definitely indicative of a strong k390 sample.
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Re: K390 PM2 | Testing

Postby JuPaul » Fri Nov 22, 2019 9:40 pm

Rutger wrote:
Fri Nov 22, 2019 6:03 pm
attila wrote:
Fri Nov 22, 2019 8:45 am
wrote:
Fri Nov 22, 2019 7:35 am
Good chance that REX45 will outperform this due to the higher hardness...
I was actually wondering about this and what experienced users of both steels have seen. I don't cut enough to have noticed any difference, and the only K390 I have is a lightly used Urban.

I'm guessing 65-66 hrc Rex 45 would support a fine edge longer, but may be passed up by the higher vanadium+tungsten content of 63-64 hrc K390 in extended cutting scenarios. At the same hardness, I think K390 would win hands down, but I can't be sure.

If K390 at this hardness outperforms the Rex 45 that the PM2 sprint featured, I'll consider buying the former and selling my copy of the latter.
Super Steel Steve did some testing between K390, Maxamet, REX45 and HAP40 cutting cardboard. The REX45 results were pretty impressive in my opinion considering it has a lot less carbides in it.

https://www.youtube.com/watch?v=fm0pv3JzQvo

If you don't wanna watch the whole video for the results i'll list them here:

________| HRC..... | Fine edge | Working edge
K390..... | 65.6HRC | 198.8ft... | 406.4ft
Maxamet | 66.2HRC | 189.9ft... | 362.2ft
Rex45.... | 65.7HRC | 178.9ft... | 331.3ft
HAP40.... | unknown| 130.3ft... | 251.8ft
Sadly we can't use bbcode for tables on this forum.

So K390 beats Maxamet if at similar hardness. Though most Maxamet knives are produced at higher HRC (68-69) so they beat K390 in most tests.

The surprising thing from this testing is that REX45 at similar hardness as Maxamet is within 10% difference of it's performance. Could be margin of error in testing even. So the extra carbides in Maxamet didn't matter that much. REX45 is like a Maxamet light in composition.
K390 has different carbides/composition so it performed better. But you could question how big of an impact the extra carbides will have if it is ran at lower HRC.

K390 beats REX45 at similar hardness here, but the differences aren't huge in my opinion. Now consider K390 being several HRC points lower in this PM2 version. There are even examples of REX45 Military's at 67HRC which would make the difference in HRC even bigger.

So unless K390 at lower HRC has some nice attributes in edge finish/aggression/character (like cruwear) i don't see why you would pick it over Maxamet or REX45 at much higher HRC. Certainly not for the fine or working edge holding.
A bit off topic, but why the huge difference btw rex45 and hap40? I see the HRC of hap40 was unknown (because of the cladding???)...did spyderco run them at significantly different hardnesses?
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Re: K390 PM2 | Testing

Postby Pelagic » Fri Nov 22, 2019 9:56 pm

JuPaul wrote:
Fri Nov 22, 2019 9:40 pm
Rutger wrote:
Fri Nov 22, 2019 6:03 pm
attila wrote:
Fri Nov 22, 2019 8:45 am
wrote:
Fri Nov 22, 2019 7:35 am
Good chance that REX45 will outperform this due to the higher hardness...
I was actually wondering about this and what experienced users of both steels have seen. I don't cut enough to have noticed any difference, and the only K390 I have is a lightly used Urban.

I'm guessing 65-66 hrc Rex 45 would support a fine edge longer, but may be passed up by the higher vanadium+tungsten content of 63-64 hrc K390 in extended cutting scenarios. At the same hardness, I think K390 would win hands down, but I can't be sure.

If K390 at this hardness outperforms the Rex 45 that the PM2 sprint featured, I'll consider buying the former and selling my copy of the latter.
Super Steel Steve did some testing between K390, Maxamet, REX45 and HAP40 cutting cardboard. The REX45 results were pretty impressive in my opinion considering it has a lot less carbides in it.

https://www.youtube.com/watch?v=fm0pv3JzQvo

If you don't wanna watch the whole video for the results i'll list them here:

________| HRC..... | Fine edge | Working edge
K390..... | 65.6HRC | 198.8ft... | 406.4ft
Maxamet | 66.2HRC | 189.9ft... | 362.2ft
Rex45.... | 65.7HRC | 178.9ft... | 331.3ft
HAP40.... | unknown| 130.3ft... | 251.8ft
Sadly we can't use bbcode for tables on this forum.

So K390 beats Maxamet if at similar hardness. Though most Maxamet knives are produced at higher HRC (68-69) so they beat K390 in most tests.

The surprising thing from this testing is that REX45 at similar hardness as Maxamet is within 10% difference of it's performance. Could be margin of error in testing even. So the extra carbides in Maxamet didn't matter that much. REX45 is like a Maxamet light in composition.
K390 has different carbides/composition so it performed better. But you could question how big of an impact the extra carbides will have if it is ran at lower HRC.

K390 beats REX45 at similar hardness here, but the differences aren't huge in my opinion. Now consider K390 being several HRC points lower in this PM2 version. There are even examples of REX45 Military's at 67HRC which would make the difference in HRC even bigger.

So unless K390 at lower HRC has some nice attributes in edge finish/aggression/character (like cruwear) i don't see why you would pick it over Maxamet or REX45 at much higher HRC. Certainly not for the fine or working edge holding.
A bit off topic, but why the huge difference btw rex45 and hap40? I see the HRC of hap40 was unknown (because of the cladding???)...did spyderco run them at significantly different hardnesses?
Yes. They really pushed the envelope when they heat treated REX45.
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Re: K390 PM2 | Testing

Postby GarageBoy » Fri Nov 22, 2019 10:52 pm

HAP40 was in the low 60s

Im guessing M4 wasn't even on the radar

What other steels would cut higher on the fine edge retention? Vancron superclean?

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Re: K390 PM2 | Testing

Postby jpm2 » Fri Nov 22, 2019 11:08 pm

JuPaul wrote:
Fri Nov 22, 2019 9:40 pm
A bit off topic, but why the huge difference btw rex45 and hap40? I see the HRC of hap40 was unknown (because of the cladding???)...did spyderco run them at significantly different hardnesses?
I have several hap40 knives and they are all significantly softer than my rex45 para 3.

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Re: K390 PM2 | Testing

Postby Pelagic » Fri Nov 22, 2019 11:09 pm

I'm sure Vancron SC would do great. 15V would likely be a monster. Anything that can reach high hardness without being chippy is likely going to do well.
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Re: K390 PM2 | Testing

Postby jpm2 » Fri Nov 22, 2019 11:20 pm

GarageBoy wrote:
Fri Nov 22, 2019 10:52 pm
HAP40 was in the low 60s
Im guessing M4 wasn't even on the radar
My m4 blades are noticeably better at fine edge holding than my hap40 blades.

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Re: K390 PM2 | Testing

Postby Chris_P_Bacon » Sat Nov 23, 2019 2:20 pm

Rutger wrote:
Fri Nov 22, 2019 7:26 pm
attila wrote:
Fri Nov 22, 2019 6:54 pm
I like mine to stay shaving sharp, so the working edge characteristics aren't as important.
I like super sharp fine edge holding too and most people here seem to prefer that. Cruwear is king at that and it's no wonder that that steel is so popular right now. Maybe Maxamet or K390 at higher HRC would beat cruwear at it, but i doubt they would beat it by a lot. And they for sure would take a lot more effort to sharpen up again.
Hand sharpening on Modern abrasives (think Diamonds and CBN) on the larger 8x3 bench stones with the larger surface area, has pretty much made this a non issue (or substantially much less of an issue). See BBB's video on sharpening Maxamet. The whole video is only eleven minutes long and he wasn't even sharpening the whole time.

But if you're strictly talking 1" wide or smaller stones, yup, I agree.

https://www.youtube.com/watch?v=FjRALYGFffg
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Re: K390 PM2 | Testing

Postby Tucson Tom » Sat Nov 23, 2019 4:01 pm

JuPaul wrote:
Fri Nov 22, 2019 9:40 pm
A bit off topic, but why the huge difference btw rex45 and hap40? I see the HRC of hap40 was unknown (because of the cladding???)...did spyderco run them at significantly different hardnesses?
It would seem clear they were run to different hardnesses, so the question would be why.

The hap40 was in a Japanese Spyderco, the Rex45 was done in Golden.

Why should this make a difference? We can only guess. Different shops, different times, different crews, different equipment.

Maybe they learned from the hap40.

More of me guessing -- the Rex45 may have had a different set of heat treat recommendations from the manufacturer. And for whatever reason they decided to be aggressive with the Rex45, perhaps encouraged by recommendations. But unless someone from Spyderco speaks up, this is all guessing.

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Re: K390 PM2 | Testing

Postby JuPaul » Sat Nov 23, 2019 4:58 pm

Tucson Tom wrote:
Sat Nov 23, 2019 4:01 pm
JuPaul wrote:
Fri Nov 22, 2019 9:40 pm
A bit off topic, but why the huge difference btw rex45 and hap40? I see the HRC of hap40 was unknown (because of the cladding???)...did spyderco run them at significantly different hardnesses?
It would seem clear they were run to different hardnesses, so the question would be why.

The hap40 was in a Japanese Spyderco, the Rex45 was done in Golden.

Why should this make a difference? We can only guess. Different shops, different times, different crews, different equipment.

Maybe they learned from the hap40.

More of me guessing -- the Rex45 may have had a different set of heat treat recommendations from the manufacturer. And for whatever reason they decided to be aggressive with the Rex45, perhaps encouraged by recommendations. But unless someone from Spyderco speaks up, this is all guessing.
It is interesting, though. I'm definitely curious to know the reasoning behind those choices, and if people notice major differences beyond edge retention. I have several hap40 knives, and only one in rex45 which I haven't carried nearly as much. From that limited comparison, I can't say I've noticed significant differences btw the two as far as ease of sharpening or toughness goes, though. But I haven't really pushed the toughness of the rex45.
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Chumango
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Re: K390 PM2 | Testing

Postby Chumango » Sat Nov 23, 2019 5:13 pm

They followed Hitachi's recommended hear treat for the clad Hap 40, and Crucible's for Rex 45, and the results were different.

From page 6 of the CPM Rex 45 Edge Performance thread

"HAP 40 is heat treated in Japan. They have their own heat treat methods due to the laminate. REX is made by Crucible in the US and we have our own heat treat methods.

sal"

viewtopic.php?t=80749&start=100

David R
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Re: K390 PM2 | Testing

Postby David R » Sat Nov 23, 2019 7:41 pm

Deadboxhero wrote:
Fri Nov 22, 2019 10:45 am
When the matrix is harder with hard carbides inside at high volume, it's a nightmare to grind and the abrasive cost goes through the roof, that's why it's so neat that Spyderco makes Maxamet so available, they deserve a great deal of respect for that.
Agree. Also for the Mule Team program that ran a long time and gives us some rare and incredible steels. Spyderco does some amazing stuff.

The Meat man wrote:
Fri Nov 22, 2019 7:37 pm
In Pete's test (Cedric and Ada Outdoors) Maxamet beat K390 by a considerable margin, and both were way ahead of CPM REX 45.
You have to consider a few factors with C & E testing: he tests knives from different manufacturers with different blade shapes/grinds, different thickness behind the edge, different edge angle, different sharpeners, and different edge finishes. Sometimes just comparing the average for a steel in his tests doesn't tell the story.

For his Mule tests he's using the same edge - 17 degrees polished. The geometry is close enough to call the same. With his Mule tests K390 did 940 cuts and Maxamet did 1075, so 14% better. If we allow for a 5-7% margin of error they're within 10% of each other or less. (We'll see how the 4V Mule does when Pete tests it. I suspect it's going to be within 10% of K390.)

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Deadboxhero
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Re: K390 PM2 | Testing

Postby Deadboxhero » Wed Nov 27, 2019 2:51 pm

There is no standard for "fine edge holding" we like to apply it to hair shaving because that is the use for it's application but it there are large differences between hair diameters between different people ranging from ~60-200um

There is also a vast difference between how well something is "shaving" from scraping skin and catching and pulling hairs to quietly treetoping the hair without touching the skin. Huge difference.

There is a huge emphasis on the steel, geometry and heat treatment which is nice but most folks need to be reminded that it's the sharpening at the end of the day if we are dissecting fine edge holding.

Also without good measurement of Geometry it's difficult to rule it out and test the Steel and HT.

Higher hardness is nice because we are chasing a high yield strength at the apex but higher hardness doesn't always translate to more yield since hardness measures Tensile Strength in the plastic region more than purely yield Strength in the elastic region.

Don't get tunnel vision on just the hardness, These steels have wildly different structures even the same steel at same hardness can have different structures that make up that hardness for better or for worse.

All things being equal, K390 will out cut Rex 45 even if the Rex 45 is at higher hardness. This is true if we define cutting edge retention as the least amount of work with the same effort with slicing since the higher volume of harder carbide in the matrix will resist the wearing of that apex in controlled slice cut testing.

If we are using a polished edge, I feel we need to rule out sharpening process since we have more of the harder Vanadium Carbides that resist being cut and shaped in ~2-5 Micron diameter ranges and we are seeking a sub micron radius for the ultimate fine edge it makes since that we need diamond and CBN to shape that down with bonded stones to improve the surface finish/roughness to keep the abrasive grains from penetrating deep into the bevel, so it's not purely just grit size that effects the surface roughness but the combination of how that grit interfaces with the bevel and burnishing effects of different bond types.

Todd Simpson's work at Science of Sharp "Carbides in Maxamet" showed clearly that the mechanism for hard, high volume carbide in high hardness tool steels and why they may not be performing as nice with ceramic. It was not tear out, but actually just breaking of the brittle carbides in the matrix exposed at the apex. They were busted to shape not cut ; giving us fatigued steel at the apex. So the carbides can be busted up to a fine radius but the Stability and Retention is dropped.


My point is, it's difficult to apply claims of fine edge holding to these PM tool steels all with ~8 to +20% carbide volumes and 60 to +69rc. Seems the biggest factor was how it was sharpened, after that is ruled out than things can be narrowed down more to the acutal properties.

This isn't an attempt to marginalize anyone's opinions or efforts but just to get folks thinking more critically about this stuff.

Yes, Cruwear is a nice steel, love that edge it takes :D
Rex 45 too.
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