Rex45 vs Rex76 - Larrin's CATRA test vs predictive estimate and real-world experiences?

[Mage7]

I had been considering getting one of the Rex76 sprints but I just haven't found one in a model or for a price I like, and reading Larrin's KSN blog it didn't really seem like I was missing much compared to Rex45. However, when looking at things more closely, I noticed a bit of a discrepancy between his actual CATRA scores and what the predictive TCC via his regression formula would have been.

I was curious about the carbide content of Rex45 but I can't find any micrographs available for it. I have found the carbide volume listed for it on Knife Steel Nerds, but I'm not sure if he used ThermoCalc or got those figures from Crucible's data sheets. He does have micrographs for Rex76.

This lists Rex45 as having 5.3% M6C and 2.5% MC for a total of 7.8% carbide volume.


This lists Rex76 as having 12% M6C and 5.3% MC for a total of 17.3% carbide volume.


He also has this micrograph and in the book specifies that with ThermoCalc and "point counting" that he estimates 5.5% MC and 12% M6C:



I was very surprised at the amount of difference between Rex45 and Rex76 here, especially because CATRA tests don't seem to place them that far apart.


https://knifesteelnerds.com/2021/05/10/ ... 15-rex-76/

This shows Rex76 was at ~67.5 HRC with ~625 TCC and Rex45 at 66.5 HRC at ~612.5 TCC



If we went by Larrin's KSN blog regression formula estimation:

TCC (mm) = -157 + 15.8*Hardness (Rc) – 17.8*EdgeAngle(°) + 11.2*CrC(%) + 14.6*CrVC(%) + 26.2*MC(%) + 9.5*M6C(%) + 20.9*MN(%) + 19.4*CrN(%)

Rex45: -157 + 15.8*66.5– 17.8*30 + 26.2*2.5 + 9.5*5.3 = 475.55 TCC

Rex76: -157 + 15.8*67.5– 17.8*30 + 26.2*5.3 + 9.5*12 = 628.36 TCC

Although the formula as it is published in his second edition of "Knife Engineering" is a bit different:

TCC (mm) = -157 + 15.8*Hardness (Rc) – 17.8*EdgeAngle(°) + 11.4*CrC(%) + 13.1*CrVC(%) + 25.1*MC(%) + 14.1*M6C(%) + 14.7*VN(%) + 18.4*CrN(%) + 5*M3C(%)

That would change the predictive values to a little bit to...

Rex45: -157 + 15.8*66.5– 17.8*30 + 25.1*2.5 + 14.1*5.3 = 497.8 TCC

Rex76: -157 + 15.8*67.5– 17.8*30 + 25.1*5.3 + 14.1*12 = 661.93 TCC


Not really a significant change, but still shows a pretty wide berth between the predictive results and the actual CATRA data he acquired from testing both.

In the article, Larrin states:

"Somewhat surprisingly Rex 76 was only about 1 Rc harder than Rex 45 despite the higher carbon and cobalt content. And the edge retention is only higher due to the increased hardness and does not seem to have benefitted from the higher carbide content that would result from the higher carbon content. So Rex 76 would primarily be useful for applications where very high hardness is desired."

Given the regression formula estimates, it seems more like Rex45 just scored a lot higher than it should have. I suppose that the difference in heat treatment could have resulted in a much different carbide content than listed? I think that this is likely the case if you consider CPM-M4 in comparison.

CPM-M4 has a pretty similar carbide volume and has about a 575 TCC score at 61 HRC on the chart, whereas the regression formula estimate puts it at 464.4 TCC to 481.6 TCC (-157 + 15.8*61– 17.8*30 + 26.2*5.5 + 9.5*5 vs -157 + 15.8*61– 17.8*30 + 25.1*5.5 + 14.15*5) so clearly real-world CATRA scores and estimates can vary widely--and it seems there's no real-world CATRA data of CPM-M4 at similar hardness to compare against. However the regression formula would land right on 575 HRC if the hardness was bumped up to 68 HRC, which approaches the real-world results (and hardness) of Rex45. If Rex45 merely had a 3% greater MC percentage and .5% M6C percentage the regression formula estimate would track much more closely with its real world CATRA scores, and since there are micrographs for Rex76 showing its carbide content I would lean towards Rex45 being the one with more carbide than actually estimated if we were to trust the formula and adjust the parameters given.

With 17%-20% carbide volumes, the nearest steel in terms of TCC score that also has carbide volume types listed on the chart is CTS-204P at about ~625 TCC when hardened to ~61.5 HRC. So going by the regression formula (-157 + 15.8*61.5 – 17.8*30 + 14.6*17.5 + 26.2*2.5) (using the KSN blog version since I assume the CATRA chart on the site was produced with that) the estimate should be 601.7 TCC, and so the estimate and real-world seem much more closely aligned and seems to point to Rex76 with a ~17.5% carbide volume and CTS-204P with 20% carbide volume both in the 600 - 650 TCC range.

Makes me wonder if maybe the CATRA tests with Rex45 could have been anomalous, or maybe the carbide content for those samples was higher than thought?

Anyway, just wrapping up my weekend geek-out after getting his book for Xmas :)

What do you all think of Rex45 and Rex76 in your use? I'm still thinking about trying to get a Rex76 mule to try out, but so far the Rex45 mule seems to be as rare as hen's teeth on the secondary market. With Crucible shutting down I feel like these will end up even more sought after. Glad to have my Manix 2 before that happened.

[Synov]

It's a similar result to Z-Max, I think the regression model just didn't have much high speed steel data when it was created so it's not very accurate for them.

[Spyderfreek]

I love Rex 76. It definitely holds an edge longer than Rex 45, CATRA testing doesn't tell the whole story. If you were to take Rex 76 and k390 and put them head to head in a cardboard cutting shootout Rex 76 will beat it by just a hair. I have a lot of experience with them both. Rex 76 reminds me more of Maxamet, if Maxamet was tougher and nicer to sharpen.

I haven't been fortunate enough to play with z-max, but all of the anecdotes I've heard regarding it sound quite a lot like what I experience using Rex 76.

[TkoK83Spy]

I've always thought people look waaaayyyy too into his findings, vs just going out and using your knives and sharpening to the best of your ability and figuring things out on your own as you go.

[silver & black]

I have a PM2 in Rex76, a PM2 in Maxamet and a Para3 in Maxamet. I'm sure there is a difference..... but I can't tell. I purchase these steels just because they are out of the norm and fun to own/use.

[Wowbagger]

EDIT : to add BBB 15V (stupid of me to not include that one) .

and it seems there's no real-world CATRA data of CPM-M4 at similar hardness to compare against.

yeeeeees . . .
way back in the day when a bunch of this first started to be put up in the forms I mentioned this and our good buddy was a bit afronted ~ = :
WHAT !
I gave you all this data on the more modern alloys and you ask for this "old school" crap that I haven't got around to yet !
SHAAAAAAAME ON YOU !

Tongue in cheek (at least that is going to be my official story) I think that M4 makes a lot of other stuff look a bit anemic and that with the data posted to compare with . . . many / most EDC users would give it all a cursory study then just get some M4 and go on with their lives.

It was kind of like : Don't talk about M4 . That would put an end to "the magic" ; to coin a phrase from The Polar Express.

Full disclosure I have lots of other stuff from S35VN to K390, Maxamet , REX 121 and 15 V . . . sure I am an unapologetic blade alloy junkie . . . and as a result a hoarder of the latest Diamond / CBN sharpening plates .
all great fun !
((((I'm still happiest / most comfortable (like coming home) reaching for my M4 ))))
((((don't tell anybody though))))

[Wowbagger]

I have a PM2 in Rex76, a PM2 in Maxamet and a Para3 in Maxamet. I'm sure there is a difference..... but I can't tell. I purchase these steels just because they are out of the norm and fun to own/use.

And don't forget the great patinas they take !
I enjoy that too.
All that funny "stainless" stuff . . . booooooooring .

[Brock O Lee]

...just going out and using your knives and sharpening to the best of your ability and figuring things out on your own as you go.

I agree. Charts and chemistries are interesting, but real world testing is what actually counts.

I got a Native Chief in REX-45 in a trade several years ago. It ended up unused and in storage because I mistakenly jumped to the conclusion that it was "nothing too exceptional, and should perform not quite as well as M4".

This year I got around to sharpening and using the knife properly over several months. I was a bit shocked to find out that it was superb and not far behind K390 in my experience. I like it much better than M4. I believe the increase in hardness over M4 bumped up the edge stability. As a result, it performed much better for me than what the theory and charts suggested.

I now feel a bit foolish for passing on the REX-76 PM2 when they were still around!

[cabfrank]

I still want to get K390 and 15V and see what I'm missing.

[vivi]

I've always thought people look waaaayyyy too into his findings, vs just going out and using your knives and sharpening to the best of your ability and figuring things out on your own as you go.

1000% this.

As an example:

Him ranking ZDP189 at or below Cruwear when it comes to corrosion resistance is absolute bananas.

I had a cruwear temp rust by simply walking forest trails in the rain.

I EDC'd multiple ZDP folder in different conditions (sweat, rain, food prep on hikes, etc.) and never saw any rust. Both clad and unclad versions.

I would never write an article about a steel I hadn't personally used.

[Deadboxhero]

I've always thought people look waaaayyyy too into his findings, vs just going out and using your knives and sharpening to the best of your ability and figuring things out on your own as you go.

1000% this.

As an example:

Him ranking ZDP189 at or below Cruwear when it comes to corrosion resistance is absolute bananas.

I had a cruwear temp rust by simply walking forest trails in the rain.

I EDC'd multiple ZDP folder in different conditions (sweat, rain, food prep on hikes, etc.) and never saw any rust. Both clad and unclad versions.

I would never write an article about a steel I hadn't personally used.

It's hard to believe but it's true.

The testing unveils the hidden inner workings of how the steels work.

[Scandi Grind]

I'm partial to real world testing, becuase how it works for me under my circumstances is what is most important for me. But charts are a good place to start and I appreciate them for the work they take. Charts can help you decide whether you are likely to prefer certain steels too, but typically I am interested in seeing a steel in use for some time before I want to invest in it.

[vivi]

I've always thought people look waaaayyyy too into his findings, vs just going out and using your knives and sharpening to the best of your ability and figuring things out on your own as you go.

1000% this.

As an example:

Him ranking ZDP189 at or below Cruwear when it comes to corrosion resistance is absolute bananas.

I had a cruwear temp rust by simply walking forest trails in the rain.

I EDC'd multiple ZDP folder in different conditions (sweat, rain, food prep on hikes, etc.) and never saw any rust. Both clad and unclad versions.

I would never write an article about a steel I hadn't personally used.

It's hard to believe but it's true.

The testing unveils the hidden inner workings of how the steels work.

I don't think it is true. ZDP189 never corroded for me over the course of years of carry and use. Cruwear rusted after being exposed to a little rain.

ZDP strikes me as a stainless steel with lower than average corrosion resistance like 8Cr, while cruwear seems like a carbon steel with better than 1095 but worse than 3V corrosion resistance properties.

[Deadboxhero]

I've always thought people look waaaayyyy too into his findings, vs just going out and using your knives and sharpening to the best of your ability and figuring things out on your own as you go.

1000% this.

As an example:

Him ranking ZDP189 at or below Cruwear when it comes to corrosion resistance is absolute bananas.

I had a cruwear temp rust by simply walking forest trails in the rain.

I EDC'd multiple ZDP folder in different conditions (sweat, rain, food prep on hikes, etc.) and never saw any rust. Both clad and unclad versions.

I would never write an article about a steel I hadn't personally used.

It's hard to believe but it's true.

The testing unveils the hidden inner workings of how the steels work.

I don't think it is true. ZDP189 never corroded for me over the course of years of carry and use. Cruwear rusted after being exposed to a little rain.

ZDP strikes me as a stainless steel with lower than average corrosion resistance like 8Cr, while cruwear seems like a carbon steel with better than 1095 but worse than 3V corrosion resistance properties.

The KSN testing used Cruwear with a different heat treatment which had more of the available chromium in solution rather than locked up with carbides.

So using a production Cruwear knife as a reference point for the corrosion resistance of ZDP189 will be misleading.

There is anecdotal evidence of ZDP-189 being more prone to rusting with a larger audience of users than other stainless PM steels with similar levels of chromium in the steel chemistry.

This counterintuitive mystery was solved with testing and metallurgy.

It is the free chromium available in the matrix that makes the big difference not the chemistry in itself.

This is not intuitive and it is a lot to articulate.

I hope I am not coming off as trying to invalidate your experiences and expertise.

I appreciate ya.

[Deadboxhero]

I'm partial to real world testing, becuase how it works for me under my circumstances is what is most important for me. But charts are a good place to start and I appreciate them for the work they take. Charts can help you decide whether you are likely to prefer certain steels too, but typically I am interested in seeing a steel in use for some time before I want to invest in it.

Yes

simulation vs experiment vs anecdotal.

All useful, knives are tricky; the edge created plays a significant role and most don't even account for geometry.

It's like trying to compare the accuracy between rifles but shooting them off hand at random distances.

It would be difficult to see the difference between a sub moa rifle and a 4 moa rifle in such a circumstance under the presumption of "real world" especially when the skill of the user has a huge factor as well.

I've always felt the end user is the greatest variable of all for that reason.

Buying a formula 1 race car is not going to make someone Mario Andretti.

[Spyderbot_matrix]

When you’re talking avout the data sheets, numbers are a great baseline in what to expect in performance. Buuuut..

You have to have steels in hand to compare to first-
Maxamet is not as hard to sharpen as people carry on about, it’s expensive. Porcelain sink lip or a ceramic mug base is gonna take a while. Also dropping a Maxamet Spyderco is usually a broken blade. Buut you are getting a silly sharp blade. If this is your first knife, you’re gonna hate supersteels.

Conversely if you start with spy27 or bd1n, you may hate spending that kind of money, knowing you could have gotten better steel for a little more. Like me for instance- VG10, AUS8 - bumped up to S30v/S45VN, then got Maxamet, S110V, S90V, 20CV Rex45.. list goes on

Pretty Pricy to just Sample and find your happy middle- but only way to make sense of the Data. CedricandAda help a lot

So Rex76- aside from being 31 more Rexier than Rex45,
I wanted in on the ground floor for the Shaman (just a slab) in that steel, I get that Jean Micarta, and I really like Rex45. And Shamans are notoriously overpriced by scalpers.

Allegedly the difference in the two steel is in High speed cutting performance where the steel will remain tempered under hot conditions. Pretty sure I will never test that theory, but it’s nice to know that’s the benefit.