Super tough super steels??

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scdub

scdub

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Howdy folks,

A question for you - how do the “tough” modern super steels (particularly 3V, Magna Cut, and other tough stainless steels) compare head-to-head with the tough carbon steels like 5160 and S7? I understand that they can retain an edge longer, but can they retain their overall shape as well under stress?

I used to believe, mostly through my reading here, that the old school carbon steels were still superior to the “super steels” in terms of toughness (resistance to impact/fracture) at a particular hardness, but recently I’m reading posts that seem to suggest I might be wrong.

So - and this is particularly a question for you metallurgy folks out there - can you describe the comparative toughness of these steels?

Essentially I’d like to know what steels will resist catastrophic failure the best at, say, 58 rockwell.

Or, asked another way: If you made a bunch of “mule” knives at 58 hrc in different steels, which one would take the most abuse before breakage?

Any references or links to scientific articles etc. would be greatly appreciated

Disclaimer: I may not be using the correct terms re: toughness/impact resistance, etc. Feel free to define terms more properly as you see fit.
 
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I have made big knives, choppers and machetes which I have ground thin and used hard. Steels I have done so with are steel from big old rusted sawmill blades, 1084, 5160, 80CRV2, 8670, and AEB-L. Their toughness was indistinguishable to me in the field. I love AEB-L and would put it up with tough carbon steels. Larrin's charts also put it up with tough carbon steels, and even a little higher than 3V.
 
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David Mary said:
I have made big knives, choppers and machetes which I have ground thin and used hard. Steels I have done so with are steel from big old rusted sawmill blades, 1084, 5160, 80CRV2, 8670, and AEB-L. Their toughness was indistinguishable to me in the field. I love AEB-L and would put it up with tough carbon steels. Larrin's charts also put it up with tough carbon steels, and even a little higher than 3V.
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AEB-L is great also!
 
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Murphjd25 said:
Head over to the CPK forum and do some research on Delta 3V. Mind blown.
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Yeah the CPK stuff looks pretty amazing - that’s one of the reasons I started this thread.

I’ve also seen 440c knives made by Enis Entrek take some incredible abuse, but nonetheless I recon even 440c with the Entrek HT protocol is going to lose to something like Delta 3V if put to a head-to-head test.

I know there are many tough steels, but I’d like to know how they RANK at a “lower” hardness (~58).
 
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Far from being a metallurgist guy, but I read here on BF recently that at 58HRC 420HC is as tough as 3V. Not sure if that"s with Bos heat treat or not.
But IIRC Larrins charts also support this.
 
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Larrin's article knifesteelnerds.com/2019/05/20/how-to-pick-the-best-steel-for-every-knife has a section on toughness.

8670 was the highest toughness he tested.

It has this cool table:
steel-recommendation-table5.jpg
 
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Super steel has no real definition but is often used to mean “high edge retention.” Edge retention and toughness are conflicting properties so almost by definition super steels will not have the highest possible toughness.
 
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Currawong said:
Larrin's article knifesteelnerds.com/2019/05/20/how-to-pick-the-best-steel-for-every-knife has a section on toughness.

8670 was the highest toughness he tested.

It has this cool table:
steel-recommendation-table5.jpg
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My opinions change with new information so several of these have changes. High alloy medium is now CPM-CruWear, high alloy high edge retention is now Vanadis 8. Stainless medium is now MagnaCut, stainless high edge retention is now S90V. Extra stainless high edge retention is now blank as I don’t think S110V has high enough corrosion resistance to qualify for the category. Of course there are alternatives in many categories as 5160 could be used instead of 8670, 14C28N gives up a little hardness to have better corrosion resistance than AEB-L, etc. And there are many in between grades such as 3V fitting in between the high toughness and medium categories.
 
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In terms of toughness, S7 beats them all, at the cost of edge retention.

These days, I'm less picky then I used to be :): CPM Cruwear, 3V, A2, modified A8 (INFI), CPM M4 are all almost interchangeable in my mind, even though they do have corrosion/edge retention/toughness tradeoffs. They all seem to have enough chrome to not corrode in my use. Just got my first S7 knife, we'll see :)

On the stainless side, AEB-L is my favorite. But don't forget properly heat treated 420HC, way up there wrt to toughness.

Note that I don't worry about fatal blade breakage, and I don't hammer knives into concrete. I'm just lazy sharpening, I hate edge chips.

Roland.
 
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Larrin said:
Super steel has no real definition but is often used to mean “high edge retention.” Edge retention and toughness are conflicting properties so almost by definition super steels will not have the highest possible toughness.
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Good point re: Super Steels - I guess I meant modern stainless steels…

Thanks Larrin for compiling all this information! I will be spending lots of time on your website. There’s information on HT of different steels there too which is great.
 
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ferider said:
In terms of toughness, S7 beats them all, at the cost of edge retention.

These days, I'm less picky then I used to be :): CPM Cruwear, 3V, A2, modified A8 (INFI), CPM M4 are all almost interchangeable in my mind, even though they do have corrosion/edge retention/toughness tradeoffs. They all seem to have enough chrome to not corrode in my use. Just got my first S7 knife, we'll see :)

On the stainless side, AEB-L is my favorite. But don't forget properly heat treated 420HC, way up there wrt to toughness.

Note that I don't worry about fatal blade breakage, and I don't hammer knives into concrete. I'm just lazy sharpening, I hate edge chips.

Roland.
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I have heard that as well and I have been very impressed with my first S7 knife from Swamp Rat that I’ve been using for about a year.
 
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Larrin said:
My opinions change with new information so several of these have changes. High alloy medium is now CPM-CruWear, high alloy high edge retention is now Vanadis 8. Stainless medium is now MagnaCut, stainless high edge retention is now S90V. Extra stainless high edge retention is now blank as I don’t think S110V has high enough corrosion resistance to qualify for the category. Of course there are alternatives in many categories as 5160 could be used instead of 8670, 14C28N gives up a little hardness to have better corrosion resistance than AEB-L, etc. And there are many in between grades such as 3V fitting in between the high toughness and medium categories.
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Your article on MagnaCut seems to suggest that it would be approximately as tough as CruWear at around 65 HRC. At that Rockwell, is there any reason to choose CruWear over magnacut other than ease of sharpening? Your article on steel micrographs also says that CruWear has a higher carbide volume than MagnaCut (10% vs 8%) and that the carbides in CruWear are larger. Is there a reason why CruWear seems to be performing better than MagnaCut and 4V in terms of toughness when MagnaCut and 4V both seem to be superior in terms of carbide volume and carbide size?
 
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nattynarwhal said:
Your article on MagnaCut seems to suggest that it would be approximately as tough as CruWear at around 65 HRC. At that Rockwell, is there any reason to choose CruWear over magnacut other than ease of sharpening? Your article on steel micrographs also says that CruWear has a higher carbide volume than MagnaCut (10% vs 8%) and that the carbides in CruWear are larger. Is there a reason why CruWear seems to be performing better than MagnaCut and 4V in terms of toughness when MagnaCut and 4V both seem to be superior in terms of carbide volume and carbide size?
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There are always mysteries and unexpected small differences that we sometimes find. One thing to keep in mind, however, is that the linear scale I use for my toughness plots can be somewhat misleading. The toughness differences are more of a log scal, so a ft-lb or two matters when you are comparing steels at 4 ft-lbs. but once you’re in the 20 ft-lb range one to two ft-lbs is basically just noise. CPM CruWear appears to be a smidgen tougher than 4V and MagnaCut but not so much that it is in another category or anything. Another thing I will mention is that when we tested the toughness of CPM-CruWear using a high temperature temper (~1000F) the toughness was significantly reduced when compared with a low temper (~400F). Using the high temper also results in a loss of some corrosion resistance which reduces another beneficial aspect of CruWear. With the high temper it would be no better than 4V or MagnaCut and potentially worse in terms of toughness. Definitely some knife companies/makers use the upper temper. In general I would say that MagnaCut could be used interchangeably in the same applications where CPM-CruWear works.
 
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