Some Guys have asked me about steel properties, such as edge retention, toughness, hardenability, corrosion resistance, sharpenability etc.

Toughness is defined as resistance to breakage, a very important feature for a knife to have.
A broken knife is useless regardless of what super-duper space steel it is made from.

When I tell guys I like AEB-L for a hard use, outdoors knife, it is because of a few things...
It was originally developed for use making razor blades, and it will get the sharpest of ANY stainless steel.
It is also THE TOUGHEST stainless steel in the world.
it has EXCELLENT stain resistance
and is easily sharpened with common stones.

please see the following graphs from Dr. Larrin Thomas, a me" />talurgist and mad genius.
This graph shows high-carbon steels compared for hardness and toughness.
I use 80CRV2 as my go-to high carbon steel.

This graph shows stainless steels compared for toughness. note where AEB-L is (upper middle) also note where all the "super steels" are as far as toughness go.
" />

while toughness is not the only attribute of steel, I feel that it is the Foundation of a good knife.
A broken blade is a useless blade.

I'm a little surprised by these.  

When Esee first came out with their S35V knives, they some social media posts showing a broken knife.  They claimed that S35 was inferior to 1095 (which is always touted for it's toughness) for hard use.  The charts above show them to be comparable.

ETA:

That book is a gold mine of information to anyone interested in knife metallurgy. I got a copy when it first came out.

That is interesting, especially since I just picked one up and now doubting it as a field knife. I know even ESEE said that the S35V isn't as tough as 1095. The best stainless I've found for my field use is S35VN (it's 3/16th, custom from Martin Knives).  There is a slight difference between the two:


ROCK6

Legit curious: Do people case-harden knives?

I remember knife tests having an s30 or s35 Chris Reeves Pacific fail before an 8cr13Mov knock off of it. If I remember right it even failed the hard cutting portion before they did the strength testing which broke it entirely.

Can’t have it all though.

I dont know anyone that case hardens knives, I am not saying it isnt done, I am just not aware of anyone doing it.  A pretty common practice is edge hardening where only the edge portion of the knife is hardened.  

There is a trade off when going to stainless steels like S35VN compared to high carbon steels like 1095.  Stainless will hold and edge a lot longer and the corrosion resistance is a lot better but the stainless isnt as tough and is more brittle.  I am a big fan of S35VN and use it pretty often on knives.

Well, with all the data we now have on steels, it would appear that CPM Magnacut just might be the perfect knife steel.
I have some, and I am testing a few designs as we speak and will post my results.
So far, it is VERY good at damn near EVERYTHING.

For metals requiring treating, the process is just as (if not more important) than the knife steel.  Plenty of "backyard" smiths out there using quality steel but lacking in process.

while talking about edge retention,
we must remember that toughness and edge retention are inversely related.
everything is a trade-off with steel, you must strike the balance of characteristics to your benefit.

"As toughness goes up, edge holding goes down"
here is a graph from Dr. Thomas showing his edge-holding test data
" />

this is absolutely true.
proper heat treat and testing is crucial to producing good blades.

This is why I built my own heat treat furnace capable of heat treating an 18" long blade, which holds within 3f @ 2000f
" />" />

and cryogenically treat my blades with Liquid Nitrogen @ -300f
" />

and test them using a Rockwell hardness tester to maintain quality control:
" />" />

These procedures are CRUCIAL to extract the performance out of whatever steel I am using.
Using heat treat recipes both from the steel manufacturer, and understanding how to manipulate the recipes to achieve desirable results.

Sweet setup.  Most of the makers I have seen that are able to product consistent, test verifiable, and quality treatments are using cryo.

I watch forged in fire, for some stupid entertainment, but their heat treating always makes me cringe.

Keep in mind toughness varies wildly, more so than most any other material property.  Take 2 samples of the same exact steel and put it in a Charpy tester and the results can vary significantly.

I conduct my own toughness testing, and grain inspection.


" />" />

This is a great article about knife steel choices

https://knifesteelnerds.com/2019/05/20/how-to-pick-the-best-steel-for-every-knife/

Can you elaborate on where Toughness really comes into play for a knife, for a fixed blade hunter or woods knife as an example?

Is it a consideration for use like batoning, chiseling through a deer sternum etc? And not as an important of a concern of one is committed to not using a knife as a prybar or makeshift axe.

to my mind, a knife should always be capable of just what you describe.

Its not a prybar until you use it as one, eh?

and this is why toughness is important as the foundation of a knife.

btw this is my philosophy, ymmv.

Today there is a tendency to over-specialize our tool kit.

"I have THIS knife for THIS thing, this one for this thing..."

you get the idea.

and that's cool and all, UNTIL...

you have to use your HRC67 Japanese purple steel fish-lung slicing knife to break down a deer and it shatters like

a budvase crackpipe on the sidewalk.

I am no metallurgist but after seeing a boatload of videos on I am a big fan of 3v steel.

I’ve been on Bladeforums for as long as I have here and have been a serious knife-junkie since the early 90’s.

I have always advocated using the “right tool for the job”, but life, and combat, rarely give you the immediate resources or time to go find the right tool. Your knife is on you, it’s a tool…for whatever job or problem it can help solve when time or other resources are in short supply.

I’ve used blades as prybars. I’ve used knives as screwdrivers (which is why I almost always carry a multitool with me now). I’ve dug up commo wire and CAT-5 cable. I’ve pounded my knife through some thick cables. The oddest is that I used my Mad Dogy Pygmy ATAK handle as a hammer…I was just impatient for that one!

A knife is primarily a cutting tool, not argument there. However, for expediency or time constraints, your knife just may be used for other tasks that are best suited to a knife. When those moments happen, knife toughness matters.

So, according to that link (which is pretty darn good), @doubleplusgood, the author’s priority is:

Edge geometry > heat treatment > steel choice

I think for solely a cutting tool, I would fully agree with this assessment.

However, for a utility knife that is a combat or survival tool, steel toughness becomes a higher priority. Edge geometry is critical, but much depends on the tool’s applications (Scandi-grind is great for wood, thinner grinds great for slicing tasks, convex edges are robust, etc.). I just think you can still acquire the right edge geometry after you address the toughness of a blade.

I appreciate your discussions here @doubleplusgood! Interesting, informative, and insightful to your knife making philosophy. I know several knife makers who don’t always explain how their methodology matches their philosophy and/or experiences.

ROCK6

These two charts would seem to validate your statement.  Note the CPM-154 toughness for both charts.




And then this chart from Dr. Larrin's "How to pick a steel for every knife" article linked above.




At the 60 HRc point, the first shows around 10; the 2nd shows just under 20.  

To me, the heat treat and tempering is the most important part in making a knife. If the heat treat isn’t right, even super steels won’t perform like they should. To achieve optimum toughness, the steel has to have the correct heat treat.

(My hypocrisy knows no bounds).    

Maybe I am missing it but where does D2 rank in the charts?

Would D2 good for large Bowie knives with 10” blades?

Just wondering because I am seeing a lot of decent looking Paki made Bowie’s that are made with D2.  Are they GTG or are they junk?

A couple posts up, the 2nd chart I posted.  Look towards the bottom.  

I don't use the charts for absolute numbers since there is variation in steel composition (probably not much), variation in heat treatment (could be a lot, especially between vendors and makes) variation in thickness for different blades and variation in blade geometry.

Having said that, I believe Dr. Larrin to do consistent blade steel testing in good faith as a disinterested, but very well qualified, testor.  Hence, the charts are useful for comparative differences between different steels.

ETA:  Me personally, I would avoid a large user knife in D2, especially a hard user knife.  Paki-anything is a hard no-go.

Thanks Merlin!  Yeah, the Paki knives look sketchy.  I was just thinking that maybe their car rebuilding skills might translate to good knives...

soon my friend, soon

It would seem from what I am reading on these graphs that AEB-L may be a good choice for a bayonet?  

I sort of been kicking around the idea of building my own full tang bayonet just for kicks

Edge profile plays a lot into this. My N690 and CPM154 blades lose their edge faster and sharpen like butter compared to my S30, S35, and 20CV blades. Oddly enough I also think S30 and S35 both are some of the most time consuming steels to sharpen, despite 20CV blowing them out of the water on edge retention.

Curious as to the control of this test. Guessing it was just a raw chunk of steel. Almost feels like it needs an abrasive sheer test to go with it.

these are toughness numbers.  resistance to breaking, not edge retention. CHARPY test is the industry edge retention test
I am gonna make a post on edge retention when I get time.

As DPG pointed out, these are toughness comparisons vs. hardness, not edge retention, which is a whole 'nother subject.

Dr. Larrin has a whole thread to his testing over on BF; too drunk to find it right now, maybe tomorrow.

I also know he's getting tired of hearing it, but I freaking love my Flat Rock knife!!!!  

That was my thought.  I suppose if I was specifically carrying for self defense, hunting, or bush craft I'd be concerned with "toughness" but for an edc pocket folder in my life, I'd hope that any modern offering will be plenty tough.