What steel takes the keenest edge?

[druid189]

in my experience, it's always been "high carbon" steels. But take note that I am not a metallurgist and "high carbon" is pretty much the 'blanket description' of steels that have little chromium in it.

If I had to hazard a guess, the bulk of my knives have been either 1080, 1095 or something similar and they sharpen up the best for what I do. What I do is mostly hunting [and fishing at the time] because I want to make the cleanest cuts in my game animals.

Even my favorite kitchen knives are carbon steel. Think of the "Old Hickory" type knives my grandparents used [I'm 45]....those get wicked sharp - way more sharp than those expensive stainless steel pieces of crap my wife buys [with or without serrations] in butcher blocks..

 

[crimsonfalcon07]

Wonder when mete is going to chime in on this one. Part of me wants to know what the criteria is for "keenest edge." I think JT is right to say that if you're just talking scary thin edge, it comes down to what will take the finest grain structure. I honestly don't know enough metallurgy to say. But then it comes to other issues, such as how long it holds said edge, what kind of durability it has etc, or even before that, how well it cuts. That makes me wonder about microserrations etc. To my mind, it's not JUST finest grain structure. It's also consistency of said grain structure, and how nice the edge comes out, etc. There are a lot of great steels with very good wear resistance, but most people can't/don't get them sharp enough, because it takes so much longer to sharpen them. I work in 3V, for instance. Polishing hardened 3V to anywhere close to a mirror finish is mind-blowingly painful, for instance, compared to a simple carbon steel. I'm honestly not sure it's even really possible. That may mean that the carbide structure of it is too coarse to achieve as fine an edge as a 10-series steel. I really don't know. But putting an edge on it, even if I work for twice as long as with, say, 52100, it's just not going to get as sharp because it takes so much longer to get the edge where I want it that the same amount of work means proportionally less.

That's leaving aside the issue of how skilled the sharpener is, what kind of edge we're trying to achieve, and what kind of tasks we're trying to perform. Keenness of edge is, in my book, largely a pointless exercise, if you leave aside the practical matter of what you're trying to do with it. Task should come first. Then you can think about what geometry, style, hardness, etc, of edge you want, and can pick a steel to match. And that's assuming the user has the skill to get ideal results from the steel. Sacrifice any of those, and you should be thinking more about what steel gives YOU personally the performance that you want. Anything else and we're dealing with tautology.

 

[me2]

13 - 1 = 12; 13 - 12 = 1... I give up...maybe we should bring in a mathematician... or a mathemagician.

If that is indeed the reasoning, and I'm not saying it is, but if so, then it's worth pointing out the % values of chromium and carbon are in weight percent, and carbide fraction is measured in volume percent typically. The two won't mix and match like that.

 

[Ankerson]

If that is indeed the reasoning, and I'm not saying it is, but if so, then it's worth pointing out the % values of chromium and carbon are in weight percent, and carbide fraction is measured in volume percent typically. The two won't mix and match like that.

I pointed out the direct relationship between C % and Cr % based on AEB-L as was laid out in plain English.

Oh, and that was the high end tempering by the way so that was 1% maximum Cr carbide in case you missed it.

And if you actually read it, the whole section I pointed to was on AEB-L and he even went on to explain why the C and Cr percentages work the way they do.

It really is very simple and straight forward.

I will however be talking to a few people while I am at Blade this week about this exact subject in person.

I already know what the answers are going to be, but I am going to find out anyway from a few different people.

Amusing really over a simple low cost strip steel that was designed for razor blades, it's really not that complicated, all the heavy thinking had already been done when they developed it in the 1st place.

And people trying to make it out to be more than it really is, even more amusing and sad at the same time, the alloy content just isn't there.

 

[Rey HRH]

Great posts and sharing by the experts in both metal compositions, heat treating, and practical edge geometry.

 

[Krissig12]

What steel takes the keenest edge? Steel that is owned by one who knows how to sharpen

 

[Ankerson]

What steel takes the keenest edge? Steel that is owned by one who knows how to sharpen

That's actually very true, people can split hairs all they want.

What it all really comes down to in the is that it really doesn't matter how sharp one can really get the edge beyond a certain point because the 1st time they cut something with it the dulling process starts.

That's were geometry, wear resistance, hardness, and compression strength start to really matter.

Start talking about razor blades and straight razors, that's really a different world than talking about pocket knives.

 

[Rey HRH]

What steel takes the keenest edge? Steel that is owned by one who knows how to sharpen

But I believe the discussion is around the idea that "All other things being equal" which steel takes the keenest edge? Otherwise, the question then would be posed as "who can sharpen the best?"


When analyzing something in question, the idea is you hold every other factor the same other than the thing you are investigating. There are other analytical models that allow for changing several factors at the same time, but that would be specified as part of the experiment design at the start. It is also possible that two or more variables are related to each other that affect the thing in question, such as (for a totally made up example) "M390 steel in a convex edge sharpened on a waterstone sharpens the keenest followed by D2 steel in a chisel grind sharpened on a diamond stone."

 

[Willem Blom]

This should be an informative post. Wish I had an answer but I have to little experience in knife making to give a comment at this point.

 

[Tyronethepro]

My Boker Plus Dark Hollow in 440C has the keenest edge, followed up by my CRKT Obake in 8CR14MOV then my Benchmade Griptilian in 154Cm. The DH really took some time on the fine diamond then the ceramics to get to where it is, the blade is just so darn thick, but It takes off hair, push cuts newsprint and took a good chunk of my left index finger. The Obake took an edge like nothing, but with the grind the way it is on the tip, I was hesitant to get it too sharp, there's just no meat behind the edge (Already chipped the tip putting it in the sheath when it hit a rivet) and my Benchmade I gave up on once it got to the point it could push cut newsprint. 4 hours was a long time to try and free hand that bevel back after I wrecked it on some rocks.

 

[Krissig12]

But I believe the discussion is around the idea that "All other things being equal" which steel takes the keenest edge? Otherwise, the question then would be posed as "who can sharpen the best?"


When analyzing something in question, the idea is you hold every other factor the same other than the thing you are investigating. There are other analytical models that allow for changing several factors at the same time, but that would be specified as part of the experiment design at the start. It is also possible that two or more variables are related to each other that affect the thing in question, such as (for a totally made up example) "M390 steel in a convex edge sharpened on a waterstone sharpens the keenest followed by D2 steel in a chisel grind sharpened on a diamond stone."

Sigh...... you don't get it yet.

 

[me2]

I pointed out the direct relationship between C % and Cr % based on AEB-L as was laid out in plain English.

Oh, and that was the high end tempering by the way so that was 1% maximum Cr carbide in case you missed it.

And if you actually read it, the whole section I pointed to was on AEB-L and he even went on to explain why the C and Cr percentages work the way they do.

It really is very simple and straight forward.

I will however be talking to a few people while I am at Blade this week about this exact subject in person.

I already know what the answers are going to be, but I am going to find out anyway from a few different people.

Amusing really over a simple low cost strip steel that was designed for razor blades, it's really not that complicated, all the heavy thinking had already been done when they developed it in the 1st place.

And people trying to make it out to be more than it really is, even more amusing and sad at the same time, the alloy content just isn't there.

I did read it again, as well as his section on stainless steels in the appendix. I still can't see how we're looking at the same thing and reaching different conclusions. Samauristuart has read it as well and came to conclusions similar to mine. So, we have 3 people with at least 2 different interpretations. If you explain how you got there, I explain how I got there, and Stu explains how he got there, we can see where the differences are. I won't make Blade this year, but I'd be very interested in what you find out.

 

[Ankerson]

I did read it again, as well as his section on stainless steels in the appendix. I still can't see how we're looking at the same thing and reaching different conclusions. Samauristuart has read it as well and came to conclusions similar to mine. So, we have 3 people with at least 2 different interpretations. If you explain how you got there, I explain how I got there, and Stu explains how he got there, we can see where the differences are. I won't make Blade this year, but I'd be very interested in what you find out.

Actually no, I have talked to more than a few other people before and they also say basically the same thing as I posted.

More than one started laughing when I told them about the latest 3% to 5% Cr Carbides in AEB-L and asked me who the hell is telling people that?

So that's why I already know what the answer is going to be.

 

[Twindog]

Carbide volume in typical powder steels ranges from less than 5 percent to more than 20 percent, according to Crucible. As Me2 says, this is volume, not weight, which is how we measure the amount of elements in steel alloys. Roughly 0.5 percent carbon by weight is necessary to harden the steel. The rest of the carbon is available to form carbides.

In the case of Bohler’s Vandadis 10, the carbide volume is 25 percent, while the elements in the alloy by weight are C 2.9 percent, Cr 8.0, Mo 1.5, Vanadium 9.8. I'm using this steel as an example because Boher actually tells us what the carbide volume is (in link below).

Sandvik’s 13C26 is advertised as a fine carbide forming steel. The carbides are a feature, not a bug. I can’t find anything definitive on what that carbide volume is, but if you look at the photo that Chiral posted, what you will see are a lot of carbides in that steel. What you see is the volume, not the weight. And you need a lot of carbides so they are available along the entire knife edge to improve wear resistance. The key feature is that the carbides are small, typically 0.5 microns and uniformly distributed. Crucible says the carbides in its powder steels are 2-4 microns. The apex of a sharp knife edge will be 1 or 2 microns wide.

For sharpening, the smaller the carbides the better. Large primary carbides, which can run as high as 50 microns and be clumped together in ingot steels, make sharpening and grinding more difficult, and I think that this is where people get the idea that simple steels can get sharper than steels with more complex alloys.

But a lot depends on the carbides, too. Chromium carbides run around 66-68 Rc, while vanadium carbides run about 82-84 Rc. It’s a lot easier to sharpen chromium carbides than vanadium carbides, especially if you are using a soft stone.

In the case of Sandvik’s razor steel (13C26), the carbides are chromium and very fine. And razors come extremely sharp. Rather than prevent the steel from obtaining a very sharp edge, the carbides in 13C26 give the edge much improved wear resistance.

In the high vanadium powder steels, the super hard vanadium carbides improve wear resistance many times over, as you can see in Ankerson’s tests. The powder steel processing techniques allow for these high levels of small, uniformly distributed vanadium carbides to be present. If the carbides at these volumes were large and clumpy, as in ingot steel, the steel would have poor toughness and be easy to break.

My sense is that with the proper equipment and techniques, these steels can get extremely sharp, too, but they are more difficult to sharpen than simple steels.

http://www.uddeholm.com/files/HPS_Steel_for_knives.pdf

http://www.crucibleservice.com/eselector/general/generalpart1.html

 

[BluntCut MetalWorks]

A simplify theoretical carbide volume calc for 2 extreme cases of ht 13C26 with end result hardness around 61rc. Yes, poor performing blade for both cases.

13C26 has 0.68C mass%

Case 1.

a. Put all C into solution by high temp austenite (2200F) and 20 minutes soak - oh crazy steel burner. Normal quench & temper. Expect RA (retained austenite) around 30%.
Very little precipitation when tempering, since a lot of C still locks in RA. So carbide volume will be less than 0.5% mostly due to precipitation of fine carbide.
​

Case 2.

a. Prep step - putting all C into Cr23C6 annealed (of course, you can do anything in theory).
b. Put 0.5%C into solution by aust around 1950F and whatever soak time needed. Quench to perfect Mf (martensite finish - yes, cryo or 0K by ET); snap temper.

Let's just calc carbide volume for 0.18%C not in matrix.
i. If calc for cementite(Fe3C), CVol = 0.18/6.67 = ~2.7%. Note: 3 iron to 1 Carbon, so ratio is 3/1
ii. Calc for Cr23C6 (23/6 ratio) = (2.7/3) * (23/6) = ~3.45% CVol.
* edit: this carbide configuration use up 3% mass of Cr, leaving only 10% for passivity, thus no longer stainless.
​

In practice, there will be a range of RA + Cr7C3 + Cr23C6 + Fe3C + misc carbide forms. OK then, what would be an ideal ht for this steel, which would give super keen & durable edge?

Ideal ht: 0.5%C use by matrix (with awesome microstructure and nano grain of course). Sub 500nm Cr7C3 carbide and whatever sub 30nm eta/epsilon/transitional carbides. ~62RC. btw - the micrograph pic Chiral's posted for 13C26 doesn't has (my 2cents) ideal carbide configuration.

FWIW, ^ my hand waving physics

 

[Rey HRH]

Sigh...... you don't get it yet.

Correct me then if I'm wrong you're saying, "It's the indian and not the arrow" in this discussion. You're saying then that blade material is not the determining factor in getting "keenest" knife edge and that given a competent knife sharpener, he can get any blade material to the same degree of keenest as any other regardless of the material?

 

[me2]

Actually no, I have talked to more than a few other people before and they also say basically the same thing as I posted.

More than one started laughing when I told them about the latest 3% to 5% Cr Carbides in AEB-L and asked me who the hell is telling people that?

So that's why I already know what the answer is going to be.

That is the answer to my question of how did you get that conclusion from the excerpt you quoted. The answer is you didn't. You got it from talking to other people. Were these the same people that told you that AEB-L/13C26 couldn't form chromium carbide, no matter how it's heat treated?

 

[Ankerson]

That is the answer to my question of how did you get that conclusion from the excerpt you quoted. The answer is you didn't. You got it from talking to other people. Were these the same people that told you that AEB-L/13C26 couldn't form chromium carbide, no matter how it's heat treated?

I took it from the data that I quoted.

That 1% was at 65+ HRC range by the way, I don't think people would actually take it that high realistically, more in the 61-62 range, highest I ever heard was 63 in an actual knife blade and that was pushing it risking blowing out the grain etc.

Take it back down to the 60 HRC norm and it would be even less Cr Carbides.

It was given as an example of what could happen etc.

A lot depends on what side of the HT graph one uses, the right or the left side for temps.

Now if you want to talk about total carbide content including the all the carbides you might get into the 3% range or so... MAYBE....

But for Cr Carbides alone that will max out at 1%.

 

[me2]

Ok, you lost me again. How does lowering the hardness reduce the carbide volume? Which HT graph are you using with different sides for temperatures? Again, how did you reach the conclusion from the data you quoted that there is only 1% chromium carbide? At least now you'll discuss chromium carbides. That's a pretty big step.

 

[JackstrawIII]

In my own limited experience Benchmade D2 seems to be the steel that takes the keenest edge. I've used some other mid level steels but this is my favorite so far. 30 swipes across a coarse diamond stone and a few more across a mystery whet stone and D2 gets to hair popping sharp and stays that way.

Agreed, I've had great luck getting killer edges on Benchmade's D2. As far as the knives that I made, 440C seems to take the edge easiest, but the 01 edge just screams.