What steel takes the keenest edge?

[jdm61]

IIRC, the chromium in very simple hypoeutectoid stainless steels like 13C26 and AEB-L does not get all bound up in big primary carbides like you said, but remains, for the most part,either "free" or possible in the form of oxides or locked in very small carbides like you said. My understanding is that the tendency of free chromium or oxides to form a "barrier' on the surfaces and to almost immediately "repair" itself when abraded is what gives stainless tell its corrosion resistance.

My own sense is that when people say that some steels get sharper than others they are referring to their own experience and their own equipment, both of which are usually the key limiting factors.

Sandvik uses 13C26 for its razor blade steel. It has 13 percent Cr for corrosion resistance. Through a proper heat treat, the large, primary carbides are avoided, along with nonmetallic inclusions, leaving a clean steel with finely dispersed carbides in the matrix. Nothing wrong with the sharpness of a fresh razor, even with the 13 percent load of carbides.

Powder steels -- usually called super steels here -- can hold much larger amounts of carbides because of both the heat treat and steel processing techniques. These steels have a fine grain structure and small, evenly dispersed carbides and few inclusions. Steels like D2 will have much larger carbides and be more susceptible to carbide shedding at the edge, but D2 is still considered one of our better knife steels.

With fine abrasives, whether as stones or pastes, at diamond or near-diamond hardness, there is really no practical limit to the sharpness that can be obtained by any of these steels, provided the right equipment and proper technique.

But without proper technique or equipment, most people will probably be able to get the simple carbon steels sharper then more complex steels.

 

[jdm61]

Now when you start talking about the simple carbon and tool steels like the Hitachi white steels, W1/W1, 52100, the 10xx steels, 115W8 and others what they DON"T contain has as much of an impact on their ability to take a super fine edge and get scary sharp as what they do contain. Some "alloying elements" are considered to be "impurities" in these applications like sulphur and phosphorus as opposed to helpful elements like vanadium, chromium, tungsten. manganese, nickel, small amounts of silicon, etc. The big selling point for the top end Hitachi steels, both the very simple white and the more heavily alloyed blue, is their HIGH levels of purity. White has very few elements other than iron and carbon and in very small amounts and blue is the same way but with precise amounts of those "helpful" alloys added to increase wear resistance at a slight cost to absolute ability to take that finest of fine edges and ease of honing.

 

[james terrio]

Sandvik says that almost all of the carbon and chromium in 13C26 are bound in carbides. This is from Sandvik's data sheet on 13C26:

Once again, you are half right. The quote you cherry-picked one phrase from, is contained in this paragraph:

Microstructure
Unhardened condition ('as delivered')

In the 'as delivered', unhardened condition, Sandvik 13C26 consists of finely dispersed carbides in a ferritic matrix, see figure 1. The carbides are of type M23C6, where M stands for iron and chromium. This type of carbide is easily dissolved during the heat treatment, which is important for good hardening results. The fine dispersion of the carbides also helps to speed up their dissolution, allowing lower furnace temperatures and higher speeds during hardening.

The ferritic matrix has low contents of carbon and chromium because these elements are bound in carbides. Since the chromium content in the matrix determines the corrosion resistance of the steel, the material has limited resistance to corrosion in the 'as delivered' condition.

They are describing annealed rolled steel, as delivered to the factory or knifemaker for further processing. They are NOT talking about hardened steel that reaches the final customer in the form of a razor blade or knife. In layman's terms, if that's your argument, you might as well describe wet clay from my backyard as being the same as a finely-finished piece of porcelain.

You may also notice that the fine folks at Sandvik are very clear about their pleasure in the fact that those carbide structures are easily broken down, and evenly distributed during various HT processes. That's what they mean by "dissolution". And that's exactly why chemists and metallurgists designed that alloy that way, roughly a century ago.

No one wants ferritic steel for a knife blade. What we want is martensitic steel. Those words have actual, clearly defined meanings, and it would serve us all well if we did not confuse them.

I respectfully and humbly advise you to study a bit more about steel structures and chemistry and what happens during heat-treat, before picking out phrases that "seem" to support your unfounded theories and making such ignorant broad-brush claims about how this stuff actually goes from the mines to the mill to the anvil/grinder to the HT shop to the customer. A little knowledge is a dangerous thing, and frankly, you are displaying very little knowledge and a whole lot of... something or other.

This is not a matter of my opinion or personality. This is a matter of facts vs. baloney.

 

[Twindog]

Once again, you are half right. The quote you cherry-picked one phrase from, is contained in this paragraph:



They are describing annealed rolled steel, as delivered to the factory or knifemaker for further processing. They are NOT talking about hardened steel that reaches the final customer in the form of a razor blade or knife. In layman's terms, if that's your argument, you might as well describe wet clay from my backyard as being the same as a finely-finished piece of porcelain.

You may also notice that the fine folks at Sandvik are very clear about their pleasure in the fact that those carbide structures are easily broken down, and evenly distributed during various HT processes. That's what they mean by "dissolution". And that's exactly why chemists and metallurgists designed that alloy that way, roughly a century ago.

No one wants ferritic steel for a knife blade. What we want is martensitic steel. Those words have actual, clearly defined meanings, and it would serve us all well if we did not confuse them.

I respectfully and humbly advise you to study a bit more about steel structures and chemistry and what happens during heat-treat, before picking out phrases that "seem" to support your unfounded theories and making such ignorant broad-brush claims about how this stuff actually goes from the mines to the mill to the anvil/grinder to the HT shop to the customer. A little knowledge is a dangerous thing, and frankly, you are displaying very little knowledge and a whole lot of... something or other.

This is not a matter of my opinion or personality. This is a matter of facts vs. baloney.

Fair enough, as Chiral and Me2 pointed out, the actual carbide load of 13C26 is lower than I thought. Thanks for their courteous correction.

But I did not cherry pick anything. I was responding to your assertion that 13C26 has almost no carbides at all. In fact, it does. And I quoted both Sandvik's description of the steel in both its unhardened and hardened states, plus I gave a link to the data sheet. I specifically included Sanvik's information about carbide loading in the hardened state so that it wouldn't be misleading to refer to only the unhardened state.

This is just a discussion where we are all trying to learn. I don't agree with all your opinions, but I do appreciate that you share your knowledge with the rest of us.

 

[whp]

Thanks for the education James Terrio.

 

[samuraistuart]

In the temperature range of 1144-1379 °C (2091-2515 °F) the microstructure of Uddeholm AEB-L stainless steel consists of just one single phase: austenite. Thus, if AEB-L steel is hardened from an austenitization temperature that is higher than 1144 °C (2091°F) the resulting martensitic microstructure will contain no primary carbides.

Below the temperature of 1144 °C (2091 °F) the chromium-rich M7C3 primary carbides start to precipitate from the austenitic matrix. At the austenitization temperature of, say, 1052 °C (1925 °F) the equilibrium amount of chromium-rich M7C3 primary carbides is 3.3 molar percent (2.6 volume percent). The equilibrium amount of carbon and chromium in the austenitic matrix at 1052 °C (1925 °F) is 0.44 wt. % and 11.4 wt. %, respectively. (The amount of carbon and chromium in the matrix is a good indicator of the steel's hardenability and corrosion resistance, respectively.)

The equilibrium value for A1 temperature (eutectoid temperature) was calculated to be 814 °C (1497 °F). Under equilibrium conditions the austenite in Uddeholm AEB-L stainless steel transforms into ferrite at this temperature.

Not written by me. I am no where NEAR that smart! I do recall reading tho that in low alloy steels that will form carbide, most of the time the carbide (even W or V) can be locked up in the cementite carbide. Only until there is significant amount of alloy (and the necessary carbon) will primary carbides form. As in Cru Forge V. There is actually enough V in there (and the excess carbon) to form PRIMARY V carbides. Fun stuff to me for sure...but gets confusing fast.

http://www.calphad.com/AEB-L.html

 

[sodak]

I don't see any difference in "sharpness" or "keenness" in any of my knife steels. Some take longer to get there, but if I'm careful - and using my Edgepro - they all get to a very sharp end result.

 

[chiral.grolim]

... if AEB-L steel is hardened from an austenitization temperature that is higher than 1144 °C (2091°F) the resulting martensitic microstructure will contain no primary carbides...

Primary chromium carbides (Cr23-C6 & Cr7-C3) dissolve more easily (lower temps/times) than harder, more stable W-C and V-C primary carbides. But the dissolved carbon does precipitate into a chromium-carbide fraction during tempering at 3-5% volume as me2 mentioned, you cannot escape the carbides only limit them by steel formulation and methods to reduce aggregation. Still, that level is comparable to A2 and similar steels, it's not a bad thing. But if you want fewer chromium carbides that is what 12C27 and 12C27M (420HC) are for.

(image of 13C26 pulled from web)

For me, ease of sharpening is less about steel type - I tend to use diamond or SiC which cannot tell the difference between steels - than about edge thickness. Thicker edges I tend to use with more force on harder tasks and so accumulate more damage that takes longer to restore due to the increased amount of metal needing to be removed. Thinner edges I use with greater care and can more easily see the damage as it accumulates, and it takes much less time to restore with so little metal to remove. This is part of the genius of thin hollow-ground blades like straight-razors: they are thin at the apex to reduce wedging in the whisker, but they're also thin behind in the primary grind to make edge-restoration a snap.

 

[Sikael]

Thanks for the excellent posts, this is great info. :thumbup: I was going to weigh in, but I know when I'm out of my depth. Still... I've heard Adamantium and Unobtainium can both take a crazy sharp edge. Try and cut a tomato, BOOM! Atomic fission. Great edge retention, too.

 

[samuraistuart]

Thanks for that image, Chiral. I saw that image somewhere but it wasn't labeled as AEB-L(13c26) at the site I was visiting. Very cool. They look like they're about 1 to 3 micron in size! If I am reading that scale right. Um is micron, right?

BTW, talking with Chiral and some of the other very knowledgeable guys here, I am WAY out of my league too! But I DO LOVE this stuff.

 

[kane22]

I'm really liking M390 so far.

 

[me2]

The 3-5% carbides I mentioned are primarily carbides that are undissolved during austenizing and remain after quenching. Tempering carbides are smaller even than the ones in the micrograph above.

 

[Ankerson]

The 3-5% carbides I mentioned are primarily carbides that are undissolved during austenizing and remain after quenching. Tempering carbides are smaller even than the ones in the micrograph above.

More like 1%.

PP 141

http://www.hybridburners.com/documents/verhoeven.pdf

To produce stainless steel blades that can be heat treated to as-quenched
hardnesses in the range of Rc = 63-64 it is necessary to be able to produce austenite with
%C values above around 0.6%C and %Cr levels above around 12 %Cr. This
composition is shown at the star on Fig. 13.11 and it happens to fall on the carbon
saturation line for heat treatment at 1100 oC. As shown for alloy D on Fig. 13.12 if one
increases the %C above 0.6 % to 1.3% and holds Cr at 13%, the tie lines through the
resulting composition predicts that the resulting austenite will produce a high hardness
martensite, as %C is ! 0.78%, but its %Cr will fall to around 9.5 %, well below the
12%Cr required for good passivity

AEB-L has .67% C and 13% Cr.

So the after HT Cr has to stay at 12% or above to retain the stainless properties.

That's what the steel was designed to do in the 1st place.

That's why the percentages are what they are.

Not enough C for the Cr carbide percentage to be any higher than 1%.

The C and Cr has to be balanced in order to maintain the stainless properties so as the C % goes up the Cr % also has to increase in order to maintain that 12% Cr after HT.

 

[BonhamBlades]

I have worked them all and in my opinion s30v and s35vn are the king

 

[me2]

More like 1%.

PP 141

http://www.hybridburners.com/documents/verhoeven.pdf



AEB-L has .67% C and 13% Cr.

So the after HT Cr has to stay at 12% or above to retain the stainless properties.

That's what the steel was designed to do in the 1st place.

That's why the percentages are what they are.

Not enough C for the Cr carbide percentage to be any higher than 1%.

The C and Cr has to be balanced in order to maintain the stainless properties so as the C % goes up the Cr % also has to increase in order to maintain that 12% Cr after HT.

I don't really follow how you get 1% chromium carbide from that excerpt. Can you elaborate?

 

[Ankerson]

I don't really follow how you get 1% chromium carbide from that excerpt. Can you elaborate?

You CAN READ right?

He makes it VERY SIMPLE.

 

[Sikael]

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

 

[samuraistuart]

To my understanding the carbide percentage is dictated by the austenitizing temperature chosen. Higher temp=less carbide fraction. Lower temp=higher carbide fraction.

 

[samuraistuart]

To my understanding the primary carbide percentage is dictated not only by the carbon percentage and alloy percentage, but by the austenitizing temperature chosen. Higher temp=less carbide fraction. Lower temp=higher carbide fraction. Depending on the temp I choose to harden 13C26, I can have either 3.3% all the way down to zero % carbide.

 

[me2]

The sharpest knife steel I saw before I started measuring was a blade made of 12C27. It would get despicably sharp with minimal effort, sharper than my old Buck Scoutlite in 425M steel with the same procedure. I will point out that the Buck was my only knife at the time and I was VERY familiar with sharpening it. It will impresses me how sharp that blade was in 12C27, and I wish I had a way to measure it at the time, but that predated measuring sharpness in a numerical way by about 15 years for me.

Stuart, that was part of the point I was trying to make. I wish Ankerson had responded in a more constructive way, as the response above was essentially meaningless with respect to anyone involved learning anything.