What is the best steel for retaining high sharpness?

[vanka]

Actually wearing off the blade is pretty easy and quick. It really depends on how you use it. This particular HH UKPK is about 3y old and has been sharpened more than 200 times. As you can imagine the tip was protruding out of the handle when closed. I had to bring it back somehow to stay safe in the pocket. With that being said, this s30v blade is being used every day at work. Cutting plasterboard, vinyl flooring (2-3mm thick), vapor membranes and whatever you can think of during a standard day on construction site.

[Mage7]

Rex 45. The fine grain structure and extremely high hardness gives it a very long lasting super scary edge in my experience. Rex 45 is pretty much all fine edge.

I have heard of rex 45 holding a good edge for a long time before, but only once. Have you used hap40 before? composition wise, they look very similar.
image.png image.png
Data from zknives

Too bad spyderco doesn't sell rex 45 or hap40 knives anymore as far as I know

They're compositionally equivalent, but the reported HRC figures for the models in HAP40 are quite a bit less than those reported for the Rex45. However, as far as I know, they have all been tested on models that were also laminated steel blades that had HAP40 as the core and I believe Sus410 as the outer layer. That could throw off testing because if one tests on a flat portion like the tang, there's a likelihood that's not got the HAP40 exposed. Then on the other hand, the portion of the blade with HAP40 exposed can't be accurately Rockwell tested because it's at an angle. Either way, many people have suggested that they don't find the HAP40/Sus410 to hold an edge as well as the Rex45, but I kind of question how much of that might be the power of suggestion because people have heard the reports that they're softer.

Either way, both still pop up on the knife swap every now and then, if you're not opposed to buying on the secondary market.

[Spyderfreek]

Rex 45. The fine grain structure and extremely high hardness gives it a very long lasting super scary edge in my experience. Rex 45 is pretty much all fine edge.

I have heard of rex 45 holding a good edge for a long time before, but only once. Have you used hap40 before? composition wise, they look very similar.
image.png image.png
Data from zknives

Too bad spyderco doesn't sell rex 45 or hap40 knives anymore as far as I know

Spyderco does a much better job heat treating Rex 45 which is why it behaves like it does. Most of the blades are 67hrc or higher. The Seki city factory just doesn't get hap 40 that hard. You can currently get a Rex 76 pm2 at GP Knives, it's very similar to Rex 45, just slightly better.

[dan31]

Not sure if ZDP-189 is appropriate. I do find when it gets sharp, it is so aggressively sharp with all those carbides, but it the way it breaks down is impressive.

[Jimandchris2]

Also, what makes a steel retain that super sharp edge as opposed to "breaking down" into a working edge?

Differences in retained austenite, carbide size/volume, hardness, stress/fatigue, grain growth, plate martensite vs lath and heat build up during processing.

Lastly, your sharpening skill is probably the biggest most immediately controllable factor.

This means even the same steel can have a different behavior depending on the factors above.

7 years ago I had a similar question, at the time it seemed like CPM 4V was the answer since it seemed like back then it was the nexus of strength and toughness.

I ran it 65rc and ground the knife as thin as possible and the edge failed hard carving wood.

Maybe it was the 8% carbide volume?

I talked to Larrin at the time and he recommended a "matrix" steel.

Caldie, which is technically a matrix of "4V" without the carbide.

However, to dissolve all the carbide causes EXTREME grain growth without carbides to pin grains along with detriments from the other variables I shared above due to overaustenitizing.

This causes the properties to drop in performance.


So, it might not be as simple as hardness, impact toughness and carbide.

7 years later and I certainly know that the factors I shared above

(retained austenite, hardness, stress/fatigue, grain growth, plate martensite vs lath and heat build up during processing, how it's sharpened)

Play a bigger role than just the carbides alone.


To actually answer your the question it requires physical experiments that factor in the variables I shared above along with good control.

Simulation and speculation alone will not work.

You'll have to invest into some equipment and gather more knowledge and skills to execute the testing and correct your procedures after scrutiny.


Regardless, you will never achieve a fine edge that holds that kind of sharpness similar to how the working edge lasts but there are certainly features that could prolong it compared to other conditions.



TL:DR

Steel chemistry is not the only factor but the name of the steel gets the credit or the blame for expectations good or bad.

Now that we got that out of the way the answer is Nitrobe 77.

This was EPIC!!! THANK YOU SIR!

[Guts]

Rex 45. The fine grain structure and extremely high hardness gives it a very long lasting super scary edge in my experience. Rex 45 is pretty much all fine edge.

I have heard of rex 45 holding a good edge for a long time before, but only once. Have you used hap40 before? composition wise, they look very similar.
image.png image.png
Data from zknives

Too bad spyderco doesn't sell rex 45 or hap40 knives anymore as far as I know

Spyderco does a much better job heat treating Rex 45 which is why it behaves like it does. Most of the blades are 67hrc or higher. The Seki city factory just doesn't get hap 40 that hard. You can currently get a Rex 76 pm2 at GP Knives, it's very similar to Rex 45, just slightly better.

The last of the REX76 PM2's in satin sold out a couple weeks ago when they put it on discount fwiw. I'm surprised the satin version stuck around as long as it did though. Great steel. The scales on it are awesome too.