2 Myths About Carbon Steel

[me2]

Just read a study where 3 carbon steels were compared to a stainless steel blade, all the same geometry, same sharpness, and same hardness. The stainless blade did better than the other three blades, doing the same cutting, with respect to edge retention. All three carbon steel blades were forged. The stainless blade was ground from stock received from the steel supplier.

This study shows that the old common knowledge about stainless steels not holding an edge as long as carbon steel isn't true. It also shows the common knowledge about stainless not getting as sharp as carbon steel is also not true. The forging of the carbon steels is only mentioned here because it was in the study. There is not enough evidence to show that had anything to do with the results.

Most members here probably already knew this, but the old myths still lurk in dark corners even here.

 

[Russ Andrews]

Putting all the steels into service at the same hardness,and with the same
edge geometry will negate the findings...IMO...because each steel is different
and hardness and geometry need to be adjusted for the steel and it's intended
use.

 

[Huntsman Knife Co. LLC.]

I think for the user the only advantage that carbon steel has over stainless is toughness.

Hopefully as technology advances we will see some more ultra tough stainless steel's that cut like demons. I think Elmax is a good start.

 

[Curtis_Lowe]

what kind of carbon steels and what kind of stainless?

 

[stanley_white]

Just read a study where 3 carbon steels were compared to a stainless steel blade, all the same geometry, same sharpness, and same hardness. The stainless blade did better than the other three blades, doing the same cutting, with respect to edge retention. All three carbon steel blades were forged. The stainless blade was ground from stock received from the steel supplier.

This study shows that the old common knowledge about stainless steels not holding an edge as long as carbon steel isn't true. It also shows the common knowledge about stainless not getting as sharp as carbon steel is also not true. The forging of the carbon steels is only mentioned here because it was in the study. There is not enough evidence to show that had anything to do with the results.

Most members here probably already knew this, but the old myths still lurk in dark corners even here.

Please post a link to the study so the members here can judge the evidence for ourselves.

Thank you.

-Stan

 

[Mark Schmitt]

I think the devil is in the details here. Could you post the reference for the study?

Common perception, I believe, is that it is more *difficult* to hand sharpen a stainless blade, not that you can't get a stainless blade just as sharp as a carbon or tool steel blade. This is largely due to the wear resistance of the stainless steel, a factor which should (all other things being equal) mean that it will hold an edge longer than a similar carbon blade in repetitive, low-stress cutting. If this was the basis for the comparison it is not at all surprising that a stainless steel would come out on top...

So many other factors here...I'd love to see the study reference.

Thanks,
Mark

 

[me2]

Putting all the steels into service at the same hardness,and with the same
edge geometry will negate the findings...IMO...because each steel is different
and hardness and geometry need to be adjusted for the steel and it's intended
use.

There is validity to that position. Many times I've heard/read critiques of knife tests when one knife was significantly softer. The critics often said the knives should be the same hardness. I didn't really agree with that. Different steels have different optimum hardness. Different steels also suit different purposes. For this test all the blades were ground to the same shape and hardness so that the only variable was steel. Even the microstructures were very similar.

I personally prefer to select a steel with proper characteristics for the use, and give the steel its optimum treatement for that use. You can underharden and/or over temper high speed steel (my current favorite) for use as a machete, but there is little point when 1055 will do better and be 1/10th the price. However, when comparing two knives in different steels, the steels need to be in the same rough categories for the comparison to make sense. It's the same concept as comparing a 4" blade Busse to a Spyderco kitchen knife, or the time someone told me their Microtech LCC could "outperform" my EDMF Smatchet. That borders on ridiculous. This can become quite complicated, since many steels can do more than one thing pretty well. 52100 makes dandy ball bearings, but it also makes a nice straight razor

what kind of carbon steels and what kind of stainless?

There was a specialty carbon steel (wootz), 1080ish steel (I forget exactly which), 52100, and AEB-L.

 

[me2]

Nevermind. I found a source with Google for free.

http://www.bestexcompany.com/parks/knives/paper_from_journal.pdf

 

[me2]

I think the devil is in the details here. Could you post the reference for the study?

Common perception, I believe, is that it is more *difficult* to hand sharpen a stainless blade, not that you can't get a stainless blade just as sharp as a carbon or tool steel blade. This is largely due to the wear resistance of the stainless steel, a factor which should (all other things being equal) mean that it will hold an edge longer than a similar carbon blade in repetitive, low-stress cutting. If this was the basis for the comparison it is not at all surprising that a stainless steel would come out on top...

So many other factors here...I'd love to see the study reference.

Thanks,
Mark

I've heard both, but I've heard more that stainless won't take an edge, carbon steel gets sharper, etc. I'll check to see that the sharpening procedure was the same for the steels involved.

Edited to add: I checked the source and it seems all the blades were sharpened the same way. No distinction I read was made of the various burrs and what steel they formed on.

 

[lava_lamp]

Just read a study... This study shows that the old common knowledge about stainless steels not holding an edge as long as carbon steel isn't true. It also shows the common knowledge about stainless not getting as sharp as carbon steel is also not true.

I'm not a steel junkie like some members. Nor am I a metallurgist. I suspect, however, that the definitive conclusions you have reached might not hold up. There may be other variations between the knives and variations in the testing procedure.

In general, though, I would have thought a high-end stainless would hold a better edge, but the carbon would be easier to sharpen.

 

[me2]

What definitive conclusions do you mean? All this shows, with respect to the topic above, is that stainless steel can take an edge as sharp as carbon steel, and hold it just as long or longer. It doesn't say it always will. There are way too many variables for that to come from any one published paper.

I have often said before that such a blanket statement as carbon is better or stainless is better is nonsensical. The number of alloys alone makes this impossible to judge for any property but corrosion resistance. I've heard, even from knife knut members here, that no stainless is as good as carbon steel in edge holding or edge taking. I've just read a study that shows this to be false. It only takes one. One reason this study is nice is all these steels are similar in microstructure, and thus, in use and behavior. It's not like the study picked S90V and Opinel's 1075 or whatever they use now.

 

[flarp]

I think there are so many variables at play that a test with 4 knives won't provide any meaningful results. There are numerous types of carbon and stainless steels (and that's not even getting to semi-stainless steels) and probably just as many heat treatment methods, not to mention differences in the grinds and even subtle blade geometry variations from maker to maker.

There's also value proposition. Sure, a S30V blade may outperform a 1095 carbon steel blade, but they're not likely to be in the same class of knife. You can pick up an Opinel Carbone w/ 3" blade for about $10. You're not likely to get a knife with a S30V steel blade for anywhere near that.

That said, I have done a couple of non-controlled side by side comparisons out of personal curiosity. They're hardly conclusive, and the verdict is actually split for my two cases. One was with two Opinel No. 8's, and the other was with a pair of Mora Allaround knives (711 & 746). Mora uses Sandvik 12C27 (HRC 57-58) and 1095 (HRC 59-60)for their stainless and carbon steels respectively. Opinel uses Sandvik 12C27M and XC90 for their stainless and carbon steels. I can't find any consistent product literature about what those are hardened to. The Moras are identical aside from the blade steel. The Opinels are pretty similar, the differences being the steel and the Inox blade is more a clip point vs. the drop point on the Carbone. Edge length and curvature of the belly are pretty much identical though.

I only use the Opinels for food (prep and eating). Over time, I have had to sharpen Carbone one a little more frequently. I don't know if it is dulling from direct wear, or rather just the oxidation eating away at the edge. There isn't anything obvious (rolling, chips, etc.) on the edge, but I do notice it dulling a bit faster. Both knives see roughly equal use. Cutting performance aside, I do like the look of the patina the carbon blade has taken on.

For the Moras, both fresh out of the box, I broke down some cardboard boxes and then took them outside for some yard work. I alternated between the two fairly evenly (I wasn't keeping record, but it should have been reasonably close). The main task outside for the knives was to clean the off-shoots off larger trimmed branches (to prepare them for bundling and bagging). I used sheers for the thicker stuff, but for off-shoots 1/4" or less in diameter, I just ran the blade along the length of the larger branch to shave them off. At the end, there was noticeable rolling along the edge of the 746 (stainless), but the 711 (carbon) edge looked almost pristine (save for some scratches and moisture transfer from the branches).

 

[hardheart]

Putting all the steels into service at the same hardness,and with the same
edge geometry will negate the findings...IMO...because each steel is different
and hardness and geometry need to be adjusted for the steel and it's intended
use.

It does not negate the findings, it is the only way to test the steels. Changes in hardness and geometry will change the edge holding as much or more than changing the alloy content. That's like saying impact testing has to be done with test samples of different thicknesses. The amount of steel in the tool is more important than the kind of steel it is.

CATRA testing of steels, heat treat, grind thickness, edge angle, and edge finish of my choosing was just completed. I will be sorting through 136 pages of data. Changing 2, 3, or more variables at the same time means you cannot ascribe any changes in results to one variable.

 

[stevomiller]

The CATRA test mainly tests the abrasion resistance of the steel. It is an excellent way to test slitters and machine knives as they always approach the material cut at the same angle and and under consistent load. However, abrasion resistance is but one part of the edge holding equation in real world human usage, as we attack from all angles and perform levering cuts, etc.

Additionally, the findings here are for a very fine grained stainless steel with very small carbides. The carbides it forms may also be harder than those found in other stainless steels (or softer) even though a Rockwell test reads at 60rc, because it isn't working on a microscopic level (although there are tests that do). Its behavior is going to be quite different from steels such as 154cm or 440c, depending on the application.

I guess what I'm saying is that the paper is correct in what it reports, but one has to be careful in how they interpret it. Because of this both Russ and Hardheart are correct in their statements, even though they contradict each other.

 

[Mike-Mike]

So they made them the same hardness and they worked the same? Thats like saying that a Ferrari and a neon responded the same on a 20mph track.

 

[Dave Behrens]

Which steels did the study test? If it compared 440C or 154cm to 1075 carbon then yeah the "stainless" is probably going to perform better. Also each steel performs differently at different hardness levels. While S90v or 10v fuction at 65HRC other steels edges would be brittle and chip, so comparing steels at the same HRC negates the study. Also what steel are they defining as "stainless" is it a 400 series dedicated "Stainless Steel", or is it a high carbon steel with more stainless properties ie, 154cm, elmax, VG10 etc? Without complete diclosure of information, the study is false in its premise.

 

[hardheart]

The study is a peer reviewed paper by a PhD who wrote a book on metallurgy and heat treating for knife makers. The steels were wootz, AEB-L, 52100, and 1086. me2 posted this information in post #7, and then posted a link to a pdf of the study in post #8. Questioning the content of the test, the amount of disclosure, and the legitimacy is a bit absurd when it is literally one click away from answering all your questions. SEM micrographs of the edges, retained austenite levels, alloy composition, heat treat procedures, edge angle measurements, HRC measurements, the composition of the CATRA test paper strips, the speed and length of cutting stroke, the downward load, it is all spelled out. AEB-L had the lowest carbon content of the steels tested.

So they made them the same hardness and they worked the same? Thats like saying that a Ferrari and a neon responded the same on a 20mph track.

If you in any way think that 5160, 154CM, and S90V all perform the same at 59 Rc, then sure. Otherwise, you realize that nobody ever thinks that, ever.

 

[stevomiller]

I'm somewhat confused on your stance Hardheart. I am very familiar with the authors and the fact that this is a peer reviewed paper, and I agree the test was well executed and the CATRA is ideal for the test it is performing.

However, do you agree or disagree that there is more to the edge holding equation than what is tested here?

 

[Dave Behrens]

me2 posted this information in post #7, and then posted a link to a pdf of the study in post #8. Questioning the content of the test, the amount of disclosure, and the legitimacy is a bit absurd when it is literally one click away from answering all your questions.

Thank you for informing us of that. I deeply, sincerely apologize for missing the link, and promise, after this post I will take my own life in the most disgusting manner possible.

 

[kurodrago]

I agree completely with me2 on the subject but doesn't dismiss the fact that out there, there's more stainless crap than carbon steel on sale today.