2 Myths About Carbon Steel

Don't read too much into this study. As usual for research, it opens more questions than it answers. The article shows that under the conditions of the study, fine grained and fine carbide size stainless steel can outperform common carbon steels in edge holding. The hardness used is indicative of the trend in hardness for knives today. The microstructures are fairly simple, as are the shapes.

Edited to clarify: by don't read too much into it, I mean don't make sweeping assumptions that the information doesn't support.

There is a lot of crap stainless out there, and this is where the myths come from probably. This study demonstrates a couple of things. One is that relatively simple medium carbon stainless steel with a good heat treat can outperform some of the most highly regarded high carbon steels around, even when they all have a quality heat treatment. It also demonstrates that wootz can outperform modern steels, but only when the modern steels are handicapped by low hardness. It demonstrates (again) the huge influence of geometry on cutting ability by comparing the two different shapes on each type of steel. It provides even more information, but you have to dig really deep to get it.

People who are adamant that stainless steel will not take or hold an edge are also frequently confident in their knowledge that there is only one kind of stainless steel. We here are more than just the exception in liking knives. We are the exception in knowing anything about the materials beyond carbon steel is grey, stainless is shiny.
 
stevomiller said:
However, do you agree or disagree that there is more to the edge holding equation than what is tested here?
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There is more to it, but that wasn't tested. The steels that were tested have low wear resistance, and the CATRA dulls edges through abrasive wear. Carbon steel has extremely low wear resistance compared to other cutlery steel *carbon steel, not tool steel or alloy steel. The other steels tested aren't much higher. Hardened steel is martensite, that is the end result of austenization and quenching. The carbide volume is going to increase wear resistance over pure martensite. So a steel that can form carbides beyond cementite is going to outperform those that don't. As noted in the paper, the carbide size and distribution of the AEB-L, 52100, and 1086 are not very far off - 0.2 to 0.6 micron sized particles, with 0.3 to 0.5 particles per square micron. 1086 had almost no chromium, so no chromium carbide, and a small amount of vanadium which would only assist in grain refinement. The AEB-L had approxmately ten times the chromium of the 52100, and was heat treated specifically for carbide formation. The wootz has a more coarse carbide structure segregated in bands of carbide, so the distribution at the edge is poor.

Changing the hardness and geometry to test on CATRA will not show one steel to outperform another, it will show one hardness or geometry to outperform another. For a portion of the recently completed testing - on the exact same test blade, sharpened to a different grit and a different edge angle, the results between the two edge finishes was 80%. Not on two separate steels, not in comparing low carbon vs medium carbon vs high carbon vs ultra high carbon vs low alloy vs high alloy vs tool steel vs stainless steel, the same steel in the same knife in the same test.
 
hardheart said:
The AEB-L had approxmately ten times the chromium of the 52100, and was heat treated specifically for carbide formation.
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Are you referring to chromium carbides? The Uddeholm metallurgist told me AEB-L was specifically designed not to make chromium carbides. They put enough carbon in the steel to get hard and not make carbides. All the chrome goes to corrosion resistance.
 
Yes, and it seems to be one reason why Verhoeven likes it and 52100 so much. But he says specifically in the paper that the heat treatment was for carbides. Of course, as the numbers show, they are still the expected precipitated sub-micron carbides, so he could not mean large primary carbide. Being on the carbon saturation line, there probably isn't much else to get in the end result, unless the steel wasn't soaked or the tempering was entirely off.
 
doesn't AEB-L have very small carbides when treated using Verhoevens preferred method? I'll have to read his section on stainless steels again. IIRC, he uses a hardening temperature so that AEB-L is just off the saturation line, having a low volume percent of very small carbides. Of course he also heat treats the 1084 to have a small volume percent of carbides as well, which is not the normal treatment.
 
Some real testing - thanks for the link. Sure is nice to see accurate and qualified conclusions based on the test.
 
So how different would the results have been if the heat treatment was different? I'm sure you could have used a cheaper heat treatment on the AEB/L and gotten the same hardness. Same for the Carbon steels, and the results would have been very different. I do beleive that how sharp any edge can get is more of how and what you use to sharpen that edge. I've gotten a killer edge on AUS-8, 1095, and D2. In fact I've gotten a great edge on almost every steel, yes some take a little more time and effert. When it comes to knife steel and edge holding there are many myths that are alive and well.
 
The results can range from possibly better to much worse. If the heat tteatment were goofed, any of them could be nearly unusable. Hardness is an easily measured variable. 1084 & 52100 have higher potential there, but toughness might be a problem. There are many ways to arrive at the same hardness, but they are not all equal. This leads to the, imo correct, notion that hardness is just a part of the process.
 
I'd agree. And really if you heat treat them all to the same hardness what hardness do you pick? A hardness that is best for AEB-L or one for 52100?I guess if you really want to find out you'd probably have to find the best heat treatment and hardness for each steel then compare them at their best.
 
Yeah but.... :D

You knew that was coming, didn't you?

While the heat treat determines the final hardness, it is more than that, correct? Doesn't it also influence toughness, carbide size, etc? Not sure what point I'm trying to make, but thought I'd ask...
 
If you know what you're doing and can get the right microstructural features, the door is wide open once you start messing around with the heat treatment. Jack the hardness of 1084 and 52100 up to 65-67. Will it outperform the AEB-L? What happens if the AEB-L goes up to 63? The variables are nearly endless. That's why so may knife makers can come up with different ways and they will all work to some degree. What happens if you undersoak 52100, leaving a lot more carbides, and then draw it back to 41 HRc. Will it out do the damascus then? How about when the knives are held in a human hand, and you have a crooked edge from hand sharpening? If the 66 HRc 52100 did better in CATRA, will it still be ahead? All these variable are why a defined purpose is needed to even choose steel, let alone design and geometry. Then there are the percieved norms for knives and what you can accomplish when everything is optimized. I have a 12" blade that I use for chopping brush up to 4" in diameter. The edge is 0.015" at the top of the edge bevel and the hardness is in the low to mid 50's, yet nothing short of dirt, rock, or metal impact has damaged the edge. What could it do with a truly optimized heat treatment and steel choice? The study is great, and gives a lot of food for thought, and does disprove 2 common myths, but it offers so many roads for more study, it's just a start really.
 
the edge holding porpertie is too complicated of a study. it really invoves almost everything. toughness, hardness, strength and how the second phase persent within the matrix...even thinking about it make me headache.

when everything else being equal, the stainless steel can be as sharp and hold edge as good as carbon steel. there are just many type of stainless and carbon steel out there. we can't generalize them and say which is better and which is not.

one thing we have to put in consideration is the steel have to be easy to sharpen. in my experience, as a knife this is as important than edge holding abiltiy. you can't stop a hard working knife getting dull, but you can always sharpen it to make it sharp again.

about forging, i think it does bring benifits if you do it right. but quiet complicated study as well. different alloy resulting difference in rate of deformation, hold time for recrystalization, numbers of heating cycles...again a lot of crap to put together. one example i can remember is they hot roll 60si2mn(similar to aisi s5) to X%deformation from 1080 to 880°C. then use the remain heat for the quenching. it increase both strength and toughness. tool life is significantly increased this way.
 
I have heard tell that if you drop the austenizing temperature of 52100 down to 1475 and have the gear to do all of the proper thermal treatment, soak, etc it will get screaming hard (67 as quenched) and can be tempered back a bit and have very good abrasion resistance. If you listen to guys like Verhoeven, Kevin Cashen, Roman Landes and a few others, you might get the impression that by tempering steels like 52100 and W2 and even the 1084 and 1086 variants we have now to 58-59RC, you are leaving a LOT of performance on the table.
 
reading this is more fun than the coffee pot discussion over eli manning VS. tom brady. is interesting to note that Udderholm developed this stainless, AEB-L, for razor blades 85 years ago and that it is low carbon/low chrome/no extras when compared to 154cm or 440C or other "Knife Stainless"(which were developed for ball bearings, plastic dies, jet engine blades, aircraft skin......). One point to consider is I can make a reasonable blade of 1084 in my basement with hand tools and a charcoal fire. I have no way of heating AEB-L(or other stainless) to >2000deg F then quench in liquid nitrogen.
I vote for carbon steel because there nothing more fun than having to polish your knife blade because you missed a spec of food when you last cleaned it.
 
Everyone has their favorites, but each steel type is perfectly capable. One thing that I can gripe about in the study is that the 1080 blade was heat treated pretty differently than most people do it. That alone could skew the way the 1080 is viewed in this study. The heat treatment used in the paper would be quite difficult to repeat in a basement type setup. Most people choose 1080 for it's simplicity and lack of carbides to deal with, but here we have someone putting them back to try and get a little better cutting endurance.
 
I'd agree that most steels are very capable of producing a good knife. It really is all in the heat treatment. I beleive the reason stainless did get a bad rep is because it is not as easy to heat treat as most simple carbin steels. Therefor back in the day you probably got alot more poorly heat treated blades that were stainless than carbin. And a myth was born, and for the time mostly true.
 
flarp said:
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).
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I found this thread in a search regarding the SS VS Carbon debate.

This particular post is the one I'd give the most weight to provided that the poster was honest.
Why? Because these aren't laboratory controlled conditions, but rather "real world" uses with
instant feedback and results. As far as material goes, it's all relative. High end carbon will do
better than low end SS and high end SS will do better than low end Carbon. Take two different
materials and put them at the same grade, one will have a different value at said grade.

I'm sure lab testing has it's place in developing materials, but let's be honest, nothing tells
the truth like actually working in differing conditions (weather, climate, temperature, etc...)
on a slew of different materials with one user doing all the testing under equal time/use.

The true test (in my humble opinion) would be to test high grade Carbon & high grade SS
(not at the same grade to each other, but rather each at their peak performance grade).
If that's already been mentioned or pointed out, pardon me for repeating it. I get lost in
all the technical talk. I'm approaching this from a very rudimentary layman's position.

I did appreciate getting the skinny from the pros here (even if I didn't come to a conclusion myself).

But hey! That's just me!

Good read.

:D
 
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