Stainless vs carbon steels: toughness and edge retention - what am I missing?

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Troopah_Knives

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If you modify that phrase to instead read:

"Maximum achievable sharpness with low to medium skill level"

Then you start to view individual steels for their real world characteristics as experienced by most people. Even with blades sporting more obtuse edge geometry. These steel types have the ability for easier sharpening.

So with this lens its easy to understand why many people gravitate and love steels like AS, White #1, or Blue #2.

The ability to sharpen your sticks to near a "razor sharp edge" or past is very desirable to most people.

Crappy Walmart, target, or big grocery chain stainless blades do not have these qualities.

Again, its important to understand steel as they actually function in the real world with use and sharpening... Not just as stats on a spec sheet.

I say this all with extensive real world R&D testing of things in real use vs. theoretical capabilities as theorized, hoped for, and told to us by those who engineered the items.

Real world always shows the truth of a product-- especially those meant for continual use and abuse.

✌️
Sure you can modify the statement I made to say that and you are correct that most people pick stuff that is easy to sharpen. but that is not the point I was making. I was specifically talking about the maximum sharpness achievable by steel taking the sharpener out of the equation.
 

McMan

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“The conventional wisdom seems to be that carbon > stainless, but these numbers paint the opposite picture. What am I missing?”

Steel A might be superior to Steel B.
But this does not equate to Knife A being superior to Knife B. Full stop.

This is an important distinction. And for multiple reasons.
For the sake of space, here are two:
--Makers make decisions about the steels they use based on multiple factors, not all of which relate to steel performance or are even knife-related. Economics and production processes matter--costs, availability, labor-time, batch scale, relative ease (or complexity) of HT, division of labor and expertise, etc.
I think of it this way—there are characteristics of a given steel that we, as end users, don’t “use”. But, in the process of making the knife, the maker does.
--Availability. Knives are not available in a pull-down menu of different steels (well, maybe Sukenari, but...). We buy what a maker makes. Then we evaluate performance and value. For a maker to move to, say, S90v is not as easy as just switching steels—many of the decisions in the first point above are relevant and would be impacted—as would, of course, price... From a maker’s perspective, then, does it make sense to move to a ‘superior’ steel? Maybe yes, maybe no...
 
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Troopah_Knives

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@McMan Yeah I think you nailed it with industry trends! It doesn't change your overall point one bit but I did want to address this one thing cause I see it everywhere.
relative ease (or complexity) of HT
This idea of harder/easier HT's seems pretty widespread but I honestly don't know where it came from. Assuming you have an HT furnace (Which most makers do) anyone can follow an HT recipe from a book and get a satisfactory HT. Sure getting every little bit of performance out of steel can take a bit more work but I wouldn't say that is steel-dependent. All steels (with one exception I can think of) have the same set of steps you just have to punch different numbers into the furnace and quench in different mediums.
 

Jovidah

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This is another one of those internet myths that we like to perpetuate. High wear resistance steels stay sharper longer regardless at which point you stop your testing. High wear resistant steels keep initial sharpness longer than low alloy steels. They can also get to the same sharpness for any practical purpose even though there might be a theoretical difference. The problem is correct abrasive and skill, so we can’t disregard ease of sharpening, because ease of sharpening is so important that it overshadows many other attributes of a steel. If anyone could as easily and consistently get to the same sharpness regardless of the steel then high wear resistant steels would rule kitchen knife world and only a tiny group would play with low alloy steels for the sharpening, polishing, forging and corrosion entertainment that they provide. Low alloy steels also allow makers to forge knives easier, so we benefit from this as well since features like integral bolsters even though possible are not very practical outside of forging. San mai of various steels and materials is also easier with low alloy steels.
Perhaps I should have worded it slightly different, but I'm not sure it's fair to assume that higher & lower alloy steels have the same level of linearity to their sharpness dropoff. The carbide content - at least according to Larrin's research - is a big driver of the higher performance in CATRA testing, but what type of edge does this really leave?
Sure this is anecdotal, but many people have this experience... And I think many of us share the experience that this 'extra retention' is mostly in the 'good for plenty of people, not good enough for us'-domain when it comes to steels like VG-10. Yes it'll keep cutting like a 6/10, but that's not very interesting if you prefer an edge that's at least an 8/10. Meanwhile Shirogami tends to just suddenly go off a cliff.
Not that I want to discredit the outcome of his testing since in general lines I do agree with it, but I think there's some extra nuance there that gets lost in simplifying it down to 2 numbers.
Another thing is how well does CATRA simulate kitchen edge retention. People bring up that food has silica too but there is a lot of board smacking as well in proportion to abrasive wear. I do think that this is really hard to properly test though.
Although it is true that consensus would be different if we all had diamond stones
Yes this is another issue with the CATRA testing; it's entirely possible that the main mechanism of edge degradation in kitchen knives is mechanical impact from hitting the board, not abrasive wear. But I have a hard time coming up with an easy and objective way to replicate this.
I think some of the testing America's Test Kitchen did with robots just moving a knife around has potential in theory, but it had so many other flaws the data coming out of it is very questionable.
 

Jovidah

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Some other things that came to mind when it comes to sharpening:
-With 'ease of sharpening' it might also be worth mentioning 'ease of deburring'. If a theoretically higher performing steel is a pain to deburr some might argue it's not really 'better'.
-I'm reluctant to go into specifics on, but from what I've seen in past testing some stones might not be able to adequately cut certain high alloy high toughness steels. Whether it's due to the abrasives being too soft to cut certain carbides (vanadium carbide usually being the main offender) or other factors, but this almost 'forces' you to upgrade towards diamond stones, which is a significant extra expense - unless you already have them. It can also influence people's perception of a steel if they don't.

I also very much agree with the sentiment that a steel is only a small part of what makes a good knife.
 

M1k3

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Even with diamond stones, white1 should still be easier to sharpen, right? (this may have been what you were saying)
In my experience, whatever grit your diamond stone is, is what grit the steel will be sharpened at. Whether that be White 1 or Rex 121 or cheap soft stainless. Diamonds are harder than the carbides in the steel.
 

Barmoley

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Perhaps I should have worded it slightly different, but I'm not sure it's fair to assume that higher & lower alloy steels have the same level of linearity to their sharpness dropoff. The carbide content - at least according to Larrin's research - is a big driver of the higher performance in CATRA testing, but what type of edge does this really leave?
Sure this is anecdotal, but many people have this experience... And I think many of us share the experience that this 'extra retention' is mostly in the 'good for plenty of people, not good enough for us'-domain when it comes to steels like VG-10. Yes it'll keep cutting like a 6/10, but that's not very interesting if you prefer an edge that's at least an 8/10. Meanwhile Shirogami tends to just suddenly go off a cliff.
Not that I want to discredit the outcome of his testing since in general lines I do agree with it, but I think there's some extra nuance there that gets lost in simplifying it down to 2 numbers.

Yes this is another issue with the CATRA testing; it's entirely possible that the main mechanism of edge degradation in kitchen knives is mechanical impact from hitting the board, not abrasive wear. But I have a hard time coming up with an easy and objective way to replicate this.
I think some of the testing America's Test Kitchen did with robots just moving a knife around has potential in theory, but it had so many other flaws the data coming out of it is very questionable.
CATRA is a very good test of wear resistance which translates very well into slicing edge retention, be it on rope, cardboard, or bananas. There is really no reason to think that cutting food is somehow different except like you point out board impact could very well be one of the main dulling mechanisms. This is why we don’t just look at CATRA results. Since we are lucky enough to get toughness numbers, hardness/strength numbers and wear resistance numbers we can make a reasonable prediction of which steels have better edge retention everything else being equal. Of course the problem is everything else is not equal in real knives and this is why most popular steels are arguably not the best steels for kitchen knives if we only care about theoretical best performance. In reality the most popular steels are the ones that are the easiest for makers to use and the easiest for users to sharpen. We could split off ease of deburring from ease of sharpening but it really is part of ease of sharpening since sharpening is the whole process. Deburring can definitely be more difficult on some steels and especially when the heat treat is screwed up.

As far as anecdotes of high alloy steels loosing their peek sharpness sooner, I think this is a myth that has been debunked by a few tests. I believe the explanation is most likely due to people using inappropriate abrasives or lacking the skill that higher alloy steels might require to not leave burrs, wire edges, overstressed apex, etc. Basically the ease of getting a clean, crisp apex on low alloy steel out weights the benefits of high alloy steels for most sharpeners. The problem with anecdotes is that it is not always clear how the edge failed, is it from deformation or micro chipping at a level that can’t be seen with a naked eye or wear. One mechanism can be mistaken for another very easily.

In addition, we don’t know if geometries are the same or how sharp the knives really are when comparing low and high alloy steel knives. It is just not very easy to compare real knives. When diamonds or CBN are used especially with guided systems people seem to not see these strange results of low alloy steels keeping peek sharpness longer. This leads me to believe that what we see when free hand sharpening on conventional stones is due to sharpening and not the attribute of the steels. High alloy steels that are commonly used in knives should keep any level of sharpness longer. I really dislike vg10, but it is a fine steel and if heat treated well and sharpened correctly will hold any level of kitchen knife sharpness longer than white class steels given similar hardness and same geometry. Or take something like aebl, there is absolutely no scenario where white steel would be superior to it if cutting performance is all you care about.
 

Troopah_Knives

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Yes this is another issue with the CATRA testing; it's entirely possible that the main mechanism of edge degradation in kitchen knives is mechanical impact from hitting the board, not abrasive wear. But I have a hard time coming up with an easy and objective way to replicate this.
I think some of the testing America's Test Kitchen did with robots just moving a knife around has potential in theory, but it had so many other flaws the data coming out of it is very questionable.
I don't think you can say this for all knives as it is both steel and geometry dependant but there are certain circumstances in which rolling or microchipping can be the dominant form of wear rather than abrasion. But that would really only support the OP's point as many common stainless steels (and even more non-stainless high alloy steels) have better balances of hardness and toughness than low alloy steels, especially the very high carbon stuff that most makers tend to use for whatever reason.
 

Benuser

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I don't think you can say this for all knives as it is both steel and geometry dependant but there are certain circumstances in which rolling or microchipping can be the dominant form of wear rather than abrasion. But that would really only support the OP's point as many common stainless steels (and even more non-stainless high alloy steels) have better balances of hardness and toughness than low alloy steels, especially the very high carbon stuff that most makers tend to use for whatever reason.
For whatever reason? Isn't it for allowing a very keen edge and high hardness by very simple means?
 

r0bz

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why is carbon steel alot easier to sharpen compared to stainless?
i have only sharpened stainless steels never had the chance to sharpen a carbon
 

Troopah_Knives

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For whatever reason? Isn't it for allowing a very keen edge and high hardness by very simple means?
Above a certain carbon content, you aren't getting more carbon in solution at the austenitizing temps used for these steels (1475F is very common) because you have reached the solubility limit of carbon in austenite at that temperature. So adding more carbon simply increase the carbide volume without increasing the hardness of the martensite (other than the normal effects of larger carbide volumes). You could austenitize at higher temperatures but this would make the toughness even worse and increase the amount of retained austenite. Cementite doesn't add much to the wear resistance of the steel because it is not particularly hard. So adding more carbon to already high-carbon steel is a very inefficient way of increasing wear resistance.
 

Naftoor

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As a materials guy, frankly stainless steels are better for cutlery than carbon in most categories. The stigma against stainless steels is a hold over from the past century, when big box stores pushed stainless knives so everyone with a kitchen would buy one, while being able to throw them in the dish washer. They were soft, and gave stainless a reputation for poor performance you can still hear the echoes of today.

All other things being equal, a good stainless out performs a good carbon in most areas. Magnacut and aebl are great steels, aebl in particular is one I’ve run into many people describing as a stainless carbon steel due to how fine the carbides are.

Diamond stones are widely available now, unlike in the days of yonder so sharpening PM steels is also possible.

I’d say the popularity of carbon vs stainless comes to a couple things

1) Many of the big makers do most of their work with carbons, whether that’s due to market reasons, ingrained prejudice against stainless or a cost issue due to the higher difficulty grinding and heat treating stainless is antibodies guess. But people want a knife from X, they care less frequently whether the blade is made out of Y. They want to say their knife came from a certain craftsmen so they can track its family line, what steel the craftsmen chose to use is frequently less important. It’s a sacrifice many make during collecting due to limited availability of pieces and jumping at chances to get a knife from X while it, or the slot is available.

2) Natural stones. There’s quite a few people with likely a solid 4 figures invested in natural stones. Due to the west resistance of many stainless offerings the rocks would be wasted, lasted a few years instead of lifetimes if actually used on them. If you’re in the hobby for the sharpening and the natural stones, PM steels will have little appeal regardless of the performance increases.

3) Patina. No but really, I’m happy to accept a blade that takes upkeep for the sake of patina. My newest piece coming in is a stainless clad carbon which makes me really sad but I wasn’t gonna say no to it (see rule 1)

Honestly I’m hoping more makers start doing carbon clad stainless. I’ve only seen one example of it, and it feels like a genius idea. You get the beauty of the patina on 90% of the blade, without the worry about the edge corroding when stored or used on acidic ingredients. I’m wondering if the heat treat us particularly tricky for that combination, or if there’s a metallurgical reason why I haven’t seen it more frequently.
 

big D

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-----..................................... I’m wondering if the heat treat us particularly tricky for that combination, or if there’s a metallurgical reason why I haven’t seen it more frequently.
Easy or difficult to make aside. I would be inclined to think, that simply no one ever thought of making a knife like this. Perhaps due it being practical, thus being over looked. Though some like or dislike patina, a patina is practical because it lowers reaction between food, along with perhaps a slight ease of care during use.
Iron cladding on a stainless core serves no practical purpose. Simply cosmetic.
Who is the maker?
 

big D

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Above a certain carbon content, you aren't getting more carbon in solution at the austenitizing temps used for these steels --------................................................................................................................................
Out of curiosity, in your opinion. what is the max. percentage of carbon before it becomes not usefull?
 

Rangen

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I have to suspect there are deeper waters here, things that are maybe not well-understood.

What I do know is that I would never throw out a lot of data about people's experiences in favor of some numbers.
 

Rangen

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why is carbon steel alot easier to sharpen compared to stainless?
i have only sharpened stainless steels never had the chance to sharpen a carbon
When I am sharpening a really good carbon steel knife, it almost feels like it wants to be sharp. When I am sharpening a stainless steel knife, it feels like what it wants most is to hang on to as much burr as it can.
 

Troopah_Knives

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Out of curiosity, in your opinion. what is the max. percentage of carbon before it becomes not usefull?
Based on the micrographs I have seen at 1475˚F with a 10min soak you can get something like 0.8-0.9% C in solution max. You can use the iron-carbon phase diagram to calculate the exact solubility limit and its pretty close to that. So carbon contents above that just leads to more iron carbide
 

ethompson

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2) Natural stones. There’s quite a few people with likely a solid 4 figures invested in natural stones. Due to the west resistance of many stainless offerings the rocks would be wasted, lasted a few years instead of lifetimes if actually used on them. If you’re in the hobby for the sharpening and the natural stones, PM steels will have little appeal regardless of the performance increases.
This is a big reason I stick with simpler carbons. I like sharpening, I like polishing, and I like natural stones. Is it rational? No. Do I care? No.

Also, I know of at least a few people with something that is more likely to be a six figure hoard. There are at least a dozen, probably 2 dozen, people here with 5 figure collections. 4 figure collections, yeah there are a lot of us...
 

Troopah_Knives

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What I do know is that I would never throw out a lot of data about people's experiences in favor of some numbers.
But we don't have a lot of data on people's experiences. we have their accounts that aren't controlled for geometry, hardness, HT, often we don't even know what steel they are using. Additionally, in the case of the steels, the OP mentioned there are probably only a handful of members of this forum who have tried kitchen knives in these steels. So even if you do consider those experiences as seriously informative data you only have data on the performance of low alloy steels, not the steels OP mentioned.
This is a big reason I stick with simpler carbons. I like sharpening, I like polishing, and I like natural stones. Is it rational? No. Do I care? No.
YES! I think this is a big part of it. Having nice knives is about the experience you want. I think a lot of people want more traditional knives and enjoy sharpening them not because they are technically better but because that is what is fun.
 

ethompson

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But we don't have a lot of data on people's experiences. we have their accounts that aren't controlled for geometry, hardness, HT, often we don't even know what steel they are using. Additionally, in the case of the steels, the OP mentioned there are probably only a handful of members of this forum who have tried kitchen knives in these steels. So even if you do consider those experiences as seriously informative data you only have data on the performance of low alloy steels, not the steels OP mentioned.

YES! I think this is a big part of it. Having nice knives is about the experience you want. I think a lot of people want more traditional knives and enjoy sharpening them not because they are technically better but because that is what is fun.
Someday I'll get around to getting one of these technically better steels. I find them interesting and love reading and learning about them, just haven't gotten around to it yet (mostly because I'm getting distracted by smooth rocks lol).
 

Troopah_Knives

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Someday I'll get around to getting one of these technically better steels. I find them interesting and love reading and learning about them, just haven't gotten around to it yet (mostly because I'm getting distracted by smooth rocks lol).
smooth rocks make fun dirt. fun dirt makes different steel contrasty lol
 

Barmoley

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When I am sharpening a really good carbon steel knife, it almost feels like it wants to be sharp. When I am sharpening a stainless steel knife, it feels like what it wants most is to hang on to as much burr as it can.
I agree with you that a lot of user data would be useful and shouldn't be disregarded, but this is a very good example of why a lot of it is really not data at all and is not useful in comparing steels.

Very few people here have used high alloy steels in kitchen knives, even fewer used appropriate abrasives, even fewer are good enough sharpeners. What is even worse is that there are a handful of makers that use these steels, so we are dealing with a tiny sample of users and makers, can't exactly make direct comparisons easily.
 

M1k3

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why is carbon steel alot easier to sharpen compared to stainless?
i have only sharpened stainless steels never had the chance to sharpen a carbon
Way less ingredients in the mix. Simple steel. Simple matrix.

Iron+carbon VERSUS iron+carbon+chromium
 

MowgFace

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I see what people are saying about "better" steels, but im not a Pro, and i enjoy sharpening so they literally don't provide me any value add. I do have a couple (R2, SRS15) but that is just because I have no self control.
 

Barmoley

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I see what people are saying about "better" steels, but im not a Pro, and i enjoy sharpening so they literally don't provide me any value add. I do have a couple (R2, SRS15) but that is just because I have no self control.
That's basically the crux of it and in a way the answer to the OP's question. Steel being technically better or rather more suitable has nothing to do with its use in a kitchen knife or its popularity. This doesn't mean that these steels are not better or wouldn't make a better cutting tool just that this has very little to do with them being used or being popular. So to directly answer OP's question what he is missing is that people at least on this forum care very little about steel's ability to hold an edge for an extended period of time once some minimum threshold is crossed. Other attributes of knives are just much more important.
 

Delat

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I just buy whatever knife I can manage to score from makers I’m stalking. If I manage to hit “pay now” quickly enough, afterwards I look at the description to see what the steel is. Honestly as long as it’s a decent steel and I like the overall look of the knife, I don’t really care if it’s carbon or stainless. As mentioned above, you choose the maker and let the maker choose the steel “for whatever reason”.

The talk of which steel is “superior” is nice in a theoretical sense. In a perfect world you’d call up Kamon and ask him for a Magnacut. In the real world you stalk a retailer for a kamon drop and grab a 1.2519 and count yourself lucky. Very few people are looking at TF and thinking “I’d love one if only he worked in SG2.”

My last custom I just told the maker “stainless clad carbon core” solely because I like how that combo looks with a forced patina, and I let the maker choose the specific steels. I think if I only had one or two knives that got heavy use maybe I’d care about high-alloy stainless steels with ultimate edge retention - and we do see new knife requests from people with that requirement. But I think once “collectors” get a few knives, things like ultimate edge retention and corrosion resistance become less important since there’s so many knives in the rotation.
 

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why is carbon steel alot easier to sharpen compared to stainless?
i have only sharpened stainless steels never had the chance to sharpen a carbon
To my mind, it's mostly about the ease of deburring. Yes, it is a little easier to grind but this is not so important for achieving sharpness.

Once I had enough skill to form a consistent edge angle, most of the subsequent improvements in my sharpening have come from producing a clean apex (minimising and removing the burr). This is just easier in simple steels (assuming, as always, a competent heat treatment).