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

[matto]

When I look at Larrin Thomas's comparison of knife steels here and compare stainless to carbon steels, this is what I see

Carbon Steels:
Super Blue: Toughness 2.5, Edge Retention 3.5

Stainless Steels:
SG2: Toughness 4, Edge Retention 5
S30V: Toughness 4, Edge Retention 6
S90V: Toughness 3.5, Edge Retention 9

Why are these steels not vastly superior for making kitchen knives? Ignoring sharpening difficulty, are there some characteristics of these stainless steels not captured by toughness and edge retention that cause them to make inferior kitchen knives?

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

 

[ch_br]

• Ultimate Sharpness
• Ease (or Difficulty) of Sharpening to a High Degree of Sharpness

Are two important factors.

Knife Steel doesn't function in the real world the way it "theoretically" does via stats on a page--inside a vaccum.

Especially when that theoretical data doesn't account for constant use and abuse of a item designed for tasks that are all use and abuse oriented.

 

[Jovidah]

The cynic in me would say 'you're missing the magic of collective internet placebo'.

But I think on forums like ours many who prefer carbon will prefer it exactly because of the ease of sharpening and the quality of the edge achieved. Then there's the aspect of 'character' that patinas bring to a knife, however subjective that may be.
Because the carbon steels grind easier they also tend to be far easier for knifemakers, which will play a role in how much it is used and the price of the end product; after all a steel that grinds easier will take less time to make, which will usually reflect in the price.

But objectively I do agree with you that 'carbon > stainless' is more internet myth than true wisdom. Both have their strengths and weaknesses.

 

[MSicardCutlery]

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

Perhaps that facility of sharpening leads to more easily established quality edges? And that leads to greater perceived quality of one over the other? In short a false attribution.

I'm just speculating here of course.

 

[esoo]

Ignoring sharpening difficulty, are there some characteristics of these stainless steels not captured by toughness and edge retention that cause them to make inferior kitchen knives?

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

You cannot ignore sharpening difficulty as we need to sharpen knives. And part of that is how fine of edge you can achieve on the knife (which is in part determine by the carbide structure). As well, many do not like using diamonds for sharpening.

And for the members of this forum, things like how well a steel holds its "off the stones" sharpness is critical. For example, VG-10 is disliked as it loses that initial sharpness very quickly, but it stays usable for a long time. Carbon steels will stay at a initial sharpness for longer, but then dull further.

And except for the pro's here, for most members, edge retention is meaningless as they will sharpen long before it really matters.

 

[ch_br]

Keep in mind, in a culture such as KKF, many of the members here LOVE sharpening.

Some love it more than the blades or its the primary means in which they interact and derive benefit from their steel.

So steel types that:

• don't get wicked shaaaap (Shoutout to all the MA peeps)
• AND are a PITA to sharpen

will almost always gonna be less desirable. Again, in this specific culture which is much more sophisticated than gen pop about all aspects of knives.

 

[Jovidah]

Perhaps that facility of sharpening leads to more easily established quality edges? And that leads to greater perceived quality of one over the other? In short a false attribution.

I'm just speculating here of course.

I think the overabundance of ****-tier stainless that's outright annoying to sharpen also plays a role. Most opinions on carbon vs stainless are not formed based on SG2, AEB-L or Magnacut...

 

[ch_br]

You cannot ignore sharpening difficulty as we need to sharpen knives. And part of that is how fine of edge you can achieve on the knife (which is in part determine by the carbide structure). As well, many do not like using diamonds for sharpening.

And for the members of this forum, things like how well a steel holds its "off the stones" sharpness is critical. For example, VG-10 is disliked as it loses that initial sharpness very quickly, but it stays usable for a long time. Carbon steels will stay at a initial sharpness for longer, but then dull further.

And except for the pro's here, for most members, edge retention is meaningless as they will sharpen long before it really matters.

In an italian accent:

We speakuh the sameuh language...

 

[esoo]

I think the overabundance of ****-tier stainless that's outright annoying to sharpen also plays a role. Most opinions on carbon vs stainless are not formed based on SG2, AEB-L or Magnacut...

I have a SG2 parer that I absolutely hate to sharpen. Will not take an edge for the life of me.

But then again, that may just be me and my skill at sharpening.

 

[Jovidah]

And for the members of this forum, things like how well a steel holds its "off the stones" sharpness is critical. For example, VG-10 is disliked as it loses that initial sharpness very quickly, but it stays usable for a long time. Carbon steels will stay at a initial sharpness for longer, but then dull further.

I think this is also a good point. Larrin's testing was CATRA testing which doesn't particularly care about how long a steel retains 'peak sharpness' it's mostly a test of 'servicable sharpness' retention.

 

[Barmoley]

I think this is also a good point. Larrin's testing was CATRA testing which doesn't particularly care about how long a steel retains 'peak sharpness' it's mostly a test of 'servicable sharpness' retention.

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.

 

[superworrier]

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

 

[HumbleHomeCook]

You can't dismiss sharpening, it is an integral part of the overall experience.

I have EDC knives in a broad variety of steels. Between them and my kitchen knives I've experienced all the steels you list. With the right abrasives, they're all alright to sharpen but you need to start getting more specialized to get the most out of them. And while you can stall sharpening for a longer period, you steel need to do it and if you use the knife enough, there will come a time when you need to thin it. I've thinned S90V and K390 and it isn't super fun.

Of course, you have to account for heat treat and geometry too and so many makers just don't have the HT experience with a lot of the HS/PM steels.

Price will jump as makers pass on their abrasive and tool wear charges,

Further, there's availability and so many of us buy from Japan where these steels are rare at best.

I'd much rather have an excellently executed shirogami than a mediocore S90V offering.

That said, you can certainly find all those steels in kitchen cutlery so you can get them if you want.

 

[superworrier]

Since CATRA is measuring wear resistance, it seems like it should be the opposite of ease of sharpening (of course not entirely, but as a general trend)

 

[blokey]

Wear resistance is also not the only factor in edge retention, resistance to deformation is quite important in kitchen use, that's why sometimes people report Aogami super or 52100 at 65 HRC have superior age retention to VG10.

 

[HumbleHomeCook]

As the legendary Phil Wilson once said, if you push them enough, they're all gonna fail. You can have chips or rolls. Your pick.

 

[coxhaus]

Give me rolls as I don't want to consume chips.

 

[matto]

Two key points raised above are:

1. how fine of edge you can achieve on the knife
2. resistance to deformation is quite important in kitchen use

Is it correct to say that neither of these are captured by the toughness testing?

I believe #2 is definitely not captured because toughness measures how much force before the steel fractures. Steels like 8670 and 5160 are very tough because they don't fracture, but they do roll.

#1 I'm not as sure about but I would assume the same issue applies. If your edge rolls easily, you can't make it a fine edge.

So what measurements exist to predict whether a steel makes good fine edge for a kitchen knife? It seems that toughness, hardness, and edge retention are really not very good predictors.

 

[Barmoley]

Two key points raised above are:

1. how fine of edge you can achieve on the knife
2. resistance to deformation is quite important in kitchen use

Is it correct to say that neither of these are captured by the toughness testing?

I believe #2 is definitely not captured because toughness measures how much force before the steel fractures. Steels like 8670 and 5160 are very tough because they don't fracture, but they do roll.

#1 I'm not as sure about but I would assume the same issue applies. If your edge rolls easily, you can't make it a fine edge.

So what measurements exist to predict whether a steel makes good fine edge for a kitchen knife? It seems that toughness, hardness, and edge retention are really not very good predictors.

I am confused about your questions. What is it you want to determine? Hardness measures resistance to deformation. Toughness measures resistance to fracturing and wear resistance measures resistance to wear. There isn't one number that will tell you what makes a good steel for a kitchen knife. Even more so because geometry makes a huge difference. On top of that how you sharpen makes a huge difference. To add to this people have preferences. So what is it you are trying to figure out? Many steels can be used to make good kitchen knives, even steels that don't necessarily shine in any of the above mentioned attributes.

 

[matto]

I am confused about your questions. What is it you want to determine?

What is confusing you? I am trying to understand what objectively measurable characteristics of steel are important for making a great kitchen knife. And moreover, why some of the most loved steels seem to rate poorly on the most commonly used objectively measured characteristics.

People say things like "It can't hold as fine of an edge". But this should be quantifiable in some measurable property of the steel.

Hardness measures resistance to deformation. Toughness measures resistance to fracturing and wear resistance measures resistance to wear. There isn't one number that will tell you what makes a good steel for a kitchen knife.

Yes, I understand all of that. On which of those three measures does super blue excel relative to SG2 or Magnacut? And if the answer is "none", why is super blue preferable over SG2 and Magnacut by so many?

Even more so because geometry makes a huge difference. On top of that how you sharpen makes a huge difference.

Of course geometry matters a lot, but that is independent of knife steel. I can attempt to sharpen any steel into any geometry. If I cannot sharpen a given given steel into a given geometry, then there is a characteristic of that steel that is preventing me, and I'd like to know what that characteristic is and how it's measured.

Many steels can be used to make good kitchen knives, even steels that don't necessarily shine in any of the above mentioned attributes.

Again, of course a lot of steels can make good kitchen knives. But if steel A is considered superior to steel B in some scenario (type of knife with a particular edge geometry for a particular cutting task) there should be SOME objective metric of that steel that can explain that steel's superiority in that scenario. If it's not toughness, hardness, or edge retention.. what is it?

 

[HumbleHomeCook]

What is confusing you? I am trying to understand what objectively measurable characteristics of steel are important for making a great kitchen knife. And moreover, why some of the most loved steels seem to rate poorly on the most commonly used objectively measured characteristics.

People say things like "It can't hold as fine of an edge". But this should be quantifiable in some measurable property of the steel.


Yes, I understand all of that. On which of those three measures does super blue excel relative to SG2 or Magnacut? And if the answer is "none", why is super blue preferable over SG2 and Magnacut by so many?


Of course geometry matters a lot, but that is independent of knife steel. I can attempt to sharpen any steel into any geometry. If I cannot sharpen a given given steel into a given geometry, then there is a characteristic of that steel that is preventing me, and I'd like to know what that characteristic is and how it's measured.



Again, of course a lot of steels can make good kitchen knives. But if steel A is considered superior to steel B in some scenario (type of knife with a particular edge geometry for a particular cutting task) there should be SOME objective metric of that steel that can explain that steel's superiority in that scenario. If it's not toughness, hardness, or edge retention.. what is it?

You've already identified some metrics to answer some of those questions but that wasn't your original question. What you originally asked was why are certain steels not vastly superior to other steels. There's a ton of variables and personal preferences in that equation.

You have a lot of information available and understand what you like so you should have no issue finding the the steel that is vastly superior for you.

 

[Barmoley]

What is confusing you? I am trying to understand what objectively measurable characteristics of steel are important for making a great kitchen knife. And moreover, why some of the most loved steels seem to rate poorly on the most commonly used objectively measured characteristics.

People say things like "It can't hold as fine of an edge". But this should be quantifiable in some measurable property of the steel.


Yes, I understand all of that. On which of those three measures does super blue excel relative to SG2 or Magnacut? And if the answer is "none", why is super blue preferable over SG2 and Magnacut by so many?


Of course geometry matters a lot, but that is independent of knife steel. I can sharpen any steel into any geometry.



Again, of course a lot of steels can make good kitchen knives. But if steel A is considered superior to steel B in some scenario (type of knife with a particular edge geometry for a particular cutting task) there should be SOME objective metric of that steel that can explain that steel's superiority in that scenario. If it's not toughness, hardness, or edge retention.. what is it?

For one you are comparing what people say to measurable, repeatable tests and seem to equate them. Someone saying steel A can't hold a fine edge is meaningless on its own where as well conducted tests like CATRA have real value. You can't determine quality of a steel and its suitability for a kitchen knife by someone's experience with a certain knife.

We can take your example of super blue being superior to SG2. In general it is not superior, but it is sometimes run harder and if you want a fine edge and if in your use deformation is the way your edges fail then it might be superior for that use. If you use conventional stones or natural stones then in that case blue super might be superior as well. In general though it is not.

 

[Troopah_Knives]

If it's not toughness, hardness, or edge retention.. what is it?

There is a lot that has been said that I would agree with. Here are a couple more thoughts.

Sharpenability is the final prong you are missing. Any steel with more than a few percent MC type (V, W, NB or Ti) carbide needs diamond or CBN stones in order to sharpen properly.

I personally don't put much stock in the "Maximum achievable sharpness" stuff because I think it is often highly geometry based (although maybe it plays a role in some very high carbide volume stuff)

I agree that there should be some objective metrics to define steel superiority in certain scenarios. I think the three you need to add to the list are carbide hardness, volume, and size. To some extent you are right if you have diamond stones I really see no reason why Magnacut would not be superior steel to something like Shiro 1 as it is better in every single other category.

 

[Troopah_Knives]

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

Taking your point on ignoring sharpability. Modern high alloy steels are better than low alloy steels. Put another way for any low alloy steel I can name high alloy steel that does what that steel does but better. Low alloy steels are still widely used because they are easy to forge, grind and finish and most people aren't willing to pay significantly more for the relatively small improvements steel choice yield compared.

 

[superworrier]

There is a lot that has been said that I would agree with. Here are a couple more thoughts.

Sharpenability is the final prong you are missing. Any steel with more than a few percent MC type (V, W, NB or Ti) carbide needs diamond or CBN stones in order to sharpen properly.

I personally don't put much stock in the "Maximum achievable sharpness" stuff because I think it is often highly geometry based (although maybe it plays a role in some very high carbide volume stuff)

I agree that there should be some objective metrics to define steel superiority in certain scenarios. I think the three you need to add to the list are carbide hardness, volume, and size. To some extent you are right if you have diamond stones I really see no reason why Magnacut would not be superior steel to something like Shiro 1 as it is better in every single other category.

Even with diamond stones, white1 should still be easier to sharpen, right? (this may have been what you were saying)

 

[esoo]

Even with diamond stones, white1 should still be easier to sharpen, right? (this may have been what you were saying)

Diamond stones aren't necessarily easier or faster. They will however cut carbides that some other stones can't.

If you have excellent stability in your hands, you will achieve a crisper cleaner edge.

Spoken as someone who has a Naniwa 3K diamond and isn't good enough to take full advantage of it.

 

[HumbleHomeCook]

Personally, other than maybe some aggressive work on coarse grits, I'd never use diamonds on low alloy steels. They are so sharpener friendly that it isn't necessary or worth wearing on the abrasives.

 

[Troopah_Knives]

Even with diamond stones, white1 should still be easier to sharpen, right? (this may have been what you were saying)

I would actually disagree. Given the same geometry (this often isn't the case) Magnacut has a lower carbide volume and smaller carbides. The carbides in both steels are much softer than diamond so I would be really surprised if there were any significant differences in the rate a diamond stone cuts either given the large amount of pressure you are exerting on the edge.

Diamond stones aren't necessarily easier or faster.

While this is correct it is kinda comparing apples and oranges. Given the same bonding method, a stone with diamond abrasives will cut faster than one with Alumina. However, bonding methods tend to differ a lot between stones so you are technically correct.

 

[Strozzi]

Getting a screaming edge on white steel when you are just learning to sharpen might influence why some people prefer simple carbon. That was me, now I love to sharpen with natural stones and look at patina. Carbon> stainless

 

[ch_br]

I personally don't put much stock in the "Maximum achievable sharpness" stuff because I think it is often highly geometry based (although maybe it plays a role in some very high carbide volume stuff)

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.