The Effect Of “Edge Aggression” Between Steels

[Barmoley]

We've discussed many times that it seems that some steels have bittier, grabbier edges than others. Even though I've experienced this myself, I tended to attribute this to my imagination or possibly the effect of the grit that I finished the edge on. It never fully made sense to me since I've experienced this even when finishing different steels on the same grid, but I still didn't fully believe that the effect is real even though there is much anecdotal evidence of there being something there. Fortunately, Shawn Houston @Deadboxhero of the triplebhandmade fame did a very cool study on the subject and the results are very interesting.

 

[eddworks]

But, but... I like 52100 a lot.

 

[blokey]

Interesting, definitely love to see more testing. I’ve also seen argument that Martensite structural difference between carbon steel and alloyed steel is also causing the bityness. (Lath martensite vs plate martensite)

 

[Deadboxhero]

Interesting, definitely love to see more testing. I’ve also seen argument that Martensite structural difference between carbon steel and alloyed steel is also causing the bityness. (Lath martensite vs plate martensite)

Which one has which?

 

[Barmoley]

But, but... I like 52100 a lot.

So do I, nothing wrong with liking 52100, but if you were making a dedicated tomato knife it might not be the best choice

It is so great to see these studies done by the juggernauts of our community. The more we know and the better we understand what is actually going on in all things knife the less mystique and misinformation there will be. At least I hope so.

 

[blokey]

Which one has which?

Lath for carbon and plate for alloyed, the original article I read was in Chinese so there might be bit translation error

 

[blokey]

But, but... I like 52100 a lot.

I like it too, and more importantly is your knife that matters the most

 

[Deadboxhero]

Lath for carbon and plate for alloyed, the original article I read was in Chinese so there might be bit translation error

Interesting. I found it was the opposite. The simple carbon steels are more prone to developing plate martensite since the cementite dissolves rapidly past Ac1 easily putting too much carbon solution if a proper time and temperature isn't selected.

Meanwhile, in tool steels, the other metallic elements in alloy carbides found in tool steels don't have as much atomic mobility in the steel matrix and the atomic bonds between the carbon and metallic elements very stable at high temperatures even with long soak times approaching equilibrium.

Most of the large amounts of carbon you see in the chemistry of tool steels remains locked up in undissolved carbides which is what contributes to the wear resistance despite having a lower carbon martensite.

 

[blokey]

Interesting. I found it was the opposite. The simple carbon steels are more prone to developing plate martensite since the cementite dissolves rapidly past Ac1 easily putting too much carbon solution if a proper time and temperature isn't selected.

Meanwhile, in tool steels, the other metallic elements in alloy carbides found in tool steels don't have as much atomic mobility in the steel matrix and the atomic bonds between the carbon and metallic elements very stable at high temperatures even with long soak times approaching equilibrium.

Most of the large amounts of carbon you see in the chemistry of tool steels remains locked up in undissolved carbides which is what contributes to the wear resistance despite having a lower carbon martensite.

Yeah I probably messed up these 2, the Chinese translation is totally different for these 2

 

[Kippington]

This study appears to align with my real-world experience.

I'm a fan of low grit sharpening for seemingly longer edge retention, plus a raggedy carbide structure tends to add to the effect. Downside would be a decrease in edge toughness/stability, which makes it kinda scary to put a nail-flexing edge on it.

It wouldn't surprise me if carbides are cracking and/or falling out of the edge of the 440c - temporarily "refreshing" it.

52100 is so silky smooth in comparison, and stuff like the White steels go even further in that direction...

 

[HumbleHomeCook]

As always, it's great seeing this work and also as always, of course @Deadboxhero is out in front of it! Good stuff Shawn.

I spend so much time in the sub-micron world that when I see those 10+um blobs on the micrograph they look ginormous!

When the Cutlery Hall of Fame is christened, you and @Larrin should be in an early class for your gold jackets.

 

[Deadboxhero]

As always, it's great seeing this work and also as always, of course @Deadboxhero is out in front of it! Good stuff Shawn.

I spend so much time in the sub-micron world that when I see those 10+um blobs on the micrograph they look ginormous!

When the Cutlery Hall of Fame is christened, you and @Larrin should be in an early class for your gold jackets.

Too fancy for me.

Thanks man.

 

[Troopah_Knives]

@Deadboxhero Maybe I missed it but how many times did you repeat the test for each blade?

 

[blokey]

This study appears to align with my real-world experience.

I'm a fan of low grit sharpening for seemingly longer edge retention, plus a raggedy carbide structure tends to add to the effect. Downside would be a decrease in edge toughness/stability, which makes it kinda scary to put a nail-flexing edge on it.

It wouldn't surprise me if carbides are cracking and/or falling out of the edge of the 440c - temporarily "refreshing" it.

52100 is so silky smooth in comparison, and stuff like the White steels go even further in that direction...

Apexultra workpony soon?

 

[HumbleHomeCook]

Too fancy for me.

Thanks man.

Steel is a mystery within the mystery of metallurgy and intimidates the hell out of me! It's awesome how you work at making it accessible and digestible for all of us.

 

[M1k3]

I think this article, the part when using the Shapton 8k and Jnat Asagi stones, is related to this topic in a way?

https://scienceofsharp.com/2019/11/03/carbides-in-maxamet/

 

[Benuser]

Forgive me if I'm getting confused by the Imperial system, but in this table I guess the inches are in fact centimetres.

 

[jedy617]

Uhh why? Pretty sure that's inches.

 

[Benuser]

Does measuring the thickness at .5" behind the edge would make much sense? 5mm were more relevant. Finding a .4mm thickness right behind the edge — worse than most Wüsthof?

 

[Yoshi]

Apexultra workpony soon?

ApexUltra Chevron grind please @Kippington

 

[jaydee]

But, but... I like 52100 a lot.

I enjoyed "your 52100" quite a lot!
It had an aggressive bite to it I only know from Aogami Super. The explanation probably simply lies in how you sharpen it, I guess?

52100 has quite high values of toughness and edge retention according to (was it Larrin?) so it is surprising you don´t see it used more often for kitchen knives. I like it very much!

 

[The Forest Ninja]

I suspect on an atomic level a Carbon steel like Shirogami #1 with it's low alloying components would
have a cleaner edge than a very alloyed steel like a Stainless due to its various cabides which would
have different sizes.

The person sharpening the blade and methods used to also factor in the end result.

 

[ahhactive]

as i come along as a home cook. steel does not really matter, but always appreciate a good 52100 .

But, but... I like 52100 a lot.

 

[eddworks]

I enjoyed "your 52100" quite a lot!
It had an aggressive bite to it I only know from Aogami Super. The explanation probably simply lies in how you sharpen it, I guess?

52100 has quite high values of toughness and edge retention according to (was it Larrin?) so it is surprising you don´t see it used more often for kitchen knives. I like it very much!

52100 has very good toughness but isn't all that great for edge retention, although I do wonder how well the abrasive tests commonly used correlate to "respectful" kitchen use.

 

[eddworks]

Forgive me if I'm getting confused by the Imperial system, but in this table I guess the inches are in fact centimetres.
View attachment 283435

Pretty sure this means the measurement point is 0.5in behind the cutting edge, and the measured thickness was 0.045in, this is pretty normal geometry I believe.

 

[TB_London]

52100 can vary quite a bit depending on the heat treat approach - would be interesting to know how the sample was HTd

 

[Barmoley]

Does measuring the thickness at .5" behind the edge would make much sense? 5mm were more relevant. Finding a .4mm thickness right behind the edge — worse than most Wüsthof?

As long as geometry is consistent between the samples does it even matter?

I suspect on an atomic level a Carbon steel like Shirogami #1 with it's low alloying components would
have a cleaner edge than a very alloyed steel like a Stainless due to its various cabides which would
have different sizes.

The person sharpening the blade and methods used to also factor in the end result.

AEB-L is very alloyed compared to shirogami #1 and it has very small uniformed carbides and I don't think anyone would complain that it doesn't have a clean edge or doesn't get sharp. Who does the sharpening and how obviously matters and this is why it is important that these were sharpened as close to each other as possible. I don't think anyone would argue that sharpening with different grits would have this effect, but it is curious to see if the steel micro structure itself creates a similar effect.

Also, no one is saying 52100 is a bad steel or bad for kitchen knives or worse than 440C for kitchen knives. A low and a high alloy steels had to be picked and these are good candidates.

 

[nopomo]

I’d like to see this repeated with different grit finishes and edge angles. 52100 should be able to handle a much more acute apex than 440C.

 

[Benuser]

As long as geometry is consistent between the samples does it even matter?

Of course not, but they would have a remarkable geometry, really fat behind the edge with 0.4mm, and a laserish thinneth halfway.

 

[Matt Jacobs]

I enjoyed "your 52100" quite a lot!
It had an aggressive bite to it I only know from Aogami Super. The explanation probably simply lies in how you sharpen it, I guess?

52100 has quite high values of toughness and edge retention according to (was it Larrin?) so it is surprising you don´t see it used more often for kitchen knives. I like it very much!

I had the same experience with my Eddworks gyuto, so much so that I reached out to him to see how he sharpened. It was so toothy out of the box I though it was done on a belt grinder. He uses DMT stones (this could have changed) and I have started to since as well. The DMT extra fine followed by a strop makes a killer edge for tomato/peppers etc. That being said if I go to a higher grit stone I understand this better. Some steels feel "sticky" on my fingers while others dont. It means nothing to me as far as retention but its what I call "scary" sharp vs just toothy.