AEB-L heat treatment from the knife user's perspective

[TeaThyme]

So I've been reading up on AEB-L and I'm trying to understand which heat treatment is desirable in which situations. My knowledge is based on this: All About AEB-L - Knife Steel Nerds This question has sort of come up in previous posts but I can't find a definitive practical conclusion.

As I currently understand, the best range is from 60-65 HRC. However going from 60 to roughly 63 HRC the steel loses more than half it's toughness in favour of the hardness and some edge retention. On paper this seems like a huge sacrifice, especially since toughness is what makes AEB-L stand out.

Can someone help me understand or direct me to sources that will help me understand what the numbers actually mean for me as a user? Would this for example mean, that 65HRC is most beneficial for a slicer that can be sharpened to a very acute angle; 60HRC is more desirable for a durable petty; and 61-63HRC is best for a chef's knife?

 

[esoo]

I've only had one AEB-L knife and currently have another on order, so take this comment with that in mind:

It is easy to over think this. As long as a knife steel is heat-treated properly, you'll get a good knife. Keep in mind that not every knife gets hardness tested, so there could be variations in a batch and a knife could be +/- from what is targeted.

So you could buy a knife from a maker today and get certain performance, and buy one two months from now and it could perform differently, just due to production variances. A maker could target 62, and you could get 61 on one knife and 63 on the next.

As for toughness, almost all the knives are tough enough for kitchen use unless you are trying to chop bones/frozen food etc. Look at where steel like Blue Super lie on the charts (unless I'm remembering wrong) and you start to realize that it becomes number chasing to compare (as a user).

 

[MSicardCutlery]

Some thoughts in no particular order. Fair warning, I haven't totally woken up yet.

The proportion of toughness lost can be less or more important depending on what the actual toughness numbers are. Going from 10 to 5 ft-lbs is not as much of an issue as going from 5 to 2.5 ft-lbs.

Compare this AEB-L to 1095, 26c3, and 1.2419. Those serve as decently close comparisons to White #3, White #1, and Blue #2. Take a look at VG10, and conventional D2 (American equivalent to SLD/SKD11) as well. You will notice that almost none of those steels have toughness levels exceeding 10ft-lbs at 63hrc. Yet those are among the most common knife steels for mass produced Japanese knives. AEB-L on the other hand hits approximately 17ft-lbs at 63hrc, being nearly 2.5x tougher than any of the more common steels mentioned, and at 65 hrc still has better toughness than the others.

Generally, people seem to be content with the toughness offered by the more typical steels that I mentioned, so AEB-L should, in terms of toughness, exceed all expectations provided you're content with the toughness offered by steels like the WH & B's.

Something else to consider, adjusting the geometry of the edge will generally have more of an influence on the toughness of an edge than can usually be obtained by adjusting the hardness of steels within the typical range of their use. Larrin has some pictures of edge deformation vs sharpening angle that demonstrate this pretty well.

Generally, thinner edges need to be harder. There needs to be a balance between hardness and thickness. The steel behind an edge can be too thin to be supported by its hardness/the steel can be too soft for the edge's thickness (it's the same problem). If that's the case, the edge will deform very easily. I can tell you first hand that with 52100 at 62-63hrc, a thickness of <.13mm @1mm bte is thin enough that the edge will deform if put through the brass rod test. At 65hrc it's not an issue to go even thinner than that, but I don't know what the thinness limit for that hardness is.


Liks to toughness charts on KSN

https://i1.wp.com/knifesteelnerds.c.../magnacut-stainless-toughness.jpg?w=755&ssl=1
https://i2.wp.com/knifesteelnerds.c...nacut-non-stainless-toughness.jpg?w=755&ssl=1
https://i1.wp.com/knifesteelnerds.c...2/09/apexultra-zoom-toughness.png?w=745&ssl=1
https://i2.wp.com/knifesteelnerds.c...lloy-steel-toughness-9-4-2022.png?w=749&ssl=1

 

[Barmoley]

In chef knives in particular you want thin and acute edges for best cutting performance. To this end you want the hardest edge that doesn't chip. When we talk about toughness we talk about chip resistance mostly in the context of knife edges. The main question is how much toughness is enough for the edge you want for the task you do with your technique. AEB-L is very tough, it looses a lot of toughness when treated harder, but it is still tough even at high hardness compared to many other popular kitchen knife steels. So as long as it is tough enough you want it as hard as possible with a good heat treat of course.
Let's say AEB-L at 64 HRC is around 10-11ft-lbs on Larrin's graphs, that's as tough as 1095/Wh2 at 57-58 HRC . People successfully use chef knives in Wh2 all the way up to 64-65 HRC at which point it is not tough at all, but AEB-L is still very tough in comparison at that hardness, so theoretically speaking it should work much better at high hardness than many common, popular low alloy steels. This is why we say that AEB-L has very high edge stability.

 

[Justinv]

I have some made from famously low toughness steels and they have held up fine with no chips. Thin acute edges need toughness to not chip and hardness to not roll. You want a mix of both.

The only chipping issues I have had are when too acute an edge is on it after thinning - typically a zero grind at about 4 degrees. I fix it with a micro bevel at a more typical angle of 12-15 degrees.

Common examples of issues with steel are Wusthof not holding an edge under ~18 degrees because the steel is too soft and the edge rolls. There are many reports of chipped Shuns due to low toughness and its too brittle for the sharpening angle. The fix for both is a microbevel or less acute angle for the edge. These makers presumably make edges too acute to perform better out of the box for reviews.

 

[Justinv]

Here is another thread on the topic with good links to @stringer and his watanabe thinning and chipping discussion.

Sharpening Angle Discussion

 

[HumbleHomeCook]

If you want to know this stuff to geek out on it and just be informed and enjoy the aspect of the hobby, by all means continue!

If you're concerned about it on a knife-to-knife purchasing decision then I'd say not to be overly concerned about it. Within any of the standard HT ranges for the steel , it should perform just fine with slight (and maybe not even perceptible in real use) tradeoffs. If working with a custom maker, then you can discuss it with them and get their expert input on the best approach for the intended use.

Just meaning, don't get caught up in numbers for numbers sake.

 

[TeaThyme]

Thanks for all the answers everyone. I actually completely missed that AEB-L at 64HRC still is tougher than most conventional stainless steels. That's actually fascinating!

So from what I gather the consequence of hardness would be minimal for average use in the kitchen. Which is a cool but slightly unexpected answer to my question. @Justinv I will read through that thread, thanks. It seems like the sharpening angle is what I should be looking into.

 

[Justinv]

AEB-L should be fine at any normal sharpening angle. Like @HumbleHomeCook says, just use it.

 

[Troopah_Knives]

Thanks for all the answers everyone. I actually completely missed that AEB-L at 64HRC still is tougher than most conventional stainless steels. That's actually fascinating!

So from what I gather the consequence of hardness would be minimal for average use in the kitchen. Which is a cool but slightly unexpected answer to my question. @Justinv I will read through that thread, thanks. It seems like the sharpening angle is what I should be looking into.

I wouldn't necessarily say that the consequence of hardness is minimal. If you truly are seeking a HT optimized for your usage it's all about getting the right balance for your personal use. On paper, you would want to try a particular edge geometry that you like and figure out how the edge is wearing (abrasive wear, chipping, or rolling are the main categories). If the blade is chipping then a tougher HT would increase edge life, if it is rolling higher hardness would increase edge life, if it is failing due to abrasive wear higher hardness or a different steel could help. In reality, I agree with @HumbleHomeCook, from a consumer point of view you are going to find it hard to optimize a knife purchase to that extent so it's not worth worrying about.

 

[TeaThyme]

I wouldn't necessarily say that the consequence of hardness is minimal. If you truly are seeking a HT optimized for your usage it's all about getting the right balance for your personal use. On paper, you would want to try a particular edge geometry that you like and figure out how the edge is wearing (abrasive wear, chipping, or rolling are the main categories). If the blade is chipping then a tougher HT would increase edge life, if it is rolling higher hardness would increase edge life, if it is failing due to abrasive wear higher hardness or a different steel could help. In reality, I agree with @HumbleHomeCook, from a consumer point of view you are going to find it hard to optimize a knife purchase to that extent so it's not worth worrying about.

Thanks for clarifying, I guess I was jumping to conclusions. Was thinking more along the lines, that the consequences for me are minimal if I use it in a standard way. Surely to a knife maker factoring in the differences in heat treatment is quite significant.

 

[enrico]

I’ve used a few aeb-l on the lower hardness end 60 and under and I’d definitely say it would be better at a higher HT. My current one is an Ashi Ginga. HT is 60 HRC.

Yeah I can crack open lobsters with it but grinding it on the stones is a bit laborious to get a thin apex for daily prep. Tomato skins provide the most problems. Doesn’t hold an acute edge as long as I’d like after I get it to where I’d like. It’s mainly my beater/loaner knife to someone who needs.


Would really like to try some higher HRC aeb-l in the future.

 

[SwampDonkey]

Only used one AEB-L at 62 HRC. Not knowing anything before I would've preferred a higher number but in use it was a straight up banger. Quite tough, supported a refined edge that wasn't babied in the slightest. I immediately turned around and ordered a custom from that maker in the same steel. That said, I'm very interested in trying a harder version like what Matt does just to compare and contrast, but it was definitely a good reminder for me to not get caught up in numbers. Very much on the AEB-L train now.

I normally ascribe way more to grind etc but I have noticed an edge retention difference between heat treats/hardness on my ginsan knives with relatively similar edge geometry.