AEB-L Cutting tests and first impressions

[Phil Wilson]

I just had the opportunity to get a hold of some AEB-L steel and make a knife and heat treat it. I also did some cutting tests on rope with the same technique and method out lined in the previous series of tests Cutting tests on 4 knife steels. This post is under the Reviews and Testing section of this forum and rather than re-post it here pls see that for detail on test method. The stock finished at .080 wide at the blade spine behind the finger guard. It is flat ground to a .006 thickness at the edge. This knife is a 9 inch fillet with Micarta handle. Rockwell hardness is 60. I did the cutting test twice and the average was 95 cuts. Here are the results of the previous tests with AEB-L added to the list.

Results:
Cuts RC hardness
CPM S 30V 210 61
CPM 154 150 62
154 CM 110 61
AEB-L 95 60
12C 27 90 59

Here is the heat treating recipe I used for the AEB-L: Turco was used for oxidation and de-carb protection
Insert blade at 1500 furnace temperature
Ramp to 1980 and hold for 20 minutes
Air quench in front of a fan
Subzero in LN2 for 2 hours. Hardness out of the LN2 was 62
Temper twice at 400 and a third time after final grind and finish at 375. final hardness is 60

I found the AEB-L to be a little “gummy” to grind before heat treat but very easy after heat treat. If finishes very nice on a 400 grit belt.

It is easy to sharpen and in fact I was able to restore the cutting edge just by back stropping on loaded leather. This steel can get very sharp and it is easy to get it to shaving quality quickly. Toughness seems to be very good. In fact I continued to cut past the 20 lb limit on the second test and “wrinkled” the edge at about 30 lbs.

Phil

 

[M Wadel]

would you say its "worth it" to resharpen often and have a fine but not as durable/long lasting edge compared to s30v and similar more abrasionresistant steels? how would you rate it

 

[Cliff Stamp]

Thanks for the information Phil, I would be interested in the performance of AEB-L from :

Austenize: 1050°C, equalize and hold for 5 minutes
Quench : oil preheated to 60-80 C.
Cryo: immediately after quench, hold 1h
Temper: 150°C for 1h, quench in water
Cryo: immediately after quench, hold 1h
Temper: 150°, quench in water

This should give a significantly higher hardness and close to maximal edge stability. Note AEB-L is designed for optimal push cutting sharpness at low angles, not for slicing aggression at coarse finishes so I would not expect it to compete with the higher carbide steels for that aspect of performance regardless of how it is hardened.

Landes recommends 1050 C as the austenization temperature for AEB-L which is where the above recipe comes from. However Verhoeven used 1100C and air+water as the primary quench and this results in a significantly finer carbide structure and a higher hardness (assuming the retained austenite can be minimized). It would be interesting to compare the two methods.

As always, nice to see some steel comparisons. Here is that last one for those interested :

http://www.bladeforums.com/forums/showthread.php?t=421773


-Cliff

 

[Phil Wilson]

Cliff, If I get some time I can follow the method you quoted and see if I can tell any difference. I honestly don't think I could measure any difference cutting rope. You might be able with your test method, more steps and a finer measure of dulling. My objective was to see if I could get RC 60 finished hardness with Turco and an air quench. If I could and I can get enough of this steel in the future in the right thickness then it would be ideal for Chef's and kitchen use knives. It would replace 420 HC for me since the attainable hardness for that one is only about 57. I have Verhoeven's paper (book) and noted his method. It is closer to what I have done as a first test. PHIL

 

[Larrin]

Austenize: 1050°C, equalize and hold for 5 minutes

The hold time depends on thickness, you need as much as 8 minutes for .138". I'm not sure why it doesn't say this in the newer Sandvik literature when it does in the older, but a couple extra minutes soak time won't hurt anything.

Quench : oil preheated to 60-80 C.

The oil doesn't need to be heated, but it may not be the best medium for thin fillet knives, if faster quenching is desired plate quenching might be better.

Cryo: immediately after quench, hold 1h
Temper: 150°C for 1h, quench in water
Cryo: immediately after quench, hold 1h
Temper: 150°, quench in water

Cryo gives no benefit after tempering if it's already been done before tempering. Quenching in water after tempering gives no benefit over cooling in air after tempering.

Just trying to make things simpler for Phil if he chooses to try your method.

Edit: Oh, and so Phil doesn't have to pull out his conversion table, 1050C is around 1920-1925F, and 150C is about 300F.

 

[Larrin]

would you say its "worth it" to resharpen often and have a fine but not as durable/long lasting edge compared to s30v and similar more abrasionresistant steels? how would you rate it

I'm not Phil, but since he hasn't answered your question I'll throw in my opinion and say it's a matter of preference. I'm a guy that likes a steel like AEB-L that offers good wear resistance but then takes back it's edge in virtually no time at all. Others might like a steel that holds its edge for a long time but take longer to sharpen. Phil can elaborate on how much of a difference in sharpening he finds between the two. If it's not very much then it might be a closer decision between AEB-L and S30V for others.

 

[hardheart]

I'd like to try it for a fine edge that won't chip too readily. Restoring a certain level of sharpness to an edge is easy, having to rebuild an edge after damage is where I waste time on the stones. I wouldn't mind having to strop twice as often if I would spend half the time grinding while resetting the bevels.

 

[Cliff Stamp]

I honestly don't think I could measure any difference cutting rope.

The main benefit for that would be the extra hardness from the low temper and oil which might be signifiant enough to show. The other effects are mainly for edge stabilization which would only be relevant with really high polishes.

If I could and I can get enough of this steel in the future in the right thickness then it would be ideal for Chef's and kitchen use knives.

Yes, there is also some discussion on Bladeforums by individuals not interested in long term slicing aggression but very high push cutting sharpness at very acute angles. Having a high end knife so optomized, in stainless, for them for light utility knives and general small EDC fixed blades would be of value.

The hold time depends on thickness ...

Yes, the above was for the knives which Phil grinds based on comments from Landes in email. Generally forced air + water would be better than oil as Verhoeven notes. The reason I suggested oil was that it is basically Landes recipe and I wanted to see how his AEB-L would compare to 154CM ingot/M for long term slicing aggression.

Cryo gives no benefit after tempering if it's already been done before tempering. Quenching in water after tempering gives no benefit over cooling in air after tempering.

Martensite transformation isn't complete after cold due to austenite stabilization which is what requires the multiple cryo/tempers. This is so significant in highly alloyed steels that you can get further martensite transformation after cold and after the first high temperature temper whereas if there was no austenization stabilization it would all be martensite after the cold.

Water quenching is mainly to prevent secondary carbide precipitation as this lowers edge stability significantly as well as reducing corrosion resistance (not relevant for low tempers) and toughness. As I noted, the above comes from Landes who has studied this in great detail specifially on the subject of optomizing steel for knives, with a focus on edge stability. Johnston does something very similar to his knives (multiple cold/tempers) and their performance is very high in many respects. He also has optomized the heat treatment especially for knives.

-Cliff

 

[Phil Wilson]

Cliff, The water quench and additional cryo after temper optimization is interesting. I have often wondered if there could be benifit from it and have tried it a few times but have not seen any improvement at least in the way I test. Are Landes and Johnston doing photo micrographs or some other laboratory type test so they can see grain structure, or retained austenite, or ? It would be very easy to do since the LN2 is always there when I am heat treating. PHIL

 

[Phil Wilson]

M.Wadel, Yes I think with the palete of steels we have to work with that we should be chosing the best steel for the application. As I have noted before the high Vanadium PM steels, at least from where I stand and look as a fisherman and hunter are the best for outdoor use where sharpening is not always convienent. I had a hernia fixed a couple years ago and I'm glad the surgeon had an AEB-L type steel to do the work on me. I am also glad that Gillete and others have a similar type steel in their razors. It is a lot nicer to use a very sharp fined grain steel for that application. I also know from experience that if I am cutting elk hair or pig bristles that the fine grain very keen steel will not last nearly as long as S30V 90V or 10V. If I have a Chef's knife in the kitchen and the work is push cutting veggies then the fine grain keen edge is great. I can also tune up that knife easily if it looses the bite on say slicing a tomoato. PHIL

 

[Cliff Stamp]

Are Landes and Johnston doing photo micrographs or some other laboratory type test so they can see grain structure, or retained austenite, or ?

It was the subject of Landes PhD thesis and studied in great detail including micrographs, measurements of retained austenite beyond what you can determine by diffraction or microscope, edge stability, etc. . He really has made a study of knife specific metallurgy.

Johnston isn't a metallurgist but has spent a lot of time on steel specific metallurgy to understand which tool steels are used for tools which need fine edges and why. He refines his knives through constant testing. He doesn't actually sell them, just gives them away to butchers and such.

The softest steel he uses is 63.5 HRC, and they are usually much harder, 1095 at 66 HRC and M2 at 65/66 HRC are the main ones. Really thin blades, 0.050" or so, very deep hollow grinds and very acute edges, meaning like 5 degrees or so per side.

-Cliff

 

[thombrogan]

Johnston also has been attending a metallurgy class where he access to a Rockwell C tester which he's used to verify the hardness of his blades.

 

[db]

I'm not really sure Alvin J has ever found a stainless steel he likes or would use for a knife.

 

[Phil Wilson]

Thanks Cliff, I always want to optimize the heat treat for steels I use and the Landes info is a leg up on doing that. I will do a search here and see if his work is availiable, I would like to know what the as quenched hardness was and how he did the oxidation protection. I have an outdoor, utility style knife and an Chef's in process in AEB-L now and will do some more heat treat and cutting tests with them. Thanks to all the others as well for feed back. PHIL

 

[M Wadel]

The hold time depends on thickness, you need as much as 8 minutes for .138". I'm not sure why it doesn't say this in the newer Sandvik literature when it does in the older, but a couple extra minutes soak time won't hurt anything. .

it could, if you soak it too long (or too short) you will get a lower hardness. too long and you will get more retained austenite. too short, the carbides wont dissolve as they should. ive read 0.5-0.8minutes/mm thickness (0.5 for high temperature)

The oil doesn't need to be heated, but it may not be the best medium for thin fillet knives, if faster quenching is desired plate quenching might be better.

oil should always be heated to 60-80C, it cools better. (i think it cools twice as fast as 25°C oil). but most stainless only needs air.l steel can crack because of the martensite formation at room temperature, i think its best to cool fast to 80, then take it out and let it cool in air to room temp, then fast to the cryo (less than 5minutes after it reaches room temp, you convert more retained austenite)

Cryo gives no benefit after tempering if it's already been done before tempering. Quenching in water after tempering gives no benefit over cooling in air after tempering.

the first cryo converts the retained austenite to untempered martensite (not all but some of it, maybe 70%??), the second one temper the untempered martensite. from what i heard you should quench as fast (oil or water) as possible after tempering (to avoid brittleness/ get tougher steel. at least in construction steel. probably good for stainless too, i mean why take a chance)

 

[Cliff Stamp]

...too long and you will get more retained austenite.

Generally this isn't a problem for a knifemaker because of the attention they can or should be able to pay to the steel. This is more of an issue for tool makers who have to look at high volume and low heat treatment times. There are however issues with grain growth at too long a soak time, especially with steels without really stable high carbides like vanadium to pin grains.

... most stainless only needs air.

Most air hardening steels are improved with faster quenches which will reduce retained austenite and secondary carbide precipitation. Though you can often just air harden it isn't the optimal. Again you are looking at high volume tool making vs high end knives which cost much more and thus you could expect much greater attention to the heat treatment.

the first cryo converts the retained austenite to untempered martensite (not all but some of it, maybe 70%??), the second one temper the untempered martensite.

The repeated cold/tempers to transform the stabilize austenite. There is some decomposition of martensite during deep cold treatments so it does act like a stress relief, but the main stress relief is in the tempering.

I have an outdoor, utility style knife and an Chef's in process in AEB-L now and will do some more heat treat and cutting tests with them.

Those sound like excellent knives.

-Cliff

 

[M Wadel]

how much hardness can one expect to gain when quenching in oil vs air/ forced air really? or do you only gain toughness? i can imgaine this is depending on what steel you are hardening, but in general when talking stainless

 

[hardheart]

trying to follow, how do you determine hold time by thickness when the blade decreases in thickness dramatically through the cross section?

 

[Larrin]

how much hardness can one expect to gain when quenching in oil vs air/ forced air really? or do you only gain toughness? i can imgaine this is depending on what steel you are hardening, but in general when talking stainless

1-2 Rc generally.

 

[Larrin]

trying to follow, how do you determine hold time by thickness when the blade decreases in thickness dramatically through the cross section?

Generally it is recommended that you go off the thickest section of the part, or in this case, knife.