Filet Knife Steel Choice

tkroenlein

Well-Known Member
I'm going to try my hand at a filet knife.

I'm debating between using 52100 or 15N20 starting with ~.065" stock. Just curious if anyone has any preferences or prejudices concerning either, or anything else. I prefer to stay in the deeper oil hardening low alloy carbon steel range.

Thanks for any input.
 

Jon Buescher

Well-Known Member
Tagging along here, I really want to make some fillet knives seeing as fishing is my #1 hobby, then hunting, then anything involving working in my shop
 

EdCaffreyMS

"The Montana Bladesmith"
I've made fillet knives of both..... there are pros and cons for each. I like 52100 better for it's performance, but if its anywhere near a salt water environment....or fresh water for that matter, it will RUST, and I mean RUST, in the blink of an eye..... way more so then 15N20. I made myself a 10" fillet knife of 15N20 for fishing trips off the northern tip of Vancouver Island..... and it too will rust rapidly..... if you don't keep it CONSTANTLY clean and dry...but not as badly as 52100. However, it does not perform as well as 52100. This becomes painfully obvious when your cleaning fish the size of a whitetail deer! :)

I did attempt to gun-kote a couple of 52100 fillet blades, a test in hopes of protecting them/keeping them from rusting..... but the blades turned out to be more flexible then the gun-kote.... and the coating looked like a spider webbed windshield...... then stated falling off in those tiny pieces. So much for that idea.


If you're just diving into fillet knives, be forewarned! There are a lot of difficulties you must overcome when building them, that are not present with other types of blade.....mainly due to how thin the blades are/should be. ;)
 
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tkroenlein

Well-Known Member
I've made fillet knives of both..... there are pros and cons for each. I like 52100 better for it's performance, but if its anywhere near a salt water environment....or fresh water for that matter, it will RUST, and I mean RUST, in the blink of an eye..... way more so then 15N20. I made myself a 10" fillet knife of 15N20 for fishing trips off the northern tip of Vancouver Island..... and it too will rust rapidly..... if you don't keep it CONSTANTLY clean and dry...but not as badly as 52100. However, it does not perform as well as 52100. This becomes painfully obvious when your cleaning fish the size of a whitetail deer! :)

I did attempt to gun-kote a couple of 52100 fillet blades, a test in hopes of protecting them/keeping them from rusting..... but the blades turned out to be more flexible then the gun-kote.... and the coating looked like a spider webbed windshield...... then stated falling off in those tiny pieces. So much for that idea.


If you're just diving into fillet knives, be forewarned! There are a lot of difficulties you must overcome when building them, that are not present with other types of blade.....mainly due to how thin the blades are/should be. ;)
Well that pretty much confirms my suspicions about performance vs corrosion resistance.
I have so trepidation about grinding a knife this thin. I suppose there has to be a first time for everything.
 

John Wilson

Well-Known Member
I am partial to AEBL for just about everything. Having said that, for corrosion resistance it is hard to beat 440C, which I think is the king of corrosion resistance. CPM154 is also very good but costs a fortune compared to 440C or AEBL.


AEBL stands up to saltwater just fine, so long as you wash it with fresh water and dry it at the end of the day. You can't just ignore it totally like you can 440C. If you want to try stainless you can send it to me for heat treat if you like. Just toss ten bucks in the box to cover foil and dry ice treatment, plus whatever return shipping costs.

Ed makes a great point about fillet knives. They are a challenge to grind due to thin geometry but there was a first time for everyone. I make mine from .070 and grind after heat treat.
 

EdCaffreyMS

"The Montana Bladesmith"
They are a challenge to grind due to thin geometry but there was a first time for everyone. I make mine from .070 and grind after heat treat.
YUP YUP!^^^^^
I've tried a bunch of different methods when grinding fillet blades (most any blade 1/8" or less get ground post heat treat in my shop)..... mainly because for me, they will always warp just enough during grinding to be very noticeable. I started clamping fillet blades to a chunk of wood at first.....then later built a "holder" out of 1/4" thick angle iron/mild steel. That seemed to do the trick for me...... I believe it draws the heat away from the thin blade during grinding, preventing the warping.

Hey John...... would you be willing to share your heat treatment for AEBL? I hear people say they love it all the time, but I have had nothing but failure due to spotty results with heat treating....when following the prescribed heat treating recipe. I've tried shorter and longer soaks..... and have only tried plate quenching....just can't seem to get good/consistent results to the point I'd be willing to sell a blade of it. Right now I use CPM154 when someone insists on stainless, but would like to be able to offer another variety, like AEBL.
 
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jmforge

Well-Known Member
Devin Thomas does a "preliminary" quench on AEB-L at like 1750, then goes to the 1900+ quench. That way he soaks the steel at the higher temp for less time. My experience with kitchen knives tells the i wold use that steel for a filet knife.
 

Chris Railey

KNIFE MAKER
It's just my opinion but if you have the ability to work stainless then use stainless. The reason I chose 15N20 is because I do simple heat treat only so it would be a waste to use stainless. If the knife I am making is for me then I do not care about it rusting because I know how to deal with that and it does not bother me. Now selling a fillet knife is a different story, that is why I rarely sell fillet knives and then I tell them more than once that it will rust, period.
 

Jon Buescher

Well-Known Member
YUP YUP!^^^^^
I've tried a bunch of different methods when grinding fillet blades (most any blade 1/8" or less get ground post heat treat in my shop)..... mainly because for me, they will always warp just enough during grinding to be very noticeable. I started clamping fillet blades to a chunk of wood at first.....then later built a "holder" out of 1/4" thick angle iron/mild steel. That seemed to do the trick for me...... I believe it draws the heat away from the thin blade during grinding, preventing the warping.

Hey John...... would you be willing to share your heat treatment for AEBL? I hear people say they love it all the time, but I have had nothing but failure due to spotty results with heat treating....when following the prescribed heat treating recipe. I've tried shorter and longer soaks..... and have only tried plate quenching....just can't seem to get good/consistent results to the point I'd be willing to sell a blade of it. Right now I use CPM154 when someone insists on stainless, but would like to be able to offer another variety, like AEBL.
That was what was going through my mind on how I would first combat warping. Makes me feel smart that I thought of doing exactly what the pros do. I did think about looking for a 1" thick piece of aluminum to back the blade with as well
 

KenH

Well-Known Member
Ed (and others) here is HT'ing info as provided by Devin Thomas (Hoss) who is generally accepted as "the" expert on HT'ing AEB-L. First the link to his thread which is fairly long and requires two ovens.
https://www.bladeforums.com/threads/how-to-heat-treat-aeb-l-in-the-home-shop.1353014/

Here is my consolidation which I ran past Hoss to be sure I had it correct to use only 1 oven (any errors are mine, not Hoss).
Hoss highly recommend making 5 test coupons, heat the first one to 1900⁰F and plate quench, second to 1925⁰F, third one to 1950⁰F, 1975⁰F, 2000⁰F. This will give you a starting place for what temperature to use. Repeat this test with 5 new test coupons except do a sub-zero (freezer) or Dry Ice quench after the plate quench. With each set of test coupons measure the HRC and you should find a peak hardness at a specific temperature for your furnace.

It is also good to break each of the test coupons and see grain size and toughness differences. All furnaces are different, each will have a different soak time and or temperature required, even two ovens of the same make can be different.

After determining correct temperature to use, then use below.

Soak blade at 1725ºF for 10 minutes, plate quench – this is called the “Pre-Quench”.

Hoss and Larrin say it’s ok to wait until next day for 2nd step (Hoss's son is Larrin who is a PHD metallurgist with a hobby of the knifemaking facet of metallurgist)

Second quench with only one oven set at 1950-2000⁰F (depending on results of test above). AFTER oven stabilizes at 1975F, then place blade in oven and soak (austenitze) for 15 minutes (Sandvick says 8 minutes for blade thickness). It’s not good for blade to be in oven the long period of time required for ramping up.

Dry ice quench right after plate quench, continuous cool down. At this point expect 62 to 63 Rc. With an extended cryo (LN) there will be some nano sized carbides that precipitate to provide slightly better wear resistance with a slight decrease in toughness.

Temper twice, first temper for 1 hour at 350F, 2nd temper for 2 hours – choose temperature based on Rc test prior to temper. Tempering at 350F doesn’t change Rc much at all. Each 25F increase in temper temp seems to drop 1 Rc point. Tempering at 375F seems to drop from 62-63 Rc range to 61-62 Rc range, and moving to 400F would expect to drop another point. There is no big drop off in toughness by using 300°F, so it is probably safe to got that low for tempering temperature with this steel, if the extra hardness is desired:

Final Rc post temper should be 60 to 61 Rc for best kitchen use. (some folks are reporting a Rc of 62 works good for a kitchen slicer)

DevinT says: For HT'ing without dry ice, Lower the quench temp to 1925⁰F, (per tests 1950⁰F in my oven) keep the soak time at temp to ten minutes, quench in oil or plate quench, faster is better, put it in your freezer (-5ºF) right after the quench, this will keep the RA down. Temper at 325-350ºF.

To anneal AEB-L wrap blades in foil, soak at 1350⁰F for 12 hours – does not require slow cooling. This is a very good condition to re-harden from. This is a simple sub-critical anneal to allow straightening before re-heat treating in cases of warpage. Once the sub-critical anneal is complete, ramp oven to 1725F, then place blade in oven for 20 minute soak. Remove blade, clamp in quench plates to cool, ramp oven to 1975F for final HT.
 

KenH

Well-Known Member
^That's why I'm in no rush to do SST of any kind.
SS really isn't any harder to do than carbon steel provided you've got a good temperature controlled oven to control heat, SS foil to wrap, and good quench plates, and a dry ice bath. Some SS requires dry ice for max, but AEB-L and others do as good with dry ice bath at a -95°F temperature to remove the RA.
 

EdCaffreyMS

"The Montana Bladesmith"
That's essentially the process I've used on AEBL in the past, and compared to my carbon steel blades, it just doesn't display what I would call good cutting performance. The test blades always dulled quickly/easily, were a pain to resharpen, and were certainly what I would call brittle in comparison to my carbon steel blades. Maybe I'm just expecting too much of the AEBL??
 

John Wilson

Well-Known Member
That was what was going through my mind on how I would first combat warping. Makes me feel smart that I thought of doing exactly what the pros do. I did think about looking for a 1" thick piece of aluminum to back the blade with as well
I used a backer the first couple of times. It works like a champ. I found a way around it, though, because I am not good with jigs and find them cumbersome. I dunk and flip sides after each couple passes. As the blade gets thinner I dunk every pass- which you won’t need any reminding of because once it gets that thin you will feel the heat in your fingers on every pass. This sounds cumbersome, too, but it’s really not. The blade is so thin that you aren’t grinding a whole lot to begin with.

YOU MUST keep AEBL cool when you’re working with thin blades because it will pull to the warm side and you will grind a bow if you don’t pay attention.
 

Daniel Macina

Well-Known Member
I used a backer the first couple of times. It works like a champ. I found a way around it, though, because I am not good with jigs and find them cumbersome. I dunk and flip sides after each couple passes. As the blade gets thinner I dunk every pass- which you won’t need any reminding of because once it gets that thin you will feel the heat in your fingers on every pass. This sounds cumbersome, too, but it’s really not. The blade is so thin that you aren’t grinding a whole lot to begin with.

YOU MUST keep AEBL cool when you’re working with thin blades because it will pull to the warm side and you will grind a bow if you don’t pay attention.
I was grinding a long AEB-L Blade the other day that was fairly thick and I couldn’t believe how much it was warping even that thick Ground a pretty good dip in the blade before I caught it luckily there was enough meat to fix it.
 
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