What Rockwell Hardness for a fillet knife?

G

gixxer

Joined
Sep 21, 2006
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Ok, so I am grinding away on this nice 18" piece of 154CPM (my father in law thinks he NEEDS a knife this big like he is gonna fillet a 450lb bluefin tuna one day...), and I am thinking to myself... SELF!! what hardness do I get this thing cooked to when I send it to the heat treater? I had searched the threads, and only found one person that actually made mention of hardening his fillet blades to 56, but I do not think he was using 154CPM. Any suggestions? I am looking for something mildly flexible, but not whippy. The blade is going to be less than 1/8 thick @ the spine, full flat grind before I pack it. I can control the final flexibility when I get it back by grinding more if need be. Hey, if I screw it up I might have a contender for the Ugly Knife honors!!
 
i did one at 60 and ground it real thin they loved it but i think i ll be going fro 58 or so less someone tells me otherwise
 
Flexibility is not a function of hardness ,it's a function of blade thickness !!!! Considering that filleting also means going through bones I'd go for 58 HRc to stay away from the brittleness.
 
Every fillet knife I have made I had it HTed by Paul Bos. I dont think he treats it differently than all the others in the same batch. Like Mete says: Flexibility is not a function of hardness ,it's a function of blade thickness !!!!
 
Gixxer, I make a lot of fillet knives and have found that it is best to just heat treat to the best hardness for the particular steel grade. In your case 154CM this would be 60/61. The flexibility is not influenced by the hardness, the grind geometry governs this. If you make a test blade, grind it thin and flexible and bend it you will find that it will plastic deform a bit before it breaks. You will be surprised how far it will bend. Just remind the user that this is not a chopping blade. All bets are off if used that way, You would have to go down to 55 or so for this steel to survive much dynamic impact loading. Hope this helps some, PHIL
 
Gixxler, A little more info. I made two posts, I have dial up here in the country and sometimes get bumped off before I finish. Here are hardness values for the steels I use for fillet knives that have worked fine for me. I have never had a broken fillet blade come back at these values.
154CM 60/61
CPM S30V 61
CPM S90V 60/61
CPM 154 61/622 (about 10 blades so far)
AEB-L 61 (just a few blades so far with this one)

Hardness equals edge holding and cutting up that big tuna you talked about needs a long lasting edge. Phil

oops, CPM 154 61/62
AEB-L 60
 
Tim Zowada gave a presentation at Ashokan this year to demonstrate the Modulus of Elasticity (Young's Modulus). He took two pieces of steel (O1, I believe), one heat treated into the Rockwell 60's and the other annealed. He attached them to an anvil and hung equal amounts of weight off of them. They each flexed the same. Then he stuck the pieces in his handy-dandy bending gizmo and demonstrated that it took about four times as much force to permanently deform the heat treated piece as it did the annealed one.

Zowada-bending-demo4.jpg
Clamping the steel in preparation of hanging the weights.​

Zowada-bending-demo3.jpg

Bending the steel.

Zowada-bending-machine.jpg
The bending machine.​

Kevin Cashen posted the following definition on the Sword Forum;
Young’s Modulus: (modulus of elasticity) The values obtained when a load or stress is applied to a metal, within its elastic range, to stretch it to a given length. For steel this is approximately 30,000 PSI for .001". This will be the case regardless of the heat treatment.​
 
Well, it's all about the thickness. I hope I can get it to a ballpark before I send it off to be cooked. Not that I have any idea how a given piece of 154CPM in the same profile will react pre and post cook.
 
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