440c filet stays bent?

[paul savage]

I have a problem with some 1/16" 440c filet knife blades I heat treated for a first time maker. they rockwell out at 58-59 rc but when you flex them they stay bent. I did two
5/32" hunters in the same batch and they are fine. He made these blades from my blanks and I have never had a problem with this batch of steel. the only differance is his grind. I flat grind with a full distal taper and can bend them 90 deg. and they return to zero every time. His are more of a convex grind with little or no distal taper except at the front 1/4 of the blade. Any thoughts?
Thanks Paul
www.savageknives.ca
savageknives@golden.net

[RJ Martin]

Paul: Interesting question. I don't think the bending is related to the grind geometry-If two pieces of 440C were HT'd to the same Rockwell hardness, they should either take a set when bent or not take a set. It might take more effort to bend one cross section than another, but, that's about it.

When you say a 90 degree bend, I'm assuming you mean the handle can be flexed 90 degrees to the tip, with the blade forming a full arc?

how much set did your blades take?

Is your rockwell tester calibrated? I'm going to guess they were at least a few points lower than Rc58.

[paul savage]

yes my blades arc the full length of the blade and return like a spring does , but this other blade just retains the arc. I thought it was still soft until I checked it on the hardness tester and it tested out 58-60 and I thought I was getting a false reading. The other thing I thought of is that I grind my filet knives in the hardened state.