your preferred method for blade hardening?

[overmodulated]

Folks: I'm still at an experimental stage with kifemaking (having only completed about a dozen to date) and would like to know your prefered methods for edge hardening. I've ruined about as many as I made, so I'm still a little trigger shy with the quench method and medium.

What seems to work best for you? I've quenched medium to high carbon steel in different oils with better luck (i.e. less destruction) than in water, but with an apparent tradeoff in edge hardness. My goal is to achieve a very soft (non-brittle) knife spine together with hard edge.

My attempt at edge-quenching in water destroyed the blade. Is it better to quench the entire blade and then temper back the spine, or avoid quenching the spine in the first place? My knives are in the 4-12 inch length range, and use simple steels between 1050-1090, and spring steel of type 5160.

Thanks!

[dablacksmith]

i use vegtable oil and full harden then temper in toaster oven ... might not get the hardest edge but still plenty hard and passes the bend test .. just tested one recently . i know a lot of people use the differential hardening(edge quench) tho but with oil .good luck! oho and dont forget to normalize ... in fact you might do a couple of normalizeing heats.

[Nakedanvil - Grant Sarver]

overmod: What exactly do you mean by "destroyed the blade"? 1090 will harden just about exactly at non-magnetic (blood red). Oil quench should give full hardness on a thin edge. Use a red hot block of steel to draw colors starting at the spine.

[overmodulated]

Thanks for inputs.

By destroying the blade I mean inducing visible crack(s) from the edge, going back to the center of the blade, due to the expansion and compression between the edge and spine. Perhaps if I repeat this using oil instead it will work better.

I read on the forum that some pour water along the edge. This seems hard to do for a long blade - by the time you move from base to tip the residual heat from the back of the knife will surely re-temper the edge to softness. What am I missing with that procedure?

I've used tempering tongs and question the effectiveness of this relative to not quenching the entire blade in the first place (i.e. doing edge only seems best).

Thoughts, experiences? Greatly appreciated. I am about to risk two more knifes to heat treatment this week and don't want to lose them.

[ThomasPowers]

Differential temper rather than differential hardening is less strain on the steel---seems rather odd that you would complain about edge cracking and then "question the effectiveness of this relative to not quenching the entire blade in the first place"

[overmodulated]

Thomas; good advise on the differential temper - I will keep that in mind.

My doubtfulness was with regard to the merits of quenching the whole blade vs just the part that needs the hardening, but if what you stated is true, question answered!

[Nakedanvil - Grant Sarver]

I'm a big fan of differential tempering. If you only quench the edge then the spine is just in the annealed state and maybe 80 - 90,000 psi tensile. If you quench the whole thing, you can draw the spine to 45Rc and you'll have around 200,000 psi tensile. Strong and flexible. Why would you give up that kind of strength?