Hey Y’all,

I finally bit the bullet and am attempting a bigger knife. It’s a chopper forged from an old leaf spring. I’ve gotten profile finished and took the bevels basically from spine to edge. 
I’m preparing to quench and have to say I’m a little scared. I haven’t quenched anything this large and fear a warp/crack/catastrophic failure especially since I’ve already put a lot of time into it. 
I’m debating just and edge quench in vegetable oil after some thermo cycling, OR putting some satinite on the spine to keep it cool and do a full quench. Thoughts? 

 

Check for straightness after doing your normalization cycles.  If it's still straight afterwards and you have a fairly thick spine it could still warp, but the odds go down.  FWIW the purpose of claying the blade is not to keep it cooler.  Clay (satanite) prevents direct contact with the quenchant which allows that portion of the blade to cool at a rate slow enough that full hardening does not occur.  The result is the same as what you were thinking, but the mechanism is a bit different. 

Nothing wrong with an edge quench either. 

For the last large-ish knife I made I did a full quench and then a differential temper to soften up the spine area.  For small warps I made a jig (or is it fixture in this case?) which allows me to isolate the affected location (basically the 3 pin method in a separate tool) and flex the blade the opposite direction a little bit.  I leave that in place while oven tempering and have had good results removing small warps that way.

When you say differential tempering is that like drawing the temper away from the spine with a torch? 
I’ll definitely have a 3 pin jig handy when I quench, and if it cools to quick I’ll try it in tempering! Thanks!

Yes, you can do it with a torch.  I made some tempering tongs so I can keep the heat more accurately where I want it.  However, no matter the method, you have to be ready to cool the blade rapidly when you get close to the colors you are after.  Once they start they do run fast.  In my case I wanted light blues near the spine area and deep straw color at the cutting edge.

When you cooled in the tempering is that safe to do with water? 

Edited October 1, 20196 yr by Mod30
Remove unnessassary quote.

Yes, the blade temperature is significantly below critical temperature at that point, so the stress when cooling rapidly is far less than in the hardening step.   If you have micro cracks in the spring you will most likely find out in the quench.  Better there than in heavy use though.

If it makes you nervous just get something set up where you can quickly quench the edge at the right color.  That's only part that has to stay fairly hard.

Perfect! I’ll try it out next time I fire up the forge and let you know how it goes! Appreciate all ur help

How thick is the edge?  Leaving a bit more thickness there can really help when heat treating larger blades.