Heat treating newbie

[WaltE99]

Today I tried my first heat treat of O1 in my new Evenheat KF18. Although I have done some 1084 heat treat, one blade at a time in the past, O1 was sent out. So I had 5 blades ready, which in hindsight was too aggressive since I really had no process for doing more than one at a time. Of course, this didn't occur to me until it was time to start taking the blades out and quenching.

Anyway, of the 5 blades, 2 were good and 3 had slight warps. (The warps could have been paranoia induced thinking since it was my first time.) I straightened the perceived warps by heating with a propane torch and when I finished that I ran the file back over them. The file seemed to bite a little (possible paranoia again). So the 2 good blades went to temper and the 3 warped ones (now straight) were put back in the Evenheat and the HT cycle repeated. Of the 3, after the 2nd HT, 2 were straight and the 3rd broke when I tried to straighten the warp which was near the tip. In to temper for those 2 good ones.

So my question is this...was I correct in going straight back to HT or should I have either a.) tempered before going back to HT, b.) annealed and/or normalized before HT, or c.) something else?

Thanks to all in advance.

Walt E.

 

[E.Carlson]

I would have straightened them out during the tempering cycles rather than taking a torch to them. No 2nd heat treat needed.
Clamp the blade to a straight bar with some shims to reverse the bend and temper as normal. If the warp is pretty bad I wait for the second temper cycle before shimming.

 

[Stacy E. Apelt - Bladesmith]

You have two periods to straighten a blade.

One is immediately after the quench while the blade is between 1000F and 400F. Make no attempt to do any other straightening until after two tempers. Attempting to straighten a room temperature and untempered blade will end up with a broken blade almost every time.

The other period is to straighten at the tempering heat ( around 400F), after the second temper is done. Straightening blades at room temperature is highly risky.
You can re-heat the blade to 400F as many times as you need, so just stick it back in the oven for 10 minutes as it cools during straightening efforts. Many people use a clamping jig to over-flex the bend and set it in the oven for 30 to 60 minutes and then take out and let cool. Once removed from the clamp, the blade is usually straight. It can take a few tries to get it straight, but there is near zero chance of breaking a blade this way. I know that no one wants to spend much time to get it straight, but it is worth the effort and time. Rushing things is the main reason for failures in knifemaking.

 

[Geoff Flato]

I made a set of wooden jaws with magnets on the back for straightening blades in a vise. Just used a bandsaw and the grinder to cut one concave and one convex. Could do it on a contact wheel too.
It's gentle enough that I've successfully straightened a number room temperature, but I definitely don't recommend it as a few have broken too. Normally I'll take it out of the oven after tempering, and straighten while it's still warm.

I've tried a few other approaches, and found the jaws to work best for me

 

[i4Marc]

I have lost a couple of blades with 3 point vise type jigs. That was the end of that. Since then I use the counter bend while tempering technique. I have never lost another blade. I always do at least the first temper with warps and all. Starting with the second temper cycle I clamp to a heavy bar with the counter bends. Sometimes it takes a long time to get everything perfectly straight but it is worth the effort. A few blades have taken as many as 16 two hour temper cycles to get every last wiggle out.

 

[WaltE99]

Thanks everyone. Regarding the clamping with shims to counter-bend during temper, I have some pieces of aluminum 3/4"x1-1/2" rectangular tube and 2"x2" square tube. Would either of these work for clamping the blade or is the aluminum too soft? I would think that since aluminum conducts heat better than steel, that would be a good thing for the side of the blade that touches the tube.

 

[scott.livesey]

try clamping your pieces between aluminum plates after quenched to black, the zone Stacy referred to. I have done that with thin O1 (1/8" or less) and have seen no loss of hardness.