Help straightening a blade

tedinatl

tedinatl

Joined
Nov 1, 2010
Messages
893
Hey guys,

Need your help on this one. I heat treated a large kitchen knife (CPM 154, 12" blade, 2 1/2" wide, 1/8" thick) and it took a slight bend during process. I've tried just about anything I know of and could read up about straightening bends, short of re-heat treating the knife. Let's see, I tried to:
  • Straighten in a vice (jig) right after coming out of the oven after the second temper cycle - snapped right back
  • Putting a lot of weight (close to 30 lbs) in the middle of the blade when it was still hot (only the blade ends were supported). It bent a lot, but just snapped right back
  • Re-heat to 425 F for 30 mins while clamped to a straight piece of angle, over-shimmed so that it bent in the opposite direction (did this three times - once just let it come to room temp by itself, once dunked the whole thing in a big bucket of water right out of the oven) - very slight reduction, but not really noticable. Did it again, no real effect either)

After all of this, there is still probably a 1/16"bend in the blade. Should I just normalize again, and re-heat treat?

BTW, the blade was straight after normalizing and before it went into the oven the heat treat.

Thanks in advance guys!
 
Warp happens. 1/16" isn't bad, but is enough to see.

Try your last effort again, but over-shim more. Also hold it at that temp for an hour, or even 1.5 hours. Dump into water when taken out.
 
You are just not done yet. Keep it up
 
I've had a similar bend in a similarly sized knife. I ended up fixing it by bending it over my knee about as had as I could. It was fairly scary, and I was sure it would break, but it didn't.

The bend can be fixed, the blade just need to be flexed further. It is possible that it will snap before it is bent far enough though.
 
Don't bend a knife with bare hands, put on heavy gloves and eye protection, should the blade snap. Hardened blades can be compared to spring steel, and when it breaks it shatters and the sharp break area is jagged and razor sharp. Better to put in into a vice and put a pipe over the handle and keep ones hands away from the knife itself while bending in this manner.
 
Ive noticed on my blades that warp (its always on a " Bowie" style knife with a pretty radical clip) theres a fair amount of twist going on as well.In my experience , twist is much harder to rectify.
 
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