Compromised heat treat?

Joe Duder

Joe Duder

Joined
Jan 22, 2013
Messages
3,003
I used to belt sand the profiles of my knives to lessen the blade geometry, until I found out that this can majorly mess up the heat treat:eek:. Never belt sanded any expensive customs, thank God.

My questions are-

At what point is the heat treat compromised?

Does the blade need to be heated past a particular temp and that's that?

Or does the blade need to be heated up to a certain temp and held there for a certain period of time?

I'm sure different steels compromise at different temperatures and conditions, but I'm looking for a ballpark answer here, if there is such a thing.

Thanks.
 
Last edited:
Ballpark answer: if you're seeing color changes on the steel (especially brown leading to purple and blue), you've gotten it too hot. It only takes a fraction of a second on thin sections like the edge. Once steel has reached those temps, that's pretty much all she wrote... unless you're able to re-anneal and re-HT the whole blade. Which is very seldom cost-effective or even practical.

What's happening is that the friction is causing at least part of the blade to heat up in the tempering range of the steel. This range varies a fair amount from alloy to alloy. What started out as a blade with a hardness of 58Rc may now be only 50Rc in that discolored area; it won't hold an edge very well.

The good news is, thin sections like edges cool down almost as quickly as they heat up, so it's entirely possible that the "damage" doesn't extend very far into the steel. It may be worth a try to (cooly and slowly!) re-sharpen past the overheated area, unless you really cooked the whole blade.

Lots of if's and maybe's in my response, I know... selectively over-tempering knife edges is not an exact science ;)
 
In all the belt sanding I've done, I've never discolored the metal. But I know I've heated it up so hot, I couldn't touch it for more than half a second. Still, no discoloration though. I wonder if I still messed up the HT and to what degree?
 
Joe Duder said:
In all the belt sanding I've done, I've never discolored the metal. But I know I've heated it up so hot, I couldn't touch it for more than half a second. Still, no discoloration though. I wonder if I still messed up the HT and to what degree?
Click to expand...

Depending on your steel you wont be damaging it unless you go over 200 C/400 F, if you are dipping in water every couple seconds or holding it in your hand and not burning yourself you are fine.
 
You must log in or register to reply here.
Back
Top