Is it bad to do this to knives?

[XiaolongJackson]

Isn't it a good way to get rust out too?

 

[timbit]

He's hot knifing mary jane.

 

[akadave2]

I dont think the lighter will get the steel hot enough to do much to it.

 

[jasperjb]

I have done that many times to sterilise my knives

Also, to use cheap china crap knife to burn stuff

This is what I initially did it for, not because I am a stupid child.

 

[jasperjb]

Buy a pack of colored Sharpie markers. You can "color" your blades all day, and in various colors too.

In all seriousness, the only time I could imagine heating up a quality knife blade would be if I had to perform some kind of emergency surgery. And man, I hope that day never comes.

I can certainly see heating a cheap knife to cut/melt certain materials. I do this to cut nylon web strap (I heat the blade with a blowtorch). But I use a designated cheapo knife and couldn't care less about how the heat might effect the blade.

I'd strongly recommend against heating the blade of a valued knife just for the fun of it. like others have said, you might negatively affect the temper.

Of course, if you're lost in the woods and have to perform an emergency appendectomy, well...

Yeah, I only did it once after digging out a splinter and was just curious. I didn't think it could affect the heat treat.

 

[Slicey]

He's hot knifing mary jane.

My first thought. Hot knives.

 

[Minibear464]

I dont think the lighter will get the steel hot enough to do much to it.

I'm pretty sure it will. Tempering 1084 knives is done at around 415 degrees F. If a knife is heated above that, it would become softer. This is different for all steels, but the tempering temperature is not very high. A lighter flame would definitely be above this temperature, and while a short exposure might not damage a knife very significantly, heating a knife with a flame will most likely soften the steel.