Weld on a knife blade?

[Sjoqvist]

Hello I've got a question regarding blade steels and heat.
Will I "ruin" the hardness/edge retaining on my Leatherman 420HC blade by welding on it with a MIG welder)? The welding will be done at the "lock notch" at the back. (The purpose of the weld is to fill the old lock notch and make a new one which makes it possible to use newer LM blades in my PST)

Also, IF this is possible, should I cool it down in water after the welding, or do anything else to prevent the steel from getting too soft?

Thanks in advance

[jzmtl]

Do you have any way to heatsink the rest of the blade while welding? If not I'd venture to say you'll ruin the temper on the last inch or so. You can try clamp a vise grip at the tang to prevent the heat from conducting forward but I'm not sure if it's enough.

If you have a way there's no reason to water cool it down after, you don't want the pivot area to become hard and brittle. I don't know the heat treat procedure for 420hc, some steel will become brittle even air cooled so you need to temper it softer to prevent brittleness.

[tattoosteve99]

In a nut shell don't do it, unless you have access to a heat treat oven. The proper way to do this is to draw the temper out (anneal), weld and refile, the re temper back. That's the only way I'd do it.

[Syph007]

I would just do your hot work, then get it properly heat treated again by a blade place.  For one blade its pretty cheap.  The local place here only charges 9 bucks. 

If you dont get it re hardened you'll end up with a soft ended tool that will likely gall neighboring tools or scales, or bend and not bend back. 

You can try to heat sync it, or freeze it in ice or a number of other tricks, but the bottom line is that whatever you weld wont be good hard tempered steel when your done.  If it's good enough for you then maybe it doenst matter.  It's probably just easier at this point to buy some blade steel and make your own.

[Sjoqvist]

Thanks for the fast replies!
The problem is that I want a "Leatherman style" serrated blade on my PST, and sadly it seems like all the Leatherman tools with dedicated serrated blades have the lock notch that will fit the "newer" LM tools.

It looks like I'm stuck with my SOG serrated blade with very aggressive teeth and with the grind on the "wrong" side for utility use. I wish I had the knowledge and tools to make my own serrated blade/put a complete new edge on a SOG blade

[zoidberg]

Just do it, it will be fine.
Make one quick large tack and file down by hand to avoid multiple re heatings.
Don't worry about trying to cool it in water etc and don't forget to take photos for us.