Advice on non critical welding mild steel to blade.

[barry burnett]

Hi guys,
I need to add 10mm to a blade I made .
The joint will not be under much stress due to the way the blade will be used in the machine.
I only need to increase the depth of the blade in order for it to fit correctly in a specific part of the machine.
The mild steel will be added to the spine of the blade and only needs to be tacked.
The blade is 40mm deep so not too much buffer between the area to be welded and the actual cutting edge.
Would it be better to weld before or after HT ?
Blade is 3mm thick.
thnx

 

[kuraki]

Before HT. Pre-heat and weld allow to cool slowly. Normalize, then harden. The specifics for pre-heat, filler, etc will depend on the alloy but as it sounds truly not critical in anything but compression, a 3-400 preheat should be enough to prevent weld shrinkage cracks. If you have a oven for tempering I would get that heated to 400, heat the blade, remove, weld, place back in the oven and then turn it off and allow to cool. Then normalize, harden, and temper.

That may be over board depending on the cutting edge alloy but welding mild to high carbon always poses a big risk of cracking as the weld shrinks. If you're only going to tack in a few places, it's even more likely to crack because you're putting less residual heat into it and giving such small surface areas for the cracks to propagate from.

 

[mete]

If you weld on a HT'd blade you should pre heat and post heat to 400 F . That would be a good idea too on an unhardened blade too . that would be done to prevent formation of untempered martensite.

 

[Stacy E. Apelt - Bladesmith]

Tack welds will come apart in the HT.

I would full weld the two pieces with pre and post heating at 400F. Any competent welder can do this.
Then harden and temper as normal.

 

[skillgannon]

What equipment do you have ?

You will want to use a preheat and normalize afterwards.

Pressed send after taking care of work. What Kuraki said.
Tig welding would probably be best. Without knowing the alloys you are welding a high nickel filler is probably a good place to start. You might get a welding shop to sell you a stick or 2 of something like Inco 625. There are probably a lot better options but I'm not a metallurgest.