I've got some 321 filler if you want some.
Works fine on carbon steel
Never heard of 321 so I did some googling.
There seems to be 2 types of 321 wire, one for mild and carbon steel.
https://www.lawsonproducts.com/products/321-mild-and-carbon-steel-tig-wire-1-8-cw1007
Another for stainless steel.
https://www.oxfordalloys.com/Oxford-Alloy-321-TIG-Wire
Which version do you have and what diameter?
Typo! I've got 312 filler!
If you already have 312 then go with it, works well on almost any type of steel and is very resistant to cracking even on high carbon steel, great for anything where you aren't sure of the composition of the steel, either mild/carbon/tool steel/stainless. If its just mild steel er70 (er70-6 or er70-2) is great choice as it is a closer match to your base metal and is way cheaper than 312 (or 309 which would be another good choice for mystery metal/steel or mild to stainless).
312 would be way over matched on strength for mild steel but unless you want/need your weld to be your failure point then there's no reason you can't use it on mild steel. As its a spade you might find that a crack forms next to the weld if you use 312 as it will be significantly stronger so you won't get as much flex out of it as the surrounding metal. Also being a spade, it might be closer to a spring steel or higher carbon so the 312 will be more crack resistant in the weld metal, er70-2 may give you a bit more flex. Try the 312 and see how you go.
and if you dont have any , twist a couple of bits of mig wire together and it will get you by , ,,, not perfect ,Mild steel is carbon steel
You can weld up to medium carbon steel with er70 filler rod. Do a bit of preheat with a torch and it'll be just fine.
316 - not the best choice, the weld dilution of the chrome can make the joint brittle.
309 or 312 would be better, as it has enough chrome and nickel in to be diluted by the carbon steel.
Honestly, I'd just weld it with mild steel.
I can't be sure as it could be 316 s/s rod.
I do the same thing at workand if you dont have any , twist a couple of bits of mig wire together and it will get you by , ,,, not perfect ,
but
have to makes a hard master.
yep ends up as some sort of high carbon and it will get you by ,,, ive seen me burn the galv off coathangers before today and gas weld with them ,,, I once welded a gate hinge on with a few six inch nails held in a pair of vise grips and welded with a cutting torch ,,,, now those were the daysI do the same thing at work
We have any kind of Tig fillers but none for carbon/mild steel .
I've ever used small broken drill bits to make cutting edges on tools
I've done the broken drill bit trick a few times with reasonable success. I bought some weldmold 958 a while ago and have been making my own center punches and chisels for black smithing out of mild steel with weldmold TIG welded on the tips and these have stood up really well, basically as good as ones I've made out of tool steel (A2, D2 and H13). Makes for long lasting tools at a fraction of the cost of full tool steel.I do the same thing at work
We have any kind of Tig fillers but none for carbon/mild steel .
I've ever used small broken drill bits to make cutting edges on tools
Also removing flux off old mma rods can be a good source of cheap filler for TIG. Especially true for cast iron rods, the high nickel TIG rods are incredibly expensive, cleaning off the flux from mma rods and using them for TIG cast iron repairs has worked very well for me in the past.