Welding Tips and Tricks

Would using hard facing mig wire for joining mild steel to 5160 or a high carbon steel work well?

Thank You

No mate, hard facing wire is a metal deposit that is designed to be durable work hardened and chip off as is wears in most applications. It has no ductility at all in a practical sense. An 81ni flux core may work as it has a slight amount of nickel more than a 71 flux and a dash more silicon, on paper thats not outstanding but in practise you definitley notice it, but in general I steer clear of welding spring steel as you either lose properties on spring or create new haz.
What process are you using, cause a little preheat with a tig and a filler that is ductile with minimal dilution say 309 or 312 may be where its at ni99 may work but not cheaply.
Whats it for , if I may ask?

If this is an art project and not mechanical than I would be inclined to glow it red with a torch in the intended weld area let cool than pre heat to 100 degree C and weld in spray arc, or as close as you can get with your machine. Tack each end of the intended weld, one side a dash bigger tack and start at other end and finish on the tack as this will provide a dash extra metal to avoid a cold short with mild mig wire, post heat about 100C and let cool. As long as its not in any sort of mechanical service. Experiment of course to find what works but that should help.
If you need to know if its going to break or not, when you finished the weld and its cooled right down, put it in the freezer or ice box for a few hours, put in vice when it comes out and get at it with a big hammer if it bends uniformly ish and doesnt crack off then it should be right forever. I am sure there is a scientific method somewhere but that is mine.

Gdarc21

The reason for wanting to try this is due to the high price of steels I use and the (Insane) high shipping costs. I can get 1018, A36 and even 1045 locally but 4340 and tool steels in thicker bars are not so easy, but I can buy different tool steels in 1/4" x whatever very easily.

It's for an axe head. To date I have been making my axe heads from solid 4140/42, but mostly from 4340 billets. Rather than do the common practice of forge welding a high carbon bit to mild steel, I thought to try welding a 1/4" x 1-1/4" 5160 piece to the edge of a piece of mild steel.

The axe head would be formed mostly to final shape. After welding, grind to final shape and heat treat.

I drew a sketch of a fixture/jig to hold the axe head and the 5160 in line and in place as they are welded.

As I have not really attempted welding sprinģs, mainly cause I have not needed to. But that weld procedure I mentioned should work as good as any. Q and T plate may work better but as you said its not economical there....or anywhere these days.
I would do that with 7016 stick or dualshield 81ni wire 25 /75 gas. 71 would go ok but 81 is better for this and same price.
Handy tips, peen each run with needle scaler while its hot. Dont weld it while its 200C or above but dont let it cool right down below 150C. I.e dont weld while its near glowing is all you need to worry about in practise.
Weld one side 2 runs flip over and back gouge, grind into weld on other side to make solid metal when you weld.
2 runs then weld out however you want if its under 40mm total. Keep in mind if its over 40mm thick than a few runs or so then flip over to other side just to stop it pulling too much one way. You may already know this but it does rate a mention.
Run on and off tabs, will stop cold starts and rough stops. Just a 5mm bit of plate at each end of weld that gets cut off after. Just dont let it rapidly cool or you will get grain growth and brittleness, you may get some anyway, but post heat and slow cool will help minimise.
I hope it helps and let us know how it goes with the heat treat after.

i would use something like 312, something made for joining harden steels.
the other, if you have access to hard facing wire you may have backing layer "buffer" filler for hard facing. thats likely to be suitable.

From my experience and talking with blacksmiths and knifemakers, the steels you mentioned are in medium to low carbon range. I’ve forged and welded coil and leaf springs with no problem of cracking. These are likely in 5160 range. With true high carbon, like files (probably 1095) you’ve got to forge it hot and heat treat properly or else cracks are common. The forging is similar to real wrought iron. I welded a tack hammer by sandwiching flats with higher carbon face probably .7 percent. Regular old ER705-6 rod. It worked very well. Also planed to make hatchet with an old file for better edge retention. On back burner now.

I’ve made good use of scrap yard steels and spark test for carbon content. Not an expert on welding, just what has worked for me.