welding mild steel to a replaceable cutting edge

[workinallthetime]

I made a landplane out of mild steel, 1/4" wall thickness, and noticed today that several of the welds were separated from the cutting edge and the angle iron. I am using a smaller Miller but still, 220 Volt unit, had it cranked up, and made several 6-8" welds across the length. I can see where I had plenty of penetration into the cutting edge but they are all breaking loose. Is this a lost cause? I did this once before on a grade blade but the forces on the welds were different so I assume that is why it never failed.
preheat the cutting edge with a torch help?

 

[etpm]

I made a landplane out of mild steel, 1/4" wall thickness, and noticed today that several of the welds were separated from the cutting edge and the angle iron. I am using a smaller Miller but still, 220 Volt unit, had it cranked up, and made several 6-8" welds across the length. I can see where I had plenty of penetration into the cutting edge but they are all breaking loose. Is this a lost cause? I did this once before on a grade blade but the forces on the welds were different so I assume that is why it never failed.
preheat the cutting edge with a torch help?

Pre and post heat would help. Are you using wire feed? For this job a stick or TIG welder would be better. That's because then you can buy the right alloy filler metal for the job. Welding rod with a high nickel content is good for this type of job, but even stainless steel rod would probably work. You could run stainless wire in a wire feed with argon gas. It would look crappy but might work. Some hardfacing wires might work too. But they are expensive and you would need to choose a ductile hardfacing wire, I don't know the specific alloys but there are some.
Eric

 

[Langanobob]

Can you post a picture?

 

[bcp]

I would bolt it on.

Is your angle still an open-sided angle, or is it now a sealed triangle?

Bruce

 

[k0ua]

If you weld with some 7018 with a stick welder set to 125 amps, I can tell you this: The metal will break before your welds do.

 

[jaxs]

To be sure we clearly understand what happened,are the welds pulling away/seperating from parent metal? If that's true you either used an unsuitable filler (wire or rod) improper gas if mig welding or you did not get good penitration. Most commonly available rod is ok for mild steel (6010-6011-6013-7014-7018-7024). Flux core, Solid wire and gas doesn't cover wide ranges for each type so choose only those reccomended for each application. An easy mistake is multi passes with single pass wire. That can trap slag and weaken bead.
If beads cracked the problem can come from a number of issues. I'm betting a couple close up pics will alow our more experienced members to get you on the right track.

 

[workinallthetime]

I will grab a couple of close up tomorrow. I used a Milllermatic 211, .033 wire solid core wire, on a 75/25 bottle. the bottle says "UN1956 Compressed gas, N.O.S. (Argon, Carbon Dioxide).
The metal did break before the welds, there are deep penetration holes that are consistent, weld held fine on the mild steel angle.
From the descriptions above sounds like it's getting bolts. I do not have access to a stick machine, remember 20 years ago using maybe a nickel rod to weld cast iron (decorative) to fence posts.

 

[etpm]

I will grab a couple of close up tomorrow. I used a Milllermatic 211, .033 wire solid core wire, on a 75/25 bottle. the bottle says "UN1956 Compressed gas, N.O.S. (Argon, Carbon Dioxide).
The metal did break before the welds, there are deep penetration holes that are consistent, weld held fine on the mild steel angle.
From the descriptions above sounds like it's getting bolts. I do not have access to a stick machine, remember 20 years ago using maybe a nickel rod to weld cast iron (decorative) to fence posts.

Yeah, if you can drill the blade it looks like the best solution for you at this time. You are probably using 70S6 wire. C25 gas mix, which you are using, is correct for this wire. Since the welds are not breaking but instead the blade is breaking in the heat affected zone, this tells you that your welds are good but the procedure and/or the filler wire alloy is wrong. You could try some stainless wire with your C25 gas mix. The welds will look really bad. It may hold. You can buy small a spool of SS wire meant for a spool gun or a smaller welder and try it, but if you can drill the blade then do it.
Eric

 

[amhicks21]

Ive used cutting edge steel for several projects because we keep em around after theyre worn down at work and have had the same problem in the past. Im no metallurgist, but I think the issue comes from the cutting edge being so hard that the contraction of the weld causes an extremely pinpoint stress riser at the penetration edge that starts the formation of a crack. I found preheating solved my issue completely. I cant guarantee we're using edges made of the exact same stuff but i'd recommend preheating.

 

[ROUSTABOUT]

I welded a road grader blade on a tractor bucket. It gets used regular and hard. Built a fire under it in half a drum. Heated and welded with 7018.