Laying 7018 over 6011

[David Spring]

I’ve used 7018 over 7018 to fill groove joints with backing, the standard thing to do with it. Same thing for a 7018 fillet weld. Get every bit of slag off or else risk a slag inclusion, but that’s no trouble since the 7018 slag comes off so easy. No problem.

I’ve used 6011 over 6011 to fill imperfect fit up, for more penetration in fillet welds, for farm repairs, etc. Wire wheel to get most all the slag off, and the little bit that remains won’t trouble 6011 on the second pass. No problem.

It was suggested on another post that I instead use 7018 for subsequent passes, since it’s less liable to crack, prettier, etc. I get that 6010 is standard for an open root groove joint, then 7018 over that, so using 7018 cover over a first pass of 6011 sounds just the same idea. Sure.

But in the open root application the root is so tiny that it all just gets cleaned up with a grinder. A first pass of 6011 on a fillet weld or corner joint is much larger, and the edge of the 6011 weld bead tends to collect a little line of slag that doesn’t all come off with a wire wheel (not enough of a crevice to be undercut, just, there’s a tiny bit of slag along the edge of the weld).

In the real world, non-code situation, how are people doing 7018 over 6011? Do you run a grinder down each side of the 6011 weld to grind out all traces of slag and prep for the 7018? Or can 7018 actually handle that little bit of leftover slag, in a non-code situation? Perhaps I’ve been too scared by hearing so much that 7018 has zero tolerance for slag, and will get an immediate slag inclusion…In principle I like the idea of a first pass of 6011 and then switch to 7018, but seems tricky to get the first pass cleaned up enough. What are you all doing for this? Thanks.

[M J D]

I don't obsess over it much. Remove what you can, wire brush or wire wheel, then go to 7018. Obviously,the cleaner the better but 7018 does deal with light slag fairly well

[cwby]

I'll put a root in, scratch it with the next rod to knock most of the slag off, then weld it up. You should be hot enough with your 7018 to float the rest of it to the top. Pipe welders usually grind the root, but it is more to level out the high spots. They call the 2nd pass (sometimes with 7018, 8010, or whatever is spec'ed) the "hot pass" & it is mainly to burn out the "wagon tracks" - the edges you are talking about.

[Louie1961]

In a filet, corner or even a lap joint I wouldn't bother laying 7018 over anything. The point of a 6010 (or 601X if you will) in an open root joint is to get a keyhole and make sure you have sufficient root build up without suck back. In a fillet, you do not necessarily need 100% penetration so long as the legs of the filet are large enough. You will be fine just using 7018 for fillets, corners and laps and just skip the 601X rod. I also believe that for any non-code situation, you would also be fine welding it all the way out with 6011 or virtually any rod (6013, 7014, 7016,7018, etc.). Mild steel has a tensile strength of about 36,000 psi. Any 6xxx or 7xxx rod is going to be much stronger than the base metal. I don't buy into the hype about 7018 being so much better because of ductility, charpy v-notch ratings, or the rest. Yes, 7018 has all those attributes, but mild steel does not. If you are working on plain old mild steel, any rod will likely hold just fine. Farmers have been proving this for many years.

[smithdoor]

If I am working on a job that has specs or Xray I grinder the for each pass.
It just safer to do a little extra but does take more time .

Dave

I’ve used 7018 over 7018 to fill groove joints with backing, the standard thing to do with it. Same thing for a 7018 fillet weld. Get every bit of slag off or else risk a slag inclusion, but that’s no trouble since the 7018 slag comes off so easy. No problem.

I’ve used 6011 over 6011 to fill imperfect fit up, for more penetration in fillet welds, for farm repairs, etc. Wire wheel to get most all the slag off, and the little bit that remains won’t trouble 6011 on the second pass. No problem.

It was suggested on another post that I instead use 7018 for subsequent passes, since it’s less liable to crack, prettier, etc. I get that 6010 is standard for an open root groove joint, then 7018 over that, so using 7018 cover over a first pass of 6011 sounds just the same idea. Sure.

But in the open root application the root is so tiny that it all just gets cleaned up with a grinder. A first pass of 6011 on a fillet weld or corner joint is much larger, and the edge of the 6011 weld bead tends to collect a little line of slag that doesn’t all come off with a wire wheel (not enough of a crevice to be undercut, just, there’s a tiny bit of slag along the edge of the weld).

In the real world, non-code situation, how are people doing 7018 over 6011? Do you run a grinder down each side of the 6011 weld to grind out all traces of slag and prep for the 7018? Or can 7018 actually handle that little bit of leftover slag, in a non-code situation? Perhaps I’ve been too scared by hearing so much that 7018 has zero tolerance for slag, and will get an immediate slag inclusion…In principle I like the idea of a first pass of 6011 and then switch to 7018, but seems tricky to get the first pass cleaned up enough. What are you all doing for this? Thanks.

[Freebirdwelds]

I've run 7018 over 6011 a lot over the years. Done right there is not a problem.
That aside.
7018 will burn off residual contaminants without a problem. Focus on your puddle and your path. 7018 is not as fragile to lay as some people think.

[bakodiver]

I do 7018 over 6011 a lot because it's faster than prepping the joint to be absolutely clean of zinc or rust, paint, or other contaminants. A quick, minimal 6011 root pass, followed by wire wheel or in critical applications, grinding the toes of the 6011 pass, and the 7018 lays over it perfectly. 7018 is very intolerant of contaminants in the parent metal, burn them off with 6011 and you're good to go.

[Sberry]

In a filet, corner or even a lap joint I wouldn't bother laying 7018 over anything. The point of a 6010 (or 601X if you will) in an open root joint is to get a keyhole and make sure you have sufficient root build up without suck back. In a fillet, you do not necessarily need 100% penetration so long as the legs of the filet are large enough. You will be fine just using 7018 for fillets, corners and laps and just skip the 601X rod. I also believe that for any non-code situation, you would also be fine welding it all the way out with 6011 or virtually any rod (6013, 7014, 7016,7018, etc.). Mild steel has a tensile strength of about 36,000 psi. Any 6xxx or 7xxx rod is going to be much stronger than the base metal. I don't buy into the hype about 7018 being so much better because of ductility, charpy v-notch ratings, or the rest. Yes, 7018 has all those attributes, but mild steel does not. If you are working on plain old mild steel, any rod will likely hold just fine. Farmers have been proving this for many years.

That is pretty well written.

[Louie1961]

Thanks Cary..high praise!

[David Spring]

Perfect, this is exactly the sort of information was hoping to understand. To summarize my understanding from this thread and elsewhere, and these quotes aren't all verbatim:

7018 is higher tensile strength than 6011, but that doesn't matter on mild steel, which is far weaker than either rod. Same thing for the hydrogen cracking, mild steel isn't susceptible to that so no need to choose 7018 for that purpose. (Please no debate here on this point.)

However, 7018 is much more ductile than 6011, which has a greater risk of cracks, and can't stand up to vibration and fatigue cycles the same as 7018 (and this true whether or not the rods came out of an oven, it's is simply about the ductility of the filler metal, not about hydrogen embrittlement).

And, although there's such a concern about pristine joint prep for 7018, in fact it will handle rustier metal than some people think it will, and doesn't even mind the little slag left over in the "wagon tracks" toes of a 6011 bead (in a non-code setting, obviously).

And it looks prettier, for when that matters.

That's all making 7018 sound pretty good!

But while 7018 CAN run over 6011 in a root with a little slag, and CAN run over a little rust, it has to be run well in order for it to work out well. Compared to 7018, 6011 is more forgiving, and easier to make as good a weld as the rod can make. A good 7018 weld is superior to a good 6011 weld, but it's easier to make the good 6011 weld, and if the 7018 weld doesn't go so well (due to prep or skill), it might very well be inferior to what 6011 would have done in the same situation.

But here's the question I think this discussion all boils down to:

Although it is technically true that 7018 will produce a prettier, more ductile, stronger weld, and it IS an actual, measurable difference...is the weld in a situation where this is actually a meaningful difference? As Louie 1961 says, "If you are working on plain old mild steel, any rod will likely hold just fine. Farmers have been proving this for many years." And my local farm repair welder, well-respected in our area for fixing anything and everything well, almost exclusively uses 6011. I don't know that that's the "official" or even the "best" procedure, but his work and his father's work shows that it is "sufficiently good for this purpose" -- his welds do not break.

Some may say to do the best process that results in the best weld possible, in every situation. Fair enough. But does anyone have a sense of when the advantages of 7018 become meaningfully better for a weld on mild steel? It sounds like for any mild steel on a farm, certainly for work related to a <100hp tractor and probably for nearly any farm equipment, the advantages of 7018 are not meaningful, and 6011 is just fine. Is it when you get up to mining and heavy construction, then--that's the amount of force and heavy use when it becomes a meaningful difference? Or, perhaps: in such heavy-use situations, things aren't built of mild steel anyway, and so of course you'd use 7018! Or perhaps, would even be fair to say that anything built of plain ol' mild steel is not built for such a high-stress application that the ductility and tensile strength of 7018 will offer an advantage that matters? (Assuming the weld is well-designed, sound, sufficient weld buildup, etc.)

[M J D]

It's either 7018 or inner shield on outdoor structural steel work. You might see some 6010 or more likely 6011 on a structural job for tacking and that's about it. No reason not to use 7018 as it's about the same price as any other electrode and it typically won't trap slag like 6013 or 7014 are more prone too .

[Louie1961]

It's either 7018 or inner shield on outdoor structural steel work. You might see some 6010 or more likely 6011 on a structural job for tacking and that's about it. No reason not to use 7018 as it's about the same price as any other electrode and it typically won't trap slag like 6013 or 7014 are more prone too .

I run 7018 more than any other rod because I like the way it runs. But I don't fret over storing it in an oven or trying to re-dry it, etc. Like you say, no reason not to use it.

[Louie1961]

But does anyone have a sense of when the advantages of 7018 become meaningfully better for a weld on mild steel?

I am not an engineer, but I would hazard a guess and say whenever the base metal begins nearing the strength of the weld metal. You can put in the strongest, best weld in the world, but that won't stop a crack in the adjacent base metal, as in the case of mild steel (A36 type stuff). Now if you are using steels where the tensile strength is pretty high (like a structural I beam made out of A572 steel with a 65,000 psi tensile strength) then it would make sense to use a 7018. But plain old angle iron has a tensile strength of 36,000 psi. A 7018 weld will hold together, but the angle iron itself will fail long before the weld.

[David Spring]

Yeah, the impression I’m getting is that for mild steel, if the weld is the weakest part of the piece (like if it’s somehow a thin weld on a thick piece of mild steel or something), then sure, a stronger, tougher, more ductile 7018 weld would be valuable over 6011 in that case…but for mild steel, a properly-designed weld will never be the weakest link, and so it doesn’t matter whether the filler metal is 6011 or 7018 — the mild steel will always fail first.

[smithdoor]

I know does not make sense.
They made at time rods for mid steel and A36 but changed in 1960's to E60XX now most think E7018 is the way to go.

In the 1960's most shops used E6013 and E7024 sometimes E7014 and E6012.

Dave

I am not an engineer, but I would hazard a guess and say whenever the base metal begins nearing the strength of the weld metal. You can put in the strongest, best weld in the world, but that won't stop a crack in the adjacent base metal, as in the case of mild steel (A36 type stuff). Now if you are using steels where the tensile strength is pretty high (like a structural I beam made out of A572 steel with a 65,000 psi tensile strength) then it would make sense to use a 7018. But plain old angle iron has a tensile strength of 36,000 psi. A 7018 weld will hold together, but the angle iron itself will fail long before the weld.

[FlyFishn]

A couple thoughts -

After switching to the green label Lincoln 7018's (not the blue label). Off the top of my head I don't recall the specific coding of the rods, however the blue label box is the same as the AC 7018 rods you find in the big box hardware stores (home depot etc). The green label I got from my LWS. It is also said to be AC, but my understanding is they run best on DC - which is what I run them on.

I get too much porosity using the AC/blue label 7018's. I am sure others have had better luck as it likely comes down to technique. However, when I switched to the green labels to try something different they ran fantastic. I've had the same good results with 3/32", 1/8", and 5/32" rods, every box.

There is a condition where running AC is preferable - that is if you are welding on magnetized metal. Running DC you will not be able to control the arc - it will wander. AC solves that issue. Though, I am not sure of any conventional welding where you would run in to magnetized metal. Pilings pounded in to the ground are a different matter - they become magnetized from getting shoved through the ground. Maybe others might have other experiences that can shed other light on the subject.

There is a group I help at times that runs small construction equipment (excavators and skid steers). Their preferred rod is 7018. We had an issue with an excavator that came with a mismatched bucket. It has a grapple also. The bucket was just big enough that the grapple would lodge inside the sidewalls of the bucket at times. The pressure from that would strain the sidewalls of the bucket to where it would eventually fail. So they would weld the failed bucket sidewall to repair it. There wasn't much science to it, the rod was run hot and slag was knocked loose with another rod or a screwdriver. It wasn't cleaned with a wire wheel. I am sure there was some slag inclusion deep in the root. However, for an evening repair to get the machine back in service for the next day, or a field repair and back in service right then - it worked. That bucket was replaced this spring/early summer with the correct one.

If I were the one doing the bucket welding I would have cleaned the joint with a cut off wheel to open it up and lay a better bead. It would also have been advantageous to root pass with 6010 or 6011. They will get down inside joints better and will flush out contaminants better than 7018 alone.

My preferred technique with 6010/6011 is whip-and-pause. It lets you put down metal easier without blowing through. Your whip motion forward gets some metal down and lets the pool behind cool a bit. Then when you back up to the pool and pause the arc blends the pool back in to the base better. When you do this it looks like more coarse stacked coins. Those coarse transitions in the bead on top trap slag. It is next to impossible to get it all out with a wire brush or wire wheel. Someone earlier mentioned pipe welders may grind the root to smooth it out. I can see where that would be a benefit - the whip-and-pause method mentioned here leaves a pretty bumpy bead.

It wouldn't bother me to wire wheel the 6010/6011 bead mentioned above, provided I can get adequate access to it, then run a few passes of 7018 over top, depending on the gap or fillet size. You don't want to go more than about 3x rod diameter on your weave with 7018. If I needed to fill a wide gap or build up a fillet it would take a few passes.

Another thought - 6011 is my tacking rod. It is real easy to run and eats through dirty metal. Depending on the joint - how heavy the metal is and how heavy the tacks are - I may get things tacked up then lighten up the tacks with a grinder or cut off wheel before laying down 7018. If the metal is thick enough and will take the heat, though - I just burn right through the tacks with 7018. The area where the tacks are won't have the penetration the rest of the bead is, so that should be considered if you are really picky with your welds.

As to cleaning metal or not for 7018 - personally I always clean. Note that mill scale doesn't easily come off with a wire wheel. Unless you use a grinding wheel you likely aren't getting all the way down to the base metal. If I can't wire wheel (access is limited) a 6010/6011 root then I use a wire brush and clean as best I can. I find I use the toothbrush size wire brushes quite a bit. They fit in places others don't.

Good luck with it. If you have any doubts - get you some scrap pieces and do some destructive testing, or cut a few samples out of the joints to inspect. That is a good way to build trust in your welds.

[ccs]

I'm no expert, but I don't know that I agree with some of the assertions being made in this thread. I also use a root pass of 6011 and cap it with 7018 fairly often, I like both rods for different reasons. But one thing I have noticed is a pretty big difference in the way these 2 rods behave when I'm using them to tack any kind of steel. Often I'll tack something and then want to adjust it a bit, so i'll move or hammer it around until it's exactly where I want. 6011 drives me nuts doing this because it just breaks off about as soon as you move it. 7018 on the other hand you can move around quite a bit. I have a hard time believing that full welds of the 2 filler metals aren't different in the same way, whether it's mild steel or whatever. So for me, if strength and flexibility in a particular joint (think a trailer frame for instance that needs to do a lot of twisting/flexing) are important to me and 6011 or 7018 were my choices, I'd choose 7018 every time. Would 6011 work fine? Probably. Would I sleep better knowing I used 7018? Definitely. Just my opinion though, take it for what it's worth, which ain't much!

[Sberry]

18 is a bit more elastic in that situation.

[smithdoor]

It is a root pass only.
In some case the root pass is not need.

Dave

I'm no expert, but I don't know that I agree with some of the assertions being made in this thread. I also use a root pass of 6011 and cap it with 7018 fairly often, I like both rods for different reasons. But one thing I have noticed is a pretty big difference in the way these 2 rods behave when I'm using them to tack any kind of steel. Often I'll tack something and then want to adjust it a bit, so i'll move or hammer it around until it's exactly where I want. 6011 drives me nuts doing this because it just breaks off about as soon as you move it. 7018 on the other hand you can move around quite a bit. I have a hard time believing that full welds of the 2 filler metals aren't different in the same way, whether it's mild steel or whatever. So for me, if strength and flexibility in a particular joint (think a trailer frame for instance that needs to do a lot of twisting/flexing) are important to me and 6011 or 7018 were my choices, I'd choose 7018 every time. Would 6011 work fine? Probably. Would I sleep better knowing I used 7018? Definitely. Just my opinion though, take it for what it's worth, which ain't much!

[BD1]

In pipe welding we use 1/8'' 6010 5P and 3/32 7018, usually up to 6'' or even 8'' depending. With jobsite welding, your machine could be 10 floors away unlike a fab shop. That's why the 1/8'' and the 3/32''.

The heat setting for 1/8'' 6010 is pretty close for burning 3/32''. Each guy has his own preference on one setting to burn both rods. One setting for both so you don't have to go to machine to readjust.

[David Spring]

I don’t know enough about engineering specs to be confident that this is meaningful data. I should go read about it in the beginning of Metals and How To Weld Them. But I did some quick googling. The question is whether 6011 is more likely to fracture than 7018, in a mild steel weld. Many people report that 7018 is more ductile and less likely to crack than 6011. This is surely true; the question though is whether this difference matters for a (properly-designed, properly-sized) weld in mild steel. Many people report that since mild steel is so much weaker than either filler metal, it’s not going to matter which filler metal is used — the steel will always fail first.

Elongation % is a measure of ductility. Various spec sheets say that 6011 and 7018 filler metal is in the realm of 25-35% elongation as welded. From people’s experience, it sounds like 7018 would be on the much higher end of that scale. But regardless, mild steel elongation is 10-20%. If am interpreting this correctly, this seems to be actual data that backs up people’s experience who say sure, 7018 is a less brittle filler than 6011 but it doesn’t matter because both are stronger and more ductile than mild steel. Regardless of filler metal, mild steel will always fail before the weld itself fails (again, assuming a properly executed weld).

Does anyone have a comment on this interpretation of the data?

[FlyFishn]

Re: ductility of the weld in 6011 vs 7018 and the base metal -

I would be curious to others' more experienced replies. That said - my feelings on the subject are 6011 and 6010, for that matter, are more brittle than 7018, irrespective of tensile strength (where all are as you stated - stronger than the base metal). The strength of the weld metal doesn't matter if it cracks under stress or vibration.

When welding - the weld metal is neither the base metal, nor the rod metal. It is a mixture of the two. Therefore, when you lay 7018 on top of 6011, or any other rod and resultant weld, you are creating another weld metal of the 3 - the base, 6011 (in this example), and 7018.

Speaking in terms of a fillet weld or thick metal joint prepped with chamfered ends that has multiple passes layered - you are going to have significantly more 7018 in there past the root than what ever rod you use for the root. If you are welding something that isn't very thick that doesn't require more than a single pass cap of 7018 - that will have less weld metal. I would imagine it will still be far and away better on ductility than straight 6011 or 6010, but I don't know if that would match the ductility of straight 7018. Interesting question.

[12V71]

Re: ductility of the weld in 6011 vs 7018 and the base metal -

I would be curious to others' more experienced replies. That said - my feelings on the subject are 6011 and 6010, for that matter, are more brittle than 7018, irrespective of tensile strength (where all are as you stated - stronger than the base metal). The strength of the weld metal doesn't matter if it cracks under stress or vibration.

When welding - the weld metal is neither the base metal, nor the rod metal. It is a mixture of the two. Therefore, when you lay 7018 on top of 6011, or any other rod and resultant weld, you are creating another weld metal of the 3 - the base, 6011 (in this example), and 7018.

Speaking in terms of a fillet weld or thick metal joint prepped with chamfered ends that has multiple passes layered - you are going to have significantly more 7018 in there past the root than what ever rod you use for the root. If you are welding something that isn't very thick that doesn't require more than a single pass cap of 7018 - that will have less weld metal. I would imagine it will still be far and away better on ductility than straight 6011 or 6010, but I don't know if that would match the ductility of straight 7018. Interesting question.

Putting in 7018 over 60XX, its just a matter of melting into the root and diluting it a bit with the 18. If you're not doing that... you're not hot enough. And you also have the effect of "heat normalizing" the 60xx with more passes over the root. No big thing.

[Leogl]

Well first all 6011 isn’t brittle in comparison you are comparing 60xx rod to 70xx rod a tack with 7018 is usually larger so tack with a 7010 and with the same mass and compare . Joint design welding procedures joint preparation all come into play operator skills rank quite high in the variable column 7018 is more user friendly I think 6010 / 6011 require a little more operator skill to do the same job when I started running a truck every rarely had 7018 so you learned to make multiple passes etc burn a few hundred pounds till you get the hang of it but remember 60xx is not a fair comparison to 7018 get some 7010 and then start comparing and I know everyone is gonna say 7018 is stronger more ductile etc but every rod has a place and time I am by no means saying 7018 is not a good rod