Hairline cracks under the beads (longitudinal)

[Toscane]

Material: 3.0 mm sheet metal
Rods: Oerlikon Overcord S 2.5 mm E6013
Setup: Inverter, clamp (-), electrode (+), ~60A
Joint: Butt

When I lay a pretty decent bead, everything seems fine; it's clean, slug erection occurs, very little splatter and nice looking bead. When I lower the amp, it becomes too tall and when I pump it up, it goes too shallow.

The problem rises when this thing starts cooling down... I hear this very tight popping sound, it's pretty high pitched but has some bass to it too but not enough low frequency to make it deep; it's loud and scary though.

Then I find this longitudinal crack going right in the middle of the bead, it's a perfect crack, it's dead centred inside the bead.

I turned the dial higher to penetrate the metal more and when it was cooling, I heard the same sound but there was no crack on the bead then I started grinding it flush to the metal and then it appeared once again. It was sitting under the bead.

I'm adding pictures of the bead before grinding process and after.

There is also this picture, it's just for reference, came from Google:

 

[the snooper]

wrong rods maybe
Oerlikon Overcord S 2.5 mm E6013 For Welding Of C-Mn Steel
All positional medium coated electrode ideal for root welds in pipe and tight joint fit up

 

[Toscane]

I'm sorry but I don't know what a C-Mn Steel is. My knowledge about steel is there is stainless, galvanized, corten and regular.

I don't think the rods are the problem because I welded about 20 more butt joints on this project and they're exactly like this one, even the measurements, 10 cm. They're holding up fine, except these two. Others seems like holding up well but these 2 keep cracking when cooling down.

I was going to try weaving instead of going straight but wanted to ask before wasting more rods and abrasives.

 

[malcolm]

Is Carbon Manganese steel not normally mild steel? See the page on welding mild steel

6013 is a fairly standard mild steel rod. A 7018 rod would be less likely to crack (lower hydroden) but it's odd that you have the problem on 3mm mild steel - someone more experienced than me might be able to suggest why this might happen.

 

[TechnicAl]

Its difficult to say from a photo.

perfect straight lines are lack of pen....cracks go for the route of least resistance which is hardly ever a straight line.

The very shiny photograph........is this the back side of the weld

or is it the weld ground back to the surface....if so its lack of pen .....you need more amps or slower travel

 

[Toscane]

TechnicAl, the shiny photograph is the weld bead ground back to the surface flush.

I am going to try a slower travelling speed because when I use more amps, weld bead looks like those photographs which say you have to turn the amp down.

 

[Drains]

Toscan, can you do a photo of the back of the weld? Also, are you leaving a gap between the two pieces of steel before welding, or not?

Certainly looks like a lack of pen!

 

[TechnicAl]

TechnicAl, the shiny photograph is the weld bead ground back to the surface flush.

I am going to try a slower travelling speed because when I use more amps, weld bead looks like those photographs which say you have to turn the amp down.

If you are using 60A on a 2.5mm you probably need more amps, more like 100A

 

[Toscane]

Drains, I can't get the picture of the back because it's a closed box shape, back of the weld is inside it. I don't leave a gap between the pieces though, they fit perfectly together, both are clean cut pieces so they're pretty tight.

TechnicalAl, when I go above 60A, beads start looking like the "high" written beads in this photohraph:

 

[decepticon]

seems rather strange, if it was lack of pen (to parent metals), surely the crack would form at plate face and not along ctr of weld? unless you mean pen through the full thickness of the 3mm plates at the joint?
were these 2 plates restrained/fixed before welding? if so when they heat up and expand during welding and upon cooling contract with quite high forces, i would imagine slag inclusions behind joint causing weakness
i think quoting amps is quite subjective as welding plants are all different but 60 is low if that is what you are really running at

 

[Toscane]

I've tried 90A today but it still cracks. I weaved instead of going straight and it held fine until I ground it back to the surface, then it cracked again. I don't understand why this particular joint does this, others seems perfectly okay and everything was same, rod, metal type amps welding type et cetera... Maybe it's because I forced these 2 plates in while others were just sat together nicely.

These 2 plates fixed together before welding and I believe I had to leave a little gap because I fixed these together with clamps before welding and they were a pain in the ass to fit together, I had to force them in with hammer and clamps. I believe decepticon is correct with the expanding issue or slag inclusion.

I should have welded underside and then fit the plates and weld on the outside once more.

I thought about cutting a line where they face each other and create a ~1 mm space with the thin cutting discs and weld that through. Maybe this space between metals, filled by welding, prevents this cracking when cooling down. Is this makes sense?

Structurally, that particular section is not that important but that crack might allow water inside so...

By the way, my inverter seems like giving more amps than the dial shows because others get same results with, for instance 70A while I get it with 60A.

Now I'm running 90A, beads look a little bit short and wide but I', sure you folks know better than I do.

 

[scarecrow]

I'm not convinced its lack of penetration is the problem as the weld doesn't look too bad and even if the weld wasn't penetrating that length of weld shouldn't crack unless it was under stress as the material looks to be only 3or4mm
is there a coating on the steel which could be reacting with the weld

 

[dannyweld]

looks like the material could be cooling to fast, some pre-heating with some sort of torch may be the answer, try shorter runs and use a ball pen hammer to tap the weld

 

[TechnicAl]

If its a perfect straight line its lack of pen. Cracks dont work to drawings

Other than that I cannot add any further comment

 

[paulmowers]

I have never had welds crack like that on mild steel but have seen it on harder types (higher carbon) regularly.
I would try tacking it first in several places, then do short infills between, say left end first, right end, centre, next in from left, etc, until done, not as neat but wont draw the stresses along the line of welding.
just an idea.

Paul

 

[R Kraft]

3mm would take about 125amps if fit up tight with no grinding prep.
Your photo of the bead labeled HIGH looks better than the lower amp one.
If you have some material of the same thickness try practice welding it and see what you need to do to weld it all of the way through.
Robert

 

[scarecrow]

If its a perfect straight line its lack of pen. Cracks dont work to drawings

Other than that I cannot add any further comment

yes i know your right
but it is unusual for weld to crack when cooling down on mild steel but common on cast steels if they were not prepared properly

 

[Drains]

Toscane - after you've ground the weld back, how thick is the weld material that's left?

 

[Toscane]

I haven't got the chance to weld yet so no updates yet folks.

Drains, I don't know how thick it is because I ground it all and make it flush to the metal. It looks like there was no welding involved, just like a solid piece of sheet metal, until it cracks.

 

[Toscane]

Drains, I added a photograph and marked the joints as 'before' and 'after' the welding/grinding. It's the same work piece but cracking occurs somewhere else on it, not those 2 particular joints.

As you can see, after the welding and grinding, you can't see the joint and it looks like never welded before.

Darn, picture got resized and it's hard to see now.