Butt weld joint always cracks when tested

[jabran200]

Hi

My neighbour where I work does metal fabircation (beams, structures etc etc) and he is having all the staff tested. I don't know what the test is called I will find it out tomorrow for you when they get in.

They are having issue with the weld cracking when tested and aren't sure what they are doing wrong so I suggested to post it on here for them just trying to help them.

10mm mild steel
1mm wire
35 degree vee
2mm gap between joints
they are using about 190amps on a cebora mig





see the fracture


Fracture


Same piece


After welding


How it looks after welding



Profile


Bottom of the weld


Just some testing of welds etc but you can see the workpiece






Any ideas what is wrong guys? If you need more info let me know and i'll find out.

Thanks

 

[jaybee]

I would say the root pen looks fine not sure but by the picture looks like no penetration after a stop/start (root) also under cut on the caps probably means welder is too hot
Personally I like to see the root run burning in so I have low wire I also keep it small to allow for 2 caps inside the v and then a final finishing weaved cap to make it look nice generally you wouldn't grind a butt weld back

 

[backpurge]

Bit hard to tell from the photos but the root looks far too heavy, also the width of the cap looks huge in comparison to the thickness of the material, can you let us have details of the run sequence etc

I would personally bring the bevell down to 60 deg (30 deg each side) to reduce the amount of required weld metal

Put the root run in at a fairly low dip transfer setting then get a hot pass over the top in spray transfer then fill out and cap with stringer beads in spray

Don't under any circumstances fall into the trap of weaving, it will nearly always split right down the middle when bent, stick with fairly small stringer beads deposited at quite high speeds with plenty of volts and wire speed to ensure good side wall and inter run fusion

 

[Hitch]

The prep looks a fair bit steeper than 30-35, looks nearer 45 in the last picture....
The second from last picture say it all. If i produced something that looked like that for testing purposes, its just not worth going any further, looks like poor technique and/or a spluttery machine.

There is wire strikes, heavy spatter, inconsistent weld metal deposits...is that chalk line meant to be a stop/start? Looks to be about 3/4 stop starts just in that one piece.

The third picture, is that a coupon cut right over a stop/start?

 

[jaybee]

Caps do look big
Root run penetration should be no more than 3mm

Backpurge
Touch wood never had a split like that
(there's still time) do you know why it splits?

 

[backpurge]

It's usually down to depositing too much weld metal in one pass

 

[jabran200]

Sorry I meant to say the second to last was meant to show the work and was just used to try different settings etc.

@jaybee
I forgot to mention the weld has to ground smooth for the test. Thanks for the input.

@backpurge
I'll get some info on the weld sequence in the morning.

@Hitch
Looking at the piece when I was taking the pictures it did seem steeper than 35 degrees.

Thanks for the input so far, their tests are on thursday so hopefully input from you guys should help them pass the butt weld as thats the only one they failed last time.

 

[Richard.]

It's usually down to depositing too much weld metal in one pass

Agreed this then is a hot weld with massive grain structure , low impact toughness and low tensile strength.

 

[Liquid Metal]

Were the stop/starts in the root feathered out to get a nice smooth transition??

 

[short circuit]

as said put the root in on dip transfer followed by a hot pass a then some thinner stringers. might help also wrapping the plate to retard the cooling rate