Just to brainstorm:
I don't see anything out of the ordinary for chemistry given dilution.
I assume its a plunger type bender?
My first guess is overall embrittlement or low elongation.
What is the tested elongation of the wire?
With plunger benders the first point of stress for low elongation will be the center of the weld. So with overall embrittlement it would make sense to fracture in the center, the first outer fibers to stretch. If you use a wrap around type it will fracture first along the first bending edge. After that it doesn't matter because the stress will be relieved.
If your elongation is less than 20% you can have trouble with ASME IX bending dimensions.
What were the weld parameters?
Heat input?
Did you measure the phase balance?
Can you tell where the fracture initiated? I know you said middle, but toward the root, the cap?
Is it possible it initiated in the HAZ near the root and propagated up the center? 2507 has a min elongation <20%. Given the high elongation of the wire (maybe) and the low elongation of the base metal the base metal may have absorbed the brunt of strain in the early bend angle.
Jim,
I am follwing this thread for some time and would like to add a few notes,hope this would add some value to this discussion.
SFA-5.34 lists no "Ti" in undiluted weld metal,but per PMI and mill cert some level of "Ti" is there in the weld.The purpose of adding some Ti in the weld is to refine grains and to act as sacrificial element towards fixing "C" in the weld, through forming carbides or carbonitrides. There are many publications from Special Metals on this.
"Fe" in the weld (10.45%) looks high, higher level of "Fe" could reduce ductility and later reduced the corrosion resistance. "Fe" level in filler is within the range of SFA 5.34 ( 6.1% vs 4-7% as per the spec).Controlled welding parameters(lower heat input) may help to reduce Fe dilution in the weld and being a butt weld this would be easy. It may be a good idea to restrict "Fe" to the lowermost limit.
If you could perform any SEM/EDS on the broken specimen, the energy peaks would tell if had been any micro seggregation about the fractured surfaces.
Thanks
Pradip Goswami
Jim,
Further to prior suggestions I added a few documents as attachments on welding with of C-276 fillers in FGD environments.As usual most of the articles are from Special Metals .They heavily emphasize a lot on Inconel-686 CPT products. However a literature search on various types of Nickel alloys (C-22, C-276 ,C-686) indicate that for there could presence of an intermetallic phase e.g "Mu Phase" which significantly reduces corrosion and ductility of weld and alloy seggregation during solidification could embrittle the metals.
In the present case , the duclity and % elongation look very low.It's quite unusual for C-276 weld failure to start @20deg bend angle, because these alloys can easily pass 180 deg bend. The weld parameters as well as the heat input (24KJ/Inch) does not look very excessive.However if the weld puddle is large (single bead, edge to edge) there could be chances of cracking due to improper solidification and possibly excessive "Fe" dilution.
SFA 5.34 does not allow "Ti" in the weld.In the present context it looks "Ti" have ingressed in the weld from flux in FCAW core. As per the the paper Samuel Kaiser (Special Metals-See attached link) Ti, IN Alloy CPT-686 primarily improves corosion resistance. I could not locate any exact reference on "Ti in C-276 weld metal.
Also "Zn" is not allowed by SFA 5.34. The presence of this element would greatly embrittle the weld.
I would liketo suggest a few things:-
1-SEM/EDAX of the failed area as mentioned in the prior email.This would provide a through analysis of the alloying seements including any seggregation (of any)
2- Good metallography/microstructural evaluation around the failed area.
3--Hardness measurement in the weld, HAZ, especially around the failed area would be important.Micro hardness measurement would be good, this could be combined during step-2.
4- Measure the "C" level in the weld --more for customary requirement. Super Duplex contain low C(0.03),Filler (0.02). If "C" in the weld is more than above values, some thing must being contributed by CO2 in the shielding gas. In that case a change to 90/10 or other recomemmended choices by consumable manufacturer may be advisable.
I would look forward to your feedbacks.
Thanks
Pradip Goswami
Welding/Metallurgical Specialist
Onatrio Power Generation Inc.
pradip.goswami@opg.com