Dual Shield Shootout (long)

Howdy gang,
I have a large project that I am having some trouble finding an economical filler material for. I am welding 12"x6"x1" rectangular A36 inserts that
have a female coil thread in the center into a torched hole in a 1" A36 street plate. The inserts are beveled @ 45deg on each side with about a 3/32" land. The torched hole isn't beveled. There is about an 1/8" gap when the insert is in position.
The application is critical, being that a lifting device is attached to the street plate for rigging. My customer tells me the whole industry is going to this.
I was using stick. 6010 5/32" root and 7018 3/16" filler (per mfg. specs). it was taking a total of four passes on each side of the plate. That's a total of 24' of weld with stick per plate. Sloooowwww process. Especially when the manufacturer reccomends preheating to 450-700 deg. I'm billing for time and materials, so my customer's jaw dropped the first week when I handed him the bill for not-so-many plates completed. Understandably so.
So begins the search for a more economical process to get these things knocked out. I talked to the mfg. of the inserts to verify metallurgy and inquire about deviating from the specs to go with a wire process. The guy I spoke with wouldn't point me towards a wire, but said anything equivalent with 7018 would be fine. No kidding. I go see my supplier to get hooked up with some dual shield. Their outside sales guy (30 years welding heavy stuff) says Esab Dual Sheild 7100 Ultra 1/16" is the way to go. The white paper on the Esab stuff says Ar/CO2 is OK for sheilding gas.
So, I show up to start on more plates with the new process. My customer appreciates me trying to save him money. After dialing in the voltage and wire speed on some drop, I tack, preheat and begin welding. One root pass, one filler/cap pass. Much faster, even though I had to grind off slag on the first pass in places. The bead isn't as pretty as 7018, but way cheaper. Flipped plates, repeated.
After cooling, I flipped the plates to inspect the first side. SHIT! Cracking outside the bead. The weld actually pulled away part of the A36 parent metal. Good thing I have a good relationship with the customer, else I'd be run out on a rail. I call my vendor & my outside sales guy shows up in about 1/2 hour. After seeing my rig and discussing the process he decides that I'm not an idiot. The only reasons for cracking that he can come up with are sheilding gas and preheat. He says I should be using straight CO2 and skip the preheat. I could see how the chilling effect of the 5'x10'x1" plate on the much smaller peheated area could cause some issues, but I'm not buying the sheilding gas bit.
Since fracture like this can be associated with dissimilar metals, my guy flows me a spool of Stultz Special Alloy. Holy crap! This stuff runs like a dream. I breathe on the first pass & the slag flies right off. Only catch is that my cost is about $4.00 per pound. That's twice what the Esab runs.
I ran some test pieces in the shop with CO2 and the Esab wire. No preheat. Cut it into strips with the bandsaw to study the weldment. Everything looked OK. CO2 gives better penetration, but more spatter.
The Stultz Special Alloy is nice but expensive. The Esab Dual Sheild 7100 Ultra is cheaper, but requires more slag removal effort, and bead isn't as pretty.
What are y'all's opinions on either?
Thanks, John
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I do not fully understand the nature of the 'female coil thread in the center' but it seems wasteful to cut out a large section of plate just to weld the piece with the coil thread back in. Can you not install the thread in the plate directly?

Suggest you try an air powered needle scaler to chip your flux. They are a real labor saver on all welds but they are especially good on heavy multi-pass welds, they have the added benefit of peening the weld while it is still hot which reduces distortion and stress due to thermal contraction of the weld metal. I guaranty that once you use one on a big job you will be hooked and will not want to ever use a chipping hammer ever again.
I have used an industrial model made by Atlas Copco for many many years but IIRC there are cheaper ones on the market. The needles eventually will fatigue and break so you should get a spare set at time of purchase.

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The large plate insert replaces slots or banjo holes that are commonly cut in these plates for chain lifting. For street plates that have no slots, small 3" coil thread inserts will be installed.
Thanks for the info in the scaler. I have been to that point with the chipping for quite a while.
John

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