Welding Tips and Tricks

I have some short production runs for a client coming up for .065" wall 4130 chromoly tubing (2-3.5" ODs). Any benefit to using 80SD-2 filler (I have non in stock) over the typical 70S-2 or 70S-6 which I already have well stocked? Specs allow for either.

Any thoughts would be appreciated.

You will be fine with ER70. I keep ER80 on hand, which has slightly different weld characteristics but absent of requirement, I’d go with what you have.

Even though ER80S-D2 yields slightly higher strengths, in as-welded condition it is more susceptible to cracking due to the higher carbon/molybdenum content compared to ER70-S2/-S6.

It's key benefits of higher strength are realized when pre-heating and inter-pass temperatures of no less than 275-300°F are used, and the parts are PWHT/stress-relieved afterwards.

Harris ER80S-D2 Spec
Midalloy ER80S-D2 Spec

That being said, it's probably not worth it to go out and get some, and ER70S-2 will be fine.

Thanks, guys. 70S-2 it is then. Appreciate the input.

What’s the part. Doubt they’d use chrome molly unless it was necessary. With that said chrome base requires chrome filler to maintain it’s specs. 70s2 on high chrome causes more cracks then chrome filler and proper preheat.

Poland308 wrote:What’s the part. Doubt they’d use chrome molly unless it was necessary. With that said chrome base requires chrome filler to maintain it’s specs. 70s2 on high chrome causes more cracks then chrome filler and proper preheat.

Tubing cluster assemblies for motorsports. Not roll cages, though. Some sort of auxiliary support structures for the under carriage. Not an automotive guy, so not entirely sure. But they did list 70S-2 as an acceptable filler in the specs. I was basically just wondering if some of the other fillers would make my job easier/faster since it will be a few dozen parts in this run.

If they spec it as an ok filler for the use then it’s fine. The critical thing with high chrome is preheat and interpass temps.

Also don’t substitute 70s6 if it’s not allowed.

Poland308 wrote:Also don’t substitute 70s6 if it’s not allowed.

Yeah, that's not listed. They just sent me the drawings and specs this afternoon. Hadn't yet seen them when I first posted....it was just the phone call at that point.

Out of curiosity, why is 70S-6 not a good substitution on 4130 tubing?

It has a higher silicon content. Changes the way the weld pool solidifies. It’s different enough from s2 that it’s not a substitute unless it’s tested and approved.

Poland308 wrote:It has a higher silicon content. Changes the way the weld pool solidifies. It’s different enough from s2 that it’s not a substitute unless it’s tested and approved.

Gotcha. Was aware of the increased silicon/deoxidizers in 70S-6, but wasn't unaware that it wasn't a good choice for 4130. Good info to have. Thanks.

I’m not positive it isn’t, it’s just for the code work I’ve been apart of it’s a no go unless it’s engineered tested and procedurally approved. Probably fine on anything not critical, I’ve used it on not critical stuff. But generally anything for automotive/ life affecting, it better be approved. Plus if your customer can’t tell you what they allow for there critical work then I’d be looking to CYA.