Video TIG tacking and 303 SS

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Just watched this video which show a super handy TIG tacking technique that a fellow taught me 30 years ago.  Then he talks about welding 303 Stainless Steel and gives some bogus advice.http://www.weldingtipsandtricks.com/...stainless.htmlOld thread on the tacking subject:http://weldingweb.com/vbb/showthread.php?t=12987Kemppi videos of tacking techniqueOn the subject of welding 303 Stainless Steel, I see in the video that this guy has a pretty weld and apparently no hot cracking issues, but his advice that 308 would give equivalent cracking resistance to 312 or 309 is just flat incorrect.  The super high sulfur content of 303 free machining SS can cause severe hot cracking depending on weld profile and joint restraint.  312 can be effective at preventing hot cracking because is has a high ferrite content which can hold sulfur in solution rather than allowing the formation of a liquid sulfur film at the solidifying weld grain boundaries.  His mention to add more filler is correct, since this will dilute the sulfur in the weld.  Below is an earlier thread on 303 SS.http://weldingweb.com/vbb/showthread.php?t=31073
Reply:Outstaning post pulser!I can't dog the guy as I have zip experience with 303 so maybe 308 is working for him in show parts. With 11XX steels you need the 312 (duplex) or lime coated electrodes to keep them from cracking down the middle of the bead. I also see he compared 303 to 12L14 (resulfurized vs leaded) sulfur generally cracks down the middle where leaded goes at the fusion line.There is also a much longer you tube vid of a 200ms pulse tac showing the puddle motion after the arc breaks. [ame]http://www.youtube.com/watch?v=dKk4Y9IWQ1c&feature=related[/ame]I was hoping to get some o'scope traces of my kemppi (first generation inverter era) and post back on the other pulse settings post and maybe get that going a bit. It only pulses up to 12pps and it is mostly a soft pulse and while it seems useful for sluggish fillers at higher settings I've never seen any benefit from it with thin stuff.Well the old tek503 scope is dead so I ordered a new one with storage, should be here next week and I can post up the traces then. The output from inverters is very different from rectified machines similar to dc generators but more pulsing (at very high rates). There are some electromotive/inductive forces you can see with a scope that explain the added punch to the arc of these machines.Thanks for posting!Matt
Reply:Thanks Matt,like I said, it worked for him in this application, but there is a lack of important information and some incorrect information provided.  I've not worked with leaded steel, I wonder why it tends to fail along the fusion line.Kemppi has some impressive close up, really clear, high speed welding video.  I think its amazing to see how much the weld pool sloshes around after the tack welding arc is extinguised.  You can see how the pool may spash up and hit the electrode.  These things that invisible to the naked eye can be really important to solving welding issues.Other really clear video and amazing welding technology is from Fronius.  Check out the precision control of cold metal transfer and the pin welding.http://www.youtube.com/user/FroniusWelding#p/uWith regard to you're statement about electromotive/inductive force and punch of modern inveters, I will soon be experimenting with a Dynasty 700 at work, and plan to look at the response time, how much time is needed for a pulse to reach full current, because even though the machine can be set to a few milli-sec at 700 amps doesn't mean it can reach that value in that time.  Also I'm interested in the short pulse time capacity of the electrode, so how many amps can an electrode handle for a short pulse time, which is much higher than the constant current value.Last edited by pulser; 09-21-2010 at 12:03 AM.
Reply:Good stuff... the slow-mo videos are fascinating.  I had no idea the liquid metal waves travel so quickly.  Or that there is such an abrupt wave action apparently caused by arc extinguishment.
Reply:Now that's impressive pulser! I looked some more at the Fronius vids and was reminded of seeing a demo of "elecrobraze welding" by them at an AWS convention some 10-12 years ago. They were welding galvanized and aluminized parts without much/any burnback of the coating. The SAE heads were standing on top of each other getting coupons and info. I think that process has now evolved to the "cold weld" (very similar to STT and DIP-Pulse).BTW I would be very interested in what you find with the Miller, one of the links on the pulse settings topic mentioned inverters are now switching at up to 60,000hz. That's 4 times as fast as my 1st gen kemppi! Wow!As for the cracking thing, showing the date of my education, I still use electron rings and charges to determine solubility (old quantum theory, I don't understand quantum mechanics and new notations at all & usually need help).Here is a guess, iron needs another atom to get together with lead and be stable, there is only so much junk that can be tossed in steel and still call it steel. Sulfur can get together at either a 1-1 or 3-4 mix with iron and be stable. The lead in 12L14 and now in some alloys are inclusions and when brought into solution must be pushed out of the puddle as the iron gets closer together. Resufurized steel also carries the sulfur as inclusions but when brought back into solution does bond with iron in a happy little family (except sulfur has no strength). The whole puddle is weak with sulfur bonded and the center cracks (hot short cracking). I would expect as lead is pushed out of the puddle with no specific fluxing agent, there are large lead inclusions at the fusion lineI do not know exactly how the leading and resufurizing are done at the melt, but they both are inclusions and not bonded.There must be some difference in the leaded steels also as 12L14 has no notch toughness at all but 41L40 has been used to replace 1045 and 1144 in high strength shafting and pays for itself in machining costs. Resufurized steels have good notch toughness OTOH.Leaded steels are welded in laminations (electrical use), with wire and electrode but it is not a critical structural weld but more to replace a rivet or something like that. Resufurized steels are welded with a duplex steel or a lime coated low alloy rod, I still wouldn't trust the weld much though (seen too many welded stressproof shafts fail).Matt