TIG welding 304 SS... could use some help

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A little background first... I've only been welding since the 24th of January this year, so I'm certainly still learning. Been attending welding classes at the community college full time, Monday through Friday. I'm 19, turning 20 in May and have no welding experience except for this course.I've progressed through the GMAW program (Both short-arc and spray transfer), FCAW Dual-shield, and the first section of SMAW (have not performed actual bend tests, only visual inspections. Except for the structural steel competency, in which a cross-section was cut to check for proper fusion & inclusions).I recently did my first ever GTAW welding a little over a week ago, starting on mild steel. I feel like I picked up on it quite quickly, I actually passed off the first weld I ever attempted (butt weld). Took me a little longer to figure out the Tee welds, until I realized I was adding filler too soon, and sucking the heat out of the puddle. Once I figured that out, I was able to consistently do a nice, even bead nearly every time, I don't often contaminate the tungsten anymore (or at least it doesn't feel like it)So I've now progressed to stainless, and this is where I'm having difficulty. With some practice, I feel like I have the tee and lap joints down pretty well, I can get a nice even bead with the right color. But the butt welds are a different story...... I'm obviously overheating the weld, it's that greyish-black color, with the tiny "fracture" looking lines on the surface. The bead looks nice once it's wire brushed off, but my instructors won't pass it, and I wouldn't expect them to.I understand that this happens more easily on the butt weld, since it heats up more quickly and the heat has less area to escape to... But I can't seem to get the correct color, and a proper looking bead at the same time. In a moment of frustration, I clamped two strips of aluminum on the area outside the weld to act as heat sinks, and I managed to get a decent bead that way. But I'd rather learn to do it right.... Any help is much appreciated.I'm sure pictures would help, but we're not allowed to take metal home. It's on coupons about 4" x 1.5", 1/8" thick material. Using 1/16" 308 filler, I've used both a 3/32 ceriated tungsten provided by the school, and 3/32" "rare earth" tungstens that I purchased from cyberweld for myself (less grinding this way, more welding  ), I personally can't tell much difference between them.Sorry for the ridiculously long post... Any help really is appreciated though! Thank you  I sure do want to figure this out...... Welding is such a humbling experience at times--When I was doing the mild steel, I actually bought 20' of 1/8" x 4" steel to practice on, that was one of the best things I've ever done in that class, since I could get so much more practice time in. I took the steel home to grind off all the mill scale, then cut it into coupons at school on the ironworkers.I'm strongly considering doing the same with stainless, and even aluminum when I get there... Any idea what I could expect to be paying per foot with these though? There's just never much metal available at school, and trying to weld with warped pieces from the scrap bin can be frustrating at times to say the least Last edited by Primetime; 03-29-2011 at 11:19 PM.
Reply:Not many tips I can give you, since you have it figured out pretty well already.  Only thing that might help is to travel faster with higher amps, or slower with much lower amps.  The goal being to balance your heat input with the amount of time that the tail of the weld is covered by the shielding gas.You could try using a gas lens in the torch, or using a 10-12 nozzle.Have we all gone mad?
Reply:With thin stainless you need to back purge  enclosed applications with argon making sure you have flow at all times and not just filling the vessel. (around 10-15 cfh ) using a small outlet hole  maybe .060......If you can't back purge then the application of Solar B  (mixed with methanol) will help keep the sugaring down.  Being a beginner with thin stainless is probably NOT  where you want to be in your learning curve....  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Hey BCGet that new blue yet??   Vinnie
Reply:I wouldn't consider using chill bars as "cheating" or wrong in any way, you gotta do what you gotta do y'know? Granted, it may not always be possible in the field, but cross that bridge when you come to it.Not being an expert myself, feel free to take anything I say with a grain (or two!) of salt, but I didn't see you mention backpurging any of your joints. It may not be necessary (or practical) for practice welds, but you will get far better results with a backpurge, especially with a butt weld. If you don't want to set up a backpurge every time, try to find a nice 4" wide piece of copper or brass to clamp your coupons onto. The whole point is to keep oxygen away from the backside of the weld. When I was first learning to TIG stainless, I was told that a joint without backpurge will sugar on both sides of the weld, even though the front is shielded. This was then proven to me with several practical demonstrations. Maybe it's not true, but I have followed that advice ever since and gotten good results. YMMV  Good luck with the welds, keep practicing!
Reply:Thanks everyone for the advice.Unfortunately.... A backpurge is simply not an option. All the argon for the TIG machines here at the school is piped in "remotely" from a system of 8-10 bottles outside of the shop area. Just no way I can set one up.It does sound like I should use a "backing plate" of copper or aluminum though, as Mechtician suggested, I'll have to look into that soon, hopefully that helps I'll also try to get into the booth with a larger cup.... I was in the booth with a # 5 today, and it was even worse. Why is that though? Is it simply the shielding gas coverage, or does a larger cup flow more gas and therefore cool the weld bead that much more? Or am I missing something? And why does lack of a back purge produce the sugaring on both sides?And B.C., is 1/8" stainless really "thin", and it would be easier with thicker material? And what is this solar B stuff? I do wish I could take more time learning this stuff, but I have to keep progress up in school & they don't give you time to leisurely practice stuff. And I'm pretty stuck with 1/8", that's all the school is providing right now.But hey, on the bright side I seem to be decent at TIGing aluminum at least.....Give me fuel, give me fire, give me that which I desire.
Reply:Originally Posted by VinnieHey BCGet that new blue yet??   Vinnie
Reply:I'm not sure I can explain this on here but I will try. Tack your plates together with a small gap big enough for the gas from your cup to get into. Put two more plates under the test plates about a 1/4" from the joint running parallel with the gap. Two more plates to trap the gas at the start and end of the joint and turn up the preflow.Last edited by fire1hawk; 03-31-2011 at 03:44 AM.Miller Dynasty 700Miller Dynasty 200Miller 350pMiller 252Hobart Handler 187Lincoln Weld pack 180Victor O/AHypertherm 1250Hobart Airforce 500IPractical cnc
Reply:Originally Posted by Primetime why does lack of a back purge produce the sugaring on both sides?.
Reply:At somewhere around 1500F, on 304 stainless, the chromium will move around.  When exposed to carbon - like in CO2 - at that temperature, the carbon will suck the chromium right out of the metal - like sponge wicking away water.You have essentially 4 choice to prevent this.1) Back purging.  Essentially keep the carbon away.2) Solar Flux - give the carbon something else to grab onto - something it likes better than chromium3) Small gap and not a full penetrating weld.  Pretty much an autogenious weld.  On 1/8, probably less than 100Amps.  Flip it over and do the same on the back side.  If you need a bead to polish down, run additional passes.  With no gap, stainless tends to 'butt together and you can warp it just from that.  Watch the bead width.  If the bead doesn't flow easily, you cannot simply add more heat, you will expose the backside.  Bottom line, if the bead gets too wide, you've had it, the weld will look like crap4) Slightly larger gap and plenty of pre-flow.  If you are trying to weld this on an open grate table, forget it.  Won't work.  If you lay the piece down on say a flat plate of aluminum it will work - but if you have a bead on the back side it will touch the aluminum and not look as pretty.Last thing.  Stainless is a bit different than most steels.   To anneal stainless - you quench it!,  Try that with medium carbon steel and it will be so brittle you can snap if off with a couple taps from a hammer.  Quenching 304 series stainless supposedly benefits the corrosion resistance as well.From my own experiments with it, the distortion by quenching was pretty bad.  I understand that some pros intentionally quench to control distortion.  I don't know.  I've only played with this on thin scrap pieces.  I have some larger plate, but I don't want to waste it on this experiment.  I'd ask the instructor(s) if they can show you.   Maybe find a company that welds food service equipment (stainless sinks, tables etc.)  Those guys have to be doing this stuff day in day out - I suspect with no back purge.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:Haven't really updated this, but I finally figured the butt welds out a couple days ago, something just "clicked" I guess. They've progressed from dull grey, to shiny grey, to finally where I'm at now where they come out in either a gold/straw, to salmon to blue shade, like my tee and lap joints    Didn't use heat sinks or a backpurge....I'll try to post some pics later when I get the chance, thanks for all the help everyone, you're great. It really did help actuallyOff topic, but I'm starting my first welding job soon.... Welding semi trailers at Utility, I can't deny I'm excited!   Not bad at all considering how much experience I had coming into the program Give me fuel, give me fire, give me that which I desire.