TIG Help please

[aczeller]

alrighty... the guys in the shop at work are now trusting me enough to let me play with their toys, and i coudln't have been happier. i just grab some scrap out of the bin (usually 1/8" / 11 GA. 304/304L/316/316L SS) and have at it... they showed me how to TIG today at lunch. they told me the welds i laid were either too hot, or i needed to move faster. they were consistant (about 75% cosistant anyway... this was the first time that i have EVER TIG'd) but they were a dull, darker grey color. i didn't use any filler since we didn't have any laying around and i was only practicing on keeping the arc consistant. no smoke or contamination though. i didn't have time to practice any more and had to get back to work, but they said it should have a consistant, colorful rainbow pattern to the bead. does anyone have any pictures of this? they have already left for the day and they didn't have time to show me a good one over lunch. i plan on goingout to the shop just about every day now over lunch. i love it.

a few things:

- we are using all miller stuff... millermatic 251 @~320-340 wire speed and ~21.4-21.8 volts. the tig is older and i'm not sure how to set it up so i don't know the settings or the model yet. it looks really old though. they said it was here over 10 years ago.

- we are using zero filler (none) when we TIG. the metal is non-structural for the most part... just water-tight, non-presurized (spelling?) 304 SS. the load-bearing stuff is either MIG'd or they have another guy in the shop use the filler in it. the SS is usually MIG'd and the Al is USUALLY TIG'd with filler.

thanks for the help guys... i really appreciate it. every time i get something posted on here, it usually gets answered quickly and correctly. i am always overwhelmed at the knowledge on this forum. it's great.

later,
Andy

[hotrodder]

do a search of the picture/projects forum for stainless- there'll be loads of pics

the dark colour is from the stainless reacting with the air while hot- the lighter the colour, the less reaction

from this it's clear that the colour is related to how hot the metal was when the gas shield was lost (as the torch was moved). assuming correct gas flow, the most common causes would be...

• too hot and/or too slow
• long arc length- this puts more heat into the work
• pulling filler out of the gas shield between dips- the hot end oxidizes and is then introduced to the weld pool, contaminating it

obviously the last one doesn't apply as you're not using filler yet. at this stage i wouldn't worry too much about colour- concentrate on keeping a short (less than an 1/8 preferably around 1/16") arc length and trying to keep the beads a consistant size.

arc length, puddle and filler control are the keys to a good weld- once you've got these down, balancing travel speed against heat will come relatively easily

[Go1lum]

Originally Posted by hotrodder

do a search of the picture/projects forum for stainless- there'll be loads of pics

the dark colour is from the stainless reacting with the air while hot- the lighter the colour, the less reaction

from this it's clear that the colour is related to how hot the metal was when the gas shield was lost (as the torch was moved). assuming correct gas flow, the most common causes would be...

• too hot and/or too slow
• long arc length- this puts more heat into the work
• pulling filler out of the gas shield between dips- the hot end oxidizes and is then introduced to the weld pool, contaminating it

obviously the last one doesn't apply as you're not using filler yet. at this stage i wouldn't worry too much about colour- concentrate on keeping a short (less than an 1/8 preferably around 1/16") arc length and trying to keep the beads a consistant size.

arc length, puddle and filler control are the keys to a good weld- once you've got these down, balancing travel speed against heat will come relatively easily

The dark color is from carbide parcipitation not from the stainless reacting with the air. This is caused by the stainless being held at and elevated temp to long. The chromium burns out of solid solution and bonds with the carbon to form chromium carbide. Cr23C6. To eliminate this you need to put less heat imput into the ss.

[aczeller]

thanks for the input... like i said... it never ceses to amaze me, all the great info in this forum. the guys don't work on mondays, unless they want to come in for overtime (our shop runs on a 4-day week, 10 hour days. the office runs 5, 8 hour days... dunno why. all i knwo is that monday is usually the free-roam day in the shop for us office guys. the welders all know that i am in there everyday at lunch now, and they don't care if i use the stuff... they know i always clean up after myself and put the stuff back in the same place i found it. i think i may just practice running some beads on monday. i'll try to run a few straights and then if i can get the coloration right, i'll try getting a t-joint together, but i think it may take me a while to get the beads looking right.

if i can remember my camera, i'll get some pictures up here.

thanks again!

later,
Andy

[William McCormick Jr]

Unless you use a giant gas lens. About 2" inches in diameter, you will more then likely get greying.

Or if the mass of the part cannot chill the weld before the gas lens is no longer over it.

Or if you don't use back up gas on thin material, you will get a greying from the stainless staying hot and cooking on the backside, in most cases.

Because to penetrate and get those little beads on the inside, you will more then likely get a greying on the outside.

If you take a stainless wire wheel to those welds they will just clean right up though. Don't use a steel wire wheel. It will cause the stainless to rust. And it won't stop.

When we do welds that have to be perfect, we use chilling blocks, and backup gas, and a giant gas lens.


Sincerely,



William McCormick

[hotrodder]

Originally Posted by Go1lum

The dark color is from carbide parcipitation not from the stainless reacting with the air. This is caused by the stainless being held at and elevated temp to long. The chromium burns out of solid solution and bonds with the carbon to form chromium carbide. Cr23C6. To eliminate this you need to put less heat imput into the ss.

no. weld colour is a function of shielding gas coverage- if the shield is lost (as the torch is moved) when the weld is hot enough it will react with O2 in the the air. taken to extremes, as in a butt weld without purging the backside of the weld results in coking/sugaring

carbide precipitation is a different phenomimum. it is dependant on temperature (occurs over a range of temps- i forget the numbers, but it's well below the melting temp) and the % of chromium present. SS has tiny amounts of carbon to help reduce precipitation (0.08% is typically the upper limit for austenitics) and certain grades are stabilized with Ti and/or niobium as these elements have a higher affinity for C than Cr does

IF some SS were welded in an inert atmosphere (say, an argon filled chamber) then the weld will have no 'colour' whatsoever regardless of how much heat was used. given enough carbon, carbide precipitation could still occur though

[aczeller]

okay folks... first off thanks for the tips. i tried it out today over lunch and got it dead on (no pictures... sorry. i need to get a camera just for work so i don't forget it). the coloration was perfect and the "rainbow" was right there. slightly yellow tint that faded to the SS color in the middle with blue and purple on the edges of the bead, fading back out to blue and light blue in the penetration zone. once again, i used no filler. i figured it'd be better to learn the proper technique before i complicate it with another hand in the way. i still have A LOT of practice getting the beads right (i tend to start off good, then they continuously shrink towards the end of the weld), but that willcome with time. i practiced on 10 ga 304 SS from teh scrap bin and was running about 30 amps (i think). anyway, i also found that i need more practice with the rigging of the parts, in order to make sure i have the pieces tight, but other than that, everything is comming together nicely. the main problem i was having is that i was dragging, rather than pushing, which made the puddle oxidize and starved of the argon. With my self-shieled flux-core wire at home, i can move whatever way i need to. there was much more part-moving today at lunch. i find that it's easiest to angle the torch away form me a little bit (nozzle closer to me than the non-arcing end), and drag the torch towards myself. i was trying to push away from myself, but was having problems seeing the puddle.

again, thanks for the advice. it really helped.

later,
Andy

[David R]

I didn't quite get all that, but the torch should always push. That would be forehand, or tungsten pointed towards the finish line. I would guess a 20* tilt (70 from the plate) with the tungsten ahead. Pull it towards you, push it away, or what ever, just fore hand. Its for the gas coverage. Sounds like you had a really nice lunch

David

Sneaking out at lunch time to weld.

[aczeller]

Originally Posted by David R

Sounds like you had a really nice lunch
Sneaking out at lunch time to weld.

yea.. i had a great lunch. it's good whne i get a chance to play with the BIG toys (work welders instead of my tiny little LE 100HD). it's a GREAT lunch when i actually do it right... or at least learn something new. i guess all 3 happened today. hehehehe

later,
Andy