Porosity Problems

[FlashBlind]

I was in my shop last night, working on a project, then started welding and breaking 3/16" and 1/4" scraps to test penetration and strength. I found several welds that looked pretty good on the surface were full of columnar type (Bio term) or worm hole porosity. The welds still took a lot of beating to break, but were not as strong as the well penetrated solid welds. I did not prep the surface and did fish around on the Amps & wire speed (Miller Vintage 250, .035 wire, 90%Ar/8%CO2/2%O2 gas). I realize that I need to eliminate the variables and common causes of porosity- contamination, settings too hot, breeze, etc., but the disturbing thing is that these welds looked good but were crap. Kind of scary.
I cranked up the settings and used spray transfer on a 1/4" butt joint with about 3/32 gap. Nice penetration and strength. When I beat it apart, the stock bent before the weld finally broke, showing nice penetration on both sides. Of course I can't spray the thinner stuff, so I'll cut a pile of flat stock for practice and work on this until I can elininate the porosity and get adequate penetration.
I keep coming back to the statements about MIG being the easiest to learn, but the hardest to learn right, and the old stick Weldor's description of MIG being a "Hot glue gun".

[Seldom]

You've jumped the biggest hurdle already FlashBlind- "awareness"!

[chip hayden]

quite possibly what you are seeing with those sub-surface voids is the bane of all large weldments. it's called hydrogen entrapment and it is what can cause bridges to fail and buildings to collapse.
if steel is damp or has contaminants like paint,grease or, oil[i.e. hydrocarbons] these substance can be "cracked" by the heat of welding or by the arc. as the hydrogen in these contaminants is liberated it can become trapped in the weld pool and frozen over as the metal solidifies. now, stainless steel with it's nickel[which is called the "***** metal" for obvious reasons] can keep the hydrogen dissolved and not cause problems with the weld. but carbon steel is another story.
remember from chem 101 how small hydrogen is? this little atomic structure will force it's way eventually, to the surface of the weld, especially if the weld is under tension[what welds aren't?]. it will gradually separate the iron/carbon grains bond to each other and start a fissure that becomes a crack.
now low carbon steel is pretty ductile and forgiving but high strength steels cannot tolerate this. that's why low hydrogen rod is required for so many jobs. metal is preheated before welding to drive off any moisture and 7018 electrode MUST be kept dry and at 250F is you are going to weld with it.
i actually think it's pretty neat that you were observant enough to notice this phnomena. you now have an idea what engineers and inspectors have to deal with on a grand scale.

[Hobart Expert Kevin]

Flashblind,
From the sounds of it I think your metal must be a little dirty. Try cleaning the metal before welding next time see if the results are better. One other thing, the gas you are using is a spray gas, if you are trying to do a short circuit transfer on the thinner material this could be causing some problems. Keep us in the loop on what you have tried and the results.

Kevin

[email protected]

[FlashBlind]

Well, I worked on more practice butt and fillet welds of varying thickness, and have eliminated the porosity problem for now. I ground all surfaces until bright, and took my time setting up the pieces to get the gap (Butt) even. On both short circuit and spray transfer, I got decent penetration and strength. I realize that there are no good shortcuts and will have to spend more time setting up my welds than welding them..
My gas mix was recommended for all types of transfer by my local welding shop, and I was naive enough (Still am) to lease a 125 cu ft. tank of it. Seems to work fine, but again, my experience is really limited. Sure is fun to spray heavy plate together. The really smooth and consistant arc makes the puddle easy to control. I've smoked my Right glove (I'm a lefty) pretty bad several times. Thanks to all for the help so far.