Having some issues MIG welding Stainless

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Hey all,This is my first time attempting to MIG stainless. I've got a couple large pieces of 304 and I'm trying to plug 1/2" holes with a section of a 1/2" stainless bolt. I'm using 0.030" 308 wire and I have 100% Ar gas. In my first attempt to plug these holes, I used SS washers and tacked around them until I had the gaps filled, but micro-cracks in my crappy beads made the repair not-so-watertight. I think some of this problem was due to low gas. Now that I have a new bottle, I've decided to try plugging the holes with 1/2" slugs and welding them tight. I removed the old repair with a grinder and I'm starting fresh. Issues:1. I'm getting a kind of spat-spat-spat-spat like I would get when the wire feed rate is too low. So by compensating with an increased feed rate, I'm still not getting very even bead flow. And the welds look pretty shoddy (more than my usual inexperienced welds).2. I have the voltage all the way up because I'm welding to chunk of stainless. With mild steel I err to the high voltage, high wire feed rate side and tune down. Is this an okay approach with stainless?3. Visbility sucks. But I guess that's just the way it's going to be with MIG. 4. Is it best to weld in short tacks or to try to lay a continuous bead? The short tacks look better but I don't think they join together very well. Thanks for reading.Hobart Handler 140 MIGHypertherm Max 43 Plasma CutterA Bernzomatic Torch, and some solder.
Reply:Never done stainless... someone will be along shortly ***************************************Lincoln AC225 stick welderLincoln HD100 WeldPak flux core wire feed welderThree of the cheapest grinders money can buy
Reply:I use a tri Mix when Mig welding stainless. Its not as pretty a Tig but it looks good. I have never used 100% argon with a Mig and stainless and am not sure if 100% argon is the best choice. I'm sure sombody more experianced with this will be on soonDrivesector Hobart Handler 140Hobart Handler 180Ready Welder 2Hobart Air Force 400Airco Stinger 225Of all the things I've lost, I miss my mind the most."OZZY"
Reply:When welding SS with MIG I use a 75/25 mix...... but I also use a dualshield wire. How thick is the material that the hole is in? You can probably do the repair without any type of a plug._________________Chris
Reply:I have welded a few kitchen sinks in resteraunts.  I found the stainless wire needs totally different settings than mild steel.  Find a piece of practice stainless and get your settings right by trial and error until you get a nice even bead and buzzzz from the arc, then go to your project.  100 % argon will work, C25 cools the weld more and requires more voltage.  I have used both.If this is thick, turn your wire up pretty good and adjust voltage to get a smooth weld.You can do it and it will look nice.Stainless is a pain to weld compared to mild steel.  Lots of wire brushing and its hard to grind off mistakes.
Reply:I should add that most of the stainless I do is with spray transfer...._________________Chris
Reply:Yeah Lorenzo we use 309l dual shield with 75-25 argon co2 for maganese bucket lips and latch bars on p&h shovels.
Reply:The big piece is about 1" by 4" block of 304. I have welded it multiple times today only to find that it isn't really welding to the block - only the plug. I have gournd the surface clean, then I gave it a rough finish with a file hoping to provide more surface area for the melt pool to wet to -  not really working. So I gave up and decided to thread the hole for 9/16" and seal it with teflon tape and a threaded plug. No such luck.... no hardware store within a 15 mile radius has a tap bigger than 1/2". Hobart Handler 140 MIGHypertherm Max 43 Plasma CutterA Bernzomatic Torch, and some solder.
Reply:Originally Posted by Dipper Welder64Yeah Lorenzo we use 309l dual shield with 75-25 argon co2 for maganese bucket lips and latch bars on p&h shovels.
Reply:Originally Posted by lorenzoI should add that most of the stainless I do is with spray transfer....
Reply:I did just realize that I had the polarity negative (default for flux core) while I was attempting to weld stainless. It is recommended that the electrode be positive for stainless. Would this make a big difference?From what I can tell, the large piece of stainless just isn't getting hot enough to wet the weld. Every time I try it, the plug has a nice weld, but if I tap it hard enough, it pops right off the large piece. It never melts into it. The other option would be to thread in a 9/16" plug with teflon tape if I could just find a place that sells that big of a tap. Hobart Handler 140 MIGHypertherm Max 43 Plasma CutterA Bernzomatic Torch, and some solder.
Reply:Bare wire, electrode positive.  Flux core, electrode neg.David
Reply:Bevel around the plug insert......... add a little heat to the surrounding block._________________Chris
Reply:Turns out the polarity was my biggest issue. Once it was switched, the weld was much easier to control. Thanks for the replies.Hobart Handler 140 MIGHypertherm Max 43 Plasma CutterA Bernzomatic Torch, and some solder.
Reply:Good thing you figured out the polarity.On the subject of gas for SS MIG, I have used 98/2 and 98/1 Argon/O2, and 95/5 Argon/CO2, for pulsed spray, and these work great.  As I understand it, a small addition of O2 or CO2 to Argon is needed to stabilize the arc.  Pure Argon may work, but one of these mixes will make it easier.I have not done short arc MIG on SS, but have read that a tri-mix of Argon/Helium/O2 or CO2 is common.  The Helium is added for extra heat needed in short arc transfer.I see several posters say they us C-25, 75/25 Argon/CO2 for SS MIG.  I guess it works for what they are doing, but I have never seen this mix recommended for any SS welding.Generally, 2% O2 or 5% CO2 is the highest level of reactive gas recommended to prevent excessive oxidation.  And in the case of 25% CO2, the weld can pick up excessive carbon from the gas causing carbide precipitation and intergranular corrosion.  Carbon pickup can also affect the balance of ferrite and austenite increasing the likelyhood of solidification cracking. If you are welding something stainless, that actually requires the corrosion resistance of SS, then it may be best to stick to the proven, lower concentrations of O2 or CO2.Here are MIG gas recommendations published in AWS Welding Journal:http://files.aws.org/wj/2006/02/wj20...j200602-46.pdf