Stainless with mig

admin

I am about to try some stainless with my mig ,what gas I have a bottle of argon .This project is nothing fancy and is not in sight but has to hold together.It is a stand for a foot valve on water line at camp.Any input or info is appreciated.ThanksMiller Big 40Lincoln SP 125Millermatic 180Century 20/50 plasmaHe who dieswith the most toys ...Still DiesThere is room for all Gods creatures .......... Right next to my mashed potatoes
Reply:When short arcing stainless, wire manufacturers typically recommend 90%helium/7.5% argon/2.5% CO2. The helium gas is used for applications where corrosion resistance is a very high concern.If you are welding something that corrosion is less important then you could use a 75%argon/25%CO2.Arguing with a Welding Engineer is like wrestling with a pig... after a while you realize the pig likes it
Reply:There have been a number of posts here saying that 100% Argon will work.  Generally, a small percentage of oxygen or CO2 will help stablilize the arc. As reddoggoose says, tri-mix with helium is commonly recommended for short arc SS.  Helium runs at a higher arc voltage and has several times greater thermal conductivity than argon, so it gives the boost in heat input needed for good fusion with short arc on metal thicker than about 14 gauge.Also posted here several times, that 75Ar/25CO2 will work for short arc SS.  This may be true, but the corrosion resistance will be severely impaired.  The SS will pickup the excessive carbon from the CO2, causing the formation of chromium carbides (carbide precipitation or sensitization), which removes chromium from providing corrosion resistance.Here is a good list of recommended gasses for MIG.http://files.aws.org/wj/2006/02/wj20...j200602-46.pdf
Reply:Tri-Mix (He-Ar-CO2), or 98-2 Ar-O2 or 98-2 Ar-CO2.  Those will let you MIG the stainless, and yet still let the stainless steel be stainless when you are done.Straight argon for MIG?   To me, if you are going to the trouble or expense or need of making something out of stainless steel, then you need stainless steel and its properties.  Most likely its corrosion resistance.  Why then do something to that stainless steel, on purpose, that you -know- is going to destroy or ruin its special properties?     So to me, that means no using C25/C20/C15/C12 gas or mild steel wire on stainless steel work.Do it once, do it right, and use the right tools and materials for the job.Or if the geometry of the parts permits, you could braze the stainless parts together.And like pulsar has posted (repeatedly), check the WeldingJournal article about welding gases for MIG/GMAW.
Reply:Moonrise,I agree with you to a point. If given the option I would take the trimix also, straight argon...absolutely not. However C25 will most likley perform adaquately for this application. Typically sensitization becomes more of an issue for food grade equipment or corrosive environment applications (sour gas service). Recently I had a discussion with another welding engineer that has seen tons of stainless welds done on pressure vessels with C25 and has never had any problems. I have personally done weld testing using austenitic stainless steels with C25 and it will give good arc characteristics.Currently there is a shortage of available helium. It may be expensive or even difficult to obtain unless your are a large bulk quantity user. If using a spray transfer I would opt for 95/5 or 98/2 argon/CO2 mixes.Last edited by reddoggoose; 08-15-2007 at 06:51 PM.Arguing with a Welding Engineer is like wrestling with a pig... after a while you realize the pig likes it
Reply:I have use pure Argon with my MIG with good results, the (unfinished) project has been outside for over a year now (1/2 mile from Atlantic ocean) and has no significant difference in the welded areas and non welded.. (304 SS)But as mentioned above a mix is better.  Also Since the Argon is cooler you welder will need big enough balls to make up for it.  Not saying it is ok, just that it will "work".
Reply:Just give you my 2 cents.  I welded some SS 1/8" unistrut to a SS 1/4" bracket about 2 years ago with straight argon (28 of them).  This was non-structural brackets to hold SS high pressure tubing at natural gas compressor station (were I work).  The welds have not rusted (on the outside of the building) and have held up good (we have an unbelievable amount of vibration and harmonics here).We had the 100% argon and did not want to purchase tri-mix for this sole purpose.  It definitely did the job.  I am not recommending this to just anybody, but for a job like this, or a hobby project, I think it works.If the project is structural, fairly thick, food service, etc. I would for sure use the tri-mix.  But for the OP, I think the 100% argon would work depending on the thickness and the machine being used.  BTW I used the MM210, plenty of machine for 1/8".I was told the by the metallurgist that the helium is needed for penetration and not for oxidation purposes.Thanks,JasonMillermatic 210 w/ SpoolgunMiller 375 ExtremeMiller Trailblazer 250GMiller AEAD 200-LEVictor Journeyman O/A
Reply:The problem with using 100% argon for mig welding is not if it will weld or not. It will weld and give good arc characteristics. The problem with 100% argon is it doesn't have the penetration that a helium based gas or CO2 gas will give. In fact 100% argon will have the least amount of penetration of any welding gas. Argon will not cause a weld to be susceptable to sensitization, that requires carbon. That's why helium is used as the primary gas in a trimix. It takes the place of CO2, but will still give an acceptable penetration profile without adding free carbon to the weld. If you want to prove it too yourself weld up a couple couples with different gases and do a macro-etch of the pen. profile. I guarantee, all things being equal, the argon will be the shallowest.Arguing with a Welding Engineer is like wrestling with a pig... after a while you realize the pig likes it
Reply:Thanks for all the input ,I understand there is a proper way to do each job and for a reason its how its done correctly.But for this little project I think I'll try argon since I have access to it .I can see if I had more stainless to play with I would purchase the correct mix.Again thanks for all the adviceMiller Big 40Lincoln SP 125Millermatic 180Century 20/50 plasmaHe who dieswith the most toys ...Still DiesThere is room for all Gods creatures .......... Right next to my mashed potatoes