problems with MIG-welding stainless

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Helly guys,this is going to be my very first post in this board, happy welding everyone and please be patient with a more or less, yeah rather less experienced/skilled , welder. Today I tried MIG welding stainless steel for the first time. I modified my little Iskra MIG 210L welder the last 3 month and I am quite happy with the results on mild steel. The problem is the surface of welded stainless which does look absolutely strange, kind of porous and oxydized.Wire material is ER308 (1.4316), base material 1.4301 I guess. Gas was 10L/min of argon 4.6. I installed a teflon/carbon liner previous in the gun.Unfortunately I could not change the appearance by changing the gas to argon/CO2 82/18 mixed. I highly doubt this is a general problem of wire feed speed, voltage or tension since I have no problems with steel although I use a 1m longer mig gun.stainless on pure argon:(Had some problems with the wire feeder here but this does not affect the weld bead surface).mild steel in 82/18 (called C18?):Quite a difference in my opinion...Any help is greatly appreciated.. Best regards from Germany,Phil
Reply:Phil, maybe I can offer you some help with the gas.  Unless I've been out to lunch for the past while, I've not heard of anyone recommending stainless MIG welding with either of the gas mixes you're using.  Pure Argon would be fine for TIG stainless.  I don't know what you'd use 82/18 for -- my guess would be mild steel, a slight variation of 75/25.I've successfully used tri-mix gas in the past, a 90 Helium/7.5 Argon /2.5 CO2 mix.  I've never heard anyone whose opinion I respected recommend a CO2 content over 5 percent, and most would like to see 2-3 percent.  This is to maintain the corrosion resistance of the weld and HAZ.There is another website around that recommends a duplex mix, but it's not the one you're using and I have no personal experience with it.
Reply:Originally Posted by tbone550Phil, maybe I can offer you some help with the gas.  Unless I've been out to lunch for the past while, I've not heard of anyone recommending stainless MIG welding with either of the gas mixes you're using.  Pure Argon would be fine for TIG stainless.  I don't know what you'd use 82/18 for -- my guess would be mild steel, a slight variation of 75/25.I've successfully used tri-mix gas in the past, a 90 Helium/7.5 Argon /2.5 CO2 mix.  I've never heard anyone whose opinion I respected recommend a CO2 content over 5 percent, and most would like to see 2-3 percent.  This is to maintain the corrosion resistance of the weld and HAZ.
Reply:c25 or pure argon will not work on stainless mig...tri mix or ~98Ar/2CO2 will work but don't expect pretty welds with short circuit mig on stainlessprice of welding gases that don't have helium in the mix is usually low--------------------------------------------------------------www.becmotors.nlyup, I quit welding.. joined welder anonymous
Reply:Originally Posted by Donoharmdon't expect pretty welds with short circuit mig on stainless
Reply:Yep, that's mig on stainless. Doesn't look nice, but works ok for some aplications. Welds don't have full corrosion resistance and they will rust in salty water.
Reply:Conclusion: buying a tig welder is unevitable for professional stainless welds? Crap. Best regards,Phil
Reply:There is a study somewhere on the internet that said that once you hit about 5% CO2, the carbon pickup of stainless goes way up.  Its the chromium that likes the carbon and you effectively loose the protection of the chromium.So you'll see stainless gas mixes that are 2-4% CO2.Some people will add O2 instead, but as you can imagine, O2 reacts will the iron and I understand the limit is about 2%.The preferred solution (at least in the USA) is various tri-mix formulas which adds helium (which I understand gets more heat into the metal and maybe a more stable arc).There was some discussion about using 4% mixtures on thinner stainless and tri-mix on thicker stuff.  Most comments (Sundown I believe) leaned toward tri-mix for everything.In US, tri-mix has gotten expensive (cost of helium) and the fact that you have to mix 3 different gases (cost of mixing).   So, not sure if its worth the cost just to practice.Note:  If you wire brush the stainless with a carbon steel brush, it will rust as well.  Playing with stainless and you want to use dedicated stainless brushes etc.   Even drilling hole with a carbon steel drill can cause rust.  There are chemical ways to help - search for "passivate stainless."  However, I don't think that will help if you weld with 20% CO2.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:I bought a bottle of TRI-MIX awhile back just to see how it worked for stainless.....My mig machine is an old Hobart Beta Mig  200 and it says it can spray weld but never got that far........I tig everything.....  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Originally Posted by con_fuse9However, I don't think that will help if you weld with 20% CO2.
Reply:The welds in the post you reference are using spray transfer, not sure if you are running at suitable parameters for spray x-fer on SS.  you will want something ~3%CO2 and you will need some decently thick base metal (3/16-1/4) at least to pull the heat out.  You should be able to duplicate the weld on the right side of his coupon without too much trouble, yours may be a bit darkerExperience is something you get right after you need it
Reply:Originally Posted by RST DriverI don't! I use pure argon and will add ~3% carbon dioxide in the future.I am quite familiar with the metallurgical processes happening during mig welding and of course the risks of using gas with too much co2 when welding stainless (chromium carbides are the big problem, as you already mentioned). But this is just theory and I was wondering if I could affect the bead surface with the gas - obviously I can't.Only one picture in the "MIG like TIG" thread shows a great stainless mig-weld:http://weldingweb.com/showpost.php?p...&postcount=331I have no idea how he did that and I don't see any possibility to duplicate this with my machine. Does a pulse function make such a big difference?I have dedicated stainless wire brushes for stainless projects. B_C, your picture shows a tig weld, right?Best regards,Phil
Reply:Originally Posted by Fred sThe welds in the post you reference are using spray transfer, not sure if you are running at suitable parameters for spray x-fer on SS.  you will want something ~3%CO2 and you will need some decently thick base metal (3/16-1/4) at least to pull the heat out.  You should be able to duplicate the weld on the right side of his coupon without too much trouble, yours may be a bit darker
Reply:Doh - pictures are way too big and I can't even click the edit button. Sorry guys. Best regards,Phil
Reply:Tri mix (90helium7.5argon2.5co2) is the way to go on gas, with 0.035inch 316L solid wire try 21volts and 275inches per min.  With solid stainless wire you have to move the wire side to side in the puddle fast to get it to go where you want.
Reply:Originally Posted by RST DriverI don't! I use pure argon and will add ~3% carbon dioxide in the future.I am quite familiar with the metallurgical processes happening during mig welding and of course the risks of using gas with too much co2 when welding stainless (chromium carbides are the big problem, as you already mentioned). But this is just theory and I was wondering if I could affect the bead surface with the gas - obviously I can't.Only one picture in the "MIG like TIG" thread shows a great stainless mig-weld:http://weldingweb.com/showpost.php?p...&postcount=331I have no idea how he did that and I don't see any possibility to duplicate this with my machine. Does a pulse function make such a big difference?
Reply:Originally Posted by colindstarkTri mix (90helium7.5argon2.5co2) is the way to go on gas, with 0.035inch 316L solid wire try 21volts and 275inches per min.  With solid stainless wire you have to move the wire side to side in the puddle fast to get it to go where you want.
Reply:Originally Posted by RST DriverTry these settings on thin sheet metal and exhaust tubes - one hole, two holes, three holes, even bigger fourth hole...Ok, that's high-tech I don't have. I really like the cursive-e technique on thicker stuff in combination with a slower welding speed to burn in the edges. Haven't tried it on thin metal but I'll give it a shot. The problem is that 1mm (0.04 inches) thick pipes for example of an exhaust system cannot handle much heat, especially when there is a little gap - the results are holes and/or a molten bath that is about to fall through and solidifies inside the pipe so it interferes the gas flow. Best regards,Phil