SS TIG filler question

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If I got it right when selecting filler for TIG, go with like materials, eg. (mild steel to mild steel use ER70), (stainless to stainless use a stainless filler).  That makes sense.  And when joining dissimilar metals (mild to stainless) use 309, which makes sense as explained in 5.11 ( http://www.esabna.com/EUWeb/AWTC/Lesson5_18.htm )  Here is my question.  In the countless welding forum threads I’ve burned my eyes on I swear I’ve read where people have used SS filler when joining mild to mild.  Am I smokin’ dope and not known it?  I tried to find at least one thread but can’t because, of course, I’m looking for it.Bottom line question, is SS filler ever used, legitimately, to TIG weld mild steel to mild steel?  If so, why? Strength, easier weld, ….?Fillethead
Reply:I have read to use 308 or 309 to weld mild to stainless. Seems more people suggest 309 over 308 but no idea why.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Originally Posted by GambleI have read to use 308 or 309 to weld mild to stainless. Seems more people suggest 309 over 308 but no idea why.
Reply:Originally Posted by filletheadIf I got it right when selecting filler for TIG, go with like materials, eg. (mild steel to mild steel use ER70), (stainless to stainless use a stainless filler).  That makes sense.  And when joining dissimilar metals (mild to stainless) use 309, which makes sense as explained in 5.11 ( http://www.esabna.com/EUWeb/AWTC/Lesson5_18.htm )  Here is my question.  In the countless welding forum threads I’ve burned my eyes on I swear I’ve read where people have used SS filler when joining mild to mild.  Am I smokin’ dope and not known it?  I tried to find at least one thread but can’t because, of course, I’m looking for it.Bottom line question, is SS filler ever used, legitimately, to TIG weld mild steel to mild steel?  If so, why? Strength, easier weld, ….?Fillethead
Reply:It is normally used, when you don't know what the base metal is, or when welding cast parts. I remember a few years ago, that talking to some guys at General Dynamics, whom have also said they've used it for welding chromoly in some case. I can't remember the exact reasoning at this point though. It provides almost no real extra corrosion resistance, as its heavily mixed into the molten weld puddle by the adjoining metals. One case I sometimes like to use stainless filler when both parts are mild steel. Is when dealing with very thin sheet metal. It flows a little nicer and seems to keep the weld a little cleaner looking.
Reply:Originally Posted by Oscarfrom  http://www.weldingelectrodes.net/welding_electrodes.htmbasically the additional chromium and nickel over standard 308L is what gives it an "edge" over 308L.
Reply:He's talking about 309 vs 308L.
Reply:Not sure what your asking but I have been using 308L  on old shotgun parts for years with good results......Not saying 309 wouldn't be a better choice but that's what I had and it worked ?   None of the guns I repaired broke so I assume it was OK?  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Originally Posted by GambleHuh??
Reply:You need a minimum of about 12% chromium (Cr) to make a steel 'stainless'. More chromium = more 'stainless' but increasing the Cr makes it more brittle. Adding some nickel changes the structure making it ductile again and the result is austenitic stainless steel. The basic austenitic stainless is 18/8 which refers to the approximate Cr & Ni content respectively for a family of stainless steels i.e. 321 is made by adding a little titanium to 304, the small amount of Ti improves it's high temp properties by reducing the formation of chromium carbides (carbide precipitation), because Ti is more reactive- you get titanium carbides instead leaving the chromium free to do it's 'thing' and form a corrosion resistant oxide layer on the surface. Another way is the low carbon version 304L which has less carbon in it to begin with so you get less carbide precipitation. 321 has better strength at elevated temps than 304LIf you weld an 18/8 stainless to an 18/8 stainless with an 18/8 filler the result will be 18/8. If you weld an 18/8 stainless to mild steel then whether you use no filler, a mild steel filler or an 18/8 filler the weld will be diluted as you're mixing 18% Cr with 0% Cr etc. Corrosion resistance doesn't really come into at as the mild steel side will never be stainless regardless of the flavour of filler wire. The dilution of the Cr and Ni can result in a brittle phase known as martensite- the same metallic phase that occurs when you quench a carbon steel. This can be predicted using a schaeffler diagram which basically plots the Cr and Ni against each other to determine whether the result will be austenite, martensite, ferrite etc or a mixture309 stainless is 'overalloyed', it's a 23/12 stainless containing more Cr and Ni. Using an overalloyed filler 'fixes' the dilution issues when making dissimilar welds. 312 stainless is also 'overalloyed' but in a different way... it's a 29/9 stainless, even more chromium but less nickel which results in a 'duplex' stainless steel i.e. it's a mix of 2 phases, austenite and ferrite Originally Posted by fillethead Here is my question.  In the countless welding forum threads I’ve burned my eyes on I swear I’ve read where people have used SS filler when joining mild to mild.  Am I smokin’ dope and not known it?  I tried to find at least one thread but can’t because, of course, I’m looking for it.Bottom line question, is SS filler ever used, legitimately, to TIG weld mild steel to mild steel?  If so, why? Strength, easier weld, ….?Fillethead
Reply:Originally Posted by hotrodderYou need a minimum of about 12% chromium (Cr) to make a steel 'stainless'. More chromium = more 'stainless' but increasing the Cr makes it more brittle. Adding some nickel changes the structure making it ductile again and the result is austenitic stainless steel. The basic austenitic stainless is 18/8 which refers to the approximate Cr & Ni content respectively for a family of stainless steels i.e. 321 is made by adding a little titanium to 304, the small amount of Ti improves it's high temp properties by reducing the formation of chromium carbides (carbide precipitation), because Ti is more reactive- you get titanium carbides instead leaving the chromium free to do it's 'thing' and form a corrosion resistant oxide layer on the surface. Another way is the low carbon version 304L which has less carbon in it to begin with so you get less carbide precipitation. 321 has better strength at elevated temps than 304LIf you weld an 18/8 stainless to an 18/8 stainless with an 18/8 filler the result will be 18/8. If you weld an 18/8 stainless to mild steel then whether you use no filler, a mild steel filler or an 18/8 filler the weld will be diluted as you're mixing 18% Cr with 0% Cr etc. Corrosion resistance doesn't really come into at as the mild steel side will never be stainless regardless of the flavour of filler wire. The dilution of the Cr and Ni can result in a brittle phase known as martensite- the same metallic phase that occurs when you quench a carbon steel. This can be predicted using a schaeffler diagram which basically plots the Cr and Ni against each other to determine whether the result will be austenite, martensite, ferrite etc or a mixture309 stainless is 'overalloyed', it's a 23/12 stainless containing more Cr and Ni. Using an overalloyed filler 'fixes' the dilution issues when making dissimilar welds. 312 stainless is also 'overalloyed' but in a different way... it's a 29/9 stainless, even more chromium but less nickel which results in a 'duplex' stainless steel i.e. it's a mix of 2 phases, austenite and ferriteNope you're not imagining it, lots of examples around and some idiots will even recomend welding 4130 with 308 and defend their choice because it 'looks pretty'...
Reply:Most of the time it's just for testing, my last inconel test was nicromo 3 to carbon. Ideally you won't EVER weld carbon with inconel wire. It just depends on what the code calls for.
Reply:I think I read somewhere about using ss filler on mild to mild to "cheat" after partially grinding out a section of weld that got contaminated, and the ss filler floats out the contaminant, eliminating the pox on the do-over pass.I also read its not an acceptable method on more critical code work.Lincoln AC/DC 225/125 and WP17. 75A AC is for pipe thawing!HH 140 - new addtion 9/2012.I didn't agree, but hoped for Hope and Change.I got change for myself and my family: for the worse.This is the reality of: Barackalypse Now. Again.
Reply:Probably not 100% accurate off the top of my head but IIRC it's more a case of the usual 'stuff' that results in porosity being soluble in austenite i.e. they're not floated away but absorbed. That's also why carbon steel wires for MIG/TIG contain deoxidisers that aren't present in oxyfuel filler yet for stainless there's no difference between TIG and O/A wireER70s-6 is kinda MIG specific and er70s-2 kinda TIG specific for similar reasons... with TIG the gas shield really is inert, with MIG it's active due to the CO2. s-6 has more silicon while s-2 has less with other elements to compensate. Any excess silicon not needed for deoxidising is dealt with by the CO2 dissociating in the arc and the result is silica deposits on the surface of the weld. ER70s-6 with TIG can increase the silicon content of the weld which lowers ductility. On the plus side the extra Si results in a wire that wets out more nicely and the reduction in ductility is rarely a big deal Originally Posted by filletheadDoes that mean SS filler could be dicey to join mild steel to mild steel (because of possible embrittlement) ?