which filler for stainless on carbon?

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Occasionally I have to tig weld on used, contaminated carbon steel, some hardened and all are contaminated by grease or other dirty crap. I have found using stainless filler in these situations provides a better, cleaner weld ability. I have historically used 316L, it being the universal stainless filler. Getting into this conversation with a buddy today, he says when using stainless filler on carbon, 309 is the better choice due to having a higher carbon content in the alloy. Anyone have knowledge or advice concerning this? Any incite is greatly appreciated.                      WAGMiller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:Yes, 309L, 309MoL and 312 are the choices for carbon steel... It is related to favourable chemistry after welding. You may consult Schaeffler chart about this.
Reply:Yep, 309 is 'over alloyed' (more Cr and Ni IIRC, can't remember if the C content is different ) to take dilution with the different parent materials into account. Using (say) 316 can result in a brittle weld due to the formation of martensite
Reply:The 309L will reduce your chances of cracking on the hardened steel, and is an overall better choice for just about all carbon to SS welds in my opinion.
Reply:309 stainless steel (SS) is generally the correct choice for welding 300 series stainless steel to carbon steel (CS), and the reason is that the chemistry of the weld metal mixture of SS and CS will affect the crystalline structure, hardenabilty, and weld cracking.  The chemistry of 309 allows the weld mixture of SS + CS to remain austenitic, non-hardenable, and ductile.  The austenitic weld metal can deform and give without cracking as thermal stresses of welding act upon it.  The mix of 308 or 316 with CS can result in a hardenable weld chemistry and the formation of a hard brittle weld deposit of martensite, which is prone to cracking.  As mentioned you can calculate the approximate dilution in the weld and look up on a chart to see if the weld may end up austenite or martensite.  The charts have evolved over the years from the Schaffler to Delong to the Welding Research Council (WRC).In applications like surface overlaying with stainless over CS, welding parameters may be adjusted to limit penetration and dilution of the weld with the CS.  Sometimes the CS side of the joint may be surfaced, buttered, with 309 SS, then the joint may be welded with less expensive 308 or 316.See this old thread: http://weldingweb.com/vbb/showthread.php...ess+steel+mild