The 2 main advantages of using a 309 instead of a 308 when joining a stainless steel to another steel is 1) the higher chemistry,Cr=22.0-25.0 and Ni=12.0-14.0 for the 309, as opposed to Cr=18.0-21.0 and Ni=9.0-11.0 for the 308. And 2) the 309 has a higher ferrite percentage than the 308. A typical 309 can have a FN of approximately 12-18 FN, while the 308 is usually approximately 4-9 FN. Ferrite is beneficial in counteracting the possibility of hot cracking, or solifidication cracking. Both the 308 and the 309 have an All-Weld-Metal Tensile requirement of 80ksi minimum, but the 309 is usually recommended for welding stainless to dissimilar metals.
Chuck
To add to what Chuck has said, the higher chromium content in 309 promotes the formation of ferrite and increases resistance to oxidation and corrosion. The higher nickel content in 309 promotes the formation of austenite, and increases high temperature strength, corrosion resistance, and ductility.
Exactly. Sorry for not going into more detail. You are totaly correct. Thanks...
Chuck
Thank you guys for the quick response. I now ordered some 309 mig wire for the job.
May I suggest you order 309Si (or 309LSi) for your job. The higher silicon content gives better arc stability and better fluidity. The higher silicon also gives a more attractive weld bead appearance and reduces porosities as well as weld spatter.
Chuck
Which is cheaper the 309L or the 309si or the 309Lsi?
Where can I find the tensile properties of 308, 309, and similar stainless weld metals?
ASM Metals Handbook Vol 6
Thanks for the suggestion. Is there a free document that I can find it in? Our office doesn't have the publication, and are under a tight deadline. I'm trying to get my boss to buy AWS D1.6, but I don't think that is going to happen.
With some dilution calculations, you can also end up with some martensite (hard and bittle without heat treatment) when using 308 for dissimilar welding. With 309, the weld is going to be austintic (with small amounts of ferrite), which is a lot more ductile and tougher.