Type 317 can be used to repair type 316 clad. Mo is added to 316 and 317 alloys to improve the chloride pitting resistance (look-up "PRN", the AvestaPolarit website)
The use of type 309 as an underlayment for the surface clad intends to ensure the weld metal diluting carbon steel substrate retains the austenite structure and avoids a martensitic transformation.
Hi Rajan
317 filler only has a marginally higher alloy content than 316 filler. As such, it is not really made for dissimilar metal welds. It merely has better pitting and high temperature creep properties.
This will be fine for repairing the 316, but if you are going to weld onto the C/Steel base metal, then you will still need the 309.
Regards
Niekie Jooste
Fabristruct Solutions