I saw a welding procedure approved for welding stainless but it is a Inconel rod welding 410SS to 410SS using ERNiCr-3. Would 410 rod not be better? Any reason why they would be using Inconel?
This all hinges on the C level of the 410 and its HT condition.
If it is low C 410 (say less than 0.08%) then you could use low C filler and plenty of preheat and weld it.
If it is higher C 410 (or unknown) then no chance of that working without full Q&T after welding.
Hence the Ni rod procedure.
This way with PWHT you are tempering the hard HAZ and you have a good tough weld.