Your ferrite number for the fillet weld will probably not be high enough and you will probably encounter cracking. This is why most applications of stainless steel to carbon steel use a E309 filler metal.

There are so many different kinds of stainless steel (austenitic, ferritic, martensitic, duplex, etc) that is not possible to give an answer to your question. You should be more especific because the weldability depends of all the materials involves in the welding.

Jorge Giraldo
Medellín, Colombia