Pay attention to the principle of doing things, even the choice of gas-wire selection should follow the principle, that is, the ability of the physical laws, principles and welding wire selected is the same. 
Of course, now there are stainless steel flux cored wire (hereinafter mentioned are austenitic stainless steel), stainless steel wire is not very wide range of applications, and more generally for bigger filling tube or plate and cover up. 
If you are welding of carbon steel and stainless steel for general use 309L can be, especially if strict requirements, you choose to play in the bottom of the time, need to consider the composition of the transition (ie, carbon steel wire side dilution of the ingredients). 
There workpiece material and structure of the service requirements like election. 
Respect the fact that respect for the law, so that the choice of gas shielded welding wire will fit your choice of electrodes for welding quality will be greatly improved.