Hi bzzzzzzzzzzzzz
Every alloy has its pro's and con's. If you have a ferritic 400 series, then it is relatively easily welded in thin material. In thicker, it suffers seriously from grain growth. If it is martensitic, then you will need to pre-heat etc..
Now for the actual question: Generally 400 series S/Steel is considdered less corrosion resistant than the austenitic S/Steels, from a "general corrosion" point of view. For your application, the 400 series may just be a better material because it has a higher thermal conductivity than the 300 series. Remember that these alloys still have at least 12 or more % Cr, and it is the Cr that really does the corrosion resistant trick.
Another advantage of 400 series is that it does not suffer from Chloride stress corrosion cracking. I don't know much about your application, but if you are going to add salt, then again, you may be better off with 400 series.
Hope this helps
Regards
Niekie Jooste
Fabristruct Solutions
Hey Bzzzzzzz,
Keep in mind that if you do silver solder this, you'll need to stay away from solder containing Cadmium, or you'll poison your syrup.
It would be kind of like drinking moonshine made in a car radiator.
Tim