There's no moisture in the stainless steel. What you are seeing is the condensation of the moisture resulting from the byproduct of combustion: CO2 and H20, both are gases at high temperature. However, if the temperature is below the dew point, the moistur (steam if you will) condenses to form water in the liquid state. Once the base metal is heat to a temperature above the dew point, no more condensation. However, if any portion of the base metal is still above the dew point, you will see condensation if the vapors reach that area.
Al