Stainless steel resists corrosion via a thin, self-healing chromium-oxide layer rather than a sacrificial coating. The two grades commonly seen in gate work are 304 (general purpose) and 316 (marine). Grade 316 contains 2–3% molybdenum and is preferred within 1 km of saltwater or in chlorinated pool environments.
Stainless is more expensive than galvanised steel (~3–5× per kg) but requires no recoating and won't develop rust runs from cut edges or weld zones (provided welds are passivated). Common stainless gate items: cable infill, hinge pins, drop-bolt sleeves, latch hardware, balustrade balusters in marine settings.
CAD60 lets you specify steel grade per part in the title block schedule.