The main difference between 304 and 316 stainless steel is that 316 contains 2%-3% molybdenum and 304 has no molybdenum. The "moly" is added to improve the corrosion resistance to chlorides (like sea water). So, while 316 stainless steel is generally considered more corrosion resistant than 304, depending on the nature of the corrosive media the corrosion rates of 304 and 316 could be similar.