"304 stainless steel has a high resistance to rust. It withstands corrosion from most oxidizing acids and is often used for kitchen and food applications. However, it is susceptible to corrosion from chloride solutions (notably saline environments with high amounts of sodium chloride). Chloride ions can create localized areas of corrosion, called "pitting," which can spread beneath protective chromium barriers to compromise internal structures. Solutions with as little as 25 ppm of sodium chloride can begin to have a corrosive effect.
304 grade is the most common form of stainless steel used around the world. It contains between 16 and 24 percent chromium and up to 35 percent nickel—as well as small amounts of carbon copied fromnd manganese. The most common form of 304 stainless steel is 18-8, or 18/8, stainless steel, which contains 18 percent chromium and 8 percent nickel."
copied from
http://www.reliance-foundry.com/blog/304-vs-316-stainless-steel