Stainless steel is not rust free; it is as described stainless. The two main types of stainless steel that we use are grade 304 and 316. The main differences between the two grades are the composition of the stainless in manufacture.
Grade 304 contains 18% chromium and 8% nickel, whereas grade 316 contains 16% chromium, 10 % nickel with the addition of 2% molybdenum. It is the molybdenum in grade 316 that helps to resist corrosion from salt in seawater and winter gritting. Grade 316 is usually referred to as Marine grade as it is better suited to coastal areas than 304.