The iron is the majority constituent of steel, but it oxidizes easily; the product of corrosion, rust crumbles or dissolves in the water, resulting in a degradation of the piece.
STAINLESS STEEL 304 AND 316 INOX: WHAT DIFFERENCES
Stainless steel is a metal composed of various alloying elements.
One of the ways to avoid corrosion is to put a significant amount of chromium (Cr) in steel (more than 10.5% mass): the chrome reacts with the oxygen in the air and form a layer of oxide chromium Cr2O3.
This layer, compact, adherent and so protective, is called “passive layer“: it forms a barrier separating the steel of his environment. Normally, it is invisible because very fine.
Other elements also have their own function: nickel provides stability and strength, and molybdenum additional resistance to rust in extreme conditions as strongly polluted places.
There are 2 major types of stainless steel: lnox 304 in which nickel and chromium are added together, and the 316 stainless steel in which also added molybdenum (2 to 3%) for resistance to additional corrosion. 2 types provide a thin layer of oxide of chrome and possibly as anti-rust protection molybdenum oxide.
Products in stainless steel 304: are recommended both inside and outside, but must be placed in a polluted atmosphere (industrial area, port, chemical industry, pool, barn and..). The location of your project must be located more than 50km from the coast and humidity must remain low.
Products in stainless steel 316: are recommended in aggressive environments (Beach, pool etc). But beware, this does not exclude a few rust spots if your product is not maintained regularly (especially in chlorine and iodine, circles or if the products are exposed to a strong permanent corrosive humidity).
In environments with high content in chloric acid, in acid hydrochloric or close to the sea, the risk of rust remains for stainless steel 304. This is further strengthened by the presence of sand, wind and high humidity of the air.
This extra molybdenum in the stainless steel 316 offers better protection.
In this case, rust resistance depends on proper care. If you regularly maintain your products (regular rinsing with clear water), the risk of rust is minimal.