If you live at the beach or own a yacht you are probably aware of the corrosive effects of salt air and sea water that can eat away at iron causing it to rust and degrade. What causes this to happen and what metals should door handles be made from to avoid this fate?
Our door handles and cabinet pulls are cast either in silicon bronze or 316 stainless steel and both are good choices for ocean or beach environments as they both oxidize in a good way.
To understand corrosion we first need to analyze the alloys that make up stainless steel and bronze.
Stainless Steel
Describes a family of metal alloys the base or main alloy being iron. The other important components are carbon, chromium, nickel and molybdenum and the last 3 make 316 stainless steel corrosion resistant.
Water causes iron to rust by combining with carbon dioxide in the air to produce corrosive carbonic acid which as it dissolves the iron creates a layer of iron oxide or rust.
Stainless steel contains the metal chromium which when exposed to oxygen in the air becomes unstable and combines with the oxygen to produce a thin protective film of chromium oxide. The film is passive and does not harm the metal but forms a tight film that clings to the surface effectively sealing it. The thin layer of chromium oxide adheres to the surface forming an almost impenetrable film that prevents harmful iron oxidation from occurring.
The Nickel component plays a supporting role and it enables the chromium oxide to rebuild and self-heal if it is damaged, it helps the chromium rebind with oxygen to create more protective chromium oxide.
While 304 and 316 grades of stainless steel contain chromium and nickel only 316 contains molybdenum a metal that is particularly effective at preventing corrosion caused by sodium chloride that is present in sea water. The salt content of water speeds up the corrosive effect of carbonic acid and molybdenum seems to slow this process down thereby helping prevent corrosion.
We make our Ergo and Morphic door handles in 316 stainless steel, the alloy is more expensive and harder to machine and finish than other grades but it’s superior corrosion resistance justifies the price tag.