Raw stainless steel alloy (active) gains its rust protection instantly when exposed to oxygen (passivation), either air or water. We then say the stainless steel is "passive". The Chrome in it forms chrome oxide that is very resistant to rust.

Unlike aluminum oxide (the white dust) this protective layer is invisible but is easily penetrated and destroyed by any halogen salt like fluorine, chlorine, etc. Bleach is based on chlorine, drinking water is treated with chlorine, and seawater contains chlorine.

But stainless steel, fortunately, recovers its protective chrome oxide layer as long as it is immersed in an oxygen-rich environment, like air or MOVING water.

STAGNANT chlorinated water, likely to be found around screws holding deck fittings, specially if you clean your deck with chlorine based products, is essentially oxygen-deprived and then, with chlorine and without oxygen, stainless steel becomes just plain steel alloy, it is "active" and therefore, rusts.