Why metals rust ?

[0 Agios]

Why is it some steel like 304, rusts more than 316? aluminum corrodes and copper and titanium don't ? In salt water.

[Randy Holmes-Farley]

It all has to do with the ease with which oxygen or other oxidizers can enter the surface region of the metal, oxidize the metals that are there, and then form an oxide layer that has less integrity than the underlying metal.

Beyond that the explanations become very chemically intensive and likely not suited to this forum (or may knowledge level without looking things up). :)

[0 Agios]

Simple explanation but very effective, NOW I got it Randy :) Thanks