Why do screws made of stainless steel also rust?

Did stainless steel rust after being used for a while? It's really frustrating. Besides encountering counterfeit materials, will stainless steel itself rust?
In fact, stainless steel can also rust under certain conditions. The rust resistance and corrosion resistance of stainless steel will vary with the chemical composition, additive state, service conditions, and environmental medium type of the steel itself.
For example, 304 stainless steel is excellent in both rust and corrosion prevention in dry and clean environments, but when used in coastal environments, the large amount of salt in sea fog can easily rust it, but 316 performs well in such environments.
No wonder some people say - there is no bad stainless steel (except for counterfeit and inferior), only unsuitable environments~
So what are the main reasons for stainless steel rusting?
1. When dust of other metal elements or attachments of dissimilar metal particles are deposited on the surface of stainless steel, electrochemical corrosion is easy to occur, resulting in rust.
2. When organic juices (such as vegetables, phlegm, etc.) adhere to the surface of stainless steel, they will form organic acids under the action of water and oxygen. Over time, they will produce corrosiveness.
3. When acid, alkali, or salt (such as alkaline water, lime, etc.) adhere to the surface of stainless steel, it is very easy to cause local corrosion.
4. When the air contains sulfides, carbon oxides, etc. (i.e. polluted air), it will form sulfuric acid, nitric acid, etc. when encountering condensate, which can also cause chemical corrosion.
The corresponding prevention and treatment methods are——
1. Regularly wiping the surface of stainless steel to remove attachments can help prevent corrosion and rusting caused by attachments.
2. If it is a coastal area, use 316 stainless steel material instead of 304 material, which can resist the corrosion of seawater.
3. To purchase guaranteed products, relevant testing reports or third-party certification reports need to be attached. (Our company can provide)