There are many classification of kitchen sinks in materials, such as, stainless steel sink, granite composite sink, ceramic sink. But most people will choose stainless steel sink for their kitchen due to the physical properties of stainless steel.
Stainless steel contains chromium, which will reacts with oxygen and form an invisible, protective film on the steel surface. Due to the chemical reaction, stainless steel is resistant to corrosion. When stainless steel sink is scratched by accident, the exposed steel will reacts with oxygen immediately. This is why we can see the scratch on surface but it won’t cause corrosion.