Steel ball bearings can rust. Bearings made of chrome steel will rust easily which is why they leave the factory with the outer surfaces coated with a protective oil. Stainless steel bearings are much more corrosion resistant but will still rust when coming into contact with certain substances.
Stainless steel bearings are corrosion resistant or very corrosion resistant depending on the grade of steel. 440 grade stainless steel bearings have good resistance to moisture, water and many weak chemicals which is why they are very popular in the food and beverage industries. They will rust quickly if exposed to many strong chemicals, acids, alkalis and salt water.
The “marine grade” stainless steel is 316 grade. This is much more corrosion resistant than 440 grade but, as it cannot be hardened by heat treatment, it is much softer. 316 stainless steel bearings can only support much lower loads and speed than 440 grade bearings but is suitable for many marine applications.
Full ceramic bearings have excellent corrosion resistance and can be used with seawater and many aggressive chemicals.
Feel free to contact the SMB Bearings team with any other questions you may have. You can reach us on +44 (0) 1993 842 555 or firstname.lastname@example.org.