Materials
Rust and magnetism: two stainless steel misconceptions
Understand corrosion, contamination and magnetism before drawing conclusions about a material.
Stainless steel is not immune to corrosion, and a magnet alone cannot identify a grade.
Where does corrosion resistance come from?
A passive surface film helps resist corrosion. Performance depends on the alloy and exposure; salts, crevices or unsuitable conditions can still cause problems. Investigate the environment as well as the material.
Why can worked 304 attract a magnet?
Cold work can change the magnetic response of some austenitic grades. Ferritic stainless steels are also magnetic. Neither attraction nor lack of attraction proves a specific grade.
What should you record if spots appear?
Record the location, close-up appearance, service history, cleaners, nearby construction, salt exposure and standing water. Locate the order and batch documents before deciding on investigation or repair.
How to reduce purchasing disputes
Agree the grade, standard, material documents and inspection method in the order. Where chemistry needs confirmation, select a method suitable for the required elements and grade.
Further reading & sources
Technical background references are listed below. Enquiry examples and checklists are prepared by Jinlaibao.