304 is essentially non-magnetic in the annealed state, but after cold rolling, bending, or stretching, deformation martensite produces weak magnetism, which is a normal phenomenon.

How to distinguish: - Very weak magnetism concentrated in deformed areas: mostly caused by processing. - Strong magnetism throughout: possibly 430 ferritic or 201 substituted. - Verification: check the mill certificate composition (Ni≥8%, Cr≥18%), perform spectral analysis or chemical spot testing.

Do not judge material solely by a magnet, and do not use a magnet as an acceptance criterion.