A common buyer question: why is my "stainless" magnetic? The answer depends on the family.

• Ferritic (430, 409, 439) and martensitic (410, 420, 440C) grades are magnetic by nature because of their body-centred crystal structure. • Austenitic grades (304, 316L, 321) are austenitic and normally non-magnetic in the annealed condition. • Cold working (bending, drawing, rolling, cutting) can transform some austenite to martensite, making 304 or 316L slightly magnetic — especially at bends and sheared edges. Annealing restores the non-magnetic state. • Duplex grades are magnetic because of their ferrite content.

Practical implications:

1) A magnet is not a grade test: a magnetic 304 sheet can be genuine, and a non-magnetic 201 can be passed off as 304. Use chemical analysis (PMI) to verify grade. 2) Some applications require low permeability (instruments, MRI environments) — specify magnetic permeability limits and use annealed austenitic grades. 3) Welding can also produce small amounts of ferrite in austenitic welds (intentionally, for crack resistance), which is magnetic.

If a customer insists on non-magnetic, clarify the condition: annealed, stress-relieved, or as-fabricated.

Conclusion: magnetism tells you about structure and processing history, not about whether the material is good.