Austenitic grades
304 and 316 are normally low-permeability in the solution-annealed condition, but cold work can create magnetic martensite in some grades.
Technical guide · P1478
Stainless Steel Magnetic Properties
Stainless steel magnetic properties depend mainly on microstructure and condition. Ferritic, martensitic and duplex grades are ferromagnetic, while solution-annealed austenitic grades normally have low magnetic permeability.
Strong response familiesFerritic, martensitic, duplex
Low response familySolution-annealed austenitic
Fabrication effectCold work and weld structure can change response
Decision summary
Specify a measurable property, not a magnet test
A handheld magnet can screen obvious differences, but attraction depends on magnet strength, geometry, distance, thickness and material condition.
Ferritic grades
Grades such as 430 have a ferritic structure and are ferromagnetic.
Martensitic grades
Grades such as 410 and 420 are ferromagnetic; heat treatment controls hardness and other properties.
Duplex grades
Their ferrite-austenite structure gives a magnetic response related in part to ferrite content.
Welded zones
Weld metal and heat-affected regions can differ from the parent material, depending on filler and procedure.
Low-permeability requirements
State maximum relative permeability, test method, field strength, specimen geometry and condition.
Reference table
Qualitative stainless magnetic response chart
The chart is a family-level screening guide. It does not provide acceptance values for a specific heat, product or fabricated part.
| Family / example | Typical supplied condition | Expected response | Key variable |
|---|---|---|---|
| Austenitic 304 / 304L | Solution annealed | Low magnetic permeability | Cold work can increase response |
| Austenitic 316 / 316L | Solution annealed | Low magnetic permeability | Cold work and weld metal can change response |
| Ferritic 430 | Annealed | Ferromagnetic | Composition, grain structure and geometry |
| Martensitic 410 / 420 | Annealed or heat treated | Ferromagnetic | Heat treatment and hardness condition |
| Duplex 2205 | Solution annealed | Ferromagnetic | Ferrite-austenite balance and fabrication |
| 17-4PH | Solution treated or aged | Ferromagnetic | Aging condition and product history |
Terms such as magnetic and non-magnetic are too broad for critical service. Use relative permeability or another specified property and a recognized test method.
Working method
Turn magnetic intent into a testable requirement
The purchase order should describe the final condition and how the property will be measured.
Define the functional need
State whether the concern is attraction, instrument interference, lifting, sorting or a maximum relative permeability.
Identify the final condition
Record grade, heat treatment, cold reduction, forming, machining, welding and any stress relief.
Choose the test method
For weakly magnetic materials, review ASTM A342/A342M and specify the applicable method and field strength.
Control sampling
Define specimen geometry, test locations, number of readings, calibration and certificate reporting.
Limits and escalation
Do not identify stainless grade with a magnet alone
Attraction is not chemistry
Different grades and conditions can show similar attraction, so PMI or certificate review may still be needed.
Cold work is local
Edges, bends, drawn areas and machined surfaces may respond differently from the bulk material.
Geometry changes the observation
Thickness, contact area, air gap and magnet strength affect a simple pull test.
Low permeability needs a method
A verbal claim of non-magnetic does not define field strength, precision or acceptance.
Interactive planning aid
Screen magnetic response by family and condition
Choose the material state to see the expected qualitative response and the verification step.
Frequently asked questions
Stainless steel magnetic properties FAQ
Solution-annealed 304 normally has low magnetic permeability, but cold working, forming and some weld regions can produce noticeable magnetic attraction.
No absolute claim is safe. Solution-annealed 316 is normally low-permeability, but fabrication history and weld metal can change local response.
Ferritic, martensitic and duplex stainless steels are ferromagnetic. Stable solution-annealed austenitic grades are not readily magnetizable.
No. Both may have low or increased response depending on condition. Use material certificates and an appropriate composition-verification method when grade identity matters.
Method, sources and review
Traceable sources and review status
Industry reference comparing magnetic behavior of stainless families.
Producer explanation of microstructure and cold-work effects.
Producer comparison of magnetizable and low-permeability families.
Official test methods for relative permeability of weakly magnetic materials.
Magnetic response is condition- and method-dependent. Final acceptance requires the specified material condition, specimen geometry, field strength, test method and documented result.
Engineering and sourcing support
Request stainless with magnetic performance controlled
Send grade, product form, condition, fabrication route, permeability requirement, test method, quantity and destination.