Short answer: first determine whether the requirement concerns residual magnetic field or magnetic permeability. AC or reversing-DC demagnetization can reduce a residual field left by magnetic particle inspection, lifting magnets, machining fixtures or other external fields. It cannot change an inherently magnetic ferritic, martensitic or duplex stainless steel into a non-magnetic material. For an austenitic grade that became more magnetic after cold work, solution annealing may reduce strain-induced martensite, but it is a metallurgical heat treatment—not a universal degaussing recipe.
Residual Field and Permeability Are Different Problems
A part may retain a measurable field after exposure to a strong magnetizing source. This is residual magnetism, and a suitable degaussing cycle may reduce it. Magnetic permeability describes how the material responds when placed in a magnetic field. It depends on alloy family, chemistry, microstructure, heat-treatment condition and cold work. A gaussmeter reading near a surface and a relative-permeability result therefore answer different questions.
| Requirement | What it indicates | What the RFQ should define |
|---|---|---|
| Residual field | Field remaining in the component after an external magnetizing source is removed | Instrument, unit, probe orientation, distance, locations and acceptance value |
| Relative permeability | Material response to an applied magnetic field | Applicable test method, field strength, specimen condition and maximum value |
| Magnet attraction | Only a qualitative shop-floor indication | Magnet type and comparison method if it is used for screening |
Where low permeability is a functional requirement, ASTM A342/A342M is one recognized reference for measuring the permeability of weakly magnetic materials. The project specification must still define the applicable method and acceptance criterion.
Start with the Stainless Steel Family
| Stainless family | Typical behavior | What demagnetization can and cannot do |
|---|---|---|
| Austenitic: 304/304L, 316/316L and related grades | Low permeability in a well-annealed condition; some grades become more magnetic after cold forming or machining because deformation-induced martensite can form | Degaussing may reduce a retained field. It does not remove strain-induced martensite. A qualified solution-annealing route may reduce that phase, subject to grade and product requirements. |
| Ferritic: 430 and related grades | Ferromagnetic by microstructure | Degaussing may reduce remanence after exposure to a strong field, but the grade remains magnetically responsive. |
| Martensitic and many precipitation-hardening grades | Ferromagnetic; hardness and heat-treatment condition influence behavior | A degaussing cycle can target residual field, not eliminate the inherent magnetic response. |
| Duplex: 2205, 2507 and related grades | Magnetic because the microstructure contains a substantial ferritic phase as well as austenite | Degaussing cannot make duplex stainless non-magnetic. Phase balance must be controlled for the grade, product and fabrication route. |
Magnetic response alone is not proof that stainless steel is counterfeit or defective. For example, cold-worked 304 can attract a magnet, while correctly supplied 430 or 2205 is expected to be magnetic. Grade verification should use traceability, chemical analysis or PMI where appropriate—not a magnet alone.
Choose the Treatment by Failure Mode
AC Coil Demagnetization
An AC coil creates an alternating field whose effective influence decreases as the component is withdrawn from the coil or as the current is reduced. It is often practical for smaller parts and near-surface remanence. Geometry, wall thickness, orientation and withdrawal path matter: a process effective for a short fastener may not be effective for a long shaft, large ring or assembled valve.
Reversing-DC or Low-Frequency Methods
Large sections, long components and complex assemblies may require deeper field penetration or treatment along more than one axis. A qualified procedure can use reversing DC or controlled low-frequency equipment with a progressively decaying field. Equipment settings should be established by trial and measurement; fixed current, frequency or travel-speed values should not be copied from an unrelated part.
Solution Annealing for Cold-Worked Austenitic Material
If the issue is increased permeability caused by deformation-induced martensite, electromagnetic degaussing alone will not reverse the microstructure. Solution annealing may be considered when permitted by the alloy, product specification and final component design. Temperature, soak time, atmosphere and cooling route must follow the applicable material standard and a qualified thermal process.
Heat treatment can alter dimensions, surface condition, oxide scale, strength, hardness, residual stress and corrosion performance. It can also affect an assembly, coating or previously qualified fabrication sequence. For that reason, a generic instruction such as “heat every stainless part to one temperature for a fixed number of minutes” is not technically responsible.
A Practical Demagnetization and Inspection Plan
- Define the requirement. Record whether the controlling value is residual field, permeability or another customer-specific magnetic property.
- Identify the material condition. Confirm grade, heat/lot, product form, heat treatment, cold reduction, machining, welding and any magnetic particle inspection.
- Establish a baseline. Record the instrument, calibration status, unit, ambient background, probe orientation, stand-off distance and measurement locations.
- Select a suitable process. Match AC, reversing DC, low-frequency or thermal treatment to the part geometry and the actual source of the magnetic response.
- Treat all relevant directions. Long shafts, rings and assemblies may retain different field components along different axes.
- Re-measure under the same conditions. Use the same locations and orientation so the before-and-after data are comparable.
- Document the result. Retain the part identity, procedure, equipment, settings, readings and acceptance decision.
Preventing Magnetic Problems at the RFQ Stage
When magnetic performance matters, prevention is usually more reliable than attempting to correct a finished component. The purchaser and responsible engineer should define the requirement before material selection and fabrication.
- Stainless grade and governing product standard
- Product form, dimensions, quantity and final component geometry
- Supply condition and maximum permitted cold work
- Welding, forming, machining and magnetic particle inspection history
- Required residual-field or permeability test method
- Instrument, locations, orientation and acceptance criterion
- Whether post-fabrication degaussing or qualified heat treatment is permitted
- Required material certificate, PMI, inspection report or third-party witness
For bar components, review the available 316/316L stainless steel round bar range. For process piping requirements, see ASTM A312 TP316L seamless pipe. Final magnetic acceptance must be stated separately from grade, dimensions and corrosion requirements.
Request a Material and Inspection Review
Send the drawing, grade, product standard, fabrication route, magnetic measurement method, acceptance value, quantity and destination. SAKYSTEEL can review material supply and available testing requirements against the RFQ; final feasibility is confirmed for the specified product condition and inspection scope.
Post time: Oct-27-2025