A practical comparison page for non-ferromagnetic and low-magnetic steel materials used in motor housings, covers, sensor brackets, retaining parts, fasteners, shielding-isolation structures, test fixtures and assemblies where magnetic interference must be controlled.
Non-ferromagnetic steel selection should consider magnetic permeability, corrosion resistance, strength, forming, welding, machining, temperature exposure and whether the material may become weakly magnetic after cold working, stamping or machining.
Non-ferromagnetic steels are selected when a part must avoid disturbing magnetic fields, protect sensors from magnetic bias, reduce attraction to magnets, or provide corrosion-resistant structure without becoming part of the magnetic circuit.
Common austenitic stainless steel for general low-magnetic structures, covers, fasteners and brackets.
Austenitic stainless steel for better corrosion resistance and cleaner environmental durability.
Used when the non-magnetic part also sees elevated temperature or thermal cycling.
Special steel direction for higher strength non-magnetic structures and fixtures.
Fastener material selection for assemblies where magnetic attraction or field disturbance is unacceptable.
Used for sensor brackets, encoder supports, probe fixtures and non-magnetic test equipment near magnets.
Use this table for early-stage material screening. Actual magnetic response depends on grade, heat condition, cold work, machining stress, welding, forming and final surface condition.
| Material Type | Typical Grades | Magnetic Behavior | Mechanical Direction | Corrosion Direction | Typical Motor Use | Key Risk |
|---|---|---|---|---|---|---|
| General Austenitic Stainless | 304, 304L, 1.4301, 1.4307 | Usually non-magnetic or weakly magnetic; cold work can increase magnetism | Good ductility and forming | Good general corrosion resistance | Covers, brackets, housings, non-magnetic fasteners, sensor supports | Weak magnetism after forming, galling, chloride corrosion limits |
| Corrosion-Resistant Austenitic Stainless | 316, 316L, 1.4401, 1.4404 | Usually non-magnetic or weakly magnetic | Good ductility, moderate strength | Better chloride resistance than 304 in many environments | Sealed motor parts, humid-environment covers, fasteners, sensor brackets | Cost, galling, magnetic response after cold work, strength limit |
| High-Temperature Austenitic Stainless | 310, 321, 347 | Generally low magnetic response | Good high-temperature stability depending on grade | Good oxidation resistance direction | Heat-exposed brackets, thermal shields, special motor protection parts | Cost, availability, welding and thermal distortion |
| Non-Magnetic High-Manganese Steel | Mn-based non-magnetic steel families | Designed for low magnetic permeability | Can provide higher strength than common austenitic stainless | Grade dependent, may need protection | High-strength non-magnetic fixtures, retaining parts, special structures | Availability, machinability, welding process and certification |
| Austenitic Stainless Fastener Steel | A2-70, A4-70, 304, 316 | Usually low magnetic, but cold-headed fasteners can be weakly magnetic | Defined by fastener strength class | A4 / 316 direction has better corrosion resistance | Non-magnetic screws, nuts, washers, sensor and cover assembly | Galling, torque scatter, cold-work magnetism, lower strength than alloy steel |
| Annealed Non-Magnetic Stainless | Solution-annealed 304 / 316 or special low-mu grades | Lower magnetic response after proper annealing | Softer than cold-worked condition | Good corrosion resistance | Precision sensor parts, encoder supports, magnetic test fixtures | Reduced strength, annealing distortion, certificate and test requirement |
| Non-Magnetic Nickel Alloy Direction | Inconel / nickel alloy families when required | Usually low magnetic depending on alloy | Good high-temperature strength | Excellent corrosion / oxidation resistance direction | Extreme-temperature non-magnetic motor parts and fixtures | Very high cost, machining difficulty, over-specification risk |
| Reference: Magnetic Stainless to Avoid | 430, 410, 420, 431 | Generally magnetic | Can be stronger or harder depending on grade | Corrosion resistance varies | Use only when magnetic behavior is acceptable | Not suitable when low magnetic response is required |
This matrix connects non-magnetic steel selection with sensor accuracy, magnetic isolation, corrosion resistance, strength and assembly process.
| Motor Part | Recommended Material Direction | Design Driver | Common Process | Inspection Focus |
|---|---|---|---|---|
| Sensor Bracket / Encoder Support | 304L, 316L, annealed low-magnetic stainless | Low magnetic interference, dimensional stability, corrosion resistance | Stamping, CNC machining, passivation, stress relief if needed | Magnetic response, position tolerance, flatness, burr, passivation |
| Non-Magnetic Cover / Shield | 304, 316, 310 / 321 for heat exposure | Protection without creating an unwanted magnetic path | Sheet metal forming, welding, laser cutting, passivation | Magnetic pickup check, weld distortion, surface finish, corrosion test |
| Fasteners Near Magnets | A2 / A4 stainless, 304 / 316 fasteners | Low magnetic attraction, corrosion resistance, serviceability | Cold heading, thread rolling, passivation, lubrication | Torque test, galling risk, magnetic response, thread quality |
| Magnetic Isolation Spacer | 304 / 316 stainless, non-magnetic high-Mn steel if strength is needed | Maintaining air gap or isolation without flux shunting | CNC machining, grinding, passivation | Thickness, parallelism, permeability check, surface roughness |
| Test Fixture Near Magnet Assembly | 316, annealed 304 / 316, non-magnetic alloy direction | Avoiding measurement error and magnetic attraction | Machining, welding, surface finishing | Magnetic response, dimensional stability, wear, repeatability |
| Retaining Ring / Spring Part | 301 / 304 spring stainless if low magnetic response is acceptable after forming | Elastic force, corrosion, limited magnetic response | Stamping, forming, heat treatment / stress relief | Spring force, magnetic response after forming, fatigue, burr |
| High-Temperature Non-Magnetic Part | 310, 321, nickel alloy direction if required | Temperature, oxidation resistance, magnetic isolation | Machining, forming, welding, heat treatment review | Thermal distortion, oxidation, magnetic response, dimensional stability |
Non-ferromagnetic steel performance depends not only on grade name. Cold work, forming, machining stress and welding can change magnetic response and must be controlled.
Confirm whether the part must be non-magnetic, weakly magnetic, or simply avoid becoming a flux path.
Compare 304, 316, high-temperature austenitic stainless, high-Mn steel or nickel alloy direction.
Define forming, machining, welding, annealing, passivation, surface finish and fastener torque process.
Check magnetic response, dimensions, corrosion protection, strength, assembly fit and sensor influence.
304 / 316 can become weakly magnetic after cold rolling, bending, stamping or machining. Test finished parts, not only raw material.
If the design is sensitive, specify a maximum relative permeability or a practical magnetic pickup inspection method.
Non-magnetic material can prevent unintended flux shunting near magnets, sensors, encoders and Hall devices.
Austenitic stainless resists corrosion but can gall in threads. Lubrication, coating and fastener process should be reviewed.
Non-magnetic stainless may have lower strength than alloy steel. Use high-Mn or special alloys if strength is critical.
Require material certificate, heat condition, surface treatment record and magnetic response check for critical applications.
Not always. 304 is usually non-magnetic in annealed condition, but cold work, bending, stamping or machining can make it weakly magnetic. Finished parts should be checked if the application is sensitive.
316 usually provides better corrosion resistance and is often preferred in humid or chloride-containing environments. Magnetic response still depends on processing condition, so sample testing is recommended.
No. 430 is ferritic stainless steel and is generally magnetic. It can be useful for magnetic stainless parts, but it is not suitable when low magnetic response is required.
Check magnetic response after processing, corrosion resistance, mechanical strength, forming behavior, welding route, galling risk, surface treatment and effect on nearby magnets or sensors.