Magnet sticks to your stainless steel screws – does that mean they're fake?
Many buyers assume stainless steel is completely non-magnetic and use a magnet to verify authenticity. This method is actually unreliable and often leads to incorrect conclusions.
Why Some Stainless Steel Is Magnetic
Stainless steel is classified by its room-temperature structure into three types:
Austenitic (e.g., 304, 316): Non-magnetic or weakly magnetic. This is the most common grade for fasteners.
Martensitic or Ferritic: Magnetic. These grades are used in specific applications requiring hardness or heat resistance.
In short: a magnet test alone cannot determine whether your stainless steel is genuine.
Why Does Austenitic Steel Sometimes Become Magnetic?
Austenitic stainless steel naturally has a face-centered cubic structure that is paramagnetic – meaning it should not be magnetic. However, cold working (such as rolling, drawing, or heading during screw manufacturing) can transform some austenite into martensite or ferrite, both of which are magnetic.
Key factors:
More cold deformation → more martensite transformation → stronger magnetic properties.
Higher deformation temperature → less transformation.
Hot-formed austenitic stainless steel products are almost completely non-magnetic.
How Manufacturers Control Magnetic Permeability
For applications requiring strictly non-magnetic fasteners (e.g., medical, aerospace, sensitive electronic equipment), we implement several measures:
Precise chemical composition control – stabilises the austenite structure.
Solution treatment – re-dissolves martensite and ferrite, producing a uniform structure.
Process adjustment – adds solution treatment and pickling sequences after forming, followed by permeability testing (targeting μ ≤ 1.05).
Tool selection – use ceramic or carbide tools to prevent tool magnetism from transferring to the workpiece.
Minimise cold deformation – use small cutting amounts to reduce martensitic transformation.
Final degaussing – for finished parts requiring zero magnetism.
What This Means for Your Procurement
If you are sourcing stainless steel fasteners for standard European construction or furniture applications, slight magnetism from cold heading is normal and does not compromise corrosion resistance or mechanical properties.
For specialised applications requiring strictly non-magnetic fasteners, specify the requirement and request magnetic permeability test reports.
As a factory, Tianyu offers stainless steel screws with controlled permeability upon request, with full material certifications and inspection reports.
FAQ
Q1: I used a magnet and my stainless steel screws stuck. Are they fake?
A: Not necessarily. Cold forming during screw manufacturing can induce magnetism in 304/316 stainless steel. If corrosion resistance meets specifications, the screws are genuine. Use a material test certificate, not just a magnet, to verify.
Q2: Which stainless steel grades are completely non-magnetic?
A: No grade is completely non-magnetic in practical conditions. High-nickel grades like 316 are weakly magnetic, especially after cold working. For extremely low permeability, specify and request test reports.
Q3: Does magnetism affect corrosion resistance?
A: In standard grades (304/316), slight magnetism from cold working does not reduce corrosion resistance. The passive chromium oxide layer remains intact.
Q4: How can I ensure non-magnetic properties for my application?
A: Specify magnetic permeability requirements (μ ≤ 1.02 or μ ≤ 1.05). Tianyu can control composition, process, and provide test reports. Applications include medical devices, aerospace, and sensitive electronic equipment.
Contact us now for samples: support1@tianyufasteners.com.
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