The Short Answer
Stainless steel fasteners — especially those made from 300-series austenitic grades — can exhibit slight magnetism after cold forming. This is a normal metallurgical phenomenon, not a quality defect.
Understanding the Metallurgy
300-series austenitic stainless steel (e.g., 304, 316) is inherently non-magnetic in its annealed state. However, during cold-forming processes such as thread rolling, heading, or stamping, a portion of the austenite microstructure transforms into martensite and ferrite phases — both of which are slightly magnetic.
Key factors that influence the degree of magnetism include:
- Degree of cold deformation: Greater deformation leads to more phase transformation and stronger magnetism.
- Forming temperature: Lower temperatures during forming accelerate martensite formation.
- Alloy composition: Higher nickel and molybdenum content (as in 316) suppresses transformation and reduces magnetism.
Hot-Formed vs. Cold-Formed Fasteners
Hot-formed fasteners (e.g., hot-forged bolts and nuts) retain a predominantly austenitic structure and are nearly non-magnetic. Cold-formed fasteners — such as machine screws, socket head cap screws, and washers — undergo more phase transformation and therefore exhibit more noticeable magnetism.
Does Magnetism Affect Performance?
In most industrial applications, slight magnetism in stainless steel fasteners has no impact on mechanical performance, corrosion resistance, or service life. National and international standards (DIN, ISO, ASTM) do not specify magnetic requirements for standard fasteners.
However, for applications with strict non-magnetic requirements — such as MRI equipment, precision electronics, or marine instrumentation — magnetism must be controlled.
Solutions for Strict Non-Magnetic Requirements
If your application demands minimal or zero magnetism, FULLERKREG recommends the following approaches:
- Specify 316 stainless steel: The higher molybdenum and nickel content in 316 significantly reduces residual magnetism compared to 304.
- Request demagnetization treatment: Parts can be demagnetized post-production, though this may slightly affect surface finish.
- Avoid annealing for demagnetization: While annealing restores the austenitic structure and eliminates magnetism, it also reduces mechanical strength — making it unsuitable for most structural fastener applications.
FULLERKREG Quality Commitment
At FULLERKREG, all stainless steel fasteners are manufactured to DIN/ISO standards with full material traceability. We supply 304 and 316 grades across our full range of socket screws, washers, nuts, and specialty fasteners. For projects with specific magnetic tolerance requirements, our engineering team is available to advise on material selection and post-processing options.
Contact us for bulk pricing, material certifications, and technical consultation.