Magnetic Stainless Steel Fasteners: Common Misunderstandings and Facts

There are many different materials used in fastener manufacturing. Among them, stainless steel fasteners are known for their good appearance, strength, corrosion resistance, ease of manufacturing, and excellent weldability.

However, a common belief among the public is that stainless steel fasteners should be non-magnetic. In fact, many people use magnets to test the authenticity of stainless steel fasteners. Judging the quality or authenticity of stainless steel solely based on magnetism is scientifically inaccurate and misleading.

In reality, austenitic stainless steel materials (e.g., 304, 316) are non-magnetic in their original state. However, during the high-speed cold forming process used in fastener production, internal stress is introduced, which causes finished products to develop slight magnetism. This is why screws tend to exhibit more magnetism than nuts — the head-forming process for screws involves much greater deformation.

The specific reasons are as follows:

1. Cold Working and Stress:
Austenitic stainless steel and its raw materials are inherently non-magnetic. However, during cold forming, internal stress can induce slight magnetism in the finished product.

2. Degree of Deformation:
The level of magnetism varies with different types of fasteners due to the degree of deformation. Even within the same product category, different specifications or positions (e.g., screw head vs. body) may exhibit varying magnetic behavior.

3. Lack of Unified Standards

There is currently no national or international standard that defines acceptable levels of magnetism in stainless steel fasteners. When customers have strict requirements — such as demanding “non-magnetic” properties — Ningbo Mianxuan Import & Export Co., Ltd. can provide demagnetization treatments according to customer needs. Common demagnetization methods include high-temperature demagnetization, vacuum demagnetization, and electrode demagnetization. Our products can be tested using our in-house Kanetec Gauss meter to measure residual magnetism. Generally, after demagnetization treatment, residual magnetism in stainless steel fasteners can be controlled within 3 Gauss.

We ensure products comply with national standards or specific customer requirements. Our magnetic permeability regulations for stainless steel components refer to Appendix G of GB/T 3098.6-2014.

Tips:

In general public perception, “real” stainless steel is assumed to be completely non-magnetic. However, it is perfectly normal for austenitic stainless steels to become slightly magnetic after cold working due to stress-induced structural changes.

Ironically, 200-series chromium-manganese stainless steels are non-magnetic in their natural state and are often mistakenly considered to be high-quality 300-series materials. Some unregulated suppliers take advantage of this misunderstanding by passing off low-grade products with nickel content below 1% or low chromium content as 304 stainless steel. Some even falsely label fasteners with designations like A2-70 in bidding documents, leading to confusion and disorder in the market.

A large number of chromium-manganese stainless steels (200 series) cannot replace 300-series grades in highly corrosive coastal environments. This is particularly critical in heavy industries such as chemical processing, petrochemical plants, nuclear power, and related equipment applications.

Customers should be cautious when selecting stainless steel components and be aware of the usage limitations of 200-series materials. At Ningbo Mianxuan Import & Export Co., Ltd., our in-house laboratory is equipped with a German-made SPECTRO direct-reading spectrometer, which enables fast and accurate material analysis to verify material authenticity and ensure reliable performance for our customers.