"The stainless steel fasteners I received stick to a magnet." This is one of the more frequently heard complaints at Fastenal Engineering & Design Support HQ in Winona, MN. Stainless steel fasteners being nonmagnetic is also one of the largest misconceptions amongst fastener users. This document will explain why most stainless steel fasteners are at least slightly magnetic and why many are so magnetic they are attracted to even weak household magnets.
There are five classes of stainless steel (ferritic, austenitic, martensitic, duplex, and precipitate-hardened) and only one is nonmagnetic (austenitic). However, the austenitic class just happens to include the most widely and universally used types of stainless steels in the market. The first four classes are defined based on the microstructure of the metal with the last class, PH, based on its heat treatment. Microstructure is important because this is what gives the stainless steel its magnetic properties.
The table below provides a brief overview of the classes of stainless steel as well as some properties of the materials.
|Details on the Five Classes of Stainless Steel|
|Class||Non/Magnetic||Crystal Structure||Common Examples|
|Ferritic||Magnetic||BCC||405, 430, 442|
|Austenitic||Nonmagnetic||FCC||201, 301, 302, 303, 304, 316|
|Martensitic||Magnetic||BCT||403, 410, 416|
|Duplex||Magnetic||Combination||2205, Alloy 255|
|Precipitate-Hardened||Magnetic||Combination||17-4PH, PH 17-7|