One of the most common misconceptions among fastener users is that stainless steel fasteners are non-magnetic. While the degree of magnetism in stainless steel fasteners might seem infinitesimal, even household magnets can be attracted to them.
There are five classes of stainless steel, of which the austenitic class is the most common, and only one of the five is non-magnetic. Those four classes of stainless are all magnetic because of their microstructures.
Austenitic stainless steel can become magnetic if a portion of its microstructure is changed to include a metal that possesses magnetism. This process, called martensitic stress induced transformation, can be the result of cold working or slow cooling.
Cold working is part of a process through which fasteners are created, and it occurs in the wire drawing, forming and thread rolling process. To create a degree of magnetism, the cold working must create the necessary levels of martensite.
Knowing what alloys are especially susceptible to the martensitic stress-induced transformation process is important. Austenitic stainless steel in general is susceptible to different degrees of magnetism, but low alloy content stainless steel are at higher risk.
Magnetism can often be a deciding factor when choosing your fastener, and in some cases the magnetism can be controlled. If you require a stainless steel fastener that is non-magnetic, the amount of cold working in the manufacturing process will need to be reduced.
A complete annealing treatment, after all of the cold working processes have been done, would help ensure that your stainless steel fastener achieves zero magnetism. For a variety of different reasons, this might not be entirely feasible, but it is one option to consider.
Even the weakest of magnets can develop a magnetic attraction with a stainless steel fastener. This is an important subject to educate yourself on, so that you know can understand why this occurs and how to take steps to prevent it in the future. To learn more about magnetism and stainless steel fasteners, contact Bossard at ProvenProductivity@bossard.com.
Magnetism and Stainless Steel Fasteners by Bossard