Why are some stainless steel fasteners magnetic?
Stainless parts that are cold worked (plastically deformed below the recrystallization temperature) will pick up some magnetism. This is not an indication of the chemical composition of the part. It is merely an unavoidable consequence of the cold working process these bolts go through during their manufacturing. Examples of cold working processes include drawing down of the bolt’s body to the pitch diameter for thread rolling, the thread rolling itself, and forming of the head. Some parts may be more magnetic than others, but every part that has been cold headed or had threads rolled will have some degree of magnetic permeability. You can read more about this by viewing the article “Magnetism in Stainless Steel Fasteners.
