Although miscellaneous steel items such as bolts, screws and nails are not normally magnetized, they can become that way if exposed to magnets or magnetic fields. The iron in certain types of steel is attracted to magnets and can itself acquire its own magnetism. You can remove the magnetism from steel nails and other objects fairly easily by heating them or with the use of a demagnetizing device.
The metals iron, cobalt and nickel possess a property called ferromagnetism; a magnet attracts objects made of these metals because their atoms themselves are tiny magnets. In a typical iron object, atoms have a random alignment relative to one another, so their tiny magnetic fields cancel each other out. However, exposure to strong magnetic fields cause many of these atoms to line up the same way and their individual fields add up to a larger, stronger field around the object.
A metal demagnetizer is a device designed to remove magnetic fields from tools and other metal objects. Sometimes called a “degausser,” the equipment incorporates a strong electromagnet powered by an alternating electric current. The electromagnet’s field rapidly and repeatedly reverses its polarity, effectively “scrambling” other magnetic fields in its presence.
Magnetized metal objects lose their magnetism if the objects become sufficiently hot. With increasing temperature, the atoms in a metal vibrate more energetically; eventually this causes the atoms to lose their magnetic alignment and any magnetic field the metal possessed. Scientists call the point at which a metal loses its magnetism the Curie temperature; for iron and steel, this is 770 degrees Celsius (1,418 degrees Fahrenheit). When the metal cools, it remains demagnetized, although contact with magnetic fields will remagnetize it.
Steel loses its magnetism slowly over time. Even at room temperature, the iron atoms in a steel nail vibrate rapidly. Occasionally the vibrations cause atoms to fall out of alignment with the rest of the object. Normally this process is slow, taking years to be noticeable.