In our earlier blogs we discussed magnetism and the Voodoo that surrounds it. This is just a little more on that mystery condition. Magnetism in steel is right up there with the loveliest things you would rather not encounter; Poison Ivy, Root Canal, Oil Canning on a steel plate, and filing your taxes. We are speaking of steel that picks up magnetism, i.e. will attract another piece of steel. This is different from whether or not the steel will attract a magnet.
How do steels pick up magnetism?
There are many situations that may induce magnetism during the performance of daily industrial procedures. Identifying the sources of magnetism is difficult; Exposure to an electrical or magnetic field, or to a device that utilizes a coil, or to, saws, grinders, power lines, etc. Exposure may mean direct contact or proximity. I have encountered steel service managers who have suspected “magnetism” they encountered was a result of changing the direction of how the steel bars were stored, North to South, or East to West. It is common to have bars leave for a destination, displaying little or no magnetism, only to arrive at their destination displaying noticeable magnetism. Burning and welding heavy plate often induces magnetism.
What type of steel may pickup magnetism?
All steels may pick up magnetism. The following is a general guideline: the lower the carbon range of the steel, the greater the degree of potential magnetism and the lesser degree of hold. (“Hold” is identified as the potential to retain the magnetism. Lesser hold would mean easier to remove.) So lower carbon steels may pick up magnetism rather easily, but it is generally fairly easy to remove. The opposite is true as carbon content increases.
How is magnetism removed, once a steel has become magnetized?
There are several means of removal; Note: these remedies are subject to the type of steel involved and the degree of hold. Striking the steel, or “Peening” (setting up a vibration). Peening with a hammer is more effective on the low carbon steels, such as 1018 and 1020. It becomes less effective as the carbon content range increases. Heating the steel to 800°F or to 900°F, and holding it at that temperature for approximately one hour per inch of greatest cross-section. The most effective method is to pass the material through a demag unit or a degaussing coil.
I have mentioned there is a past blog on the subject but is worth repeating for quick reference; Several years ago, an expert on removing magnetism advised me;
“Well son, you can heat it, you can beat it, but short of running it through a heavy capacity de-gauss unit, there’s not guarantee you’re going to fix it.”
-Howard Thomas, October 5th 2020