When making a custom steel wire basket or sheet metal form order, Marlin’s clients often have questions about corrosion resistance, life expectancy of the metal, how their parts will be held in place, and many other practical concerns.
One question that comes from time to time is “will the basket be magnetic” or “will magnets work on my stainless steel product?” The answer to the question of whether or not your stainless steel wire form will have magnetic properties depends on a few different factors, such as:
- The specific alloy of stainless steel being used
- Heat treating and reshaping
- Exposure to magnetic fields
How do each of these factors impact the magnetic properties of a stainless steel alloy basket?
Stainless Steel Alloys and Magnetism
There are many different alloys of stainless steel, such as grade 304, grade 316, and grade 330 stainless, among the many other alloys on the market. Each of these alloys will fall into one of three categories:
- Ferritic Alloys
- Austenitic Alloys
- Martensitic Alloys
Austenitic alloys are not innately magnetic. Why is this?
According to an article by Scientific American, the reason why the austenitic steel alloys aren’t magnetic is that “the metallic atoms in an austenitic stainless steel are arranged on a face-centered cubic (fcc) lattice. The unit cell of an fcc crystal consists of a cube with an atom at each of the cube’s eight corners and an atom at the center of each of the cube’s six faces.”
This arrangement of atoms prevents the molecules in the austenitic steel from aligning in a unified direction, preventing it from developing magnetic domains that can generate what Scientific American refers to as “magnetic movement,” or magnetism.
Ferritic and Martensitic alloys, on the other hand, are magnetic in nature, possessing a “body-centered (bcc) lattice… with one atom at each of the eight corners and a single atom at the geometric center of the cube.” This structure allows for magnetization of the alloy, although ferritic alloys might be unmagnetized when first made.
How Exposure to Magnetic Fields Affects Stainless Steel Magnetization
As stated by the Scientific American article, this is because “in its natural state ferritic steel consists of small regions called magnetic domains, which are fully magnetized, but in general the direction of magnetization is different in each domain. As a result, the sum total of all the domains gives the piece zero magnetic movement.”
In short, countless tiny pieces of the alloy might be magnetic, but because they aren’t aligned, there is no magnetic pole in the alloy. This is changed when the alloy is exposed to a very strong magnetic field, such as from an electromagnet or a rare earth magnet.
A powerful enough magnetic field overrides the direction of the magnetic domains in the ferritic alloy, orienting all of them to a single direction. This magnetizes the alloy, and the alloy may retain some magnetism even after being removed from the magnetic field.
Magnetism and Reshaping
Some austenitic steel alloys, such as grade 304 stainless, have both an fcc crystal structure and a bcc crystal structure inside of them. The fcc structures prevent the alloy from magnetizing.
However, as pointed out by the Scientific American article, “if the alloy is mechanically deformed, i.e. bent, at room temperature, it will partially transform to the ferritic phase and will be partly magnetic, or ferromagnetic.” In other words, the act of reshaping steel can deform the molecules, changing them so that they can be magnetized.
Magnetism and Temperature
Ferritic steel alloys can lose their magnetism if heated to a sufficient degree.
As stated by the Scientific American article, “all ferromagnetic alloys, when heated to a high enough temperature—their Curie temperature—the ferritic stainless steels lose their ferromagnetism and become paramagnetic—that is, they do not retain their own magnetic field but continue to be attracted to external ones.”
Why Would You Care?
If you have an automated system that relies on magnetic detection to “see” if a basket is in place for starting a process, then the magnetism of that basket would be a very important factor in your process.
On the other hand, if you have magnetic products and a strongly magnetic basket would be a hindrance, causing parts to “stick” and slowing down production, then you wouldn’t want a magnetized basket.
There might be any number of reasons why you may or may not want your custom steel wire basket to be magnetic or nonmagnetic.
Learn more about how you can choose the right basket for your needs by checking out the free guide at the link below: