If you are wondering whether steel is magnetic and how that affects its use in your project, you are in luck. This article reveals the magnetic properties of steel and practical considerations for your appliance.
Basics of Magnetism in Metals
These are the basics of magnetism in metals.
Magnetic Behavior: Ferromagnetism vs Paramagnetism vs Diamagnetism
Ferromagnetism, paramagnetism, and diamagnetism are three categories you can use to describe magnetic behaviour in objects. The ferromagnetic metals like iron are highly magnetic. They can also be permanently magnetized.
Paramagnetic metals aren’t highly magnetic. And you cannot turn them into permanent magnets. Meanwhile, diamagnetic metals such as gold are weakly repelled by magnets.
Role of Iron (Fe) and Crystal Structures
Iron, cobalt, nickel, and gadolinium are the only naturally occurring ferromagnets. However, artificial Heusler alloys may exhibit magnetism without containing any of these elements.
Influence of Alloying Elements & Phases
Alloying elements play a big role in the magnetic behaviour of your alloy. Elements like chromium and manganese are not magnetic. On the other hand, elements such as carbon and silicon favor ferrite or martensite phases that give your alloy magnetic potential.
Is Steel a Magnetic Material?
Definition of “Steel” and Its Iron Base
Steel is made from iron and carbon. Since iron is strongly magnetic, most steels start with that magnetic potential. But this can change depending on what you add and how you shape it inside.
Common Carbon & Alloy Steels: Magnetic Behavior
Most everyday steels, like carbon and structural steel, are magnetic. These steels usually have a ferrite or martensite structure, which makes it easy for their electrons to align.
Exceptions & Edge Cases
Steel has some exceptions and edge cases when it comes to its magnetic properties. For instance, if you cold work on a 304 stainless steel, some areas might become martensite.
On the other hand, other austenitic stainless steels like 304, 316, and 321 have high chromium in their composition. Because of the high chromium, they lose magnetism.
Some tool steels, like 01 or D2 steel, may lose magnetism temporarily when you soften them by heating slowly. After hardening and quenching, your steel will become magnetic again due to martensite formation.
Magnetically Soft vs Magnetically Hard Steel
Steel behaves very differently with magnets. So you can classify them into two groups: magnetically soft and magnetically hard steel.
What “Magnetically Soft” Means
Magnetically soft steel is the type of steel that can become magnetic quickly. But it loses magnetic properties as soon as you move away from the magnet. Examples of steel types in this category include: pure iron, mild steel, structural steel, ferritic stainless steel, etc.
What “Magnetically Hard / Permanent” Means
In contrast, magnetically hard steel is harder to magnetize. But once it acquires magnetism, these steels retain those properties for a long time. These steels are also ideal for making permanent magnets. Examples include high carbon steels, spring steels, martensitic stainless steels, and hardened low-alloy steels, among others.
Stainless Steel & Magnetism
Some steels are magnetic in nature. So, why aren’t others? Keep reading to know why.
Overview of Stainless Steel Microstructures
This microstructure of stainless steel plays a crucial role in how your steel responds to a magnet.
Is stainless steel magnetic or not?
Some stainless steels are magnetic, while others aren’t. It all depends on their iron content. But this property can be weakened by work hardening or welding.
Specific Grades and their Behaviour
Discover the magnetic properties of different steel grades.
304/18-8 stainless steel
18-8 stainless steel is non-magnetic due to its face-centered cubic (FCC) structure. However, cold working can temporarily change your metal to martensite, inducing slight magnetism.
Austenitic stainless steel
This steel isn’t naturally magnetic. It has a face-centered cubic (FCC) structure.
Ferritic stainless steel
Ferrite steels are magnetic because of their body-centered cubic (BCC) structure. Even after thermal processing, your ferrite alloys remain magnetic.
Martensitic stainless steel and Precipitation-hardened steel
Martensitic stainless steels exhibit a body-centered tetragonal (BCT) structure that is magnetic. Precipitation-hardened steel, on the other hand, is characterized by a strong magnetic response.
Duplex stainless steel
You can create duplex stainless steels by alloying austenitic and ferritic grades, hence the name duplex. These steels are partly magnetic.
Effects of Cold Work, Deformation, and Welding on Magnetism
Even if a stainless steel starts non-magnetic, it can acquire magnetism after bending, hammering, forming, or welding. When stainless steel, like 304 or 316, is bent or rolled, the inside changes slightly and forms martensite. This aertensite attracts magnets, so the steel starts to show a magnetic pull in the area you’ve worked.
Welding can also make small magnetic spots because the heat changes the structure around the weld. You can reduce these changes by annealing your alloy. Light heating for stress relief helps a little, but full annealing works best to minimize magnetism.
Magnetism in Other Steel / Metal Types & Comparisons
Other steel types, like galvanized and surgical steel, have unique magnetic behavior.
Galvanized Steel: Magnetic or Not?
Galvanized steel is regular steel covered with a zinc layer to prevent rust. The zinc doesn’t change anything about magnetism. Since the inside is still regular steel, your galvanized steel remains magnetic, allowing a magnet to stick to it.
Ferromagnetic Behavior of Carbon Steel / Mild Steel
Carbon steel and mild steel are strongly magnetic. Since they are mostly made of iron, with very little added to change their behavior, the magnetism of your carbon steel is not easily altered. Their structure makes it easy for magnetism to pass through, so magnets hold on to them very well.
Surgical Steel
Surgical steel is not one single material. It’s just a general name for stainless steels used in medical tools or implants. If your surgical steel is made from austenitic stainless steel, it won’t attract magnets.
But if your surgical steel is made from martensitic or hardened stainless steel, it must exhibit attraction to a magnet. So, the composition of surgical steel plays a role in its magnetic attractiveness.
Ferromagnetic Behavior of Pure Iron (Fe)
Pure iron (Fe) is magnetic in nature. This property comes from having a lot of unpaired electrons in its atomic structure.
Which Metals Are Magnetic vs Non-Magnetic
Cobalt, iron, nickel, and gadolinium are the only natural ferromagnets. The elements that aren’t magnetic include titanium, aluminum, brass, etc.
Practical Considerations & Testing
Here are practical considerations when you are working with magnetic steels.
How to Test Magnetism
There are various methods for testing the magnetism of steel. You can use a simple magnet or a magnet-sensitive gauge. A normal magnet tells you quickly if it sticks or not. Meanwhile, a magnet gauge tells you the strength of the magnetic pull.
Limitations:
However, testing has its limits. Slight magnetism can sometimes be too weak to be detected by hand, so a normal magnet might not show anything. That means that metal can still have a light magnetic response even if you think it’s non-magnetic at first.
Impacts on Design & Fabrication
Magnetism matters in real use. In machines that have sensors, motors, or sensitive electronic parts, unwanted magnetic pull can disrupt their operation.
Furthermore, during fabrication, clamping, and fixturing, magnetism can affect how you secure the parts in place. This magnetic force can pull or shift thin parts slightly. Welding can also change the magnetic behavior.
The heat from welding can create areas that can suddenly become magnetic or even twist the magnetic flow. This can cause what is called hot spots, where the magnet sticks more in one location.
Material Selection Tips When Non-Magnetic Behavior Is a Factor
First things first, you need to choose the right material from the start. Remember that not all steels are magnetic, so just picking any random stainless steel is not enough.
Austenitic stainless steel, like 304 and 316, is usually the best choice when you need low magnetism. But even all these can pick up slight magnetism when you bend, roll, hammer, machine, or cold work the steel. So you must consider both grade and processing.
Also, request the supplier to confirm the magnetic level if you require very low or almost zero magnetism. In some cases, designers choose aluminum or titanium because they don’t become magnetic even after working or welding.
If you must preserve the non-magnetic behavior, it’s also smart to avoid sharp forming and heavy deformation. If you cannot avoid forming, apply a stress relief or annealing heat treatment later to reduce any unwanted magnetic response.
Conclusion
Most steels are magnetic because iron is the primary element. However, your steel may lose magnetism after thermal processing or welding. Additionally, if you alloy non-magnetic elements to your steel, the resulting metal may exhibit a weak magnetic response.
FAQs
Is steel always magnetic?
No, steel isn’t always magnetic. Most steel is magnetic when its structure is like iron, but it loses magnetism if you change the structure to austenite.
Is steel magnetic or non-magnetic?
Steel can be both. Most everyday steels, like carbon and structural steel, are magnetic, but austenitic stainless steels are non-magnetic.
Is steel ferromagnetic?
Yes, steel made from iron is usually ferromagnetic.
Is steel magnetically hard or soft?
It depends on the composition of the steel. Magnetically soft steels, like mild or structural steel, lose magnetism quickly. Meanwhile, the magnetically hard steels keep being magnetic for a long time.
Is stainless steel magnetic?
It depends on the composition of your stainless steel. Ferritic and martensitic stainless steels are magnetic. Austenitic stainless steels are non-magnetic.
Is 304 stainless steel magnetic?
Pure 304 steel is non-magnetic. However, bending or welding can make small areas magnetic.
Is 316 stainless steel magnetic?
No, it isn’t. But after processing, some parts may attract magnets.
Is 18-8 stainless steel magnetic?
No, it isn’t. But bending or forming can induce the martensite phase, causing your 18-8 to attract magnets.
Is mild steel magnetic?
Yes, mild steel is magnetic. Its structure allows magnetism to pass through easily, making magnets stick strongly.
Is surgical steel magnetic?
It depends. Surgical steel made from austenitic stainless steel isn’t magnetic, but martensitic or hardened types are magnetic.
Is iron magnetic?
Yes, it is. Iron has a ferromagnetic nature.
Which metals are magnetic and which are not?
Magnetic metals include cobalt, iron, nickel, and most carbon steels. Non-magnetic metals include brass, aluminum, titanium, and copper.
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