Is Cast Iron Magnetic? Know the Reality

Cast iron is prevalent due to its specific properties. Its high-temperature resistance, durability, and rust resistance make it stand out. However, there is confusion about its magnetic behavior. So, the question is: Is cast iron magnetic?

 

The answer is yes—pure cast iron sticks to magnetic. It contains 90% iron, which is magnetics and induces magnetism in cast iron. The unpaired electrons of iron produce magnetic domains. This domain aligns perfectly when exposed to a magnetic field, making cast iron show magnetism. 

 

However, cast iron metal has various types that vary in magmatism. Multiple types and their differences in magnetism create confusion. In this article, I will explain everything regarding the magnetism of cast iron and its types. So, let’s get started!

 

What is Cast Iron?

Before discussing the magnetism of cast iron, let’s first look at what this cast iron is!

 

Cast iron is fundamentally an alloy primarily consisting of iron and carbon. Iron is the main ingredient, and carbon content is just around 2 to 3%. Along with these elements, many other elements are present in traces. Those include silicon, manganese, sulfur, and phosphorus.

 

Cast iron is well known for its excellent strength and heat resistance. Due to this, manufacturers use it to make home utensils. Cast iron utensils don’t get affected by extreme temperatures. Its magnetic behavior further enhances its value in various industries. 

 

Are you wondering why this metal is known as cast iron, as it primarily consists of iron? Why don’t we name it iron instead of cast iron? The reason behind this lies in its production process. The iron undergoes melting and is then mixed with carbon (in a small quantity). This molten liquid is then poured into a mold of a specific shape to create the mold iron. 

 

Due to this casting process, this metal is known as cast iron. It has been in use for several centuries. However, manufacturers considered using it in construction work during the 18th–19th century. It is common in various industries, including construction and home appliances.

 

Is Cast Iron Magnetic? If So, Why?

Yes, pure cast iron is magnetic and can stick to magnets. I explain the logic behind cast iron’s magnetism in the section below.

 

First, you need to understand how magnetism is produced. As you know, every atom has electrons that spin around the nucleus. Right? Each electron has its spin. If electrons are paired, they cancel each other’s spin. But if the electrons are unpaired, their spin creates the magnetic field. Remember, cast iron consists of 90% of pure iron. Right? 

 

This iron has unpaired electrons. The spin of these unpaired electrons is not canceled out, so their spin creates magnetic fields. In iron, regions where unpaired electrons create a magnetic field are called magnetic domains. These magnetic domains have random orientations and don’t create strong magnetic fields. 

 

However, exposure to magnetic fields changes the orientation of these magnetic domains (regions). These domains align together when you bring the magnetic field close to it. Their alignment in one direction creates a strong magnetic effect. As a result, the cast iron becomes magnetic and sticks to the magnet. 

 

When you remove the magnetic field, it means the magnetic field is removed. So, some domains change their orientation and cut the magnetic effect. Similarly, some magnetic domains still orient in the same direction and keep the cast slightly magnetized. This magnetism is negligible and is called residual magnetism.

 

Types of Cast Iron & Their Magnetic Behavior

As I said earlier, cast iron is an alloy of various elements. Iron (over 90%) and carbon (2 to 4%) are the main ingredients. Different cast iron types have different proportions of carbon content. Due to varying carbon content proportions, those types show different magnetic behavior.

 

Remember, the cast iron with higher carbon proportion will be non-magnetic and vice versa. The reason is that the carbon does not allow the alignment of the magnetic domain. As a result, when the magnetic field comes close, those domains fail to align strongly due to the presence of carbon. As a result, cast iron shows weak magnetic or non-magnetic behavior. 

 

Here is a table showing different types of cast iron, their carbon percentage, and their magnetic behavior.

 

Type of Cast Iron	Carbon Proportion	Magnetic Behavior
White Cast Iron	1.8–3.6%	Strongly magnetic due to iron carbide.
Gray Cast Iron	2.5–4%	Weakly magnetic or non-magnetic due to graphite (carbon) flakes.
Malleable Cast Iron	2–2.6%	Weakly magnetic due to tempered carbon.
Ductile Cast Iron (Nodular)	3.2–4.1%	Weakly magnetic due to carbon nodules.

 

This table shows white cast iron has a lower carbon proportion of around 1.8 – 3.6%. Therefore, it is magnetic and can stick to magnetic. On the other hand, Gray and ductile cast irons have higher carbon content. As a result, these cast iron types are non-magnetic. If you expose them to powerful magnetic fields, they will still show very weak magnetic properties.

 

Does Cast Iron Stick to Magnets?

 

The answer to this question is both YES and NO.

 

The pure cast iron always sticks to the magnet. The reason is that it is magnetic and shows strong magnetism. The unpaired electrons of iron create magnetic domains. When magnets come close to pure cast iron, these domains orient and align in one direction. As a result, the cash iron sticks to the magnet.

 

However, some cast iron is not pure and has a higher carbon content. The presence of carbon does not allow the magnetic domain to align. As a result, the magnetic domains do not align when the magnetic comes close to such cast-iron types. As a result, cast iron with higher carbon content does not stick with magnets.

 

Factors that Affect the Magnetism of Cast Iron

 

Generally, cost iron is magnetic due to over 90% iron proportion. However, some factors can affect how cost iron reacts to magnets. Let’s discuss each of those factors in detail.

 

1- Proportion of Alloy Elements

 

The alloy elements highly influence the magnetic behavior of the cast iron. As I said earlier, cast iron consists of many elements: iron, carbon, silicon, manganese, and chromium. The proportion of each of these alloy elements affects how cast iron reacts to magnets. 

 

For example, gray cast iron with a higher silicon proportion will be non-magnetic. Silicon promotes the formation of graphite (carbon flakes). These flakes disrupt the alignment of magnetic domains. On the other hand, cast iron with higher manganese will be magnetic.

 

This is because manganese supports the formation of carbide instead of graphite. So, there happens to be no hindrance to the alignment of magnetic domains. So, cast iron becomes magnetic. The prime example of cast iron with higher manganese is white cast iron. In this way, the proportion of each alloy element affects the magnetism.

 

2- Heat or Temperature

 

Temperature also affects the magnetic behavior of cast iron. Remember, all the ferromagnetic materials have a curie temperature. At this temperature, these materials lose all of their magnetic properties. Cast iron is no exception and becomes non-magnetic when the temperature reaches curie temperature. 

 

However, this curie temperature varies for each type of cast iron. Are you wondering how an increase in temperature makes cast iron non-magnetic? Let me explain. When the temperature increases, the vibration between the atoms increases. As a result, the magnetic domains do not remain stable and don’t align perfectly. Cast iron shows non-magnetic behavior when the temperature is increased.

 

3- Strength of External Magnetic Field

 

Have you ever heard of someone saying they magnetized grey cast iron? Generally, its higher carbon content makes it non-magnetic, right? The question is how it gets magnetized despite having higher carbon content. This is due to the strength of the magnetic field. 

 

The magnetic domain starts to align if you take a grey iron cast in a strong magnetic field. This is due to the impact of the external magnetic field. However, this impact is short-lived and less intense. However,  the strong external field creates a magnetic implication. On the other hand, a weak external magnetic field will not induce magnetic properties in gray cast iron. 

 

Frequently Asked Questions

 

Is cast iron magnetic or not?

Yes, pure cast iron is magnetic and sticks to a magnet. It consists of 90% iron, and such a huge iron content induces magnetism in this metal.

 

How does cast iron compare to steel in terms of magnetism?

Steel is more magnetic than cast iron due to its lower carbon proportion. Steel generally contains less than 1% carbon, while cast iron contains 2% to 4%. This difference in carbon proportion gives steel better magnetism.

 

Why does gray, malleable, and ductile cast iron have weak or no magnetism?

These types of cast iron are non-magnetic. The reason behind their non-magnetism is their higher carbon content. Remember, carbon does not allow the magnetic domains to align. When exposed to magnetic fields, the material becomes non-magnetic if these domains don’t align.

 

How do you check the magnetism of cast iron?

Checking the magnetic behavior of cast iron is straightforward. Take a magnet and bring it close to the cast iron. If the material (cast iron) sticks to a magnet, it is magnetic, and vice versa. You can also check magnetism by measuring the carbon content of specific cast iron.

 

Conclusion

 

Cast iron is a popular material with applications in various industries. From construction to home appliances, this material has a dominant presence. However, many people don’t know its magnetic properties, as it has multiple types varying in magnetism.

 

Some types of cast iron are magnetic, while others are not. I’ve explained everything about cast iron and its magnetism in this article. In short, pure cast iron is always magnetic. However, its magnetic behavior weakens since it has a higher carbon content. This article goes in-depth on the logic of how higher carbon contributes to cast iron’s non-magnetism.