Carbon steel is an iron-carbon alloy that consists of about 0.05 to 2.1% of carbon by weight. It usually also contains other elements like cobalt, nickel, and chromium, although there is no minimum required specification for these. It is used to create a wide range of products, from cutting tools to automobile parts.
Have you ever wondered if carbon steel is magnetic? In this article, we are going to discuss just that. We will begin by looking at the properties of carbon steel. Then we will discuss how low-carbon steel and high-carbon differ from each other. Finally, we will talk about the magnetism of steel.
Read: Is Aluminium Magnetic?
Is Carbon Steel Magnetic?
Yes, carbon steel is magnetic. This is because it is mainly composed of iron, which is a ferromagnetic substance. However, the magnetic nature of carbon steel is dependent on the temperature; its structure changes with temperature, resulting in a change in magnetism.
Magnetism is a force caused by the motion of electric charges. Every substance is made up of tiny units known as atoms. These atoms have electrons (particles that carry an electric charge) that circle the atom’s centre, called the nucleus.
In most substances, equal numbers of electrons spin in opposite directions. This cancels out their magnetism, and so they are said to be weakly magnetic. These include things like paper, cloth, wood, etc.
However, in some substances like iron, the electrons spin in the same direction. This allows their magnetic fields to combine together and produces a magnetic field extending beyond the atoms. These objects are strongly magnetic and are known as ferromagnetic.
Because carbon steel is largely made up of iron, it inherits its ferromagnetic nature. However, the structure of carbon steel changes with the temperature. At room temperature, the steel’s atoms have a body-centred structure, which allows the electrons to spin in the same direction, leading the carbon steel to become magnetic.
But at temperatures over 1300°F (704°C), carbon steel atoms acquire a face-centred structure. This does not allow the electrons to spin in the same direction, and carbon steel effectively becomes non-magnetic.
Carbon Steel Properties
Carbon steel is an iron-carbon alloy containing 0.05 to 2.1% of carbon by weight. The American Iron and Steel Institute (AISI) states that no minimum content is required for other alloying elements like nickel, cobalt, etc.
The maximum percentage, however, should be within the specified limits: 1.65% manganese, 0.60% silicon, and 0.60% copper. These are the properties of carbon steel:
- As the carbon percentage increases, the steel can become stronger and harder through heat training. But then it becomes less ductile (the ability to be drawn, say into a wire).
- A higher carbon content decreases weldability (ability to be welded), regardless of its heat treatment. Higher carbon content also lowers the melting point.
- Carbon steel has a high magnetic permeability, which is the measure of magnetization that a material obtains in response to an applied magnetic field.
- The magnetic saturation of carbon steel decreases with the amount of cobalt and nickel present in the alloy. The alloy achieves magnetic saturation—a state when an increase in the magnetic field cannot increase magnetization—when its permeability drops to 1.
- Carbon steel’s hysteresis loss is high, meaning that they lose magnetism rapidly.
Carbon steel can be classified into three categories: low-carbon steel, medium-carbon steel, and high-carbon steel.
Is Low-carbon Steel Magnetic?
Yes, low-carbon steel is magnetic. This is because it consists of a ferrite microstructure, which is ferromagnetic (high susceptibility to magnetization). It has less than 0.25% of carbon content by weight, and it is the most widely used carbon steel.
Low-carbon steel is relatively low in hardness, strength, and cost. They cannot be hardened by heat treatment, so usually, cold work is needed to convert them into martensite. While it lacks strength, low-carbon steel is excellent for machining and welding because of its high ductility.
High-strength, low-alloy steels (HSLA) are also usually classified as low-carbon steels; they contain other elements such as copper, molybdenum, and nickel, which make up about 10% of the steel content.
These have higher strengths due to heat treatment. They are also easily machinable and formable since they retain their ductility. They are also more resistant to corrosion compared to regular low-carbon steel.
Low-carbon steel is magnetic because it largely consists of iron. It has a body-centred cubic structure, which allows its electrons to spin in the same direction, making the steel magnetic.
But, even though low-carbon steel is ferromagnetic, its low coercive force makes it hard to turn it into a permanent magnet.
Is High-carbon Steel Magnetic?
Yes, high-carbon steel is magnetic because it is largely made up of iron. Its ferrite microstructure consists of unpaired electrons that spin in the same direction, making the high-carbon steel ferromagnetic.
High-carbon steel has a carbon content of 0.60 to 1.25% by weight and a manganese content of 0.30 to 0.90%. Amongst the carbon steels, it has the highest level of hardness and toughness, although its ductility is the lowest.
Tool and die steels are types of high-carbon steel, and they contain additional alloying elements like chromium, vanadium, and tungsten. The addition of these leads to the formation of compounds like tungsten carbide, which makes the steel very wear-resistant.
Read: Is Zinc Magnetic?
High-carbon steel has a ferrite microstructure, whose unpaired electrons spin in the same direction. This makes high-carbon steel ferromagnetic.
Is Alloy Steel Magnetic?
Alloy steel is a huge category, which consists of steel that is alloyed with a variety of elements (ranging from 1% to 50% in weight) to improve its mechanical properties. Many of these include iron, and they are ferromagnetic.
Alloy steel is basically steel (carbon + steel) containing other alloying elements like manganese, nickel, chromium, silicon, etc. Some less alloying elements include aluminium, cobalt, etc. The different elements lead to changes in properties like strength, wear resistance, and hardness.
Many of these alloy steels are ferromagnetic, and this makes them quite important for products like electric motors and transformers.
Low Carbon Steel vs High Carbon Steel
Low-carbon steel and high-carbon steel differ in the following ways:
- Carbon content: Low-carbon steel has 0.05 to 0.25% carbon, while high-carbon steel has 0.60 to 1.25% carbon content by weight.
- Other Elements: Low-carbon steel has a very small amount of manganese to retain its flexibility; high-carbon steel has plenty of tungsten and chromium.
- Strength: Low-carbon steel is soft, while high-carbon steel is hard.
- Cost: Low-carbon steel is affordable and easy to mould; high-carbon steel is expensive and difficult to shape.
- Uses: Low-carbon steel is used in automobile parts, construction materials, and pipes. High-carbon steel is used in the farm industry, spring industry, and for making high-strength wires.
How Can You Tell if Steel is Magnetic?
You can find out if steel is magnetic by bringing a magnet near it and seeing if it sticks. However, this does not really tell us much about the quality of the steel. Some stainless steels are magnetic, while others are non-magnetic.
Ferritic and martensitic stainless steels have a ferritic microstructure, so they are magnetic. Austenitic stainless steels contain nickel, and they are non-magnetic.
Austenitic stainless steels may be non-magnetic but it is highly resistant to corrosion. In many cases, it can be better than ferritic/martensitic stainless steel. In other words, stainless steel’s magnetism does not necessarily determine its quality.
For consumers, there is no foolproof way to test the quality of the steel. So, the best thing to do is to buy high-quality stainless steel from a reputed brand.
Can all Steel be Magnetized?
Ferritic steel can be magnetized. In order to be magnetic, a material should have free electrons that spin in the same direction. We can achieve this with steel by creating an electromagnet, stroking the steel, or placing it in a strong magnetic field.
When a material has a lot of unpaired electrons spinning in the same direction, the magnetic fields of the atoms combine together and extend beyond themselves. This makes the whole material magnetic.
We wrap an electric wire through the steel multiple times and then run a current through the wire. This will create an electromagnet, and the steel will become somewhat magnetized after being in the magnetic field.
Steel can also be stroked with a magnet, and repeated stroking will orient the electrons in the same direction. This can also be done by placing the steel in a strong magnetic field for some time. However, it is more difficult to magnetize steel than a piece of iron; the harder the steel is the more difficult its magnetization.
Check out this video by K&J Magnetics to see how different kinds of stainless steel interact with magnets.
Read: Is Wood Magnetic?
In this article, we have looked at the magnetism of carbon steel. Carbon steel is magnetic because it is largely composed of iron, a ferromagnetic metal; even the other alloying elements are also usually ferromagnetic. We looked at the different properties of low-carbon and high-carbon steel. Finally, we discussed how steel can be magnetized.