Plain Carbon Steels, Classification, Designation

To understand the plain carbon steel, you need to understand the term ‘steel’ which is explained in Mechanicalland. In this article, we will explain the plain carbon steels, the designation of plain carbon steels, and the classification of plain carbon steels with the applications they are used in.

Metals and Materials: Science, Processes, Applications

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What Is Plain Carbon Steel?

Plain carbon steel is steel that includes only carbon elements as alloying elements inside it. But there can be other elements inside the plain carbon steels such as 0.4% of manganese and lesser amounts of other elements.

According to the iron-carbon phase diagram, plain carbon steels are included cementite+ferrite microstructure. These cementite particles are distributed along with the ferrite microstructure that they act as obstacles to dislocation motions in the material. This is a very important phenomenon to obtain strength in steel. So if we add much more carbon alloying elements, the strength of steel will be much higher because these obstacles are created in the microstructure of the steel.

How Is The Designation Of Plain Carbon Steels?

If we take a look at the designation of plain carbon steels, it is very easy. According to the AISI and SAE, the designation of plain carbon steels is in the form of 10XX. 10 means, this element is plain carbon steel and the XX is the carbon content inside the material. For example 1030 means, plain carbon steel that includes 0.3% of carbon as an alloying element.

How Is The Classification Of Plain Carbon Steels?

Carbon content, hardness, and tensile strength graph of plain carbon steels(Fundamentals of modern manufacturing).
  • Low Carbon Steels: This type of plain carbon steel includes less than 0.2% of carbon. And this type of low-carbon steel is the most widely used steel in the industry. Railroad rails, sheet metal parts, automotive sheet metal parts, etc. are generally produced with Low Carbon Steel. If an application does not need strength, low carbon steel can be a very good candidate for it.
  • Medium Carbon Steels: This type of plain carbon steel includes 0.3-0.5% of carbon inside them. Applications of medium carbon steels that need some strength bigger than low carbon steels such as machinery components, crankshafts, etc.
  • High Carbon Steels: 0.5% or higher carbon content that they are including. If stiffness, hardness, and strength are important in an application, high carbon steels can be a very good candidate for it. Wear-resistant parts, cutting tools, springs are examples of the application of high carbon steels.


As you understand above if the carbon content in steels increases, hardness and strength increase. But the ductility decreases.

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