Plain Carbon Steels, Classification, Designation

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

What Is Plain Carbon Steel?

Plain carbon steel is the 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 include cementite+ferrite microstructure in it. These cementite particles are distributed along the ferrite microstructure that they act as obstacles to dislocation motions in material. This is a very important phenomenon to obtain strength in steels. So if we add much more carbon alloying element, the strength of steel will be much more higher because of these obstacles are created in the microstructure of 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 are in the form of 10XX. 10 means, this element is plain carbon steel and the XX is the carbon content inside material. For example 1030 means, plain carbon steel that includes 0.3% of carbon as 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 steels in industry. Railroad rails, sheet metal parts, automotive sheet metal parts etc. are generally produced with Low Carbon Steels. If an application that does not need strength, low carbon steels can be very good candidate for it.
  • Medium Carbon Steels: This type of plain carbon steels 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 thet are including. If the stiffness, hardness and strength is important in an application, high carbon steels can be very good candidate for it. Wear resistant parts, cutting tools, springs are examples of application of high carbon steels.

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

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