There are 4 they are Low Carbon steel, Medium Carbon Steel, High Carbon Steel and Eutectiod

En8 is low carbon steel and it can be toughned.

En24 is medium carbon steel and it is generally called forged steel.

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High carbon steel is a metal.The addition of carbon makes the steel harder after heat treatment.

The amount of carbon in iron metal determines the strength and type of steel.Steel with low carbon is called low carbon steel and carbon with medium carbon called medium carbon steel.

It is called low carbon steel if the carbon content is around 2.5 % or less. Others may be called medium or high carbon steel like that used in Die Steel of cutting tools. Generally low carbon steel are preferred if welding is adopted.