Spheroidizing is a form of heat treatment for iron-based alloys, commonly carbon steels, in order to convert them into ductile and machinable alloys. It is conducted at temperatures that are slightly below the eutectoid temperature (temperature at which the solution is a solid solution rather than liquid), followed by a slow cooling process.
The resulting spheroidite structure is a microstructure that contains sphere-like cementitie particles. Spheroidite is known as the most ductile and machinable form of steel. This article will look into the technique and applications of spheroidizing process.
Technique of Spheroidizing
Spheroidizing of high carbon steel is a method of prolonged heating at a temperature below the eutectoid temperature. By heating at this temperature pearlite, which is the lowest energy arrangement of steel, gets converted to ferrite and cementite. The graphite content of steel assumes a spheroidal shape after spheroidizing and after prolonged heating the pearlite layers are broken down and spherical lumps of cementite, or spheroidite, are formed.
The structures in spheroidite are one thousand times larger than those of pearlite and are spaced further apart. This means the spheroidite steel is extremely ductile. However, the process of spheroidizing does consume a lot of energy.
Advantages of Spheroidizing
Some of the advantages of spheroidizing are mentioned below:
- Increases ductility of high carbon steel
- Spheroidite structure reduces energy needed for subsequent operations
- Machinability is increased.
Some of the industrial applications of spheroidizing are listed below:
- Machinable steel
- Rail road tracks
- Tyre cords
- Bridge cables.
Sources and Further Reading