Microstructure of Low Carbon Steel After Annealing
Low carbon steels are highly malleable materials that are used to create a variety of products. These steels are economical and offer good mechanical properties. The components manufactured out of low carbon steel need to be robust and reliable. To achieve this, the structure has to be subjected to various processes like annealing. Annealing helps in removing internal stresses, enhancing toughness and flexibility of the parts. It is also used for improving machinability, corrosion resistance and conductibility of the steel. The success of the entire process depends upon the configuration of microstructure of the steel.
Microstructure is the arrangement of atoms within a ferrous material and it is used to describe its strength, toughness and ductility. When molten steel is poured and allowed to cool, a number of metallurgical phases will form during phases. In low carbon steels, ferrite and pearlite are the two major constituents along with some trace elements.
When low carbon steel is subjected to annealing, the microstructure changes. This is because of the heat treatment process which includes heating the steel to certain temperature,hold it at that temperature required time and then cooling the material under controlled environment. During annealing, ferrite and pearlite separate into smaller particles. As a result, the cementite precursor (a chemical composition out of which cementite is formed) changes or dissolves depending on the type and total amount of heat used. Due to this, the amount of carbon present in the steel is reduced, further increasing its ductility and making it easier to work with.
The microstructure of low carbon steel after annealing consists of dendrites, spheroids and lamellae. Dendrites are tree-like structures that are made up of fine grains, while the spheroids are spherical structures which can be found in greater concentration in the alloy. Lamellae are the intergranular boundaries of the grains, which are produced by the nucleation and recrystallization of the ferrite. All these phases together give a fine grain distribution throughout the material which helps in making the metal tougher and ductile.
In addition to that, the annealing process also helps in improving machinability and corrosion resistance of the metal. This is because the microstructure that is formed during annealing has a finer grain size which helps in reducing the grain boundary energy and decreasing the friction between material and tool during machining process. Furthermore, the presence of finer grains reduces the amount of corrosion by allowing a uniform coating of protective oxide layer.
To sum up, annealing of low carbon steel produces a microstructure which has a finer grain distribution which makes the material tougher and ductile, and helps in improving its machinability and corrosion resistance. This is why annealing is a necessary step in the manufacturing of low carbon steel components.
