Difference Between Annealing and Normalizing

Main Difference – Annealing vs Normalizing

Both these terms, Annealing, and Normalizing, refer to methods of heat treatment used to change various properties in materials. This is very common among metals. Upon heat treatment, metals are able to not only to change their physical properties but also to change their chemical properties. In this process, metals are often heated above their critical points/ recrystallization temperature and cooled down afterward. Therefore the term ‘heat treatment’ can be used only if the heating and cooling is done purposely to change the properties of the metal in question. Heating and cooling can occur at different stages in many other processes, but then they are not referred to as ‘heat treating’. The main difference between annealing and normalizing is that the annealing is a method of heat treatment used to make metals ductile and less hard while normalizing is a type of annealing process which is only specific to ferrous alloys.

What is Annealing

As mentioned above, Annealing is a method of heat treatment that usually alters physical properties and at times the chemical properties of the material when exposed to heat. In the annealing process, the material is first heated beyond its critical point/recrystallization temperature and is being held at this temperature for a while before cooling it. This is usually done when the material’s hardness needs to be reduced in order to make it easily mouldable. Annealing also increases the ductility of a material. Ductility is the ability of a material to deform under tension making it softer and easier to handle. The cooling process is usually done at a slow pace by letting the material cool in air, or it can be also done much quicker by quenching it in water.

The process of annealing also reduces the number of dislocations present in a metal while making it more ductile. Dislocations are tender deformations within a structure of a metal, where certain layers of atoms appear to be shifted from an otherwise obvious alignment. Due to the presence of dislocations, the metals tend to be more rigid. Therefore, the reduction of the dislocations makes atoms move very freely and tend to ease the internal stress of the system. This in turn makes the metal ductile and softer. In general, atoms within a system move spontaneously to release the internal stress of the system and this occurs even at room temperature. However, this process happens very slowly at room temperature, and heating facilitates the process. Therefore, heating reduces the amount of energy trapped inside the material, bringing it to a more stable position upon cooling.

Difference Between Annealing and Normalizing

Annealing Furnace

What is Normalizing

Normalizing is another type of heat treatment, applied specifically to alloys made from Iron, in order to achieve a uniform grain size. It is actually considered as a type of annealing which is only done for Ferrous or Iron alloys. In the normalizing process, the metal/alloy is heated to a temperature above the critical point and then is cooled in air. In this case, it is important  to cool it slowly in the air rather than quenching it in the water like for the other metals. This step helps to get a uniform grain size throughout the alloy. However, normalizing produces less ductile alloys in contrast to a full annealing process.

Difference Between Annealing and Normalizing

Definition

Annealing is a method of heat treatment used to make metals ductile and less hard.

Normalizing is a type of annealing process which is only specific to ferrous alloys.

Cooling Process

In annealing, the metals can be cooled down after heating either by cooling them in the air or quenching them in water.

In normalizing, it is important that the cooling process takes place slowly, that’s why it is always cooled in air and not quenched in water.

Grain Size

It is not crucial to achieve a uniform grain size during the process of annealing.

Obtaining a uniform grain size is important for the normalizing process.

Hardness of the final product

The metals are made to be less hard and ductile after annealing.

The alloys remain harder after normalizing when compared to a full annealing process.

Image Courtesy:

“Annealing furnace Saltford Brass Mill” by Rodw – Own work. via

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