Heat Treatments

Introduction to Heat Treatments

Heat treatment is a series of operations involving the heating and cooling of materials in a controlled environment.
These processes are employed in order to alter the physical and mechanical properties of a material without modifying its shape.
Most often utilised in metals and alloys, heat treatments aim to improve the workability, enhance durability and increase resistance to wear and tear of the materials.
By controlling the rates of heating and cooling, it is possible to modify the microstructure of a material and thus its properties.

Hardening is a heat treatment process in which a metal is heated to a certain temperature and then cooled rapidly to make it harder.
This process alters the crystal structure of the metal, making it more resistant to deformation and breakage.
It involves heating the material to its austenising temperature, holding it at that temperature to transform the structure, and then rapidly cooling, often via a process known as quenching.

Annealing is a heat treatment process used to reduce hardness, increase ductility and help eliminate internal stresses.
It consists of heating a material to a certain temperature, holding it at that temperature and then cooling it slowly.
This process can improve the machinability, formability, and stability of the material.

Normalising is a heat treatment process used to refine and homogenise the grain structure of a metal, and to remove any hardness caused by previous processing.
It involves heating the metal above its upper critical temperature, and then air cooling it back to room temperature.
This results in a more uniform microstructure, generally with enhanced mechanical properties.

Tempering is a process of heat treating, which is used to increase the toughness of alloys.
It follows hardening and involves heating the metal to a temperature below its critical point for a set period of time, then allowing it to cool in still air.
This process makes the metal less prone to cracking, while maintaining some of its hardness.

When applying heat treatments, it’s important to consider factors like the type of material, desired properties, and end application.
Heat treating insufficiently or excessively can result in the material becoming over-hardened, overly soft, or having unwanted mechanical properties.
Therefore, careful control of time, temperature, and environment is crucial in heat treatments.