Heat treatment of metals refers to a controlled thermal cycle that combines defined phases of heating, soaking and cooling, aimed at modifying the metal’s microstructure and optimizing its mechanical and technological properties.
To perform heat treatments correctly, it is essential to understand how the metal behaves at different temperatures and the corresponding microstructural transformations, enabling proper control of thermal cycle times and cooling rates.
The final result depends on the correct combination of temperature, soaking time and cooling rate, which together determine the mechanical properties of the metal.
Main Heat Treatments of metals
There are several types of heat treatment commonly used across the industry. Some of the main processes include:
Quenching (Hardening)
Quenching is a heat treatment consisting of heating the metal to the austenitizing range, followed by rapid cooling in oil, water, polymer solutions, pressurized gas or quench press systems, depending on application requirements.
This process is used to increase the hardness and strength of the metal.
Learn more about oil quenching and vacuum hardening.
Tempering (post-quench reheating)
Tempering is the process of reheating the metal to temperatures below its melting point after quenching. This treatment reduces residual stresses generated during quenching, stabilizes mechanical properties and enables the correct balance between hardness and ductility.
Annealing
Annealing is a heat treatment that involves heating the material to elevated temperatures followed by controlled cooling. This process improves ductility and workability.
The main variants include isothermal annealing, recrystallization annealing, subcritical spheroidizing annealing, stress-relief annealing, process annealing and magnetic annealing.
Learn more about magnetic annealing.
Normalizing
Normalizing is similar to annealing but involves air cooling.
This process improves microstructural homogeneity, equalizes mechanical properties and prepares the metal for subsequent mechanical or thermal processes.
Carburizing
Carburizing is a thermochemical treatment that enriches the surface layer of the metal with carbon, increasing surface hardness and wear resistance. It is commonly used to enhance the wear resistance of components.
Other heat treatment processes include quench and temper, solution heat treatment and ageing, particularly for alloy steels and light alloys such as aluminum.
Heat treatments can be applied to carbon steels, alloy steels, cast irons and aluminum alloys.
Benefits and Advantages of Heat Treatments
The main objectives of heat treatment vary depending on the material type and application, but several benefits are common across these processes:
Improved Mechanical Strength
This is often achieved through structural transformation that produces a harder and more compact microstructure. Rapid cooling can generate high-hardness phases such as martensite, increasing resistance to wear and mechanical stress.
Increased Hardness
Heat treatment can be used to increase the hardness of a material. Tempering, for example, consists of heating the material below its melting point followed by controlled cooling. Heat treatment allows the hardness-ductility ratio to be finely adjusted, obtaining metals that are both resistant and stable in service.
Increased Ductility
In many applications, materials must deform without breaking. Heat treatment can be used to achieve this goal. Annealing improves ductility and the metal’s ability to deform without failure, making it better suited for subsequent machining or forming operations.
Enhanced Wear Resistance
Wear resistance is essential in many industrial sectors. Heat treatment can increase the material’s resistance to wear, often through the formation of harder or more durable surface layers.