Primary Types of Heat Treatment and When to Apply Them

17 November 2022

When transforming metals into parts and products, blacksmiths before do not have any option but to forge and temper metals. But technological advancements today have provided metallurgists and material engineers with many heat treatment options for producing the same things. One great thing about these advancements is they can now choose the right option in creating parts and products tailored to the specified requirements and applications.

Heat treatment intends to alter the physical and sometimes the chemical properties of workpieces through a bund of industrial, thermal, and metalworking processes. Here are some types of heat treatment and the best cases to apply them.


Some workpieces like aluminium alloy and steel are heated above their critical temperature until their microstructure changes to an austenite phase. Once this happens, the workpieces are then quenched, which is a process of placing them in water, oil, or a polymer solution to decrease their temperature. The purpose of quenching is to freeze the microstructure of the workpieces and maintain their mechanical properties. The resulting microstructure of the quenched metals may be either martensite, bainite, or pearlite.


Tempering is a heat treatment wherein workpieces are exposed to a temperature bellowing their melting point. The workpieces are then cooled in air, making sure that their brittleness and internal stresses will be minimised. When tempering metals, metallurgists should be aware of the temperature and time to ensure they can produce the desired final hardness. Even the strength and ductility of metals can be affected by these tempering parameters. Tempering can be utilised in processing drill bits, bolts, nuts, screws, and springs.

Stress Relieving

Stress relieving is a heat treatment process often conducted after welding, grinding, cold working, or final machining the workpieces. It is also done once the metals have been quenched and tempered. This process is done by exposing workpieces to a temperature below their lower transformation temperature. The workpieces are then cooled in the air. Stress relieving should be done to eradicate any internal defects and dislocations from the workpieces. It must also be conducted to ensure that the workpieces will be more dimensionally stable in the long run.

Precipitation Hardening

Precipitation hardening is a heat treatment technique that enhances the yield strength of metal workpieces. This technique can only be maximised by workpieces that have undergone quenching and with an oversaturated solution. When carrying out precipitation hardening, the workpieces are heated to 500 to 550 degrees Celsius and held for an hour to four hours. As precipitates nucleate and grow uniformly, the workpieces are expected to attain high tensile and yield strength and improved wear properties.


Some metal workpieces require better wear resistance for their surfaces while retaining their soft yet strong core. By exposing these things to carburisation, they are expected to be heated to 900 to 950 degrees Celsius and diffused with carbon. Since the heating temperatures are beyond most metals’ critical temperature, the quenching process would then allow their carbon-rich surface to develop martensite while leaving the core soft. This process is great when processing gears, cutting tools, and blades.

Many heat treatment processes can be utilised to generate excellent products. If you will be heat treating some metal workpieces, you can contact us at Alpha Detroit Heat Treatment.

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