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Common Applications of Heat Treatments

Heat treatment is a controlled process of heating and cooling material in order to improve its properties, performance, and strength. In this manufacturing process, a metal is altered by heating and cooling cycles under different thermal boundary conditions and wide temperature ranges. Most metals and alloys are in some way heated, and their importance is seen in many products in the aerospace, automotive, construction, agriculture, consumer goods, and mining industries. There are three main steps in the heat treatment process, which include heating the metal to a specific temperature, soaking or maintaining the specific temperature for a certain amount of time, and cooling to a suitable rate following prescribed methods. There are seven main techniques used for the heat treatment of materials, they are:

Normalising
Annealing
Tempering
Hardening
Ageing
Stress Relieving
Carburisation

Normalising

Normalizing heat treatment helps remove impurities and improve metal´s ductility and toughness after it has been exposed to thermal or mechanical hardening processes. During this process, the material is heated to 750 °C -980 °C, and it is then cooled back to room temperature by exposing it to room temperature air after being heated.

Normalising causes microstructures to reform into more ductile structures. This is important because it makes the metal more formable, machinable, and reduces residual stresses in the material that could lead to unexpected failure.

Annealing

Annealing is a heat treatment process that is used to increase the ductility and reduce the hardness of a material. Annealing is often performed after material has undergone a hardening or cold working process to prevent it from brittle failure or to make it more formable for subsequent operations.

Depending on the alloy, the temperature ranges from 260 °C to 760 °C. Annealing changes the physical and chemical properties of a material to increase its ductility and reduce its hardness. For more insights, our Annealing Article is very useful.

Tempering

Tempering is a heat treatment process that consists of reheating hardened steel to a temperature below the lower critical temperature in order to decrease its hardness, improve its toughness, and remove internal stresses caused by the rapid cooling of steel.

There are three types of temperatures used in the tempering process: low temperature 100°C -200°C, medium temperature 200°C to 500°C and high temperature 500°C to 700°C. For more information on tempering please refer to our Tempering Article.

Hardening

The hardening process consists of heating the material above the critical point, followed by rapid cooling, usually from 800-900°C; it is the most common heat treatment process of all.

The material can be cooled rapidly in air, water, oil or others. The rapid cooling process is known as quenching- applied to stainless and high-alloy steels.

The use of metal hardening results in an improvement of the metal´s mechanical properties, and its hardness, making it more durable and tougher.

Ageing

Also called precipitation hardening, ageing is a heat treatment method used mostly to increase the yield strength of malleable metals. The process produces uniformly dispersed particles within a metal´s grain structure which bring about changes in properties.

Ageing usually comes after another heat treatment process that reaches higher temperature- ageing only elevates the temperature to medium levels and brings it down quickly (95°-205°C).

Properties of ageing include high tensile strength and hardness, improves wear resistance, allows for easy machinability of material, and allows for little to no distortion of the component.

Stress Relieving

Stress relieving heat treatment is intended to remove internal residual stresses generated by prior manufacturing processes such as machining, welding, and cold rolling.

Without a stress relieving process, subsequent processing may give rise to distortions or stress corrosion cracking.

Stress relieving does not produce significant changes in material structures or mechanical properties, and is therefore normally restricted to relatively low temperatures (between 550°C and 650°C).

Carburisation

Carburisation is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-rich gas atmosphere. The process of heating a metal component in a high carbon environment allows for the diffusion of carbon atoms directly into the surface of the part that needs to be case hardened.

The carburizing temperature varies between 870 °C and 940°C. The amount of carbon and resultant case depth that gets diffused into the metal surface depends on the carbon potential of the atmosphere, the temperature at which it is heated and the time it is exposed to that temperature.

Longer carburizing cycle times, higher temperatures, and higher carbon potentials will increase the amount of carbon diffused into the surface and the depth of the case.

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A range of vertical ovens from 50-240 litres that operate at up to 300°C. Ovens are lined with a stainless steel chamber and include a fan and digital controls.

Stock No: NEW060
Category: Laboratory & Bench Top Ovens
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Common Applications of Heat Treatments

Normalising

Annealing

Tempering

Hardening

Ageing

Stress Relieving

Carburisation

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