Hardening steel is one of the most widely used heat treatments for metals . Employed since antiquity, this technique has undergone numerous evolutions, and no longer simply involves immersing a hot part in cold water or oil. Today, there are several methods of quenching steel, the most recent of which is based on vacuum technology and the use of pressurized gas.
Appearance of the quenching technique
Historically, blacksmiths worked metal parts over fire to shape or sharpen them, before immersing them in water or oil. This sudden cooling allowed them to freeze instantly, hence the name "tempering".
This metal-treatment technique, which has been in use for centuries, involves influencing the physical and chemical properties of a metal part by heating it up and then cooling it down more or less rapidly. However, heating, holding and cooling times, the temperatures used and the ambient atmosphere can have a considerable impact on the final properties of the part. Several quenching techniques have therefore been developed over the course of history.
How vacuum quenching of steel works
The metal treatment cycle therefore comprises three phases and three determining factors: the duration of each phase (heating, holding and cooling), the temperatures and the atmosphere. While the first two are relatively easy to control, working on the environment in which the steel is immersed is more complicated.
Over the past twenty years, vacuum vacuum processing has enjoyed growing success in the industrial world. Carried out in special furnaces, this technique consists in heating steel to austenitizing temperature (which gives the metal the desired metallurgical structure), avoiding all contact with the ambient air. The cooling phase takes place in a neutral environment, using pressurized gas or oil.
The primary objective of vacuum quenching is to eliminate all risks associated with the interaction between metal and ambient air at high temperatures, such as oxidation, decarburization or over-carburization. This method is widely used in the precision mechanics, aeronautics, medical and automotive sectors.
Gas cooling: the ecological solution of the future
Vacuum quenching followed by gas cooling offers several advantages, starting with reduced deformation of the final part. This technique also reduces the amount of excess material.
Finally, one of the main advantages of gas cooling is the final cleanliness of the parts. Unlike oil cooling, parts are perfectly clean, with no need for washing or microsanding. What's more, pressurized gas cooling is also environmentally friendly.
Vacuum quenching furnaces are heated using electricity rather than gas, making them a low-carbon industry. Moreover, quenching oil, which remains a petroleum product, is often replaced by nitrogen, a gas present in large quantities in the atmosphere. Nitrogen can also be mixed with hydrogen, argon, helium or other gases.
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