Nowadays, there are several ways of working industrial metal. Among the most widely used is the heat treatment of metals, to modify the appearance, strength and resistance of metal parts.
Definition of metal heat treatment
Standard NF EN ISO 4885, which replaces standard NF EN 10052, defines heat treatment of metals as "a succession of operations during which a solid ferrous or metallic product is subjected in whole or in part to thermal cycles in order to obtain a change in its properties and/or structure".
In other words, this process involves subjecting metal parts to specific temperature cycles with the aim of modifying their initial properties. For example, it can make parts stronger and more resistant to wear, or improve their ductility, i.e. their ability to deform without breaking.
Heat treatment of metals takes place in a furnace, where they are heated to a specific temperature in a controlled atmosphere or vacuum, giving the metal the desired properties. This process is used in most industrial sectors: aeronautics, automotive, high-precision industries, etc. It applies to steel, stainless steel, as well as iron, copper, titanium and aluminum alloys, generally in the form of a layer.
Metal heat treatment cycle: the case of quenching
The heat treatment cycle for metals comprises three phases: temperature rise, temperature maintenance and cooling. The process then involves influencing time, medium, atmosphere and temperature.
Once installed in the furnace, the metal parts to be transformed are first subjected to a heating phase, then maintained at a certain temperature and cooled more or less rapidly.
The gaseous atmosphere can also be neutral or reactive if it contains carbon or nitrogen. The cooling phase can also take place in a vacuum, water, salt bath or oil, depending on the material.
Metal heat treatment techniques
Among the most common methods of transforming metals through temperature changes are quenching, annealing and tempering. Each serves a specific purpose, from modifying the physical appearance of a part to improving its resistance to wear.
Metal hardening techniques
The best-known hardening methods are quenching and tempering.
In the case of hardening by quenching, the part is first heated and then cooled at a defined rate by immersion in water, oil or exposure to a gas. This technique considerably hardens the metal, but does not affect its ductility.
This stage is sometimes supplemented by tempering. In this case, the part is heated in one or more phases, held at a given temperature for a given time and then cooled in a special way. As the name suggests, tempering takes place after a hardening operation.
Other methods for hardening metal include case-hardening, carbonitriding, nitriding and nitrocarburizing. Some complementary operations are carried out at low temperatures, down to -150 degrees, using liquid nitrogen in cryogenic cells.
Machinability and part appearance modification techniques
Metal heat treatment can also be used to improve the machinability or appearance of metal parts. Other techniques are used, such as annealing or hyperquenching for stainless steels.
In the first case, the metal is heated to between 450 and 1,100 degrees Celsius, held at this temperature for a certain period of time and then cooled more or less rapidly, thus influencing its shape.
Hyperquenching implies faster cooling, but also allows us to influence the appearance of the part and its resistance to corrosion.
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All about surface treatment
What is a surface treatment?
Surface treatment involves applying a technique to modify the surface properties of materials, whether metals or other industrial materials. The process can be used to improve resistance to corrosion or wear, or to modify the appearance of parts. Metal surface treatment can include a variety of techniques, such as electroplating or the application of specific coatings, improving the durability and performance of components. In industry, metal treatment is essential to extend the life of parts and ensure their proper functioning in demanding environments.
What types of surface treatment are available?
There are several types of surface treatment for modifying the properties of materials. Among the most common surface treatments is electrolytic treatment, which involves applying a protective coating via an electric current. Hot-dip galvanizing is another popular method of protecting metal against corrosion. Chemical treatment, often used to improve wear resistance, includes processes such as phosphating. Industrial painting and surface hardening are commonly used to modify the appearance or hardness of part surfaces.
How does a surface treatment work?
The surface treatment process begins with careful preparation of the workpiece. This usually includes cleaning, degreasing and even pickling to remove any impurities that might hinder the adhesion of the treatment. Once the surface is ready, the treatment is applied according to the chosen method, be it coating, electrolytic or chemical. Treatmentapplication varies according to the type of protection required, but always guarantees improved part properties, whether in terms of corrosion resistance, wear resistance or aesthetic modification.
