As the name suggests, sulfonitriding is a heat treatment based on sulfur and nitrogen. The addition of the first element gives treated parts greater resistance to friction, in addition to the properties naturally conferred by nitriding. Widely used in the automotive and screw industries, this process can be further enhanced by the addition of carbon. This is known as sulfonitrocarburizing.
Sulfonitriding: sulfur-doped nitriding
Sulfonitriding is above all based on nitriding, a well-known surface heat treatment which consists of diffusing nitrogen atoms onto parts to improve their resistance to wear, fatigue or abrasion. This operation can take place in different media: ionic, liquid or gaseous. If vacuum technology is used, this ensures perfectly clean parts at the end of the treatment, with no need for reworking - another major advantage of this method.
In sulfonitriding, nitrogen is combined with sulfur to enhance other properties of the steel. This operation generates iron sulfides on the surface. These have excellent tribological properties, i.e. they give parts high resistance to friction. Sulfonitriding is therefore more resistant to friction and wear than simple nitriding.
For a more complete treatment, sulfonitrocarburation
The sulfonitriding process can be even more complete when a third chemical element is added: carbon. This is known as sulfonitrocarburizing. The addition of carbon atoms to sulfur and nitrogen improves anti-friction and wear properties. As a result, this technique considerably enhances steel's resistance to seizing. After this treatment, the parts are more resistant to wear, fatigue, friction and seizure. As a result, sulfonitrocarburizing is often referred to as a multifunctional treatment.
Sulfonitrocarburizing can be carried out in salt baths, under vacuum or under plasma. In the latter case, Thermi-Lyon has its own treatment, Trionic 100 R. This technique offers many advantages, not least of which is the ability to deliver perfectly clean, finished parts without the need for reworking.
Environmentally-friendly heat treatment
Ion or plasma treatments have no impact on parts, in the sense that they cause little or no deformation and produce no residues to be cleaned up. The result is finished parts that can be used directly after treatment. In addition to this advantage, this method is also more respectful of the environment. Nitrocarburizing or sulfonitrocarburizing, for example, requires a relatively low temperature of 570 degrees Celsius, so requires less heating and consumes less energy overall. Insofar as the treated components do not require re-machining, this choice not only saves resources, but also time and money for customers. It's an ideal solution for shorter, simpler ranges.
Examples of sulfonitrocarburizing applications
Sulfonitrocarburizing is particularly effective for parts subject to high friction and in environments prone to seizing. Many professionals choose this treatment to reinforce the resistance of their parts, particularly in the building and civil engineering sector.
Construction crane masts, for example, are stacked and interlocked. When cranes are assembled and dismantled, these components must slide extremely smoothly. In addition, to lock the masts in place, pins are inserted into the bores of the brackets. As it seems rather difficult, and above all perilous, to coat the pins with oil or grease to facilitate crane dismantling, sulfonitrocarburizing appears to be an ideal solution. This method ensures that the pins slide smoothly in the joint bores, and a treatment such as Trionic 100 R greatly reduces the risk of seizure.
This type of treatment is extremely useful when it comes to screws and bolts. Screws or nuts that have been in place for a long time in certain tapped holes often end up rusting and, ultimately, seizing up. Removing them from their place then entails a significant risk of breakage. A treatment such as sulfonitrocarburation facilitates unscrewing and prevents this problematic seizing.
Sulfonitriding is a surface heat treatment based on the diffusion of sulfur and nitrogen atoms. The combination of these two chemical elements results in the formation of iron sulfides and nitrides, giving parts greater resistance to wear and friction. This process can be further enhanced by the addition of carbon, known as sulfonitrocarburizing. This solution also enhances the anti-seizing properties of steel, making it an ideal treatment for screws or masts on site cranes, for example, which present a high risk of seizing.
