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Heat Treatment of Metal Surfaces

Heat Treatment of Metal Surfaces How nitrogen makes steel especially hard

Ever more cost-effective production, but without compromising quality; ever higher legal and social requirements; ever greater customer demands for environmentally friendly and sustainable products: the metalworking industry is facing many challenges.

With the BALITHERM product family, Oerlikon Balzers offers thermochemical heat treatment processes such as nitriding and nitrocarburizing in gas and plasma. These are environmentally friendly alternatives to treatments such as hard chrome plating or salt bath nitriding and, depending on the process and material, allow hardnesses of up to 1,100 VHN*.

* VHN = Vickers Hardness Number. For comparison: quartz has a similar hardness of 1,120 VHN and can scratch window glass. A diamond has 10,060 VHN.

In these processes, the diffusion of nitrogen into a surface creates improved mechanical and chemical resistance properties for the functional surface. In other words: no coating is applied, but instead, the material itself is given a higher surface hardness.

Plasma nitriding and nitrocarburizing are carried out using an ionized gas mixture consisting of nitrogen and hydrogen or carbon. These processes take place in a vacuum by means of low-energy plasmas and at relatively low treatment temperatures of 380–560 °C. Gas nitriding, on the other hand, takes place under atmospheric pressure using ammonia, which is split and thus serves as a donor for nitrogen and hydrogen. If the process takes place in a carbon-donating atmosphere, this is referred to as gas nitrocarburizing. Typical treatment temperatures are 430–580 °C. Gas nitriding/nitrocarburizing can be combined with plasma nitriding/nitrocarburizing and subsequent oxidation to provide excellent corrosion protection, as well.

Thanks to the individuality of the processes, we can adjust the nitriding depth and temperature
as well as the resulting surface hardness to suit the component with precision.

Bernhard Reisert, Key Account Manager Automotive Nitriding, Oerlikon Balzers

Depending on the process variant, this influences the performance and fatigue strength of the parts and components. At the same time, it increases resistance to corrosion and wear. Design measures can be used to achieve material savings and protect the components’ stressed surface zones against abrasive, adhesive and corrosive wear.

The BALITHERM solutions make it possible to adapt many parameters to customer-specific requirements: “The decision as to which process is suitable for the respective component depends on its geometry, the stress profile, the required properties and the permitted tolerances. Thanks to the individuality of the processes, we can adjust the nitriding depth and temperature as well as the resulting surface hardness to suit the component with precision and thus match customer requirements. This makes BALITHERM extremely flexible,” explains Bernhard Reisert, Key Account Manager, Automotive Nitriding at Oerlikon Balzers.

Contact

Oerlikon Balzers Coating AG; Iramali 18, 9496 Balzers, Liechtenstein

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