High Temperature Nitriding Services

High Temperature Nitriding of Stainless Steel (Solution Nitriding):

The steel used in the food sector, chemicals industry, medical technology and turbine construction sectors is often subjected to particularly high levels of wear and tear. This steel has to be both extra-hard and also highly resistant to corrosion.

Stainless steels are applied in various industries to take advantage of their corrosion resistance. Unfortunately, the most corrosion resistant are not very durable in wear or load-carrying applications. Producing a nitrogen-enriched surface layer with increased hardness and higher residual stress increases the wear resistance and load-carrying capability in addition to improving the resistance to cavitation, erosion and corrosion attack.

The strength of stainless steel can in theory be increased by alloying with nitrogen. However this cannot be done using conventional alloying techniques, as the low solubility of nitrogen in molten steel makes it difficult to add.

We offer solution nitriding which is a unique solution to this problem. Nitrogenising at a depth of 0.1 to 3 mm can be used to surface-harden both austenitic and martensitic stainless steels. The dispersion of nitrogen atoms into steel leads both to a considerable increase in strength and an improvement in corrosion resistance. The quenching process is a key part of this procedure. Steel treated with nitrogen at temperatures of between 1,050 °C and 1,150 °C is cooled so quickly that the otherwise normal precipitation of corrosion-creating nitrides does not take place.

The process technology of the solution nitriding process is comparatively simple. The process gas used is nitrogen instead of the standard nitriding gas – ammonia. Nitrogen is usually a protective atmosphere and has no nitriding capability. But at temperatures above 1050°C (1920°F), the otherwise stable nitrogen molecule dissociates at metallic surfaces into atomic nitrogen. Despite the passive chromium-oxide layer at the surface of stainless steels, the dissociated atomic nitrogen is able to penetrate the surface and produce a nitrogen pickup.

Two different process variants are available for this purpose: Solution nitriding M(SNM) & Solution Nitriding Austenitic (SNA)

The SNM process is designed, for example, for use with stainless steel roller bearings and tools used in medical technology, along with the food industry and polymer processing sector, as well as being ideal for consumable parts used in the mineral-processing, chemicals and pump-construction sectors. This variant of the process creates a hard, martensitic top layer, while preserving a tough core section.

The dissolved nitrogen provides greater resistance to corrosion, in both an acid and chloride environment.The SNA process is used for such flow related items as pumps, turbines and their corresponding valves and fittings, as it greatly increases resistance to cavitation erosion.

In these cases, the process creates a hard, tough austenitic layer that offers great resistance to surface damage caused by corrosive, hostile environments.