GAS NITRIDING
CONVENTIONAL AND LOW-PRESSURE NITRIDING
Nitriding is a process that involves the creation of a hardened surface layer through the formation of nitrides.
The nitriding process is intended for special grades of steel that contain nitrogen-forming elements such as chromium, molybdenum, or vanadium, which have been previously subjected to appropriate heat treatment. However, hardened layers with varying properties can be produced on almost all steels.
GAS NITRIDING
After these processes, a thin layer of nitrides, not exceeding a total thickness of 0.6 mm, forms on the surface of the metal. This layer contains nitrides and iron nitrides and/or nitrides of other elements.
This layer has several highly desirable properties. First and foremost, it is very hard, and its resistance to corrosion and abrasive wear is much higher than that of ordinary steel.
We offer conventional nitriding as well as regulated low-pressure nitriding in deep furnaces.
In all gas nitriding processes, the nitrogen source in atomic form, obtained for the diffusion saturation of the surface layers of steel objects, is ammonia dissociating catalytically on the surface of the treated charge.
Process flow
Gas Nitriding Process
Gas nitriding is carried out under conditions of dynamic ammonia flow (or a gas mixture containing ammonia) through a retort. Some of the nitrogen atoms acquired on the surface of the steel as a result of the reaction recombine into diatomic molecules, return to the atmosphere, and then exit the retort along with the exhaust gases. The remainder of the nitrogen is absorbed by the steel substrate.
The entire process occurs in a gas environment using ammonia and involves ensuring the proper thermodynamic activity of the nitriding atmosphere.
During the entire process, two main processes occur:
Ammonia dissociation
This is the breakdown of molecules of ammonia gas heated to a temperature above 450°C, resulting in the release of active nitrogen atoms.
Absorption
This refers to the absorption of nitrogen into the steel, where it reacts with iron and other elements to form nitrides. This process is accompanied by core diffusion of metallic elements.
Modern, regulated gas nitriding processes are carried out using atmospheres consisting of mixtures of ammonia with hydrogen and/or nitrogen. Our advanced technological equipment for performing regulated gas nitriding continuously adjusts the nitrogen potential (composition of the ammonia – nitrogen – hydrogen mixture) throughout the entire process, based on computer-controlled regulation of the dynamic growth of the individual zones of the nitrided layer.
Application of Nitriding
Nitriding is used for structural and tool components exposed to abrasive wear and corrosion during operation, such as engine and pump parts in the shipbuilding, aerospace, and automotive industries, tools for plastic working and cutting, and elements of extruders and injection molding machines.
The basis for controlling the nitrogen saturation of surface layers in the vacuum nitriding process is a compromise between the increasing nitrogen potential of the atmosphere and the decreasing adsorption of ammonia molecules on the surface as the pressure of the processing atmosphere is reduced.
The combination of high mechanical properties of vacuum-nitrided layers makes this technology particularly suitable for surface hardening of machine components used in conditions conducive to contact fatigue – in rolling, rolling with slip, or sliding friction. Examples of applications include heat-treated gears, crankshafts, camshafts, shaped couplings, and spline surfaces, among others.
Low-pressure nitriding can also be applied to cutting tools, various types of dies, punches, and molds. Creating a hard, yet non-brittle nitrided layer on these tools and devices leads to a significant increase in their durability.
Max. working chamber size for gas nitriding:
We offer the execution of gas sulphonitriding processes in pit furnaces with a maximum load capacity of 1800 kg gross, and the working chamber size is as follows.
Nitriding, gas sulphonitriding, tempering, aging, and annealing in a pit furnace:
h = max 1900mm
r = max 1000mm
