Nitriding and nitrocarburizing in pulse glowing discharge (pulsed plasma nitriding and nitrocarburising) are efficient methods to increase hardness and wear-resistance, corrosion resistance and durability in large cycle exploiting of metals and alloys. Basic technological advantage of nitriding technique is the low temperature at which the process is directed (450 – 600°C) resulting in partly volume deformations and piece distortions, and there is no phase change of the structure of the processed tools. Thus for all tools and parts nitrided by this method, but being made by appropriate steels, there is no need of additional treatment after the process of nitriding. Compared to gas and liquid nitriding where the working environment (gas or liquid) is insufficiently active or toxic; ion-nitriding is processed by "illumination transmission of electricity into plasma", and the process is completely environmental. Heating of parts is done directly from plasma without additional heaters.
Plasma Nitriding and Nitrocarburising are thermochemical heat treatment processes. The aim of these processes is to enrich the surface of a ferrous metals with nitrogen (nitriding) or nitrogen and carbon (nitrocarburising) in order to improve the mechanical properties of the surface of the component. Nitriding produces a hard, wear resistant layer on nitridable steels and cast iron. In addition, it considerably improves fatigue strength and by oxidizing the nitrided surface, it enhances corrosion resistance. The main advantage of nitriding and nitrocarburising over other means of surface hardening is the low process temperature (450-600°C). Components can often be nitrided in the fully hardened and tempered condition without the core properties being adversely affected. An additional advantage of the low temperature process is the low risk of distortion. Consequently the parts can be machined to final dimensions and do not need costly finishing work such as grinding or straightening after nitriding. Nitriding and nitrocarburising are mainly used for ferrous components such as valves, camshafts and piston rods in the mechanical engineering and automotive industries. Other applications are cutting tools or large forming dies. Cast iron parts, such as pump and gear houses, can also be nitrided.
Plasma nitriding normally occurs at temperatures of 450 to 600 °C in a vacuum with the aid of plasma generated by a glow discharge on the workpiece surface. A special technical feature of this process is the possibility of using mechanical masking to provide accurate partial nitriding.
The plasma nitrocarburising process is usually carried out at temperatures between 570 and 580 °C in a gas mixture that provides both nitrogen and carbon to the surface of the material. The addition of carbon to the atmosphere reduces the overall time of the nitriding process to generate a specific case depth.
Plasma nitriding meets all stringent requirements for hydraulic systems in terms of corrosion, which have been protected by chroming so far. The corrosive resistance of plasma nitriding compared with chroming is approximately the same, but with plasma nitriding are eliminated all other disadvantages of chroming, such as: brittleness, weak stroke resistance, encircling of curves, splitting, significantly smaller hardness etc.
All commonly used steel, cast and sinter materials can be treated. Non-alloy steels and low and medium-alloy steels are also suitable. High-alloy steels with over 13% chromium are only suitable to a limited extent because of their surface passivity. Nitride forming elements such as aluminium, vanadium, chromium and titanium are responsible for the increase in hardness within the diffusion zone.
The process provides abrasive wear resistance as a result of the high surface hardness achieved and also adhesive wear resistance which results from the characteristics of the compound layer and its ability to maintain a lubricant film. The following improvements in properties can be achieved with nitriding and nitrocarburising:
Nitriding and nitrocarburising are functional treatments for various components in many industrial sectors:
The result of the plasma nitriding or plasma nitrocarburising process is increased surface hardness and wear resistance, lower wear coefficient, increased fatigue resistant, ductility, increased corrosion resistant, resulting with many times increased tool life of the machine parts or tools. If during this technological process is putted O2 IN SITU on the surface are formed oxynitrides and oxynitrocarborides except nitrides or nitrocarborides which results in additional increasing of all surface characteristics mentioned above, especially the corrosion resistance. Oxynitriding and oxynitrocarburising are original plasma techniques, developed by Plasma D.O.O.