Plasma Nitriding

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.

NITRIDING & NITROCARBURISING TECHNOLOGIES

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.

PROCESSES – PLASMA NITRIDING & NITROCARBURISING

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.

EQUIPMENT

Overall dimension of vacuum chamber, mm: Ø 1360 х 1800
Overall dimension of vacuum chamber, mm: Ø 1360 х 1800
Max. weight of tool for processing: 1000 kg
Working gases: nitrogen, hydrogen, propane, argon
The whole process is completely computerized and authomatised

ADVANTAGES

Advantages of Plasma Nitriding compared with gas nitriding:

The cycle times for nitridable steels are typically one third to a half of conventional gas nitriding, thereby reducing operating costs
Reduced distortion because plasma nitriding is performed under a vacuum
Masking with simple mechanical masks and dispensing of finish grinding improve productivity
Improvement in metallurgical properties often enabling cheap materials to replace costly ones of lower cost is another attraction
Hard wear resistant surfaces can be generated without brittleness or causing galling usually associated with conventional nitriding
It can provide uniform case on complex geometry
High flexibility of the process
High grade of automation
No porous zone in the compound layer
The results of the process are very good reproducible
Determination of the layer structure
Less roughing of the surface
Possibility of using low process temperatures (below the tempering temperature)
Optimized dimensional stability
Easy removing of passivated surface layers on high chromium-alloyed steels by sputtering (surface activating)
Possibility of partial nitriding
Since the process is free of toxic salts or toxic gases, it is clean and environmentally friendly.

Advantages of plasma nitriding compared with chroming:

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.

PLASMA NITRIDABLE MATERIALS

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.

PROPERTIES

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:

high surface hardness
high resistance to adhesive wear
reduction of the friction coefficients
increase in corrosion resistance
high temperature strength (up to 500 °C)
high resistance to abrasion
good dimensional and shape accuracy
aesthetically pleasing finish
improvement in bending fatigue resistance

APPLICATIONS

Nitriding and nitrocarburising are functional treatments for various components in many industrial sectors:

mechanical engineering in general
valves and fittings
the automotive sector
fastening technology
mining
printing machinery construction
railway technology
electronics/electrical engineering
domestic appliances
hydraulic and pneumatic industry
medical technology
textile machinery construction
defence technology
tool manufacture
cement industry
plastics processing moulds
aluminium forming pressure casting dies, extrusion dies
paper manufacturing and recycling
plastics recycling etc.

TIPS FOR PLASMA NITRIDING TECHNIQUE

The tools and components should be metallic shining and free of oxidation and corrosion
The bores must be free from lubrication and cooling liquids, lacquers or plastic residue
For the partial nitriding please attach a drawing where you please indicate, which parts have to be nitrided
In your order you should mention the tensile strength and the lowest tempering temperature
Please indicate the exact description of the material and the requested nitride case depth.
Please use brazing filler metal only with melting temperatures above 800°C
Already at an angle of < 90 ° the edges are bulging

SPECIAL TREATMENTS – OXYNITRIDING & OXYNITROCARBURISING

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.