On this market, many customers are looking for the qualified nitriding process for stainless steel parts. As a result of many factors, several commercial heat treaters stated their capabilities to provide this service, but usually were not satisfied by the customers in terms of uniformity, and reliability.

Nitriding of stainless steel has been supposed as niche process and curiously requested by many customers. SAMT is going to provide the qualified process to this market by our thermal processing service by either the independent or the cooperative with commercial heat treater.

The rules applying to nitriding of stainless steel or refractory alloys are no different than those for the other groups of steels, with one exception. The exception is the proprietary de-passivation stage that allows for a removal of oxides of alloying elements such as Cr, Ni and others which, if not removed, will effectively block the nitriding process. The same way they block the rust formation on the stainless steel surface.

All types of stainless steel can be nitrided. The martensitic, austenitic or PH materials inclusive.

ONE REVOLUTIONARY TECHNOLOGY FOR NITIRIDING PROCESS
A classic cold wall plasma nitrider represents a reliable technology that has proved itself. It is right that this technology is not very easy to handle. It is evident to an operator that all the parts do not achieve a uniform temperature. Hollow cathodes, local overheating & arcing are all on the agenda.

Active Screen Nitriding Process (ASPN)
With active screen nitriding process, the parts to be nitrided are no longer directly exposed to the plasma.

The process using the "Active Screen " technology has both the advantages of the cold wall and the hot wall technology and a unique trump card, which distinguishes this technology from all the others known up to date:

Functions of the "Active Screen"

The illustration shows the "Active Screen", which is installed inside a fourfold heat shield. It constitutes the hot wall of the vessel and surrounds all parts to be nitrided.

The Active Screen has two roles to play:

Firstly, the Active Screen is heated by the plasma and then evenly transmits heat to the parts (radiation heat). The heating is done inside the chamber. Secondly, the "Active Screen" produces all necessary active and neutral particles necessary to nitride steels, titatium and its alloys TO take the best advantage of the nitriding gases they are introduced to the vacuum chamber at strategically correct places. The pumping of the gases is done in a way to ensure a gentle flow of the gases over the parts.

A serious earning in the economical field

As the parts are no longer directly exposed to the plasma all previously listed problems are avoided. It has become easy to nitride mixed loads. The different geometry of the parts as well as their weight do no longer matter. Even different steel grades can be nitrided together. It is no longer necessary to close all holes unless one really wants to prevent them from being nitrided.


Equipment
Parts to be treated are placed on the central worktable and are maintained at floating potential. Current is supplied to the metal screen that surrounds the work pieces ; it therefore constitutes the cathode of the furnace.

Radiation from this screen provides the heat that brings components to the required temperature for treatment. Gas is introduced between the furnace walls (earthed) and the screen by means of several injection conduits, distributed over the entire inner surface of the furnace, therefore producing blanket coverage of the grid. The plasma generated at the active screen contains a mixture of ions, electrons and other active energized neutral gaseous particles, which are able to come into contact with the parts to be treated.

The direction of gas flow has also been carefully designed to encourage the motion of these active particles through the screen towards the centre of the furnace, then down through the middle of the worktable, from where gas is pumped out. Therefore, all parts placed on the worktable are subjected to a continuous flow of plasma species towards and around them during processing, maximizing the opportunity for mass transfer of nitrogen to component surfaces. The active screen is designed to surround the entire workload and as its characteristics are fixed, the temperature of the furnace can be very closely controlled by adjusting the current provided to this screen. Therefore, a uniform temperature distribution around the components during treatment is produced, assisted by the direction of gas flow. The parts bathe continuously in a gentle flow of the active plasma species.

Components can be force-cooled post treatment, by means of the vacuum-tight electric motor and fan at the top of the chamber.

The furnace capacity can be customized in accordance with the dimension requirement of parts and load efficiency. Two stations system will help for the productivity further.