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Neu-Ulm, Germany

Klumper-Westkamp H.,Stitung Institute For Werkstotechnik | Gaus J.-H.,Nabertherm GmbH | Bischof S.,ROHDE Schutzgasofen GmbH | Rohde J.,ROHDE Schutzgasofen GmbH | Winter K.-M.,Process Electronic GmbH
HTM - Journal of Heat Treatment and Materials

Plasma nitriding and nitrocarburizing has been established in industrial production since many years. his thermochemical surface treatment is applied to various steel components in order to enhance wear resistance, corrosion resistance and fatigue resistance. he process is done at the state of art in a pulsed discharge technique in the region of anomalous glow discharge in a conventional heated furnace. By adjusting the gas composition and plasma parameters diferent compound layers with diferent thickness, composition, hardness and morphology can be produced. Up to now applications run under constant gas and plasma parameters, which have to be investigated and evaluated before. A lot of expert knowledge and experience is necessary to get the right parameters for the production of the intended compound layer speciication and to secure the reproducibility. Further inluencing aspects on the compound layer formation as batch size, batch surface, batch cleanliness, jigging, temperature distribution, cleanliness and leak rate of the plant are diicult to take into account and can cause large deviations. To overcome these disadvantages a new concept for controlled processing is developed. Investigations in analyzing the exhaust gas of the plasma nitriding process gas showed a signiicant amount of ammonia, although no ammonia is added to the process. Based on process gas analysis together with plasma process parameters and thereof derived speciic characteristic numbers a closed loop control for deined nitriding and nitrocarburizing of well deined layer characteristics is invented. Source

In recent years, nitriding and nitrocarburizing have gained more and more importance in the heat treatment of components. While only a few years ago, it has been common to perform these processes with fixed set temperatures and gas flows, today so-called potential control became state of the art. Consequently, besides appropriate temperature uniformity nowadays also permissible tolerances in atmosphere potential control are required. The article uses the example of the American aerospace specifications SAE AMS2759/10 and 2750D on the extent to how the therein required tolerance bands allow for staying within the specified tolerances of e.g. compound layer thickness. Intensive experiments were conducted using pure iron, carbon steels AIS11018 and 1070, the high-tensile steel AISI4140 and the hot work tool steel AISIH13, where potentials and temperatures have been varied over a wide range in order to make qualified conclusions. Source

Zurecki Z.,Air Products and Chemicals Inc | Winter K.-M.,Process Electronic GmbH
ASM International - 27th Heat Treating Society Conference 2013

Due to the absence of oxygen-containing gas components, nitrogen-based atmospheres offer a low-cost alternative to the case hardening treatments typically carried out using vacuum furnaces and, in several local economies, may cost less than the traditional atmospheres. When activated at the furnace inlet with electric plasma, nitrogen mixed with just a few percent of hydrocarbon, e.g. methane or propane, is effectively carburizing, and nitrogen mixed with ammonia and some hydrocarbon can be used to carbonitride lean steels within the high, austenitic temperature range, as well as nitride stainless steels in the low-temperature ranges. While offering quality advantages such as intergranular oxide-free cases, critical for non-machined surfaces or diverse near net shape products, the nitrogen atmospheres are non-equilibrium, i.e. require different sensing and process control techniques than the endothermic or methanol atmospheres. This paper provides an update on recent developments concerning process control of nitrogen-based carburizing atmospheres. Copyright © 2013 ASM International®. All rights reserved. Source

Winter K.-M.,Process Electronic GmbH | Hoja S.,IWT - Foundation Institute of Materials Engineering | Klumper-Westkamp H.,IWT - Foundation Institute of Materials Engineering
HTM - Haerterei-Technische Mitteilungen

The process of gaseous nitriding is considered to be fully controllable by temperature and the nitriding potential. Most of the commercially used control systems are based on the Lehrer Diagram showing the relation between nitrogen-iron phases, temperature and the partial pressure ratio of ammonia and hydrogen. This is also reflected in the measuring equipment used to determine the nitriding potential. Lehrer's phase diagram was created out of the reactions between set gas mixtures of ammonia and hydrogen and pure iron powder. In industrial nitriding cycles, dealing with real materials and real parts, the results often do not match the expectations. This paper will try to explain the parameters that have to be taken into account and how to measure, set and control the nitriding and carburizing potentials by giving an overview of the available equipment. © 2012 Carl Hanser Verlag, München. Source

Winter K.-M.,Process Electronic GmbH
Journal of Materials Engineering and Performance

Recent research projects show that retained austenite, if stabilized by nitrogen, has a positive influence on the fatigue strength of work pieces. The combined diffusion profile of carbon and nitrogen applied in a carbonitriding process plays a major role, besides the process temperature. Yet today, only the carbon potential is somehow controlled and even this is not easy to achieve. This paper will present a new system able to measure and control both the carbon potential and the nitrogen potential independently. The knowledge of the activities of nitrogen and carbon in iron and the effect of alloying elements on such activities as well as the solubilities offers a way to apply the potentials on real steels. © 2013 ASM International. Source

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