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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 | Year: 2013

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

Clausen B.,Stitung Institute For Werkstotechnik | Hofmann F.,Stitung Institute For Werkstotechnik | Zoch H.-W.,Stitung Institute For Werkstotechnik
HTM - Journal of Heat Treatment and Materials | Year: 2013

Due to the special mechanical properties of carbonitrided surfaces containing martensite and nitrogen stabilized austenite, carbonitriding is of increasing interest to industry. he interaction of carbon and nitrogen in the reactive atmosphere calls for tedious pre-trials, if deined nitrogen and carbon depth proiles are required. However, the results of pre-trials carried out at one furnace, are not applicable to other furnaces and oten cannot even be employed reproducible to the same furnace if other processes are carried out in between. Practical experience implies strong conditioning and memory efects in the furnaces, depending on the furnaces refractory material. In this paper the atmosphere changes in long term carbonitriding processes in a furnace with refractory lining are presented. From the gas composition the carbon and nitrogen levels are calculated and compared to the results obtained at thin iron foils. Short term and long term conditioning efects are visualized. he results show that through calculation the processes are suiciently good described and how a control of carbonitriding processes is possible. © 2013 Carl Hanser Verlag, München. Source

In order to adjust speciic properties like strength and the amount of retained austenite, bearing steels are normally quenched and tempered at diferent temperatures. Martensitic steels are characterized by high strain hardening (dissolved carbon; ine microstructure). However, martensite shows comparatively low plasticity. Austempering could be an alternative heat treatment for these steel qualities. For diferent steels, the TRIP efect (Transformation Induced Plasticity) is used to increase strength with suicient ductility. These beneicial material properties are based on the deformation induced transformation of austenite into martensite combined with an increase in volume. From first reports in the literature concerning the behavior of these steels during cyclic loading it can be expected that the fatigue behavior will also be positively afected by the TRIP efect. In material areas that are subjected to high stress, increased strain hardening and high compressive residual stresses will result from the martensitic transformation. Both represent an additional resistance against crack propagation. An adequate proportion of metastable retained austenite is an essential requirement for using the TRIP efect Therefore the alloying concept and the heat treatment have to be harmonized among each other. By alloying with silicon and aluminum, carbide precipitation is retarded during soaking in the temperature range of martensite and bainite transformation, respectively. In this phase of the heat treatment cycle austenite is stabilized due to an enriched carbon content, which in addition suppresses the martensite transformation during cooling to ambient temperature. So modiied bearing steels appear to be potential candidates for using the TRIP efect. Source

Bischof S.,Stitung Institute For Werkstotechnik | Klumper-Westkamp H.,Stitung Institute For Werkstotechnik | Hofmann F.,Stitung Institute For Werkstotechnik | Zoch H.-W.,Stitung Institute For Werkstotechnik
HTM - Haerterei-Technische Mitteilungen | Year: 2012

Carbonitriding is a thermo-chemical surface treatment. It is applied increasingly to steel components to improve the mechanical properties and adjust them to the expected load while reducing the weight. he developed carbonitriding system consisting of a set of sensors and a closed loop for controlling the carbonitriding atmosphere composition facilitates reproducible results according carbon and nitrogen depth proiles independent of furnace type, furnace condition or furnace load. he nitrogen potential is controlled by measuring the residual ammonia content in the exhaust gas and the carbon potential is controlled by an oxygen probe with respect to decreased carbon monoxide content during ammonia addition. © 2012 Carl Hanser Verlag, München. Source

Hoja S.,Stitung Institute For Werkstotechnik | Klumper-Westkamp H.,Stitung Institute For Werkstotechnik | Epp J.,Stitung Institute For Werkstotechnik | Hofmann F.,Stitung Institute For Werkstotechnik | Zoch H.-W.,Stitung Institute For Werkstotechnik
HTM - Haerterei-Technische Mitteilungen | Year: 2012

In order to resist to high loads in hot massive forming, the surfaces and boundary areas of the used tools are nitrided. High residual compressive stresses are induced in the near surface region during nitriding. But also the conditions of surface inish lead to residual stresses, which are only partially relieved during nitriding of the creep resistant steel X38CrMoV5-3. he presented investigations concern residual stress measurements of samples with diferent surface inishes. he compressive and tensile stresses, which result from surface inish, do not relieve during nitriding of the hot working steel. Compressive stresses of up to -1000 MPa were measured ater nitriding. © 2012 Carl Hanser Verlag, München. Source

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