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Hybrid surface treatment technology for increase of hot forging dies

Smolik J. A.

Archives of Metallurgy and Materials

2012

Vol. 57, iss. 3

657-664

Hot working dies are influenced by three main factors causing their destruction: the cyclically changeable mechanical loads, intensive thermal shocks, as well as intensive friction, and erosion. Modification of surface properties with the use of hybrid plasma methods seems to be an effective way of improving its durability. The best known and widely used surface treatment hybrid technology is a combination of the nitriding process with the deposition of hard antiwear coatings by means of PVD methods. The designed composite layer "nitrided layer / Cr-CrN" was obtained with the use of the hybrid technology, which consist of ion nitriding followed by arc-evaporation coating deposition. The maintenance testing was performed on the forging dies employed for production of various parts in the automotive industry. The best durability was obtained for the dies used for the forging of rolling bearing tracks. In comparison with the durability of the dies subjected solely to the gas nitriding, nearly an increase of 600% in the durability was noticed.

W procesie obróbki plastycznej na gorąco matryce kuźnicze narażone są na działanie trzech głównych czynników niszczących: cyklicznie zmiennych obciążeń mechanicznych, intensywnych szoków cieplnych oraz intensywnego tarcia i erozji. Jednym z najbardziej efektywnych sposobów zwiększania trwałości matryc kuźniczych jest modyfikowanie właściwości warstwy wierzchniej matryc hybrydowymi technologiami obróbki powierzchniowej. Najbardziej znana i jednocześnie najbardziej rozpowszechniona technologia hybrydowa jest połączenie procesu azotowania z osadzaniem twardych powłok o charakterze przeciwzużyciowym metodami PVD. Wybrana do badan warstwa hybrydowa typu "warstwa azotowana/powłoka Cr-CrN" została otrzymana z wykorzystaniem technologii hybrydowej będącej polaczeniem procesu azotowania jarzeniowego oraz nakładania powłok metoda odparowania łukowego. Testy eksploatacyjne zostały przeprowadzone z wykorzystaniem matryc kuźniczych wykorzystywanych w produkcji różnych elementów dla przemysłu samochodowego. Najlepsza trwałość uzyskano dla matryc wykorzystywanych w procesie kucia bieżni łożysk tocznych. Opracowana hybrydowa technologia obróbki powierzchniowej umożliwiła uzyskanie blisko 6 krotnego wzrostu trwałości matryc kuźniczych, w porównaniu z trwałością matryc standardowych poddawanych jedynie procesowi azotowania.

The wear mechanism of hybrid layer “PN+CrN” during the hot forging process

Smolik J. A.

Journal of Achievements in Materials and Manufacturing Engineering

2011

Vol. 49, nr 2

215--223

Purpose: One of the most perspective development directions of surface engineering is related to hybrid technologies, which best fulfil the expectations of the industry concerning the obtainment of adequate properties of the surface of tools and machine components. The best known and widely employed hybrid technology of surface treatment using the diffusion phenomenon is the combination of gas nitriding or plasma nitriding (PN+CrN) followed by the deposition of hard, wear resistant coatings by the PVD methods. In this paper the wear mechanisms of forging dies, covered with the PN+CrN hybrid layer were analysed. Design/methodology/approach: The hybrid layers PN+CrN selected for testing were obtained by means of a multi-stage technology of surface treatment encompassing plasma nitriding (PN) and arc-evaporation process. Maintenance tests were conducted at Institut für Umformtechnik und Umformmaschinen in Hannover, according to different forging time. Findings: It was demonstrated that the dominating mechanisms of the wear process of forging dies covered with the PN+CrN hybrid layer are: thermo-mechanical fatigue of the CrN coating and thermo-mechanical fatigue and plastic deformation of steel substrate. Research limitations/implications: The CrN coating is of great importance in the wear process of forging dies covered with the PN+CrN hybrid layer. Very important in the die wear process is the resistance of the CrN coating to brittle cracking. CrN coating reduces, and as a result significantly limits, stresses initiated in the substrate in the forging process by the operation of external impacts. According to the results of simulation tests, 3 μm-thick CrN coating limits stresses initiated in material and hence reduces the possibility of plastic deformation occurrence in substrate. Practical implications: The obtained results of the tests have been practically applied in the surface engineering laboratory to develop modern surface engineering solutions aimed at increasing the effectiveness of different hybrid layers PN+CrN. Originality/value: In order to ensure the required level of effectiveness of the use of layered composites of the PN+PVD type to increase the durability of forging dies, it is necessary to properly select the composites on the basis of the analysis of the intensity of forging dies wear mechanisms.