caa a22 4500 445844272 CHVBK 20180317145354.0 cr unu---uuuuu 170323e20111201xx s 000 0 eng 10.1007/s11085-011-9263-5 doi (NATIONALLICENCE)springer-10.1007/s11085-011-9263-5 Birol Yucel Materials Institute, Marmara Research Center, TUBITAK, Gebze, Kocaeli, Turkey aut Investigation of Isothermal and Cyclic Oxidation of Plasma-Nitrided Hot-Work Tool Steel at Elevated Temperatures [Elektronische Daten] [Yucel Birol] The oxidation of a plasma-nitrided, hot-work tool steel at temperatures that cover a range of operations from post-plasma-nitriding oxidation to steel thixoforging processing was investigated. Thermal exposure at 500°C led to the formation of a thin Fe-Cr spinel layer and an even thinner outermost layer of hematite. The former is the only oxide that grew on samples exposed to oxygen-lean conditions at 750°C. A thick, multi-layered oxide scale formed on the surface when the plasma nitrided hot-work tool steel was held at 750°C under atmospheric conditions. In this scale, the outermost hematite layer and the inner Fe-Cr spinel were separated by a magnetite layer. The oxide scale produced during thermal cycling at 750°C was also multi-layered with an identical oxide scale configuration to that formed during isothermal exposure at 750°C. The hematite layer, which retained its integrity during isothermal exposure at 750°C, suffered small cracks that were instrumental in its fracture and spallation during thermal cycling. The distinct feature resulting from cyclic oxidation, however, was the wide gap that formed along the magnetite-spinel interface. Thermal expansion mismatch produced compressive stresses which in turn led to buckling of the magnetite layer and to its detachment; while, the spinel layer adhered to the tool steel substrate and survived throughout thermal cycling. Enrichment of nitrogen and the subsequent precipitation of N2 gas were also believed to have contributed to the gap formation. Formation of such a gap poses a serious threat to the integrity of the oxide scale and was shown to be responsible for the spallation of the magnetite layer upon thermal cycling. Springer Science+Business Media, LLC, 2011 Oxidation nationallicence Plasma nitriding nationallicence Hot work tool steels nationallicence Oxidation of Metals Springer-Verlag 76/5-6(2011-12-01), 399-417 0030-770X 76:5-6<399 2011 76 11085 https://doi.org/10.1007/s11085-011-9263-5 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11085-011-9263-5 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Birol Yucel Materials Institute, Marmara Research Center, TUBITAK, Gebze, Kocaeli, Turkey aut NATIONALLICENCE 773 0- Oxidation of Metals Springer-Verlag 76/5-6(2011-12-01), 399-417 0030-770X 76:5-6<399 2011 76 11085 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer