Indian Journal of Engineering & Materials Sciences

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Vacuum Oxy-nitro carburizing of tool steels: structure and mechanical reliability


Affiliations
1 Deptartment of Material Science and Technology, University of Ruse A. Kanchev, 8 Studentska Str., 7017 Ruse, Bulgaria
2 Metallurgical and Materials Engineering Department, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
3 Fraunhofer Institute for Material and Beam Technology, IWS, Dortmunder Oberflächen Centrum DOC, 44145 Dortmund, Germany

AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using “phase diagram” module of FactSageto predict the steels’ phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe3O4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance.
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  • Vacuum Oxy-nitro carburizing of tool steels: structure and mechanical reliability

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Authors

Maria Nikolova
Deptartment of Material Science and Technology, University of Ruse A. Kanchev, 8 Studentska Str., 7017 Ruse, Bulgaria
Danail Nikolov
Deptartment of Material Science and Technology, University of Ruse A. Kanchev, 8 Studentska Str., 7017 Ruse, Bulgaria
Emil Yankov
Deptartment of Material Science and Technology, University of Ruse A. Kanchev, 8 Studentska Str., 7017 Ruse, Bulgaria
Bora Derin
Metallurgical and Materials Engineering Department, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
Slavcho Topalski
Fraunhofer Institute for Material and Beam Technology, IWS, Dortmunder Oberflächen Centrum DOC, 44145 Dortmund, Germany

Abstract


AISI H10, H11, H21, and D2 have been vacuum oxy-nitrocarburizing at 570 °C in cycling gas flow manner. Metastable diagram calculations belonging to Fe-N-C and Fe-N-C-X systems (X = Cr, Mo, W), have been performed by using “phase diagram” module of FactSageto predict the steels’ phase compositions. The reactive diffusion of both N and C into the tempered martensite has been discussed on the base of different chemical composition, size, and distribution of phases in the microstructure. The compound layers consisted mainly of not pre-saturated and poreless ε-carbonitride and magnetite (Fe3O4). In D2 steel, nitrogen diffusion caused a complete transformation of the primary carbides in 50 μm depths from the surface affecting the growth of grain boundary carbides. In contrast to the sharp compound/diffusion layer interface of H10, H11, and D2 steels, in H21 carbon and nitrogen were deeply absorbed in the diffusion layer while chromium strongly increased underneath the surface. The vacuum process enhanced the hardness and decreased the friction coefficients down to 0.13-0.15 at 100 N normal load for all samples. Since the compound layer thickness was relatively small for all tool steels, the phase composition and structure of the diffusion layers were found to be crucial for the scratch wear performance.