Hardening of Ferritic Corrosion-Resistant Steel by the Method of Internal Nitriding
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HARDENING OF FERRITIC CORROSION-RESISTANT STEEL BY THE METHOD OF INTERNAL NITRIDING S. A. Nikulin,1 S. O. Rogachev,1 V. M. Khatkevich,1 and A. B. Rozhnov1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 9 – 12, July, 2013.
Possibility of hardening of ferritic stainless steel 08Kh17T by the method of high-temperature internal nitriding is considered. Results of studies of the microstructure and mechanical properties of nitrided steel at test temperatures ranging from 20 to 700°C are presented.
Key words: internal nitriding, ferritic corrosion-resistant steel, dispersion hardening.
Test pieces in the shape of “blades” with length 165.0 mm and width and thickness of the functional part 6.0 ´ 0.5 mm (Fig. 1) were cut from a sheet using an electric erosion wirecutting mill FANUC ROBOCUT 0iD with CNC FANUC Series 310is-WA numerical control. This equipment provided a high-quality surface of the test pieces after the cutting, namely, a roughness Ra = 0.07 mm. The pieces for the tensile tests had special protrusions for fastening an extensometer. We tested three pieces per point. Internal nitriding was performed in a quartz reactor in an atmosphere of pure nitrogen.
INTRODUCTION Today nitriding is an effective and widely applied method for hardening steels and alloys [1]. As a rule, nitriding is used for raising the combination of properties of the surface of parts due to formation of a surface nitride layer possessing a high hardness and wear resistance. In contrast to the traditional nitriding process internal nitriding is aimed at raising the properties of the whole of the volume of the material. During high-temperature internal nitriding the formation of a layer of nitrides on the surface is suppressed. The zone of internal nitriding is represented by fine particles of thermodynamically stable nitrides distributed in the matrix, which stabilize the structure at elevated temperatures providing effective dispersion hardening of the material [1 – 9]. It is known that high mechanical properties stable for a long time at high temperatures and stresses can be obtained in steels (including corrosion-resistant ones) by combining solid-solution hardening with hardening by particles of a second phase (intermetallics and carbides) in an iron-base matrix [10, 11]. The aim of the present work was to study the structure and properties of steel 08Kh17T after hardening it by the method of high-temperature internal nitriding.
125.0
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METHODS OF STUDY We studied steel 08Kh17T of the following chemical composition (in wt.%): 0.08 C, 18 Cr, 0.8 Ti, 0.5 Si, 0.8 Mn, 0.025 S, 0.035 P. 1
National University of Science and Technology “MISiS,” Moscow, Russia (e-mail: [email protected]).
Fig. 1. A drawing (a) and appearance (b ) of rupture specimens.
351 0026-0673/13/0708-0351 © 2013 Springer Science + Business Media New York
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We compared the properties of steel 08Kh17T in three condition
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