Physical fundamentals of criterial estimation of nitriding technology for parts of friction units
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TION. WEAR UDC 621.785.53:621.891
PHYSICAL FUNDAMENTALS OF CRITERIAL ESTIMATION OF NITRIDING TECHNOLOGY FOR PARTS OF FRICTION UNITS L. I. Kuksenova,1, 2 S. A. Gerasimov,1 V. G. Lapteva,2 and M. S. Alekseeva2 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 39 – 47, December, 2012.
Characteristics of the structure and properties of surface layers of nitrided structural steels and alloys, which affect the level of surface fracture under friction, are studied. A generalized structural parameter for optimizing the nitriding process and a rapid method for estimating the quality of the surface layer of nitrided parts of friction units are developed.
Key words: nitriding, structure, structural steels and alloys, wear resistance.
layer and choice its optimum structure, which makes it possible to design nitriding regimes for parts of friction units. The aim or the present work was to develop a methodology for estimating the quality of surface layers of nitrided steels and alloys from the standpoint of their operating capacity in friction units.
INTRODUCTION Fracture of surface layers under friction is the main cause of failure of parts of standard movable joints in operation. The mechanism and the kinetics of the fracture process and the tribotechnical characteristics (the level of surface fracture, the friction factor, the ultimate carrying capacity of the joint) depend on the structure and properties of the friction surface, which change in service of the friction unit as a result of severe plastic deformation, diffusion, mass transfer, and phase transformations [1]. Recent requirements on tribotechnical structural materials determine the direction of theoretical research and methods of advancement of triboengineering. A known process promoting effective elevation of the hardness, wear resistance, fatigue life and corrosion strength is nitriding. This process is widely applied to joints fractured primarily due to friction force. In order to form a wear resistant structure by nitriding we should determine the laws describing the relation between the initial structure of the surface layer and the structure formed in the zone deformed by friction and the tribotechnical characteristics of the joint. In this connection one of the ways for advancing the nitriding process employs tribotechnical methods of estimation of the quality of the nitrided 1 2
METHODS OF STUDY We studied steels of pearlitic and martensitic classes (40Kh, 38Kh2MYUA, VKS-7), model iron-base alloys with bcc lattice alloyed with Cr, Mo and Al in an amount of up to 4 at.%, and iron-base alloys with fcc lattice alloyed with 29 at.% Ni and with Cr, Al and Ti in an amount of up to 4 at.%. Steels 38Kh2MYuA, 40Kh and VKS-7 were subjected to a standard hardening. The model alloys were annealed at 900°C for 2 h prior to the nitriding. Saturation of the surface of the steels and alloys with nitrogen was performed by the method of single- and double-stage gas nitriding. The experimental methods for studying the structure and properties
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