Evolution of the dislocation structure of corrosion-resistant steel in the process of plastic deformation
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EVOLUTION OF THE DISLOCATION STRUCTURE OF CORROSION-RESISTANT STEEL IN THE PROCESS OF PLASTIC DEFORMATION I. Yu. Nahorna and V. Yu. Ol’shanets’kyi
UDC 621.73.143: 669.14.018.8
The microstructure of steels is characterized by the distributions of hardening phases, nonmetallic inclusions, and other inhomogeneities [1] directly connected with the behavior of dislocations and their multiplication. For practical purposes, it is important to establish relationships between the microscopic characteristics of materials (density of dislocations, mean free path, the degree of concentration of phases, etc.) and their macroscopic characteristics. Strain hardening affects the technological characteristics of metallic materials (e.g., their stamping index [2]) and is connected with the distribution of density of dislocations [3] and their behavior. The degree of hardening is determined by the mean free path of dislocations from the sources to barriers (boundaries, submicroscopic precipitations, dislocation pileups, etc.) whose distribution is essentially stochastic. However, the number of works devoted to the investigation of this problem is relatively small (see, e.g., [1, 4]) and, as far as we know, the works devoted to the stochastic analysis of the free paths of dislocations are absolutely absent in the literature. The most widespread model of the evolution of dislocations in the process of plastic deformation is based on the hypothesis of permanent mobility of dislocations [5] whose behavior is strongly affected by structural inhomogeneities (first of all, by particles of precipitations whose number is characterized by the concentration coefficient). For particles of the hardening phase, the concentration coefficient was experimentally measured as the ratio y =
H1 H2
of its microhardness H1 (including the microhardness of concentration clusters) to the microhardness of structurally free ferrite H2 . As a result, for different modes of treatment, we obtain the following values of this coefficient: 1.2, 1.0, and 1.4. In the present work, we make an attempt to establish the law of distribution of the free paths of dislocations depending on the concentration of structural inhomogeneities for 03Kh18TBch chromium corrosion-resistant ferrite steel. Steel specimens were subjected to thermal and thermomechanical treatment in order to model different structural states [4]. Stochastic Model of the Behavior of Dislocations Our aim is to establish the relationship between the mean free path and density of dislocations [5]. Assume that the density of dislocations permanently increases due to their multiplication caused by the appearance of new inhomogeneities, which fix some dislocations and transform them into acting sources. To take into account the influence of inhomogeneities, we introduce a special coefficient y. It is assumed that the density of dislocations (and, hence, the number of sites of fixed dislocation segments acting as Frank–Read sources under loading) Zaporozhye State University, Zaporozhye; Zaporozhye National Tech
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