Fractal approach to assessment of mechanical properties of steel ST6

Abstract

Problem statement. The relevance of the work lies in the development of an approach to the rapid assessment of the mechanical properties of medium-carbon steels for general purposes in the state of factory delivery. To solve this problem, it is proposed to use the apparatus of fractal analysis, which allows you to evaluate the structural elements of various geometric complexity. Object of study. The object of the study is the fractal dimensions of structural elements of steel Ст6 in a state of factory supply and its mechanical properties. Materials and research methods. For fractal studies of the ferrite-pearlite structure of Ст6 steel, the developed and patented methodology was used. The essence of the technique is to find the convergence of the values of the fractal dimension of the structure, calculated using the point and cell methods. Fractal analysis was carried out at a 400-fold increase in the structure. Mechanical tests were carried out according to ГОСТ 535-2005. Results and its discussion. The dependencies between the tensile strength, yield strength, hardness, elongation of steel Ст6 and the fractal dimension of ferrite and perlite are obtained. A one-to-one correspondence is observed between the strength, hardness, plasticity and fractal dimension of perlite (pair correlation coefficients are fixed within 0,66…0,86). A connection was also established between the relative elongation and the fractal dimension of ferrite (r2 = 0,61...0,77). An increase in the strength and hardness of steel was recorded with an increase in the fractal dimension of perlite. An increase in the ductility of steel (elongation) was also recorded with an increase in the fractal dimension of ferrite. This may be due to the fact that equiaxed metal grains are characterized by better mechanical characteristics and have a dimension close to the topological dimension of the thin section plane 2. Conclusions. Models for predicting the mechanical properties of medium carbon steel Ст6 are obtained based on an analysis of the fractal dimensions of its ferrite-pearlite structure. The proposed approach can be considered as a methodology for the rapid assessment of the quality criteria of medium-carbon steels in the state of factory supply based on an analysis of their structure.