Study of the effect of carbon on the fractal dimension of steel

Abstract

Introduction.The martensitic structure of steels arising by the mechanism of atomic lattice shift due to rapid cooling in various media has a complex shape at various scale levels of its representation. Traditionally, the analysis of the martensitic structure at the microstructural level is carried out using a point scale, which is a semi-quantitative characteristic. However, this approach does not always satisfy the results of a quantitative assessment of the martensitic structure of steels and the prediction of their service characteristics, in particular, mechanical ones. A fractal approach was used to quantify the martensitic structure of steels. Materials and methods. The work investigated the point scale of the martensitic structure (point grade 1−10) according to ГОСT 8233 using fractal formalism. The method for determining the fractal dimension is based on a patented technique, including the search for the convergence of the values of the fractal cell and point dimensions. The applied technique increases the adequacy of the obtained values of the fractal dimension of the structure of the material under study. Experiment Results. By determining the dimension of the point martensite structure, it was established that it is fractional, that is, it is fractal. An increase in the fractal dimension of martensite needles with an increase in their score was recorded. A similar trend is also observed for the fractal dimension of the grain boundaries (needles) of martensite, which increases with an increase in the score. An increase in the fractal dimension of martensite may be due to a change in its morphology from latent-acicular to coarse-acicular. Conclusions. The analysis of the point martensite structure is carried out in accordance with the normative documents. Regression models for evaluating the martensitic structure in terms of its fractal dimension (R2 = 0,81) and grain boundaries (R2 = 0,67) are obtained. This indicates the possibility of using the fractal approach, as an alternative, when controlling the structure of martensite after different modes of heat treatment.