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RAR RUS 11402-11402 0000-0002-7422-5494 Peter the Great St.Petersburg Polytechnic University Vafaeva Khristina Maksudovna vafaeva_hm@spbstu.ru

Saint Petersburg, Russian Federation

Fractal structure of cast iron and its strength characteristics The object of research is the structure and hardness of cast iron rolls used in section rolling mills. The study focuses on the use of multifractal analysis to assess the microstructural features of cast iron and their correlation with hardness. Method. Quantitative metallography methods and a multifractal approach were employed to analyze the microstructure of cast iron. Statistical characteristics of the microstructure were calculated using Rényi's formula. Hardness measurements were conducted on rolls made from SPHN and SSHNF grades of cast iron at three equidistant points along the barrel. Correlation coefficients were computed to evaluate the relationship between hardness and both traditional structural characteristics (length, diameter, area) and multifractal parameters. Results. The analysis revealed the significant influence of statistical fractal dimensions and the morphology of carbides and graphite (lamellar and spheroidal) on the hardness of cast iron rolls. Correlation coefficients for hardness prediction based on traditional structural features ranged from , while prediction using multifractal characteristics showed higher coefficients:  to  for SPHN rolls and  to  for SSHNF rolls. These results demonstrate the effectiveness of multifractal analysis in assessing the quality of cast iron rolls. A novel approach for evaluating the hardness of SPHN and SSHNF rolls is proposed. It includes the calculation of the statistical dimension spectrum of cast iron structural elements, determination of sensitivity coefficients of hardness to the spectrum, and the development of a mathematical model for hardness prediction. This method offers an alternative framework for assessing the quality of cast irons by analyzing their structural characteristics. 10.4123/CUBS.114.2 69 Cast iron Fractal analysis Microstructure Strength characteristics Structural integrity Fractal dimension Mechanical properties Metallic materials Quality evaluation https://unistroy.spbstu.ru/article/2024.114.1/ 11402.pdf

RAR RUS 11403-11403 0000-0002-7422-5494 Peter the Great St.Petersburg Polytechnic University Vafaeva Khristina Maksudovna vafaeva_hm@spbstu.ru

Saint Petersburg, Russian Federation

Structural inhomogeneity of metallic materials and quality criteria The object of research is the microstructure and hardness of low-alloy steel with a ferrite-pearlite structure. The research focuses on applying a multifractal approach to evaluate the relationship between microstructural features and mechanical properties, particularly hardness, under varying thermal treatment conditions. Method. Multifractal analysis was applied to steel samples subjected to thermal processing, including heating to 920°C for 300 seconds and subsequent cooling to 500°C over durations ranging from 29 seconds to 93 000 seconds. Structural parameters, such as the Hausdorff-Besicovitch dimension , uniformity , and dimensional coefficients ( , ), were calculated to establish correlations with mechanical properties. Hardness measurements (HV) were performed to evaluate the impact of cooling time on structural evolution and mechanical performance. Results. The research revealed that increased cooling time led to a reduction in hardness, which corresponded to changes in the dimensionality of structural elements in ferrite and pearlite. Specifically, extended cooling times resulted in significant alterations to the microstructure, demonstrating a clear relationship between multifractal parameters and mechanical properties. The proposed multifractal approach proved effective in predicting hardness variations based on structural features, offering a robust tool for quality assessment and process optimization in metallurgy. 10.4123/CUBS.114.3 69 Metallic materials Structural inhomogeneity Material quality Microstructural features Mechanical properties Grain size variation Defects Quality standards Material performance https://unistroy.spbstu.ru/article/2024.114.2/ 11403.pdf

RAR RUS 11404-11404 0000-0002-7422-5494 Peter the Great St.Petersburg Polytechnic University Vafaeva Khristina Maksudovna vafaeva_hm@spbstu.ru

Saint Petersburg, Russian Federation

Mechanical properties of construction steel under rapid assessment The object of research is the fractal modeling methodology applied to the structure and properties of materials, specifically metals. The study explores the relationship between the fractal (fractional) dimensions of structural elements and the physical and mechanical properties of materials, such as steel and cast iron. This work aims to analyze and refine the stages of fractal modeling to improve the prediction of material quality criteria. Method. The study employs a systematic fractal modeling approach, which includes the following steps: calculating the fractal dimension  using Hausdorff’s formula, determining self-similarity and scale invariance, assessing sensitivity conditions, selecting a target function and variables, and formalizing results through appropriate modeling. The heterogeneity of fractal objects is evaluated using Rényi’s formula to detect multifractality, and the results are interpreted in the context of material structure-property relationships. Examples of algorithm implementation and its augmentation with fractal formalism for ranking quality criteria are provided. Results. The analysis demonstrates that the proposed algorithm improves the prediction of material properties based on structural and macrostructural analysis. It highlights the importance of correlating fractal dimensions with mechanical properties and emphasizes sensitivity assessments. The findings confirm that applying fractal modeling allows the ranking of quality criteria for materials, thereby establishing new structure-property relationships. Suggestions for algorithm enhancements include integrating advanced methods to evaluate sensitivity and quality metrics within specific operational ranges. 10.4123/CUBS.114.4 69 Construction steel Mechanical properties Rapid evaluation Stress-strain curves Material testing Plastic deformation Structural steel Static loads Steel calibration https://unistroy.spbstu.ru/article/2024.114.3/ 11404.pdf