STUDY OF STRUCTURAL FACTORS WHICH DETERMINE THE LEVEL OF STRENGTH AND PLASTICITY OF DUCTILE CAST IRON
DOI:
https://doi.org/10.32782/3041-2080/2024-1-2Keywords:
ductile cast iron, modification, spheroidization, ultimate tensile strength, relative elongation, ferrite, pearliteAbstract
The work is devoted to the study of the influence of structural parameters on the strength and plasticity of ductile cast iron for further improvement of the technological process. As a material for research, ductile cast iron was used, which meets the requirements of the EN 1563:2018 standard. Cast iron was melted in an induction furnace with a capacity of 5 tons. Obtaining of ductile cast iron was carried out by processing metal in a ladle. Secondary modification was also carried out during the pouring of metal from the furnace, and tertiary modification – in the mould. Tensile tests were performed on a universal testing machine in accordance with DSTU EN ISO 6892-1 standard, Brinell hardness - in accordance with the DSTU EN ISO 6892-1 standard. The parameters of the graphite phase and the microstructure of cast iron were investigated by the method of optical metallography in accordance with the ISO 945-1:2019 standard. The peculiarities of the influence of the characteristics of the graphite phase on the mechanical properties of ductile cast iron were determined. The peculiarities of the influence of the structural composition of the metal matrix of ductile cast iron on its mechanical properties are determined. The complex of mechanical characteristics mostly depends on such microstructure parameters as the degree of spheroidization of graphite particles and their dispersion. The influence of the degree of spheroidization is of a threshold nature and its value below 50% does not allow obtaining a value of relative elongation higher than 6–8%. The main parameter is the integrity of the graphite particles. In the studied range from 50 mm-2 to 200 mm-2, particle refinement leads to a simultaneous increase in strength and plasticity. An increase in strength with an increase in the proportion of pearlite is observed only if favorable parameters of the graphite phase are obtained, while an increase in strength leads to a certain decrease in the plasticity of the material. Further research should be directed to the study of methods of controlling the dispersion of the graphite phase. Also, to achieve progress in increasing the strength of cast iron, it is necessary to continue research in the direction of controlling the structural composition of the metal matrix.
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