INFLUENCE OF THERMAL INSULATION COATING PARAMETERS ON THE MICROSTRUCTURE AND HARDNESS OF CENTRIFUGAL SPECIAL CAST IRON
DOI:
https://doi.org/10.15407/plit2026.02.055Keywords:
piston ring, special cast iron, centrifugal casting, thermal insulation coating, microstructure, hardnessAbstract
The influence of the physicochemical parameters of thermal insulation coatings on the structure formation and hardness development of centrifugal castings made of special cast iron alloyed with chromium, titanium, and tungsten has been investigated. Based on industrial trials, the regularities of the effect of coating density and composition on the heat dissipation kinetics within the «casting–mold» system have been established. Using optical emission spectral analysis and metallographic studies at magnifications of ×100 and ×500, the phase composition of the casting’s working zone was analyzed. It was found that for cast iron alloyed with chromium, titanium, and tungsten, the cooling rate is the decisive factor in stabilizing the pearlitic matrix. It is shown that a low coating density (less than 1.30 g/cm³) leads to intensive heat dissipation, which shifts the phase equilibrium toward the formation of structural free cementite (chill formation). Conversely, excessive density (above 1.33 g/cm³) and increased sodium silicate content cause delayed crystallization and the formation of a ferritic component, which does not meet the requirements of the OST 1 90079-72 standard. The scientific novelty of the work lies in establishing a quantitative relationship between the density of the thermal insulation layer and the equilibrium shift in the «pearlite–ferrite–cementite» system, allowing for the determination of the critical limits of coating thermal conductivity for centrifugal casting. The optimal range of suspension density (1.30–1.33 g/cm³) was determined, ensuring a stable pearlitic structure and standard hardness (302–255 HB). The practical value of the results lies in the development of technological recommendations for the composition of thermal insulation coatings, which allow for stabilizing the quality of cylindrical castings, reducing the scrap rate due to structural defects, and adjusting the casting modes for special cast irons with a high tendency toward carbide formation.
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