INFLUENCE OF HEAT TREATMENT ON PHYSICAL-MECHANICAL PROPERTIES OF HIGH STRENGTH CAST IRON VCh 50

10.25712/ASTU.1811-1416.2024.01.014

Abstract

The paper presents the results of microstructural analysis of high-strength cast iron VCh 50. The degree of globularity of graphite inclusions was determined through the shape factor F2, which in turn is defined as the ratio of the diameters of the circle inscribed in the particle to the diameter of the circle described around the particle: the closer this ratio is to 1, the higher degree of globularity. From the data on the shape factor F2 of graphite inclusions it follows that only 32.7 vol. % of graphite inclusions have a close to globular shape. This indicates a violation of the cast iron modification technology and the production of unmodified graphite in the sample. The studies also showed that the cast iron sample submitted for research did not undergo heat treatment, or, in the case of heat treatment, it was carried out with incorrect parameters: most likely the heat treatment temperature was lower than the recommended temperature (700 °C). Violation of the technology of modification and further heat treatment of the casting leads to a deterioration in the performance characteristics of cast iron. Carrying out repeated heat treatment according to the correct regime made it possible to improve the microstructure and level out these shortcomings. After repeated heat treatment in the form of annealing at a temperature of 700 °C for 4 hours, followed by cooling to 400 °C together with the furnace, then in air, it was possible to increase the proportion of spheroidized graphite particles from 32.7 to 65 vol. %. Annealing was carried out to increase the strength properties of the material, as well as ductility and toughness.