OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 metal matrix of ChMN-35M cast iron as well as by the increased level of relaxation properties of the material alloyed with molybdenum and nickel. However alloying cast iron with molybdenum and nickel does not have a significant effect on the overall picture of destruction. Complex alloying of SChMN-45 cast iron with molybdenum, nickel and vanadium accompanied by an increase in the dispersion of the pearlite structure leads to a significant refinement of the cleavage facets (Fig. 6, c). Approximately 30 % of the fracture surface is formed by the mechanism of intercrystalline fracture. The sensitivity of SChMN-45 cast iron to the presence of stress concentrators is also less noticeable which indicates the decisive role of graphite inclusions of lamellar morphology in the manifestation of the mechanisms of crack initiation and development [11, 27, 39]. Conclusions 1. Complex alloying with molybdenum, nickel and vanadium provides the hardness of SChMN-45 gray cast iron at the level of 295 HB and the ultimate strength during tests according to the tensile scheme at the level of 470–505 MPa, which exceeds the values corresponding to SCh35 gray cast iron (290 HB and 365 MPa, respectively). 2. The addition of nickel (0.4–0.7 wt. %), molybdenum (0.4–0.7 wt. %) and vanadium (0.2–0.4 wt. %) into gray cast iron leads to a decrease in the interlamellar distance in pearlite by 2 times and a decrease in the length of graphite inclusions. These changes explain the increase in the strength properties of alloyed cast iron in comparison with the SCh35 cast iron. 3. Alloying of gray cast iron with molybdenum and vanadium provides an increase in the microhardness of ferrite grains decorating graphite inclusions by about 1.4 times. This factor has an additional effect on the level of strength properties of the materials under study. 4. Cast iron alloyed with nickel, molybdenum and vanadium is characterized by a higher complex of tribotechnical properties compared to serial gray cast iron. The total wear of shafts made of SChMN-45 cast iron is approximately 1.3–1.8 times lower compared to SCh35 cast iron and 1.1–1.2 times lower compared to ChMN-35M cast iron. Analysis of the research results testify to the efficiency of using SChMN-45 cast iron in friction pairs with counter bodies made of steels 30CrMnSiA, 20MnL and 09Mn2Si. 5. Significant refinement of cleavage facets at fractures of dynamically fractured specimens recorded by the method of fractographic studies of the complexly alloyed SChMN-45 cast iron indicates an increased level of energy consumption for the process of destruction of the material compared to unalloyed cast iron. The chemical composition of cast iron providing the required parameters of mechanical properties (ultimate strength 450–505 MPa, hardness 265–330 HB) includes: 2.3–2.8 % C, 1.3–1.5 % Si , 0.6–1.0 % Mn, 0.4–0.7 % Mo, 0.2–0.4 % V, 0.4–0.7 % Ni. Such cast iron can contain no more than 0.3 % Cr, 0.3 % Cu, 0.2 % P, 0.1 % S. References 1. Bagesh B., Rahul K., Anil K.S. Effect on the mechanical properties of gray cast iron with variation of copper and molybdenum as alloying elements. International Journal of Engineering Research and Technology, 2014, vol. 3 (5), pp. 81–84. 2. Sujith B., Mukkollu S.R., Harish B.B., Leman Z. Effect on the mechanical properties of grey cast iron with variation of molybdenum and as – cast alloying elements. Universal Journal of Mechanical Engineering, 2020. vol. 8 (6), pp. 298–304. DOI: 10.13189/ujme.2020.080602. 3. Razaq A., Zhou J., Hussain T., Tu Z., Yin Y., Ji X., Xiao G., Sen X. Effect of alloying elements W, Ti, Sn on microstructure and mechanical properties of gray iron 220. China Foundry, 2019, vol. 16, pp. 393–398. DOI: 10.1007/s41230-019-9035-4. 4. Ankamma K. Effect of trace elements (boron and lead) on the properties of gray cast iron. Journal of the Institution of Engineers (India): Series D, 2014, vol. 95, pp. 19–26. DOI: 10.1007/s40033-013-0031-3. 5. Ma Y., Li X., Liu Y., Zhou S. Effect of Ti-V-Nb-Mo addition on microstructure of high chromium cast iron. China Foundry, 2012, vol. 9 (2), pp. 148–153.
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