Improving Cylindrical Inconel 718 Ingots Produced at PAO Ruspolimet

Аннотация

Abstract—Analysis of the smelting and casting of cylindrical ingots of Inconel 718 alloy produced in a vacuum induction furnace at PAO Ruspolimet shows that existing technology does not ensure the production of a dense ingot of the required quality on account of porosity in the axial zone and segregation of elements such as chromium, nickel, and niobium. The results show that the casting and solidification of the Inconel 718 ingots must be corrected so as to obtain high-quality dense ingots, without changing the basic features of the production process: a 3-t vacuum induction furnace, a ceramic lining based on aluminum oxide (Al₂O₃), a cylindrical mold for ingots of diameter 410 mm, and a mold of diameter 450 mm for vacuum-arc remelting. By means of Thermo-Calc software (2017a version), the solidus temperature for equilibrium solidification (1211°C) and nonequilibrium solidification (1091°C) are refined. On the basis of the results, by computer simulation of the casting processes, the casting rate is corrected by decreasing the diameter of the casting nozzle from 32 to 28 mm and the casting temperature from 1470 to 1460°C. A batch of ingots is produced by the corrected technology. Transverse templates are taken from such a sample to determine the chemical composition, and longitudinal sections are taken for metallographic analysis. Metallographic data indicate decrease in porosity of the ingot’s axial zone and decrease in the segregation. On the basis of the results, the introduction of appropriate changes in the casting technology is proposed. Computer simulation of the casting and solidification processes permits the development of a technology in which high-quality ingots are produced in the first step. All of the products meet the customer requirements.