QUALITY IMPROVEMENT OF CAST CYLINDRICAL BAR OF VACUUM INDUCTION MELTING FROM INCONEL 718 ALLOY AT PJSC “RUSPOLIMET”

Abstract

The analysis of technological processes of smelting and casting of cylindrical bars from Inconel 718 alloy, obtained in a vacuum induction furnace at PJSC “Ruspolimet”, was performed. The existing technology does not ensure the production of a sound bar of the required quality due to the presence of porosity in the axial zone, and also due to liquation at the macro level of elements such as chromium, nickel, niobium. The results have shown the need to adjust the parameters of casting and solidification of bars from the Inconel 718 alloy. The task to get high-quality sound bar was set without changing the main technical parameters of production, namely: type of furnace – vacuum induction furnace with capacity of 3 tons; material of the furnace lining – ceramics based on aluminum oxide Al2O3 ; type of the casting mold – cylindrical mold for bar diameter of410 mm; diameter of crystallizer for vacuum-arc remelting –450 mm. With the use of the Thermo-Calc program (version 2017a), the solidus temperatures for the equilibrium solidification process and for the non-equilibrium process were clarified, which were 1211 °С and 1091 °С, respectively. Based on the results obtained, the casting speed (SCM LP) system corrects casting speed by reducing the diameter of the casting nozzle from 32 to28 mm and casting temperature by reducing it from 1470 to1460 °C. According to the corrected technology, a batch of bars has been smelted. From the bar of the first batch, transverse templates were selected to determine the chemical composition and longitudinal temp lates for metallographic analysis. Metallographic studies have been carried out that suggest a decrease in porosity of axial zone of the bar and a decrease in phase separation at the macro level. Based on the results obtained, the authors proposed to introduce approp riate changes in casting technology. It is shown that computer modeling of metallurgical processes of metal casting and crystallization allows developing a technology of obtaining a high-quality bar already at the first redistribution, while avoiding appearance of products that do not meet customer requirements.