1317 ISSN 2075-1133, Inorganic Materials: Applied Research, 2020, Vol. 11, No. 6, pp. 1317–1324. © Pleiades Publishing, Ltd., 2020. Russian Text © The Author(s), 2019, published in Voprosy Materialovedeniya, 2019, No. 4, pp. 42–52. Structure and Properties of Nickel-Based Alloy EP718 in the Process of Manufacturing E. L. Gyulikhandanov a , E. L. Alekseeva a, *, A. V. Shakhmatov b , A. S. Loshachenko c , and A. A. Lapechenkov a a Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia b Weatherford Ltd., Moscow, 125047 Russia c St. Petersburg State University, St. Petersburg, 199034 Russia *e-mail: alexeeva_el@spbstu.ru Received November 12, 2019; revised December 16, 2019; accepted December 17, 2019 Abstract—The inf luence of the manufacturing process of semifinished products (forging, solution annealing, and aging) on the structure and corrosion properties of the EP718 nickel-based alloy (KhN45MVTYuBR) used in the oil and gas industry is investigated. The corrosion-electrochemical properties of the alloy are determined using gravimetric and electrochemical techniques. The microstructure is studied by optical and transmission electron microscopy. It is shown that the EP718 alloy in the delivery state (without heat treat- ment) has the highest corrosion resistance, and its corrosion properties degrade during subsequent solution annealing at 1080°C. Keywords: nickel-based alloys, oil and gas industry, alloy EP718, corrosion, nonmetallic inclusions, precipi- tation hardening, carbides DOI: 10.1134/S2075113320060076 INTRODUCTION In the 1980s, nickel-based alloys began to be widely used in the aerospace, chemical, and nuclear indus- tries. Somewhat later, they found application as struc- tural materials in other industries, in particular, in oil and gas production, for which the combination of strength and plasticity, corrosion resistance, and non- magnetic properties is especially important [1–3]. Currently, in the oil and gas industry, nickel and iron- nickel alloys are used for manufacture of parts and equipment assemblies that are operated in drillings with high pressure and temperature and aggressive media containing hydrogen sulfide, carbon dioxide, and chlorides [4, 5]. Therefore, increasing the resis- tance of the applied structural materials to local types of corrosion is an urgent task. At present, the iron-nickel-based alloy Inconel718 is widely used in foreign industry, the analog of which is the EP718 alloy. This alloy belongs to precipitation-hard- ening materials that are hardened as a result of heat treat- ment (quenching and aging), during which nanosized intermetallic phases are precipitated: the main strength- ening phase γ ''-phase Ni 3 Nb in the form of plates and a spherical coherent γ'-phase Ni 3 Ti,Ni 3 Al [6]. The standard heat treatment regime for EP718 alloy involves quenching and subsequent two-stage aging. This alloy can be supplied without heat treat- ment, which allows equipment manufacturers to select more efficient heat treatment modes for specific tasks, as well as use the alloy as delivered (after forging) if the requirements for strength properties are met. There are conflicting data on the effect of the pro- duction technology and heat treatment on the corro- sion resistance of nickel-based alloys. For example, the authors of [7] recorded positive effects in the release of secondary phases during aging, and in [8], it is shown that the metal has the highest corrosion resis- tance in the state of delivery. Despite the fact that there is a sufficient amount of published data on the corrosion resistance of the Inc- onel 718 alloy [9–13], there is no such information for the EP718 alloy, including no data on the effect of heat treatment on the corrosion resistance. In connection with the above, the purpose of this work is to study the corrosion resistance of the EP718 alloy and its struc- ture as delivered, after quenching, and after aging. MATERIAL AND RESEARCH TECHNIQUE In this work, samples of the domestic EP718 alloy produced in accordance with TU14-13905-85 (here- inafter, STD is scientific and technical documenta- tion) were studied. The alloy production technology included vacuum induction smelting and vacuum arc remelting, and forging by direct pulling from the ingot. METAL SCIENCES. METALLURGY