Structure and Properties of Nickel-Based Alloy EP718 in the Process of Manufacturing
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L SCIENCES. METALLURGY
Structure and Properties of Nickel-Based Alloy EP718 in the Process of Manufacturing E. L. Gyulikhandanova, E. L. Alekseevaa, *, A. V. Shakhmatovb, A. S. Loshachenkoc, and A. A. Lapechenkova aPeter
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: [email protected]
Received November 12, 2019; revised December 16, 2019; accepted December 17, 2019
Abstract—The influence 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 treatment) 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, precipitation hardening, carbides DOI: 10.1134/S2075113320060076
INTRODUCTION In the 1980s, nickel-based alloys began to be widely used in the aerospace, chemical, and nuclear industries. Somewhat later, they found application as structural materials in other industries, in particular, in oil and gas production, for which the combination of strength and plasticity, corrosion resistance, and nonmagnetic properties is especially important [1–3]. Currently, in the oil and gas industry, nickel and ironnickel 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 resistance 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-hardening materials that are hardened as a result of heat treatment (quenching and aging), during which nanosized intermetallic phases are precipitated: the main strengthening phase γ''-phase Ni3Nb in the form of plates and a spherical coherent γ'-phase Ni3Ti,Ni3Al [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 production technology and heat treatment on the corrosion resistance of nickel-based alloy
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