A Review of Methodology Development for Controlling Loss of Alloying Elements During the Electroslag Remelting Process
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INCONEL
INTRODUCTION
718,* a precipitation-strengthened nick-
*INCONEL is a registered trademark of the Special Metals family of companies.
el-based superalloy, has been widely applied in different high-temperature industries in consideration of its adequate strength, ductility, and fatigue resistance up to 923 K.[1–5] In the Ni-based alloy, the increased
SHENG-CHAO DUAN, XIAO SHI, MAN-CANG ZHANG, YE SUN, HAN-JIE GUO, and JING GUO, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), 30 Xueyuan Road, Haidian District, Beijing 100083, P.R. China and also with the Beijing Key Laboratory of Special Melting and Preparation of High-End Metal Materials, University of Science and Technology Beijing (USTB), Beijing 100083, P.R. China. Contact email: [email protected] FEI WANG, is with Tianjin Cisri-Harder Materials & Technology Co. Ltd., Central Iron and Steel Research Institute (CISRI), Tianjin 301721, P.R. China. Manuscript submitted March 12, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
additions of Al and Ti to the face-centered-cubic matrix increase the volume fraction of Ni3(Al, Ti, Nb) type c¢ and Ni3(Nb, Al, Ti) type c¢ phase, which are responsible for the heat resistance and mechanical properties of Ni-based superalloy.[6–8] With the increasing demand for remarkable comprehensive performance of steels and alloys, electroslag remelting (ESR) is widely performed in the refining process to facilitate the production of clean, fully dense, and homogeneous castings of these important materials by removal of undesirable elements and nonmetallic inclusions.[9–12] However, contrary to the aforementioned beneficial aspects on the product side, there remain some typical difficulties in ESR of steels and alloys containing easily oxidized elements, i.e., Inconel 718 alloy, which is due to strong chemical reactions taking place in the slag-metal interface.[13–15] Consequently, in many cases, it is not possible to hold Al and Ti within specification or to maintain them uniformly from the bottom to top of the resultant ingot. These changes are primarily a result of the reactive elements reacted with oxygen, i.e., air atmosphere and soluble oxygen [O] in metallic melt and weak oxide in slag, such as FeO, SiO2, and TiO2. In order to overcome these shortcomings, the conventional method used to prevent loss of reactive elements in the ESR process is to
add a certain amount of the reactive oxide species determined by thermodynamic equilibrium to the slag bath and further keep the reaction from proceeding in the direction of forming the oxide species.[17] There are problems, however, associated with this approach[17]: (1) different equilibria would exist for MxOy (M = Al, Ti, Si, Cr, Mn, etc.), resulting if the added oxides have an inhibiting effect on those oxidation reactions; and (2) excessive addition of a particular oxide species will alter the physical properties of ESR-type slag. All of the physical properties, such as, but not limited to, viscosity, elec
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