Effects of Remelting Current on Structure, Composition, Microsegregation, and Inclusions in Inconel 718 Electroslag Reme
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INTRODUCTION
ELECTROSLAG remelting (ESR) has long been viewed as an important secondary metal processing route for refinement of Inconel 718 (IN718) superalloy ingots, which are produced by the vacuum induction melting (VIM). Compared with another refining method, vacuum arc remelting (VAR), the ESR route can avoid creation of white spots and produce a remelted ingot with good surface quality.[1–3] This route also shows a superior capacity for oxide and sulfide cleanliness via slag–metal interfacial interactions.[1,4] However, relative to the VIM + VAR material, the VIM + ESR material suffers from two distinct drawbacks. First, easily oxidative elements such as Al and Ti generally present longitudinal inhomogeneity in the
XIAO SHI, SHENG-CHAO DUAN, WEN-SHENG YANG, MING-TAO MAO, HAN-JIE GUO, and JING GUO are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China and also with the Beijing Key Laboratory of Special Melting and Preparation of High-End Metal Materials, Beijing 100083, China. Contact e-mail: [email protected] Manuscript submitted April 24, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
ESR ingot and a difference in their contents between the consumable electrode and the remelted ingot due to dynamic redox reactions on the slag–metal interface.[1,5] Second, the extent of solidification segregation, including macro- and microsegregations, is increased by a deeper molten pool relative to the VAR ingot.[2,6,7] Inevitably, such problems have a considerable adverse effect on subsequent thermal processing steps and even on the performance of the final castings. Many researchers have reported that the inaccurate chemical composition in the ESR ingot is strongly dependent on the slag composition. Therefore, abundant slag systems and reliable strategies have been designed according to the different uses of the IN718 target products to minimize the changes in alloy composition and improve the metallurgical quality in light of the actual situation.[5,8–11] The ESR process parameters, which consist of input power, current, voltage, slag quantity, electrode filling ratio, etc., also play a decisive role in maintaining the stability of the ESR process, thus ensuring the solidification quality of ingots, and obtaining good technoeconomic indices. The process parameters have important effects on the behavior of solidification, the extent of segregation, the level of cleanliness, and the uniformity of chemical composition in the IN718 alloy during the ESR process.
Extensive studies have established various types of mathematical models to depict and predict the remelting process in terms of the fluid flow, heat transfer, mass transfer, etc.,[12–16] and the findings offer a variety of valuable information that can guide improvement and the effective control of the solidification quality of ESR ingots. However, although the ESR process has been widely applied in industrial manufacturing, systematic investigations of the solidification features of IN718 ESR ing
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