Investigation of Oxide Inclusions and Primary Carbonitrides in Inconel 718 Superalloy Refined through Electroslag Remelting Process

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2012-12, Vol.43 (6), p.1596-1607
• Main Authors: Chen, Xi-Chun, Shi, Cheng-Bin, Guo, Han-Jie, Wang, Fei, Ren, Hao, Feng, Di
• Format: Article
• Language: English
• Subjects: Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Materials Science; Melting; Metallic Materials; Metallurgy; Metals. Metallurgy; Nanotechnology; Production of metals; Slag; Structural Materials; Superalloys; Surfaces and Interfaces; Thin Films
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-012-9723-6

The effect of remelting atmosphere and calcium treatment during electroslag remelting (ESR) of Inconel 718 superalloy on the oxide inclusions and primary carbonitrides was investigated. The results show that after ESR refining combined with calcium treatment, the original oxide inclusions in the electrode, mainly MgO·Al 2 O 3 spinels and some MgO inclusions, were modified to CaO-Al 2 O 3 system inclusions or the inclusions of MgO·Al 2 O 3 spinel core surrounded by CaO-MgO-Al 2 O 3 system inclusion layer. Without the calcium treatment in ESR process, all the oxide inclusions in superalloy ingots are MgO·Al 2 O 3 spinels. All the oxide inclusions in ESR ingots act as the nucleation site for carbonitride (Nb,Ti)CN with two-layer structure precipitation, except for those with a single (Nb,Ti)CN layer containing a small amount of Ti and N in the ingot refined by a proper amount of calcium addition in ESR process. The carbonitrides (Nb,Ti)CN formed directly on the oxide inclusion have a small amount of Nb and C as well as a relatively fixed atomic ratio of Nb/Ti (about 0.6:1). There is a Nb-rich and C-rich (Nb,Ti)CN layer on the pre-existing (Nb,Ti)CN formed on the oxide inclusion. The size of the observed carbonitrides is in the range of 5 μ m to 15 μ m. The calcium treatment in the ESR process has a significant effect on the morphology of carbonitrides in superalloy ingot due to modification of oxide inclusions by Ca-treatment resulting in the change of precipitation and growth conditions for carbonitrides. The morphologies of carbonitrides were changed from clustered block or single octahedral to skeleton-like after calcium treatment.