Abstract:Overview
Melting TechnologiesRemelting is performed to facilitate the production of clean, fully dense, homogeneous castings of superalloys and aerospace titanium alloys and is crucial to the defectfree production of these important materials. Modern electroslag remelting and vacuum arc remelting control systems are closedloop, single input-single output systems that oversimplify the physical properties of the processes; the ever-increasing demand for cleaner, more highly engineered, chemically tuned alloys ha… Show more
“…When the parameters of defect-producing microscale processes can be as precisely determined as the macroscale parameters now being estimated, 32 it becomes conceivable that multiple-input, multiple-output control can maintain desired solidification condition throughout every melt. 33 …”
“…When the parameters of defect-producing microscale processes can be as precisely determined as the macroscale parameters now being estimated, 32 it becomes conceivable that multiple-input, multiple-output control can maintain desired solidification condition throughout every melt. 33 …”
“…24) This is due to the fact that the area of the electrode in contact with the slag increases with the increase of current. 31) Consequently, this increase in surface area of electrode tip will result in the increase of liquid metal film-slag interface. Based on the above discussions, it can be concluded that the average radius of droplets decreases and the area of liquid metal film-slag interface increases with the increase of remelting current.…”
Section: Effect Of Remelting Current On the Content Andmentioning
The current paper focuses on the effect of different operating conditions on the content of inclusions and cleanliness of remelting ingots. For these investigations, eight ingots were remelted with two slag amount and with two current intensity under otherwise comparable remelting conditions. A twodimensional (2D) coupled mathematical model was employed to simulate the velocity field, solidification and inclusion motion for a system of electrode, slag and ingot in electroslag remelting (ESR) processes, to reveal the inclusion removal mechanism. The results showed that the content of large-sized inclusions in ESR ingot was decreased by approximately 66.18% when the slag amount was increased from 17.85 kg to 20.50 kg. Because of the increase of slag amount, the metal and slag flow faster and the maximal velocity increases by 10.3%, thus there is an increasing trend in trajectories of inclusions (i.e., inclusion motion) in slag pool resulted from the stronger natural convective flow, which is beneficial for the inclusion removal. When the average current was increased from 4 kA to 5 kA, the content of large-sized inclusions in ESR ingot was decreased by approximately 51.38%. Because of the increasing of current, the flow in the middle of the slag pool becomes stronger and the maximal downward velocity increases by 2.7%, thus there is an increasing trend in the renewal rate of the metal film surface due to the stronger washing by slag flow, which can promote the inclusion removal.
“…Strong chemical reactions usually occur at the electrode-slag interface (ESI) or the droplet-slag interface (DSI) as well as at the metal pool-slag interface (MSI), as shown in Fig. 1 8 . Consequently, in some cases, the concentrations of critical elements cannot be maintained within specifications or the elements cannot be uniformly distributed along the height of the ingots during the ESR process 9 .Figure 1Schematic of the electroslag remelting (ESR) setup.…”
In the current study, the thermodynamics of the slag-metal equilibrium reaction between Inconel 718 Ni-based alloy and CaF2-CaO-Al2O3-MgO-TiO2 electroslag remelting (ESR)-type slags were systematically investigated in the temperature range from 1773 to 1973 K (1500 to 1700 °C). The equilibrium Al content increased with increasing temperature, whereas the equilibrium Ti content decreased with increasing temperature at a fixed slag composition. The important factors for controlling the oxidation of Al and Ti in the Inconel 718 superalloy were TiO2 > Al2O3 > CaO > CaF2 > MgO in ESR-type slag and Al > Ti in a consumable electrode. The conventional method of sampling by means of a quartz tube could result in contamination of the molten metal and changes in the size of the “special reaction interface”. Therefore, a novel method was used in the present study to investigate the slag-metal reaction kinetics to accurately obtain the kinetic parameters. The mass transfer coefficient was determined by coupling with the kinetic model derived from the assumption that the reaction rate ([Al] + (TiO2) = [Ti] + (Al2O3)) was controlled by the mass transfer of [Ti], [Al], (TiO2) and (Al2O3) in the boundary layer, respectively.
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