Abstract
The non-isothermal crystallization characteristics of the electroslag remelting (ESR)-type slag with varied B2O3 contents were investigated by non-isothermal differential scanning calorimetry (DSC), field emission scanning electron microscopy (SEM-EDS), and X-ray diffraction (XRD). The crystallization mechanism of the B2O3-bearing slag was also identified based on kinetics analysis. The results showed that the primary crystalline phase was CaF2, there was no change in the type of the primary crystal as B2O3 content increased, and the morphology of the CaF2 crystal was mainly dendritic. The sequence of crystal precipitation during the cooling process was CaF2 to Ca12Al14O32F2 and MgO/MgAl2O4, followed by Ca3B2O6. The activation energy of CaF2 crystallization increased firstly, then decreased and reached stability, while the activation energy of Ca3B2O6 crystallization increased continuously with the increasing B2O3 content. The crystallization behavior of CaF2 was three-dimensional growth with a constant nucleation rate. The proper B2O3 content added into the CaF2-based ESR slag should be around 1.0% to limit the precipitation of the CaF2 crystal to attain good surface ingot quality and stable ESR operation.
Highlights
Most turbine manufacturers employ the electroslag remelting (ESR) process to produce the rotor ingot.ESR is a secondary refining technique that is used for the production of some varieties of high-grade specialty steels and alloys due to its extraordinary advantages [4,5]
The precipitation temperature of the first crystalline phase decreased with the increasing B2 O3 content
The precipitation temperature of Ca12 Al14 F2 O32 decreased with the increasing B2 O3 content, and ranged from 1307 to 1270 ◦ C
Summary
Most turbine manufacturers employ the electroslag remelting (ESR) process to produce the rotor ingot.ESR is a secondary refining technique that is used for the production of some varieties of high-grade specialty steels and alloys due to its extraordinary advantages [4,5]. Most turbine manufacturers employ the electroslag remelting (ESR) process to produce the rotor ingot. Metals 2019, 9, 1331 production, and the surface quality of the ESR ingot is related to the molten slag [8]; generally, it is a consequence of inappropriate lubrication and horizontal heat transfer in mold through the slag film, besides the melting rate and electrode immersion depth [9,10]. Horizontal heat transfer of the slag is strongly dependent on the crystallization characteristics of the slag [11,12]. It is necessary to study the crystallization behavior of the ESR-type B2 O3 -bearing slag to control the appropriate horizontal heat transfer across the slag film in mold during the ESR process
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