The effect of electroslag remelting on the cleanli...
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Ali, M., Porter, D., Kömi, J., Heikkinen, E., Eissa, M., El, F., Mattar, T. (2019) The effect of electroslag remelting on the cleanliness of CrNiMoWMnV ultrahigh-strength steels. Journal of Mining and Metallurgy, Section B: Metallurgy, 55 (3), 381-395. doi:10.2298/JMMB190211042A
The effect of electroslag remelting on the cleanliness of CrNiMoWMnV ultrahigh-strength steels
Ali, M.1,2; Porter, D.1; Kömi, J.1;
Heikkinen, E.-P.3; Eissa, M.2; Faramawy, H. El2; Mattar, T.2
1Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, Oulu, Finland
2Steel Technology Department, Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo, Egypt
3Process Metallurgy Research Unit, University of Oulu, Oulu, Finland
University of Belgrade, 2019
The cleanliness of ultrahigh-strength steels (UHSSs) without and with electroslag remelting (ESR) using a slag with the composition of 70% CaF₂, 15% Al₂O₃, and 15% CaO was studied. Three experimental heats of UHSSs with different chemical compositions were designed, melted in an induction furnace, and refined using ESR. Cast ingots were forged at temperatures between 1100 and 950°C, air cooled, and their non-metallic inclusions (NMIs) were characterized using field emission scanning electron microscopy and laser scanning confocal microscopy. Thermodynamic calculations for the expected NMIs formed in the investigated steels with and without ESR were performed using FactSage 7.2 software while HSC Chemistry version 9.6.1 was used to calculate the standard Gibbs free energies (ΔG°). As a result of ESR the total impurity levels (TIL% = O% + N% + S%) and NMI contents decreased by as much as 46 % and 62 %, respectively. The NMIs were classified into four major classes: oxides, sulphides, nitrides, and complex multiphase inclusions. ESR brings about large changes in the area percentages, number densities, maximum equivalent circle diameters, and the chemical composition of the various NMIs. Most MnS inclusions were removed although some were re-precipitated on oxide or nitride inclusions leading to multiphase inclusions with an oxide or nitride core surrounded by sulphide, e.g. (MnS.Al₂O₃) and (MnS. TiN). Also, some sulphides are modified by Ca forming (CaMn)S and CaS.Al₂O₃. Some nitrides like TiN and (TiV)N are nucleated and precipitated during the solidification phase. Al₂O₃ inclusions were formed as a result of the addition of Al as a deoxidant to the ESR slag to prevent penetration of oxygen to the molten steel.
Journal of mining and metallurgy. Section B, Metallurgy
10.2298/JMMB190211042A
OADOI:
https://oadoi.org/10.2298/JMMB190211042A
Electroslag remelting
Nonmetallic inclusions
Synthetic slag
Ultrahigh-strength steel
The authors acknowledge the Egyptian Ministry of Higher Education (Cultural Affairs and Missions Sector) for the financial support during this work.
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