Evolution of Oxide Inclusions in G20CrNi2Mo Carburized Bearing Steel during Industrial Electroslag Remelting

• Published in: ISIJ International 2018/10/15, Vol.58(10), pp.1781-1790
• Main Authors: Li, Shijian, Cheng, Guoguang, Miao, Zhiqi, Dai, Weixing, Chen, Lie, Liu, Zhiquan
• Format: Article
• Language: English
• Subjects: bearing steel; electroslag remelting; evolution mechanism; oxide inclusion; thermodynamics
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.ISIJINT-2018-072

Industrial experimental and thermodynamic analyses were carried out to investigate the evolution of oxide inclusions from consumable electrode to droplet and refined ingot during electroslag remelting (ESR) of G20CrNi2Mo carburized bearing steel. All the oxide inclusions in electrode were CaO–MgO–Al2O3, most of which compositions were located in the liquid region. During droplet formation, most electrode inclusions were absorbed by molten slag, and it was inferred that the Ca content in metal film obviously decreased. A few inclusions were still remained in the liquid steel mainly owing to low interfacial energy. In addition, pure Al2O3 inclusions smaller than 2 µm were generated in droplet, indicating that significant Al-oxidation occurred. The ingot inclusions were low-MgO-containing MgO–Al2O3, Al2O3-based irregular CaO–(MgO)–Al2O3 and spherical CaO–Al2O3, all of which compositions were outside of the liquid region, indicating that no ingot inclusions could be identified as the relics of that in electrode. Thermodynamic calculations showed that the dissolved Ca and Mg reduced by Al at slag/metal interface could not transfer into the metal pool. FactSageTM 7.0 was used to elucidate the formation of inclusions in metal pool, and the results were basically in accordance with the experimentally observed inclusions, showing that a quasi-thermodynamic equilibrium could be established.