Original Article

Research on electroslag system for ultra-supercritical FB2 rotor steel

Department of Metallurgical Technology Research, Central Iron and Steel Research Institute, Beijing, 100081, PR China

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Received: 21 October 2025
Accepted: 2 January 2026

Abstract

Actively developing ultra-supercritical turbine units cannot only improve the power generation efficiency of thermal power plants and save energy, but also reduce significant carbon dioxide emissions, which can be described as killing two birds with one stone. FB2 steel is a rotor material for ultra-supercritical turbine units applicable to 620 °C steam parameters, and developing and designing a slag system suitable for its electroslag remelting is a top priority. In this paper, the phase diagram of CaF₂-Al₂O₃-CaO-3%MgO-0.5%B₂O₃ was plotted using FactSage thermodynamic software based on the eutectic point principle to optimize the electroslag system suitable for FB2 steel. Moreover, slag-metal equilibrium experiments were conducted to study the control effect of the designed slag system on B, an important strengthening element in FB2 steel. Furthermore, through 10 kg-scale electroslag remelting experiments, a comparative study was carried out on the differences in metallurgical quality such as composition, macrostructure, and inclusions of FB2 steel ingots (named 1# ingot and 2# ingot respectively) smelted by the traditional binary slag system (1# slag) and the designed slag system. In addition, Meltflow was used to conduct process simulation verification for 100-ton grade FB2 steel electroslag remelting. The results show that the optimal slag system composition obtained from FactSage thermodynamic calculations is 40.2%CaF₂-34%Al₂O₃-22.3%CaO-3%MgO-0.5%B₂O₃ (2# slag). The FB2 steel smelted by the designed 2# slag has good composition, better internal and external solidification quality, and better inclusion characteristics, which can meet the requirement of stable control of B element during electroslag remelting. The process simulation results indicate that the designed 2# slag has more sufficient power, better slag skin thickness than 1# slag, and a more stable molten pool.