In order to develop low fluoride or fluoride free CaO–Al ₂ O ₃ based mould flux for casting high aluminium steel, an investigation was carried out to study the effect of substituting CaF ₂ with B ₂ O ₃ on heat transfer and crystallisation behaviour of CaO–Al ₂ O ₃ based mould flux by employing a heat transfer simulator of mould flux and a single hot thermocouple technique. The results showed that addition of CaF ₂ promoted heat transfer of CaO–Al ₂ O ₃ based mould flux, which was opposite to the effect of CaF ₂ on heat transfer in conventional CaO–SiO ₂ based mould flux. Addition of CaF ₂ inhibited crystallisation of CaO–Al ₂ O ₃ based mould flux by lowering the start crystallisation temperature and prolonging the incubation time of crystallisation. B ₂ O ₃ showed similar effects to CaF ₂ on heat transfer and crystallisation of CaO–Al ₂ O ₃ based mould flux, but its ability to promote heat transfer and suppress crystallisation was stronger than CaF ₂ . Ca ₃ B ₂ O ₆ (melting temperature 1480°C) was found as the primary crystalline phase in fluoride free CaO–Al ₂ O ₃ based mould flux compared with the primary crystalline phase Ca ₂ Al ₃ O ₆ F (melting temperature 1507°C) in fluoride bearing (20% CaF ₂ ) CaO–Al ₂ O ₃ based mould flux.

Following a series of laboratory studies on the development of fluoride-free or low-fluoride CaO–Al₂O₃-based mould flux for continuous casting of high-aluminium steel, the viscosity properties of CaO–Al₂O₃-based mould flux with B₂O₃ as a substitute for CaF₂ were investigated using the rotating cylinder method. It was found that B₂O₃ behaved in a similar manner to CaF₂ in changing the viscosity of the flux system. From calculations of the viscous activation energies, it was found that similar changes in the concentrations of CaF₂ and B₂O₃ resulted in almost the same changes in activation energy. A viscosity prediction model was developed using the optical basicity concept as an indicator of melt behaviour. Predicted viscosity values showed good agreement with measurements reported in the literature.

High-carbon steel wires used for bridge cables, tire reinforcement materials and cutting materials of silicon ingot for photovoltaic industry require an extremely fine diameter and high strength. Poor control of centerline segregation, inclusion and microstructure of high-carbon steel is detrimental to drawability and subsequent fatigue performance. Prof. Weiqing Chen’s group at the University of Science and Technology Beijing (USTB) has been investigating the quality control of high-carbon steel through a low-cost one-stage hot rolling process since 2000. This paper reviews the main research from this group. The laboratory-scale and industrial results are presented. Intensive secondary cooling, final electromagnetic stirring (F-EMS), final permanent magnetic stirring (F-PMS), and soft reduction are investigated and applied to control centerline segregation, and the application scope is also discussed. A combination of redesign of submerged entry nozzle (SEN) and refining slag, utilization of Al-free refractory and the addition of low-melting-point compounds is studied and applied effectively to control inclusions. Measurements and mechanisms to control network cementite, martensite, banded structure and undesired texture are investigated and discussed. Integration of the above research has achieved industrial application in more than 10 steelworks and was further extended to application in spring steel, welding wire steel and some other wire rods.

Control of solidification structure and segregation is crucial to improve the service performance of high carbon martensitic stainless steels. Design of the electroslag remelting (ESR) process based on the essential parameters of melting rate, filling ratio, and slag thickness is a precondition to achieve optimal control of solidification structure and segregation of the steels. However, there is still a lack of coupled works giving deep insight into the overall effect of the parameters on the expected control. With this background, a 2D numerical model was established to probe into the effect of process parameters. The results showed that: (1) With the increase of melting rate from 90 kg/h to 180 kg/h, the molten metal pool depth increased by about 4 cm. Meanwhile, the center LST, PDAS, and SDAS increased by about 450 s, 100 μm, and 12 μm. The segregation index of C and Cr increased by about 0.15 and 0.09. (2) As the filling ratio increased from 0.16 to 0.43, the depth of the metal pool decreased by about 4.5 cm, LST and SDAS received a slight increase of about 41 s and less than 5 μm, but PDAS had little change. The segregation index of C had an increase of about 0.03, but the segregation index of Cr demonstrated tiny changes. (3) As the slag thickness increased from 0.08 to 0.14 m, the metal pool depth presented a first increase of about 1 cm and then a slight decrease. The center LST, PDAS, and SDAS first increased by 148 s, 30 μm, and 4 μm and then decreased slightly. The changes of the segregation index of C and Cr presented a similar tendency than that of LST, but the changes are extremely small. (4) A low melting rate less than 120 kg/h, a filling ratio of about 0.23–0.33, and a slag thickness of 0.08–0.10 m were appropriate to obtain good performance for ESR of high carbon stainless steels in this study.