During continuous casting of high‐alloy (Al, Mn, Ti) steels, the operational issues and quality problems caused by interfacial reaction or peritectic features need to be solved by applying suitable mold fluxes. Intensive efforts have been made to optimize properties, and hereby, several types of mold fluxes, including mold fluxes with high basicity and high glassy property (dual‐high mold fluxes), mold fluxes with strong oxidizing components to protect SiO2 from reduction, mold fluxes with high SiO2 content to decrease the viscosity and basicity, mold fluxes with low SiO2 content for the purpose of attenuated reactivity, and molten mold fluxes to increase consumption, have been developed. Significant efforts have been made to study the theoretical basis and practical application of these mold fluxes. To summarize, the most potential solution of mold fluxes for high‐alloy (Al, Mn, Ti) steel continuous casting is to further optimize the nonreactive mold fluxes systematically to achieve a coordinated control of lubrication and heat transfer.

Nozzle blockage is a major problem during continuous casting of Al-containing steel. Herein, we analyzed the thermodynamic equilibrium behavior between aluminum and oxygen in steel at 1873 K (1600°C) and demonstrated that, the dissolved [O] initially decreases with increasing the dissolved [Al] until approximately 0.1 wt pct [Al], and after that, the dissolved [O] increases with dissolved [Al]. Thus, for high-aluminum steel with 1.0 wt pct dissolved [Al], the precipitation of Al 2 O 3 inclusion can be avoided during cooling from deoxidation temperature to the liquidus temperature, if the actual dissolved [O] can be kept from increasing when the dissolved [Al] further increases from 0.1 to 1.0 wt pct. Hence, a method of inclusion control for highaluminum steel without traditional Ca treatment technology was proposed based on the thermodynamic analysis. Industrial tests confirmed that low-melting point Ca-aluminate inclusions were observed typically through a slag washing with SiO 2-minimized high-basicity slag during tapping, accompanied by two-step Al-adding process for production of high-aluminum steel. Moreover, there was no nozzle clogging occurred for five heats of continuous casting.

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Controlling the morphology of the sulfide inclusion is of vital importance in enhancing the properties of structural steel. Long strip-shaped sulfides in hot-rolled steel can spherize when, instead of the inclusion of pure single-phase MnS, the guest is a complex sulfide, such as an oxide-sulfide duplex and a solid-solution sulfide particle. In this study, the inclusions in a commercial rolled structural steel were investigated. Spherical and elongated oxide-sulfide duplex as well as single-phase (Mn,Ca)S solid solution inclusions were observed in the steel. A thermodynamic equilibrium between the oxide and sulfide inclusions was proposed to understand the oxide-sulfide duplex inclusion formation. Based on the equilibrium solidification principle, thermodynamic discussions on inclusion precipitation during the solidification process were performed for both general and resulfurized structural steel. The predicted results of the present study agreed well with the experimental ones.

The mixing time of molten steel has a decisive impact on the refining efficiency during the RH (Rheinsahl-Heraeus) degassing process. In the present work, a coupled volume of fluid method −discrete phase model has been developed to investigate the effect of bottom injection on mixing and slag layer behaviours in the RH degasser. The fluid flow, mixing characteristic, and the formation of slag eye in the RH degasser with bottom injection are well revealed. Numerical results show that X = −0.75 m (under the up-snorkel) is the optimal injection location to obtain a shortest mixing time, as well as avoid the formation of slag eye in the RH degasser. At the same time, the result of industrial trial shows that the decarburisation efficiency can be accelerated remarkably when the bottom injection is located at X = −0.75 m.