Ce has been widely used in oxide metallurgy for modifying inclusions and refining microstructure. Effect of Ce contents on the evolution and characteristics of non-metallic inclusions and the formation of acicular ferrite (AF) in Ce-treated Ti-Mg-killed EH36 steel was investigated. The results showed that the main type of inclusions in Ti-Mg deoxidized steel was MgO·Al₂O₃-MnS. After 0.014%, 0.024% and 0.037% Ce were added into the steels, dominant inclusions became CeAlO₃-MgO-MnS, Ce₂O₂S-MgO-MnS and Ce₂O₂S-MnS, respectively. The precipitation of pure MnS was suppressed in the steel with 0.024% Ce, while the number density of total inclusions increased significantly in the steel with 0.037% Ce, causing the inclusions distributing densely. Ce addition refined the microstructure of tested steels by promoting AF formation and polygonal ferrite distributing evenly. Dispersive distribution, low lattice mismatch against α-Fe, as well as lower number density of pure MnS caused the highest number density of effective inclusions (nucleus of AF formation) in 0.024% Ce-treated steel.

Amounts of rare earth oxides were transferred into mold fluxes for the continuous casting of rare earth alloyed heavy railway steels. B₂O₃ was added to improve the viscosity properties and the crystallization behavior of this traditional mold flux. Thus, in this paper, effects of B₂O₃ on viscosity, structure, and crystallization of CeO₂-bearing mold fluxes for casting rare earth alloyed heavy railway steels were investigated by rotating cylinder method, Raman spectroscopy, and magic angle spinning nuclear magnetic resonance (MAS NMR). Experimental results revealed that with the addition of B₂O₃, viscosity values of mold fluxes at some certain temperatures decreased significantly. By analyzing the structure of glassy mold fluxes, it can be observed that B₂O₃ behaved as a network-forming oxide within the studied system. However, the introduction of the weak bond energy of B–O and the transition from four-fold coordination boron to three-fold coordination boron with loose structural units mainly reduced the viscosity. Moreover, results of X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed that B₂O₃ decreased the crystallization of the crystal phase Na₄Ca₄(Si₆O₁₈) and the solidus temperature of mold fluxes. Thus, these results obtained can provide guidelines for designing new mold fluxes for casting rare earth alloyed steels.

In this study, an optimum tempering temperature after a thermo-mechanical control process (TMCP) was proposed to improve the hydrogen-induced ductility loss of high-vanadium X80 pipeline steel. The results showed that with increasing tempering temperature from 450 to 650 °C, the size and quantity of granular bainite decreased but the spacing of deformed lath ferrite and the fraction of massive ferrite increased. The number of fine vanadium carbides increased as well. However, as the tempering temperature increased to 700 °C, the microstructure of T700 steel completely converted to massive ferrite and the grain size became larger. Additionally, the amount of nanoscale precipitates decreased again, and the mean size of precipitates evidently increased in T700 steel. The steel tempering at 650 °C, containing the most vanadium precipitates with a size less than 20 nm, had the lowest hydrogen diffusion coefficient and the best resistance to hydrogen-induced ductility loss.

The CaO-Al₂O₃-based mold fluxes are proposed for the Ce-bearing heavy rail steel continuous casting because of the low reactivity. Effects of CeO₂ on the melting temperature, the viscous property, and the crystallization behavior of the CaO-Al₂O₃-Li₂O-B₂O₃ mold fluxes were studied using hemisphere melting point method, rotating cylinder method, and X-ray diffraction (XRD) in the present work. The microstructure of the mold fluxes was analyzed by Fourier-transform infrared spectroscopy (FTIR). The results revealed that the addition of CeO₂ would increase the melting temperature, but decrease the viscosity at each temperature due to its influence on increasing the depolymerization of the mold fluxes at high temperature. The precipitation of CaO was restrained and CaCeAlO₄ generated with increasing CeO₂ content since the crystal phases were affected by the microstructure of the melts. The change of the crystalline phases in mold fluxes influences the break temperature and the viscosity of the mold fluxes below the break temperature. These results obtained can provide guidelines for designing new mold fluxes for casting rare earth alloy heavy rail steels.

The possibility of vanadium and titanium participating in the CaO desulfurization reaction has been evaluated. The desulfurization products of CaO which were added to liquid iron containing vanadium–titanium in lab conditions were observed. At the early stage of adding CaO, titanium and sulfur ware agglomerated on the surface of CaO particles. The particles were composed of CaO, TiO₂, and CaS. However, vanadium oxide was not detected. It was proposed that the titanium rather than the vanadium could react with CaO and sulfur. The desulfurization kinetics experiment showed that the high titanium content in liquid iron reduced desulfurization velocity, while vanadium had little effect on the desulfurization. The reason for this was that the TiO₂ which surrounded the CaO particle impeded the mass transfer of sulfur. The vanadium and titanium had a little influence on the final sulfur content of CaO desulfurization. The theoretical discussion of these phenomena was carried out. The controlling reaction of final sulfur content was (CaO) + [S] + [C] = (CaS) + CO(g).