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As one of the vital ways to improve the converter heat balance and increase the scrap ratio, scrap pre-heating technology has attracted much attention from researchers. The aim of this paper is to reveal the effect of the oxy-fuel lance parameters on the temperature field, flow field, and scrap pre-heating temperature in the ladle by means of numerical simulations. For this, a three-dimensional mathematical model containing the turbulence model, the porous medium heat balance model, and other models has been developed. The research results show that the rational and correct choice of gas flow rate, lance position, and nozzle angle has an important influence on the temperature field and the average scrap temperature. When the gas flow rate increases, the internal annular combustion zone of the scrap gradually expands, the cold zone at the bottom of the scrap continues to decrease, and the average scrap temperature keeps increasing. When the gas flow rate is 5000 m3/h, and the average scrap temperature reaches 1197 K, the pre-heating time is 9.98 min. Lowering the oxy-fuel lance position helps to reduce the cold zone at the bottom of the scrap and increases the average temperature in the cold zone. Reasonable selection of the nozzle angle is conducive to improving the uniformity of the flow field. When the angle of the nozzle is 15°, the gas circulation zone is the largest, and the time to reach an average scrap temperature of 1197 K is the shortest.

Na2O is an alkaline oxide, which can significantly improve the dephosphorization ability of converter slag. The effect of Na2O on the dephosphorization of converter slag was analyzed with a high-temperature dephosphorization experiment in a MoSi2 resistance furnace. We found that the dephosphorization rate increased with the increase of (Na2O) in the dephosphorization slag. The elements of Ca, Si, O, and P in the dephosphorization slag are distributed in the same area, mainly in the form of phosphate minerals, such as Ca2SiO4·0.05Ca3(PO4)2 and 6Ca2SiO4·Ca3(PO4)2. After adding Na2O, part of the Na will replace the Ca in the phosphorus-containing phase to form Ca2SiO4·Ca2Na2(PO4)2. The industrial test showed that the average dephosphorization rate in the early stage of the test heats with the CaO-MgO-FeO-SiO2-0.5%Na2O slag system could reach 62.39%, which was 19.62% higher than that of the conventional heats. The average basicity of the final slag was 0.19% lower than that of the conventional heats, while w(P2O5) increased by 0.36%, and T.Fe decreased by 0.69%. The average consumption of the slagging materials was 35.93 kg/t, which was 7.24 kg/t less than that of the conventional heats. Through thermodynamic calculation, we found that with the increase of (Na2O), the phosphorus distribution ratio between slag and steel increased significantly, the area of the liquid phase zone of the slag system increased continuously, and the viscosity decreased continuously.

The problem of nitrogen pickup in the smelting process of the electric arc furnace (EAF) has not been solved well. Using seven slag–steel equilibrium experiments and theoretical analysis, the relation of the foaming index and optical basicity with the nitrogen capacity of slag was clarified. Meanwhile, the effect of slag composition on the equilibrium distribution ratio of nitrogen and the mass transfer coefficient of nitrogen pickup was also studied. The results show that, with the increase in slag basicity, the nitrogen pickup amount, nitrogen pickup rate, and nitrogen equilibrium distribution ratio LN increase. Increasing the foaming index of slag and reducing its optical basicity will increase the nitrogen capacity of slag, which is conducive to hindering the nitrogen pickup of molten steel. The relationship between slag optical basicity and nitrogen capacity can be expressed as lgCN = −5.59lgΛ − 12.41. With the increase in the Al2O3 content of slag, the nitrogen pickup amount of molten steel decreases and the nitrogen pickup rate decreases. The test with MgO = 7.5% showed the highest nitrogen pickup rate and the highest nitrogen pickup mass transfer coefficient, which were 0.21 × 10−4%/min and 1.97 × 10−4 cm/s, respectively. The test with Al2O3 = 7.5% in slag showed the lowest nitrogen pickup rate and the lowest nitrogen pickup mass transfer coefficient, which were 0.08 × 10−4%/min and 1.35 × 10−4 cm/s, respectively.

The effects of the Y- and Ti-containing inclusions on the tensile and impact properties of reduced activation ferritic martensitic (RAFM) steels were evaluated. Four steels with different Y and Ti contents were produced via vacuum induction melting. The size and quantity of inclusions in the steels were analyzed using scanning electron microscopy, and the oxide particle formation mechanism was clarified. These inclusions helped to enhance the pinning effect of the austenite grain boundaries based on the Zener pinning force. The average prior austenite grain sizes, measured via the linear intercept method, were 12.34 (0 wt.% Ti), 9.35 (0.010 wt.% Ti), 10.22 (0.030 wt.% Ti), and 11.83 (0.050 wt.% Ti) μm for the four steels, in order of increasing Ti content, respectively. Transmission electron microscopy was conducted to observe the fine carbides. The strength and impact properties of the steel containing 0.010 wt.% Ti were improved, and the ductile-to-brittle-transition temperature was reduced to −70.5 °C. The tensile strength and impact toughness of the steel with 0.050 wt.% Ti were significantly reduced due to the coarsening of both the inclusions and grain size, as well as the precipitation of large TiN inclusions. The RAFM steel with approximately 0.015 wt.% Y and 0.010 wt.% Ti exhibited an optimized combination of microstructures, tensile properties, and impact properties among the four steels.

This study investigated the microstructural stability and mechanical properties exhibited by China low activation martensitic (CLAM) steels with different yttrium (Y) contents over 3000 h of aging at 550 °C. Scanning electron microscopy, electron backscatter diffraction analysis, and transmission electron microscopy were employed to investigate the microstructural evolution of the steels. Results indicated that grain boundary migration was slow and the Laves phase precipitation was delayed in Y-containing steels. Grain boundaries at different angles in 0Y and 6Y CLAM steels were significantly affected, and those in 36Y and 71Y alloys exhibited negligible changes during the long-term thermal aging. Moreover, Y contents had appreciable effects on the strength and toughness of the aged steels. The stable microstructure of Y-containing CLAM alloys is responsible for improved strength and impact toughness during aging.