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.

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.

The nozzle structure has an important effect on the fluid flow in the mold, which can significantly improve the solidified shell and product quality of alloy steel round bloom. The transient fluid flow, heat transfer, and solidification behavior under different nozzle structures and mold electromagnetic stirring (M-EMS) are investigated using a 3D transient mathematical model. The results show that a third small recirculation zone appears near the meniscus after the application of the swirling flow nozzle (SFN). The impact depth of SFN is shallower than that of the original submerged entry nozzle (SEN) impact, and the lower circulation zone is shifted upward. The horizontal swirling flow generated by SFN can significantly weaken the washing of the initial shell by high-temperature steel and improve the uneven growth phenomenon of the inner and outer curved solidified shell caused by mold curvature. The swirling flow produced by M-EMS in the mold can also improve the washing of the initial shell by the high-temperature jet and the uneven growth of the inner and outer curved shell. M-EMS can expand the high-temperature zone in the upper part of the mold, promote the superheat dissipation of the molten steel, and promote the growth of the solidified shell. In addition, after the application of M-EMS, the tangential velocity of –15° SFN in the meniscus is smaller, and the resulting liquid level fluctuation is lower at 5.07 mm, which is less likely to produce slag entrapment and is conducive to improving the quality of round bloom.

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.