Zhiwei Liu

The mechanism by which Sb influences the hot ductility and fracture behavior of corrosion-resistant steel within the temperature range of 650–1200 °C was systematically investigated using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The temperature interval of the ductility trough and the underlying mechanisms responsible for its occurrence were elucidated. The results indicated that ductility troughs for the 0.09Sb and 0.15Sb steels occurred at 726–949 °C and 736–995 °C, respectively. Increasing Sb content broadened the ductility trough temperature range and shifted the minimum ductility temperature to higher values. The ductility trough was attributed to the combined effects of grain boundary ferrite films, coarse precipitates, and non-equilibrium grain boundary segregation of Sb. During deformation in the austenite–ferrite two-phase region at 800 °C, the hot ductility is primarily governed by the thickness of the grain boundary ferrite film. These ferrite films are prone to stress concentration, thereby reducing the hot ductility of both the 0.09Sb steel and the 0.15Sb steel. In the single-phase austenite region at 900 °C, coarse Ti(C,N) and MnS precipitates readily act as crack initiation sites, leading to intergranular fracture in the 0.15Sb steel. Non-equilibrium Sb grain boundary segregation further weakens grain boundary cohesion, thereby deteriorating the hot ductility of the steel. Moreover, increasing Sb content enhanced the magnitude of non-equilibrium grain boundary segregation and elevated its peak temperature, thereby raising the minimum ductility temperature. This work provides a theoretical basis and technical guidance for optimizing the continuous casting of Sb-containing corrosion-resistant steel in industrial production, thereby contributing to improved surface quality of continuously cast slabs.

To address the strength fluctuation observed in Ti microalloyed steel, the effects of final rolling temperature, coiling temperature, and Ti content on the microstructure, secondary phase precipitation behavior, and grain size were investigated through simulation experiments. Various characterization techniques were employed to elucidate the underlying causes of the strength variation, and key control strategies were proposed. The results indicate that the strength fluctuation is primarily influenced by the presence of nano-sized TiC precipitates. The precipitation behavior of TiC can be effectively controlled by adjusting the content of non-metallic elements as well as the final rolling and coiling temperatures. Higher final rolling temperatures combined with appropriate coiling temperatures promote increased TiC precipitation; however, excessively high temperatures may result in grain coarsening and inhomogeneous precipitate distribution. The optimal processing parameters were determined to be a final rolling temperature of 860 °C and a coiling temperature of 600 °C.