Optimization of Continuous Casting for Preventing Surface Peeling Defects on Titanium-Containing Ferrite Stainless Steel.

The surfaces of cold-rolled titanium-containing ferrite stainless steel (TCFSS) strips produced from scrap are prone to severe peeling owing to cracking near slab inclusions during hot rolling. In this study, the Taguchi method was used to prevent peeling defects and clogging of the submerged entrance nozzle, and the optimal casting parameters, such as the degree of casting overheating, casting speed, stirring time, and inclination, were determined. The results showed that increasing the degree of casting overheating and decreasing the casting speed prevented clogging and effectively mitigated peeling defects. Sample A3B1C3D2 had the optimal parameters to reduce the clog thickness to less than 1.5 mm, i.e., a degree of overheating of 60 °C, a casting speed of 0.80 m/min, a stirring time of 12.0 s, and an inclination angle of 6.0°. Sample A3B1C1D3 had the optimal parameters to prevent peeling defects, i.e., a degree of overheating of 60 °C, a casting speed of 0.80 m/min, a stirring time of 10.0 s, and an inclination angle of 6.2°. When casting using these optimal parameters, no peeling defects were observed on the surfaces of the TCFSS strips. The TCFSS strips produced using the optimized parameters exhibited the required mechanical properties and satisfied the design criteria. The parameters included a tensile strength of ≥415 MPa, a yield strength of ≥205 MPa, an elongation of ≥22%, and a hardness of ≤89 HRB.

Optimization of Hot Rolling Scheduling of Steel Strip with High Bending Performance.

Poor formability in hot-rolled strips may be attributed to the many pearlite-banded structures (PBSs) that develop in steel during the hot-rolling process. The challenge of manufacturing strips with minimum PBSs is that multiple factors influence the amount and distribution of the PBSs. This study used the Taguchi method to find the optimum hot-rolling parameters to obtain strips with a reduced number of PBSs. The strips were then subjected to bending tests to evaluate their ductility. The first part analyzes the contribution of selected parameters to the hot-rolling process: (1) finishing rolling temperature, (2) finishing rolling speed, (3) coiling temperature, and (4) coiling speed. The second part confirms, using bending tests, the influence of the finishing rolling temperatures 780, 800, 820, 840, 860, 870, and 880 °C on the formability of an A36 hot-rolled strip. Based on the experimental protocol for the study, the optimal process parameters were determined to be the finishing rolling speed (0.80 m/s), finishing rolling temperature (870 °C), coiling speed (2.80 m/s), and coiling temperature (650 °C). When the A36 strip was prepared at the optimum parameters, the average length and thickness of the PBS were 108.61 ± 0.11 µm and 10.18 ± 0.12 µm, respectively. According to the Taguchi analysis, the finishing rolling temperature had the most significant influence on the dimensions of the PBS. In tests where the hot-rolled A36 strip was bent to 90° and 180°, at the finishing rolling temperatures of 870 °C and 880 °C, no cracking was observed at the R angle.