Metals

The strong coupling between the dynamically evolving thermal roll profile and strip shape across a multi-stand hot finishing mill poses a major challenge to shape control. To address this issue, this paper proposes a multi-stand collaborative zone cooling method based on a thermo-mechanical coupling inverse problem. A dynamic heat-transfer coefficient model incorporating multi-source disturbances (spray angle, water flow density, and roll surface temperature) is established, and an online inversion based on the Gauss–Newton method using measured post-service roll temperatures improves the temperature prediction accuracy to over 95%. A cascade-inheritance mechanism is revealed, whereby the thermal crown formed at an upstream stand alters the incoming strip profile and thereby affects the roll gap of downstream stands; the associated decrease in rolling-force regulation efficiency from F1 to F7 is explained by the increasing strip plastic stiffness. A differentiated strategy is accordingly developed: upstream stands (F1–F3) actively regulate lateral metal flow through the thermal crown, whereas downstream stands (F4–F7) rely on zone cooling to compensate for plastic stiffness effects. A mapping from the loaded roll gap profile to the zone cooling flow is established, and a Mamdani fuzzy adaptive algorithm provides real-time compensation within the 150 ms control calculation cycle (distinct from the up-to-10 s physical response time of the actuators). Industrial validation on the downstream stands (F5–F7) of a 1580 mm hot strip finishing mill reduced the upper/lower work roll temperature difference from 7 to 12 °C to within 5 °C, decreased the average C40 crown by 8.7%, raised the excellent edge rate (C15–C40 ≤ 20 µm) from 59.4% to 83.4%, and expanded the adjustable range of the thermal crown by more than 2.5 times. In addition, numerical analyses extend the collaborative regulation strategy to the full mill (F1–F7) and demonstrate its applicability; these full-mill results are model-based predictions rather than directly validated industrial responses.

This study investigates a two-stage duplex process for producing low-carbon ferrochrome based on sequential mixing of molten ore–lime and metallic melts, with emphasis on its adaptation to the raw materials and operating conditions of the Aktobe Ferroalloy Plant. Unlike the conventional process, in which the chromite ore–lime charge directly interacts with ferrosilicochromium, the proposed approach distributes FeSiCr between two successive stages of melt interaction to improve chromium reduction and metal–slag separation. Kempirsai chromite ore, lime, and ferrosilicochromium (FeSiCr 48) were used as raw materials. Thermodynamic analysis using HSC Chemistry 6.0 confirmed the feasibility of the main reduction reactions at 1600–1800 °C. Pilot-industrial trials produced ferrochrome containing 71.42–73.15% Cr and 1.28–1.31% Si, while the final slag contained 1.54–1.58% Cr₂O₃ and 0.11–0.14% FeO. X-ray diffraction analysis identified merwinite, gehlenite, and spinel-type solid solutions containing chromium. Dicalcium silicate was not detected, consistent with the observed stone-like structure of the cooled slag. Chromium recovery reached approximately 70%, compared with approximately 65% for the conventional process. The results demonstrate the potential of sequential FeSiCr distribution to improve chromium utilization and reduce chromium losses to slag under the specific conditions of ferrochrome production at the Aktobe Ferroalloy Plant.

The strength–ductility trade-off limits the wider application of high-strength titanium alloys in aerospace. Here, a new Ti-3.7Al-3V-3Fe-1.7Mo-0.5Cr alloy is designed based on d-electron alloy design theory and molybdenum equivalence, and the dual-phase microstructure is tailored by varying the cooling rate after solution treatment, which governs both the phase fraction and the spatial connectivity of the primary α (α_p) and β phases. In the furnace-cooled (FC) condition, the α_p phase exhibits the highest fraction (76%) and a continuous network with isolated β islands, whereas higher cooling rates (AC and WQ) yield lower fractions (50% and 38%) and a continuous β matrix, confirming that decreasing cooling rate promotes α_p connectivity and β isolation. Consequently, the FC sample achieves a tensile strength of 1250 MPa and a total elongation of 18.4%, significantly higher than those of the AC (14.0%) and WQ (10.0%) samples. This interconnected architecture enhances dislocation storage and work hardening, while enabling effective load transfer and strain compatibility between phases, thereby suppressing strain localization and interface debonding. In situ SEM observations further confirm that high-density α_p/β interfaces, crack deflection, and deformation twinning also play a key role in enhancing damage tolerance. These findings identify phase connectivity as a key microstructural parameter for overcoming the strength–ductility trade-off in α/β titanium alloys.