Energy-aware planning of continuous casting and hot rolling considering steel grade upgrades

Abstract Continuous casting (CC) and hot rolling (HR) are the key processes in steel production for turning liquid steel into solidified coils with order-specific properties and dimensions. Due to different process restrictions, planning and scheduling of both processes is traditionally completely separated. As a result, the intermediate products after CC, so-called slabs, are stored temporarily for further processing, where they cool down considerably. However, for HR slabs have to be reheated to a process temperature of approximately $$1,200^\circ $$ C, making the CC-HR interface one of the most energy-intensive stages in steel production. Integrated CC-HR planning could help minimize slab waiting times and maximize energy efficiency. To address this issue, we formulate a mixed-integer non-linear program (MINLP) that utilizes flexibility stemming from steel grade upgrades to improve coordination. We investigate the potential of integrated CC-HR planning and its dependence on upgrade flexibility and product variety through a numerical study. Problem instances with increasing planning horizons are considered to assess scalability. As larger instances cannot be solved by an exact solver within practical time limits, a GRASP-based heuristic enhanced by a local branching improvement phase is employed. The findings indicate considerable improvement potential at the CC-HR interface, with most benefits attainable under moderate flexibility. These effects remain stable across different planning horizons.