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 the very different process restrictions, the planning and scheduling of the two processes traditionally follows a separated regime. As a result, the intermediate products after CC, so-called slabs, are stored temporarily for further processing. During this process they cool down considerably and must be reheated to the required HR process temperature of approximately 1,200°C, making the CC-HR interface one of the most energy-intensive stages in the entire steel production. Integrated planning of CC and HR could help minimize slab waiting times and maximize energy efficiency. To address this issue, we formulate a generally applicable mixed-integer non-linear program (MINLP) model that exploits flexibility stemming from steel grade upgrades. Based on a linear reformulation of the model and four different flexibility modes we investigate the potential of upgrades on the energy-aware planning of CC and HR as well as how this potential is influenced by upgrade flexibility and production variety. The objective is to minimize the total costs consisting of penalties for unassigned material in CC and unused capacity in HR, the energy costs incurred for reheating the slabs, tardiness costs and steel grade upgrade costs. A comprehensive numerical analysis demonstrates that even moderate upgrade flexibility reduces total costs, with savings escalating alongside production variety. This study highlights the untapped potential of integrated planning, offering actionable insights for the steel industry to align economic and sustainability goals through process coordination.

# Bio

Thomas Volling is Professor and Head of the Production and Operations Management research group at TU Berlin and visiting lecturer at the University of St. Gallen. His research centers on problems of production and operations management particularly the modeling and solution of challenges in the manufacture and sales of high-variant products. He is also engaged in topics related to sustainability and digital transformation in operations. Thomas Volling has played a key role in acquiring and conducting more than 15 publicly and industrially funded research projects, collaborating with companies such as Volkswagen, Salzgitter, ThyssenKrupp, Bosch, MAN, and PSI. His research has been published in leading international journals, including Applied Energy, Computers & Operations Research, European Journal of Operational Research, International Journal of Production Economics, and Transportation Science. Since 2025 he is deputy and designated chairmen of the German Academic Association for Business Research and serves as department editor of the Journal of Business Economics, responsible for the area Production, Logistics, and Operations Research.