Recent technology developments in the production of grain-oriented electrical steel

Despite a long history of continuously improved magnetic properties, the further development of grain-oriented electrical steel is still an exciting field for industrial and joint fundamental research. Today, the driving forces for research and development (R&D) are on one hand increasing quality demands, i.e. still lower losses for more energy-efficient transformers and less transformer noise, and on the other hand the pressure to reduce manufacturing costs in order to stay competitive on the market. Evidently in the last years, the latter aspect has become the mainspring for most of the industrial R&D activities. Now nearly all producers are aiming at more compact and less expensive production routes. From the new techniques under development, most advanced in commercial realization is the application of low slab reheating temperatures in the range 1150...1300°C instead of up to 1400°C in the classical processes. A radical new method is thin slab casting and direct hot rolling used for steels with a system of inherent plus acquired inhibitors, the latter formed by nitriding the cold rolled strip. This method is very promising and far advanced in industrial tests. Another way for process shortening is to cast directly the hot strip from the steel melt by a twin-roll method. In pilot line tests, good cold workability and good magnetic properties have been achieved by optimising chemical composition, casting conditions, and subsequent thermo-mechanical treatments and by working with inherent plus acquired inhibitors. Another theoretical potential for cost and time saving is to replace box annealing for secondary recrystallization by short-time continuous annealing. Such processes are under development, partly using special in-line procedures to realize fast inhibitor creation after primary recrystallization, but are today still far away from commercial realization.