Even the new, lighter Audi A8 structure is not completely aluminum, and that is testament to the developments in steel—more specifically, high-strength steel (HSS). “High-strength steel is an excellent solution, combining high stiffness and low intrusion,” said Heinrich Timm, head of the German company’s aluminum and lightweight design center in Neckarsulm.
It is a view that is shared by Jon King, Director of Corus Automotive Engineering. “Lightweight materials push costs up but you get a better ride and handling setup in the vehicle,” he said. “From a steel industry perspective, if we can still produce a steel-based material that affords equivalent lightweighting opportunities, and can be produced reasonably conventionally, where is the need to make the shift to a completely different material for volume vehicles?”
Corus is busy working on new products that will further aid the automotive industry. “One material we have got in development is our version of Twinning Induced Plasticity (TWIP) steel, called HSD (High Strength and Ductility),” he shared. By introducing a high proportion of manganese content, somewhere between 10 and 15%, the overall density of the steel comes down by 6 or 7%, and it is a much more formable material.
King said that Corus is also looking at hybrid materials to get stiffness and dent-resistant performance benefits. “The industry has looked at sandwich materials before, with two thin layers of steel, with a piece of plastic in between,” he said. “To get the most benefits of that configuration today, we would use advanced high-strength steel. So I can see further development in sandwich steels, or even in one side of laminated steel, with a different material on the nonvisible side to enhance stiffness, while still allowing steel to present the appearance of a surface finish quality and structural performance.”
King noted that there is a range of potential areas that the steel industry is looking at, as well as continuing to strengthen the formability envelope with regular advanced high-strength steel. “The current generation of advanced HSS that are either in production or the final stages of development will account for somewhere in the region of 40 to 45% of the application that you see in a steel body including closures.”
Over the next seven years, the industry will see these changes coming through, said King, but it will not increase beyond that 45% barrier. “Because the way vehicle structures are defined at the moment, only an element of its performance is strength limited, which is where the main HSS opportunities are; it doesn’t give much benefit in bending properties,” he said.