Automakers are having to rethink their supply chains, now that new varieties of lighter, stronger steel are changing the ways that cars and trucks are made.

For years, carmakers have been shaving kilos off of their vehicles by incorporating lightweight, flexible aluminum and carbon fiber in their designs.  Lighter weight generally has meant more fuel efficient cars.

But new varieties of lighter, stronger steel are appearing in new vehicles:  Fiat Chrysler's Pacifica van, Honda's Ridgeline pickup truck, and several General Motors models.  Audi AG's latest A8 executive sedan is using steel again after years of running with an all aluminum body.

Steel and mining giant ArcelorMittal N.V. expects that worldwide, automakers' demand for press-hardened steel sheet will grow 36 percent by 2020.  The company is opening a third plant in Detroit to produce the next generation of lightweight, super-strong sheets of steel that are strong and malleable to use to create complex stamped parts.