CAFE standards will require auto-makers, on average, to produce vehicle fleets that average 54.5 mpg by 2025, considerably higher than current requirements. Since mass plays a major role in fuel economy, the immediate reaction is that low-density materials, specifically aluminum with a smattering of carbon fiber, are the solution, and that the days of steel’s hegemony are quickly coming to an end.
Not so fast, says Ron Krupitzer, vice president, automotive market for Steel Market Development Institute (autosteel.org
). “We find a lot of novice engineers, and those just coming into structural engineering from other parts of the company, who believe that low-density materials are the only solution. However, they are unfamiliar with the process issues, the cost, some of the limits on the design, and may be unaware of the new grades of steel that are in the 1800-1900 MPa range that will meet their needs.”
It’s an old story. In the early 1990s, Ford was proudly showing off its lightweight aluminum Taurus prototypes that made up its Synthesis 2010 program. A deep-dive into how a high-volume automaker would design, engineer and assemble an all-aluminum family sedan, Synthesis 2010’s greatest claim to fame is that much of the work was pulled off the shelf and used in Jaguar’s aluminum XJ and XF production cars. No high-volume production Ford ever used stamped and welded aluminum panels in its main structure. Nor did any other mainstream vehicle.
The reason? Steel fought back. Faced with the prospect of losing its meal ticket, the industry banded together and pooled its knowledge. New steel grades were investigated, engineering assumptions were challenged, and solutions were put forward that cut weight and retained strength. Says Krupitzer, “We had to educate the industry, and prove to them that we could do what we said was possible.” Unfortunately, automakers were all-too familiar with steel, having used it since the earliest years of the industry. They were certain they knew everything there was to know about the ferrous material, and a steel industry in decline and scratching to save its largest user base wasn’t going to change its mind. But it did, and it claims it will again.
] did a study with EPA on the Honda Accord, and FEV [fev.com
] did some multi-material work on the Toyota Venza,” says Krupitzer, “and these studies show it’s possible to get up to a [body-in-white] 20% weight reduction with steel, at a much lower cost.” In fact, he says, most of the steel solutions being forwarded are cost neutral because, despite the fact that the news grades cost more, automakers don’t have to use as much. Still, automakers are quite interested in aluminum panels at the moment, despite their cost. Aluminum panels may have the short-term future, but Krupitzer says that as long as steel stays close on weight saved, the cost advantage will tip the equation in steel’s favor. Thus, the aluminum-bodied Ford F-150 rumored to hit the market in 2015 may be neither as aluminum-intensive nor as long-term a program as is projected. The same goes for numerous other similar projects rumored to be moving forward throughout the auto industry. Unlike aluminum, steel has a robust recycling stream and low-alloy composition that means it doesn’t have to be sorted by grade, two big advantages.
This wouldn’t be the first time that steel has played the tortoise to aluminum’s hare. Consider the last-generation BMW 5 Series. BMW developed the structure from the A-pillar back around steel, and added on an aluminum front end for lighter weight. Yet the most recent version uses steel throughout with a smattering of other materials. Then there’s the work steel is now doing on the chassis; an area of study still in its infancy, but one that’s already paying big dividends. “Two years ago,” says Krupitzer, “we did a project with GM and Multimatic [multimatic.com
] to match the weight of the forged alumi-num lower control arm on the Malibu.” The result was a thin steel clamshell that matched the weight of the aluminum part, but was 30% cheaper. GM switched the part to steel.
Still, despite the steel benefits Krupitzer cites, don’t expect the car or light truck of the future to be made exclusively from steel. He explains that vehicles will be made from a variety of materials to reduce mass—aluminum, carbon fiber composites, magnesium, plastics, and steel. Of all these materials it is plastic, not aluminum, that Krupitzer sees as the greatest potential threat. If the cost can be kept down—a big “if” with volatile petroleum prices—expect to see plastic floors and bulkheads bonded within a steel superstructure.
According to Krupitzer, steel’s biggest problem “is convincing automakers that steel is a high-tech material that’s very appealing in terms of strength, recyclability, formability and cost. We’re sort of like the internal combustion engine,” he says. “There’s still a lot of life left in it.”
Steel: The Next Generation
With the help of a grant from the U.S. government to study integrated computational materials engineering of advanced high-strength steels, the steel and auto industries expect to create the third generation of advanced steels. The $6-million federal grant is funding a four-year study that includes the American Iron and Steel Institute (AISI), Ford, GM, Chrysler, the national labs, and scientists from five leading universities. “The goal is to look at the materials models we have to try and figure out how we go from the atomic and nano scales, and build up these properties all the way to the final parts,” says Ron Krupitzer of the Steel Market Development Institute. “That way, you could use computer-aided engineering and determine exactly what is needed and in what amount before anything was ever built.” Already steel makers expect to drop high-strength steel gauges from today’s 0.60-0.65 mm to 0.50 mm.