Automakers continue to have problems reducing the weight of motor vehicles that improve fuel economy without sacrificing safety characteristics. Much strategic sourcing attention is focused on the battle of materials for future changes of body-in-white metallics. And that has given steelmakers a chance to work with automotive engineers and buyers to develop new grades of lighter, stronger and more formable sheet products for the automobile body.

Some auto designers even see a time when 90% of the body structure could be some form of high-strength steel. That would be somewhere around 17.5 million tons/year, as compared with an estimated 3.5 million tons last year. And that's despite the fact that high-strength steels can carry a price premium above mild steel grades; on average, ultra high-strength sheet sells for about twice the price of automotive-grade cold-rolled sheet.

However, an economic analysis by Porsche Engineering Services Inc., Troy, Mich., says: "It will cost no more to build a typical auto body structure in its class with high-strength steels, and could even yield potential cost savings," as processors and automakers become more accustomed to the material. Jim Fekete, senior advisor in the metal fabricating division of General Motors Corp., agrees that total production costs are the same or less because less material is used to fabricate car parts from laser welded tailored blanks than benchmarked averages for traditional hot-rolled, cold-rolled ands coated carbon steels.

John Fillion, chairman of the U.S. Automotive Materials Partnership at the U.S. Council for Automotive Research ( USCAR ) says researchers have found composites and other generations of new materials that could reduce vehicle weight by more than 60%. "But, so far, the cost of these materials, the ability of engineers to design cars with them, and the processes required to manufacture them are inadequate for high-volume production of safe, durable, recyclable and affordable automobiles," he says. Fillion, who is also senior manager for body materials engineering at DaimlerChrysler, believes "the cars of the future will continue to be a mix of materials, with the most likely metals being aluminum, magnesium, titanium and high-strength steels.

"CAFE regulations represent the main force behind our choice of metal," says Brett Hardy, senior manager for raw materials purchasing at DaimlerChrysler Corp. in Auburn Hills, Mich., discussing the federal government's "corporate average fuel economy" ( CAFE) requirements. Under the current CAFE standards, passenger cars are required to achieve a corporate vehicle, or fleet, average of 27.5 miles per gallon (mph) and light-duty trucks are required to average 20.7 mpg. There is a move in Congress to boost these standards by 10%, which auto engineers say would mandate the use of more aluminum, magnesium, plastics and varying types of composites and the high-strength lightweight steels.

DaimlerChrysler—and the other automakers—still primarily use steel for auto production. "Aluminum clearly offers us opportunities to cut weight to meet fuel-efficiency guidelines," says Hardy, "but it is still much more expensive than steel." In all probability, the automakers would find a way to keep the lowest-cost materials in the highest number of applications, says Andy Sherman, chairman of the materials technical team at the Partnership for a New Generation of Vehicles, a unit of USCAR , "which means that steel of some type would continue to be the dominant material in autos."

A rule of thumb in Detroit and among the transplants is that new materials are added to the production cycle only when they reduce costs and create competitive advantage. Still, high-strength grades have risen to 20% of the steel used by automakers from 14% a decade ago. High-strength steels aren't new in automotive applications. But, the percentage could be higher, says Dan Kelly, supplier quality manager for steel at DaimlerChrysler. "Steel suppliers aren't as familiar with these materials as they could or should be."

Ed Opbroek program manager for the Ultra Light Steel Auto Body (ULSAB) project in Middletown, Ohio, admits that "most of the car companies have gotten bloody noses the past several years with high-strength steels." First, the uniformity of the early materials' properties was not all that uniform. And, second, auto manufacturing organizations usually had part designers in one place, tool designers in another, production people somewhere else and purchasing personnel trying to figure out what each design group wanted. The prevailing experience base for all concerned was with "mild" (carbon) steel grades, yet high-strength steels have a substantial amount of springback when it is being formed. Now, there is more uniformity to the steels. And design-purchasing organizations are cross-organized, so communications between designers, buyers and suppliers has improved.

Still, "buyers and engineers at Tier I and Tier II suppliers have more expertise with high-strength steels than the automakers," says Jay Baron, director of manufacturing systems at the University of Michigan's Center for Automotive Research. He believes that expanded communications will be necessary between auto industry purchasing and engineering teams with steel components suppliers "very early in the design phase" to boost the use of high-strength steels in the future.

Steel parts are already more dent-resistant and up to 30% stronger than a decade ago because of the new use of high-strength steels. Now, the automakers—through their various engineering and materials research groups and purchasing organizations—have been lobbying steel suppliers to use their processing technologies to continue developing lighter grades of high-strength sheet steels. "This is especially important," says Barbara Whittaker, executive director of worldwide metallic commodities purchasing for General Motors Corp. in Detroit, "as we get into different kinds of metals to adjust to some of the demands that our vehicles are requiring these days."

She says that "the next generation of high-strength steel materials that are being developed will have to fit the exteriors and structures of our vehicles of the future." In the development process, "we need to come up with steels that can reduce mass and do things that we look for in these other materials," she adds. Purchasing executives at the car companies are already learning a whole new set of acronyms when ordering sheet steels to meet tougher durability requirements at reduced weight. Buying high-strength steel isn't a commodity buy, so purchase orders now specify such products as HSS, high-strength steel; UHSS (ultra high-strength steel) and AHSS (advanced high-strength steel).

To help reduce weight, improve safety and ride quality, minimize noise and increase the durability of vehicles, North American auto engineers created a substantial number of new applications for these higher-strength yet lighter steels for 2002 model cars, pickup trucks, sport utility vehicles, vans and crossover vehicles. Although several 2002 vehicles—including the Chevrolet TrailBlazer, GMC Envoy and Nissan Altima—are bigger than their 2001 predecessors, the increased use of lighter steel grades and forms has kept weight and fuel economy ratings within the automakers' targets. Ford uses high-strength steel in the Windstar and for both the body structure and exterior body panels of the Focus.

Other automakers are taking the lead from Honda of America in Marysville, Ohio, which is working with its steel suppliers to settle on specific grades of mild and high-strength steel to cut costs. "Changeover times, the setups associated with different materials, and the processing varies quite a bit depending on the material itself," says Jeff Tomko, Honda's senior purchasing manager. "If you can reduce the number of grades of material and increase the volume, that decreases the setup costs." However, "commonizing" grades of steel requires cooperation between steelmakers and automotive purchasing and design departments. "When a new drawing or material comes out, we try to adapt it to our current system, or we change part of our system to accommodate the new material to see what the benefits are," Tomko says.

In general, conventional high-strength steels have a good combination of formability and weldability when stamped into body panels. However, formability is limited when these grades are attempted for such crashworthy-critical components as front and rear rails, rocker panels, pillars, and cross members. This has led to the development of the ultra high-strength and now advanced high-strength steels, which include dual phase and transformation-induced plasticity ( TRIP ) grades. These steels are easier to form than high-strength grades with similar initial yield strengths because they have much higher final part strength. As a result, the advanced high-strength steels are more suitable for thin-gauge exposed panels or formed parts that must be durable and resist metal fatigue.

Ispat Inland Inc. in Chicago has ultra high-strength steel in its product line-up—which it calls Generation 2000—that is cold rolled, continuously annealed and, when necessary, electrogalvanized. The basic benefit of this material is a higher strength-to-weight ratio when used to make door intrusion beams, bumper reinforcement beams, structural cross members and such seat parts as tracks, pillars and risers as well as side sill reinforcements, belt line reinforcements, springs and clips.

Ispat Inland is already selling 590 MPa ultra high-strength to Honda for bumpers on the Accord and for rocker panels and rocker reinforcements on the Cadillac CTS and other GM models. Charles Wilson, automotive steel products manager for Ispat Inland, suggests that door beams, seating tracks and bumpers are markets of opportunity for high-strength steels. "It's a complex sourcing issue, but the fact is that buyers and the engineers want to use lighter metal, to get more pieces off each coil and to use fewer parts per vehicle," he says, "and all that makes a highly engineered product like ultra or advanced high-strength a good choice."

In fact, steel executives are hoping the purchasing of ultra and advanced high-strength steels will be boosted by two Auto/Steel Partnership projects involving automotive front-end structures and closure panels. Ted Diewald, executive director of the Southfield, Mich.-based engineering team, says projects are trying to cut weight as much as possible—25% in the case of hoods, doors and other closures—with advanced high-strength steels and without the need for costly new equipment in metal fabricating plants and production body shops. The partnership involves the Big Three automakers and 10 U.S. and Canadian steel companies.

The first Auto/Steel Partnership project is focused on optimizing auto body front ends—i.e., everything from the front bumper back to the left-side and right-side B pillars on a vehicle—and using advanced high-strength steels, assuring compliance with current and future government safety standards and validating the formability and manufacturability of such steels. The second project is intended to determine methods and materials to reduce by one fourth the weight of hoods, doors, deck lids, rear hatches and tailgates using existing parts-making processes as much as possible.

The baseline for the front-end study is the ULSAB body-in-white engineering work sponsored by 35 steel producers from 18 countries around the world. Meanwhile, the Ultra Light Steel Auto Closures (ULSAC) consortium is using the 2002 Jeep Liberty as the reference vehicle for the its focus on front doors. Thomas W. Sidlik, executive vice president for procurement & supply at DaimlerChrysler and general manager of Jeep operations, says the use of advanced high-strength steels in the Liberty allowed the automaker to install innovative and lower-cost manufacturing technologies at assembly operations in Toledo, Ohio.

"These doors are lightweight, efficient structures that offer superb crash performance, and they are affordable to manufacture in large quantities," according to Sidlik. Darryl Martin, who just retired as senior director for automotive applications at the American Iron and Steel Institute, acknowledges that "the use of advanced high-strength steels demonstrates ongoing potential for reducing mass in automotive body panels, while maintaining dent resistance."

Patrick H. Loney, manager of customer satisfaction at WCI Steel Inc. in Warren, Ohio, says the firm's cold-rolled and galvanized ultra high-strength steel sheets are already being used by various automakers for door beams. Metallurgist Benda Yan at Ispat Inland's research department in East Chicago, Ind., believes the use of advanced high-strength dual phase and TRIP steels could reduce the production requirements of current high-strength steels by 25%. He is leading a steel industry study on six ultras and advanced high-strength steels to provide quality data on fatigue and other durability criteria needed by the automakers.

At present, most advanced high-strength steels are available to auto industry buyers are grades with 500 megapasal (MPa) minimum yield strength and 600 MPa minimum tensile strength. A U.S. Steel spokesman in Pittsburgh says these advanced high-strength steels will soon replace conventional high-strength steel grades for front and rear rails, crush cans, rocker reinforcements, pillar reinforcements, cowls, back panels, cross members, bumpers and door intrusion beams. "That's because they have improved formability, better capacity to absorb crash energy and an advanced ability to resist fatigue," he says. The purchasing organizations at Honda and General Motors have already qualified U.S. Steel's dual-phase galvanized advanced high-strength steel with a 590 MPa rating for fenders. U.S. Steel is involved in a cooperative research and development program in automotive high-strength steel sheet technology with Kobe Steel, a leading producer of high-strength steel sheet in Japan.

Their U.S. joint venture, PRO-TEC Coating Co. in Leipsic, Ohio, now makes hot-dip galvanized steel sheet of the same quality as that made in Japan and is the only U.S. company that can produce 590 MPa class galvannealed high strength steel. This structure enables them to supply the same quality products worldwide, ranging from general materials to upper-end high strength steels needed by carmakers. PRO-TEC Coating is already supplying the Big Three and several Japanese transplants with this high-strength steel product.

Recently, National Steel Corp. of Mishawaka, Ind. enlarged the advanced high-strength steel family with a grade having 500 MPa yield and 800 MPa tensile strengths. National Steel's new advanced high-strength steel (developed in partnership with NKK Corp. of Japan) retains good formability in presses even after being coated in hot-dip galvanized or galvannealed processes. "Auto manufacturers have wanted to use higher strength level steels for some time, but have been held back by the restricted formability of conventional steel designs," says Blake Zuidema, director of National Steel's automotive-focused Center for Product and Applications Development in Trenton, Mich. "Our joint National/NKK engineering studies have shown this new 800 MPa tensile strength dual phase steel provides equivalent energy absorption as conventional 350 MPa minimum yield strength HSLA steels, but at thicknesses which are up to 24% lower.''