All eyes turn to new ways of making high-strength grades

Late last year, AK Steel became the first U.S. steelmaker to attain certification under a new international standard for quality management in the production of automotive-grade steel sheet products. The new certification is called the ISO/TS 16949:2002 Quality Management System. "It is a new

The International Automotive Task Force and the Japan Automobile Manufacturers Association developed the new quality standard in conjunction with the International Standards Organization. The Automotive Industry Action Group has adopted the standard for North America, and has decreed that producers of all automotive-grade steels must achieve certification by the end of 2006. "The focus is to provide value for the entire automotive supply chain," says Linda Plawecki, executive director of the Southfield, Mich., trade group and previously the purchasing manager for Ford Motor Co.'s Powertrain Machinery and Tooling organization. "These cutting-edge manufacturing techniques offer all automakers newly available options in structural design and assembly."

The body structures of North American-made motor vehicles consist of 54% steel, and almost a quarter of that steel has become hard-to-handle high-strength steel. That's 423 tons of the typical 2004-model sedans, which weigh 3,392 tons. High-strength steels also 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. They can be problematic to fabricate, but provide other characteristics important to cost-effective auto assembly.

The North American steel industry has been undergoing a transformation highlighted by bankruptcies, corporate consolidations and even plant-ownership switch-overs. However, Andrew G. Sharkey III, president of the American Iron and Steel Institute (AISI), insists that "a new steel industry is emerging that is providing its customers with innovative new steels designed to answer society's changing needs." In the midst of all the recent turmoil, Sharkey says the industry "has been taking an aggressive approach focused on finding steel solutions to the challenges that steel customers are facing."

For example, motor vehicle weight reduction has become a key issue in automotive engineering, opening the materials door to new-generation high-strength steel products for auto body parts, drive systems and suspension parts. Sharkey asserts the fastest-growing new automotive material segment is not aluminum or plastics. "It is these advanced quality high-strength steels, which are redefining the metal's role in the automotive market," he says.

In fact, steel industry efforts to create more lightweight grades of metal for the automotive market have resulted in the development of some new high-strength steel with unusual metallurgy and good parts formability and performance characteristics. By introducing the advanced steels and encouraging greater use of more common, high-strength grades, the steel industry hopes to maintain its dominant position in the auto market against increasing competition from aluminum, magnesium and plastic.

In addition, the auto industry's drive for improved fuel economy and emissions levels has encouraged the development of such advanced high-strength steels (AHSS) as dual phase (DP), complex phase (CP), martensitic, transformation-induced plasticity (TRIP) and bainitic. Production of all multiphase AHSS involves controlling the cooling rates on the hot mill's run-out table or the continuous annealing furnace's cooling section, depending on whether the steel is hot-rolled, continuously annealed or hot-dip coated.

Already, these technologically ultra high-strength steel grades are being used to make crankshafts and steering knuckles, auto suspensions and car frames, wheels and bumpers, and fuel tanks. These extra-clean steels provide increased fatigue resistance, allowing designers to use less material in critical components without compromising performance. In addition, progress is expected to continue in cooperative projects by automakers, parts suppliers and steelmakers, includes projects under the Auto/Steel Partnership in Southfield, Mich.

Steelmakers are trying to avoid lost market share to such alternative materials as aluminum, plastics and magnesium in the assembly of passenger cars and light trucks. "Because of the steel developments, parts-design and manufacturing technology improvements that occurred in the 1990s, we're in a good position to maintain, and even expand, our applications in the automotive market during the next few years," says Ron Krupitzer, senior director of automotive applications at the American Iron and Steel Institute. "We expect to see a lot of technology-transfer work carried out that will help the auto companies improve the safety and performance of their cars and trucks while also reducing vehicle weight for the benefits they're seeking in fuel economy and emissions."

Pete Peterson, director of automotive marketing at U.S. Steel Corp., Pittsburgh, says several steelmakers are carrying out a number of light-weighting projects in cooperation with the Big Three domestic automakers. These projects, he says, are "aimed at improving and expanding the use of steel—including advanced high-strength grades—by resolving technical issues and eliminating concerns or problems associated with the manufacturing of parts." New and recent projects include steel mill products used to make automotive closures; doors, hoods and lift gates; front-end structures and engine compartment frames, and lightweight frames for sport utility vehicles.

Pay attention to AHSS

In fact, an automotive engineering team has successfully applied high-strength and new advanced high-strength steels (AHSS) to reduce the body frame weight of an existing sports utility vehicle by 23%. Achieved without major assembly or packaging issues, and with only a minimal cost increase of 31¢/lb, the new frame design for the Ford Expedition/Lincoln Navigator maintains the same structural performance characteristics as the original design for the 1997-2002 models.

"While improvements have been made, the basic architecture of the large SUV and truck frame has not changed much in the past 25 years," says Ted Diewald, executive director of the Auto/Steel Partnership in Detroit. The research into new grades of automotive steels is aimed at supplying automakers with metal possessing "significant savings potential during mass assembly without jeopardizing structural performance."

To satisfy customer demand for cost reductions during parts manufacturing, metal-body and structural-systems suppliers Visteon Corp., Delphi Corp. and Cosma International are starting to use advanced high-strength steel (AHSS) grades instead of conventional high-strength steel.

Various AHSS grades have been developed by a consortium of 33 world steelmakers united as ULSAB-AVC (Ultra Light Steel Auto Body-Advanced Vehicle Concepts). A recent study of these steels by the Auto/Steel Partnership found high levels of crash safety performance at no cost increases. The partnership, formed in 1987, has helped keep steel at the forefront of automotive materials technology by leveraging the research and development resources of the automotive and steel industries, Diewald says.

He expects continuing progress in the application of AHSS to welded subassemblies in cars and light-duty trucks. He also anticipates progress in the development and use of inexpensive styled steel wheels to replace aluminum wheels on such vehicles, as well as in the Big Three automakers' use of steel engine crankshafts as replacements for cast iron units. AISI's Krupitzer expects steel to regain some of the fuel tank market lost to plastic during the 1990s, and to recapture some of the bumper applications lost to plastic and aluminum in the 1980s and 1990s.

All of the major car companies are actively embracing new steels as they adapt new architectures to meet the needs and desires of today's customers. For example, General Motors Corp.'s Epsilon midsized car platform, the basis for the Chevy Malibu (which is about 60% AHSS) and Malibu Maxx and Saab 9-3, represents GM's most significant AHSS project to date, including the automaker's first use of dualphase steel in a welded body structure.

In addition, the just-completed IMPACT program (Improved Materials and Powertrain Architecture for 21st Century Trucks) is an initiative between AISI, the U.S. Army and Ford to develop a tactical truck that is commercially based. Sharkey of AISI says innovations developed through the use of AHSS grades are being translated into the design of the next Ford F-150 series of trucks. The 2004 F-150 is already applying a number of these steel developments.

The environmental implications of the new steels "have definitely grabbed the automotive industry's attention," Sharkey says. Recent research estimates that the annual reduction in carbon dioxide emissions per vehicle is approximately four times the weight of the steel used in each ULSAB-AVC sedan. And, for every million ULSAB-AVC vehicles (roughly 7% of vehicles built in an average year), the estimated annual savings would be $225 million from a reduced fuel consumption of 171.3 million gallon.

New steel is a global effort

One ultra-high-strength cold-rolled steel sheet that has been used for almost a decade for such structural parts as pillars, bumpers and door impact beams is now being tested in car seat parts. This 980 MPa steel sheet, first developed by Kobe Steel of Japan, offers high strength with excellent formability, therefore reducing weight without compromising strength. "In general, the stronger the steel the less formable it is. High strength steel, however, offers both excellent tensile strength and high formability," says steel engineering project leader Yukihisa Komiya. "This makes 980 MPa steel an ideal material for car seat parts, which undergo bending, stretch flange forming, and bulging in their manufacture."

And as a result of arrangements with JFE Steel of Japan, by mid-2004, Canada's Dofasco will be supplying North America with 400,000 tons of value-added automotive-grade galvanized sheet capacity from the jointly owned DJ Galvanizing plant in Windsor, Ontario. This arrangement helps promote Dofasco's "Solutions in Steel" strategy, which is meant to address customers' value chain issues, says Don Pether, president.

Actually, there are various new corporate partnerships on technology transfers, joint research and development, and user support: U.S. Steel and Kobe Steel of Japan; Corus of England and Sumitomo Metal Industries of Japan; Nippon Steel of Japan and Boashan Iron & Steel of China; Kobe Steel and Lucchini Group of Italy. These partnerships are developing new uncoated, galvanized and galvannealled high-strength strip, free-cutting bar and new-generation wire rod steel products for use by the automotive industry.

For example, Kobe Steel transferred to Ascometal of France, a Lucchini Group company, the technology to produce a high-strength steel wire rod product called UHS 1900 used to fabricate automotive suspension springs. In return, Ascometal transferred to Kobe Steel its technology for low-distortion gear steel, which is being tested by Japanese automobile manufacturers in Japan and Europe. In late 2002, Ascometal began supplying UHS 1900 for parts sold to Japanese automobile transplants in Europe. Japanese transplants in North America use UHS 1900 made under license by special bar quality (SBQ) steel supplier Republic Engineered Products in Fairlawn, Ohio.

Bar stock also upgraded

Republic also has entered into a manufacturing technology agreement with Daido Steel of Japan to develop the next generation of machinable lead-free automotive steels for Japanese automakers in the U.S. "Leaded steels are used to improve machinability, but growing interest in removing lead from the recycling stream has created demand for a suitable lead-free replacement," says Joseph F. Lapinsky, president of Republic. "We also believe these new lead-free, machinable steel bar products will offer benefits to U.S. automakers and non-automotive companies."

Also, a new high-volume automotive application for forging-grade steel bar stock will open up late in 2005, when Ford begins producing its next generation of V-6 engines for cars and light-duty trucks in Lima, Ohio. The new V-6s are expected to consume at least 24 million pounds of crankshaft forgings per year, according to Ford. Eventually, as the automaker increases its output of the Duratec 35 engines—3.5-liter dual-overhead-cam units with four valves per cylinder—the crankshaft applications for steel bar could quadruple. Some Ford sources say the annual production volumes could eventually reach 1.2 million units.

Ford currently uses iron crankshafts in most of its North American-built engines, so Ford's decision to use steel instead of iron for the new V-6 components has drawn considerable interest from the steel bar industry. So also has GM's decision to use steel crankshafts in three new engines this year. Lapinsky of Republic explains that crankshafts are major applications because of their size and high production volumes and the use of steel proves their claims that steel can provide weight reduction and improved strength, stiffness, durability and vibration-resistance.