Southfield, MI--Just as plastics have benefited by lightening the load in auto designs, steel hopes to regain strength in the automotive market with the introduction of a lighter-weight product known as Ultra High Strength Steel (UHSS). The material has already proved its worth in critical safety-related vehicle applications, according to the Auto/Steel Partnership, an international association that includes the largest North American automotive companies and major sheet-steel producers.
UHSS steels have a minimum tensile strength of 100 ksi (about 700 MPa). They are designed primarily for their load-carrying and crash-energy management. For most grades, accelerated cooling methods are employed to achieve the requisite strength levels through the development of martensitic or ferritic martensitic (dual phase) microstructures. The material family consists of several bare-metal or galvanized grades, each of which have distinctive features.
General Motors uses UHSS in a front-door impact beam on its high-volume, extended-cab C/K pickups, while Ford applies it in a bumper beam on the Taurus/Sable platform. For the C/K trucks, GM modified an existing front-door impact beam. Not only did the new beam meet safety standards, but it reduced beam weight by 22% and required fewer components. At Ford, engineers incorporated the bumper beam in 1996-model vehicles. The design increased structural performance to the point that the beam rated best in its class for 5-mph crash tests. It also provided a cost savings due to its roll-formed design, when compared with a stamped or injection-molded bumper.
The UltraLight Steel Auto Body (ULSAB) Consortium, made up of 35 sheet-steel producers from 18 countries around the word, hopes to make an even greater impact on the automotive community with the ULSAB, which it debuted last March in Detroit. It contains 447 lb (203 kg) of steel. That's about 36% less weight than nine mid-size sedans benchmarked in the concept phase of the ULSAB study.
"With ULSAB, we demonstrate that the steel industry can and will help its automotive partners meet fuel economy, safety, and environmental challenges that loom into the next century," says Robert J. Darnall, this year's chairman of the American Iron and Steel Institute. "And steel will continue to be used in bodies of the future because of its strength, ease of manufacture, recyclability, and relatively low cost," adds Darnall, who also is CEO of Inland Steel Industries.
Darnall has challenged the Partnership for a New Generation of Vehicles (PNGV) super car program to commission the design and production of a steel-bodied, affordable midsize car weighing just 2,000 lb. "We have shown that light weight and steel are not an oxymoron," Darnall notes. "Now we want to take weight reduction to the next level, and test the true potential of steel."